Welcome to The Ophthalmic Lexicon, making sense of some of the terminology used in ophthalmology with simple, concise definitions
(updated July 2019)

Click a letter to view medical terminologies belonging to that letter…


  • Aberrant reinnervation :
    This term describes the abnormal regrowth of (previously damaged) nerve fibres which regenerate to innervate an alternate structure. This can occur following facial nerve injury or surgery in which the facial nerve is injured. In this case, fibres within the facial nerve destined to innervate one structure, such as the face or the salivary glands, are redirected to another structure within the territory of the facial nerve. When fibres destined for the salivary glands are redirected to the lacrimal gland, tearing when eating occurs, this termed ‘gustatory epiphora’ or ‘crocodile tears’.
  • Anterior chamber drainage angle :
    The area at the root of the peripheral iris where aqueous humor drains from the eye into the annular canal of Schlemm, and thence away from the eye. Failure of drainage can lead to raised intraocular pressure, which if untreated can lead to atrophy (decay) of the optic nerve fibres (glaucomatous optic neuropathy).
  • Anterior lamella :
    The skin of the eyelids. Shortage of skin can cause incomplete eyelid closure, or the eyelids to be held away from the eyeball (ectropion).
  • Anterior segment :
    The front section of the eye, including the cornea, the anterior chamber which lies in front of the lens, the iris, and the crystalline lens.
  • Arnica montana :
    Arnica is a genus of about 30 herbaceous plants which belongs to the sunflower family, and has been used in medicinal preparations since the sixteenth century. Currently available in tablet and gel form, patients often report that Arnica formulations reduce swelling, bruising and scarring after surgery, although the medical evidence for its use remains limited.
  • Artificial eye :
    Refers to the prosthesis worn in the socket. This is made of an inert material, and with good colour-matching with the fellow eye, can even be indistinguishable from a real eye. Readily removed for regular cleaning at home, it requires periodic polishing and occasional replacement to maintain a good fit within the socket.


  • “Ball” :
    Often refers to an inert synthetic sphere inserted into the eye socket after an eye has had to be removed. If not inserted at the time of surgery, a ball may subsequently need to be inserted under general anaesthetic (secondary implant) to give ‘volume’ to the socket and prevent a hollowed appearance.
  • Basal cell carcinoma (BCC) :
    A surface skin cancer with relatively slow growth which can extend locally and which very rarely (if ever) spreads to more distant sites. Being more common in sun-exposed areas, BCCs are relatively common on the face, and commonly involve the medial canthal region (inner corner of the eyelids) and the lower eyelid. Treatment includes complete excision, and reconstruction only after confirmation by the pathologist that no tumour remains. Confirmation of clearance can be achieved with Mohs’ micrographic surgery (see below), paraffin section, or frozen section analysis. With all techniques, recurrences can occur.
  • Bell’s palsy :
    A facial paralysis with no clearly identifiable cause, Bell’s palsy, described by the Scottish anatomist in 1821, is presumed to be due to inflammation along the course of the nerve. Symptoms can include ocular dryness, discomfort, and / or watering. In the great majority there is spontaneous improvement within the first few weeks, but during the recovery phase ocular lubricants are required until eyelid blinking and closure (particularly at night) returns to normal. However, even following an apparent complete recovery, patients can still experience a watery eye due to persistent muscular weakness of the inner eyelids (where tears are ‘pumped’ away from the eye), or due to subtle incomplete closure of the eyelids (due to eyelid retraction).
  • Bell’s phenomenon :
    The natural tendency for the eyeball to move upwards under a closed eyelid – a protective mechanism.
  • Blepharitis :
    Inflammation of the eyelid margins. This includes anterior lid margin disease, and posterior lid margin disease. Frequently associated with rosacea (v.i.). Treatment is seldom completely curative, but can provide very significant relief. Blepharitis is a common cause of a watery eye, and is associated with lid cysts. Where symptoms occur on only one side, other potentially serious causes for redness or irritation must be excluded. Blepharitis can also cause conjunctival inflammation (termed blepharoconjunctivitis).
  • Blepharoplasty :
    Surgery to change the contour and/or fullness of the eyelid(s). This may include any combination of skin, muscle and fat.
  • Blink cycle :
    The complete cycle of eyelid closure and opening during involuntary blinking.
  • Body Dysmorphic Disorder (BDD) :
    BDD is defined as ‘a preoccupation with imagined or slight defect in appearance that leads to significant impairment in functioning’.
    BDD is not uncommon among certain patients seeking facial or eyelid surgery. It is important that, when present, BDD is recognised before surgery is considered, as frequently the patient has unrealistic expectations of surgery, and is dissatisfied after surgery irrespective of the objective outcome.
  • Brow elevation :
    Frequently adopted unconsciously to compensate for a droopy upper eyelid (ptosis)
  • Brow lift :
    Surgery to raise the brow is indicated where the brow tissues have become heavy or appear to droop (brow ptosis). This can be achieved in many different ways, including (i) directly by removing skin and muscle from above the eyebrow or beneath the hairline (a highly effective technique, but one that leaves a fine linear scar), (ii) indirectly by lifting the brow with internal sutures via a skin crease incision, and (iii) indirectly by operating with an endoscope via small incisions in the forehead skin. Few techniques last indefinitely.


  • Canaliculus :
    The fine tear drainage channel in each of the lower and upper eyelids. Canaliculitis describes a chronic inflammation of the canaliculus, this resulting in a chronic discharge from the punctum and requiring a minor procedure to release the build up of debris and micro-organisms from the canaliculus.
  • Cellulitis :
    Inflammation of soft tissues – e.g orbital cellulitis. Frequently due to an infection although not necessarily so.
  • Chalazion (Meibomian cyst) : 
    A Meibomian ‘cyst’ is not a ‘true’ cyst histologically, but rather contains retained oily secretions produced within the Meibomian glands in the eyelid. A ‘cyst’ (also referred to as a chalazion) can also become inflamed (causing a red uncomfortable pea-sized lump within the eyelid), and even cause generalised eyelid inflammation or infection. Many chalazia resolve spontaneously and need no treatment. Others require local hygiene and antibiotic ointment to the lid margins, and some require release of the inflammatory contents under local anaesthesia. Lid lesions that are presumed to be benign but which do not resolve within a month or two with medical measures should be biopsied to exclude malignancy.
  • Conjunctiva :
    The transparent membrane covering the white coat (sclera) of the eye. With surface irritation or inflammation (e.g., allergy), the conjunctiva becomes red (‘injected’).
  • Conjunctival fornix :
    The space under the eyelids lined by the conjunctiva which allows free and full movement of the eye relative to the eyelids. The fornix can be shortened as a result of injury, or cicatricial disease, such as mucus membrane pemphigoid, or chronic topical treatment or blepharoconjunctivitis.
  • Cornea :
    The clear ‘window’ of the front of the eye. Injury, inflammation, or dryness (exposure) of the cornea can cause blurry vision. The cornea is clear, the coloured structure behind being the iris. The function of the eyelids is to protect the cornea and to distribute the tear film efficiently.
  • Corneal exposure :
    Local or generalised areas of corneal dryness. In its most severe form, this can result in microbial infections of the cornea, scarring with visual loss, and even corneal perforation. The treatment depends on the severity, ranging from lubrication drops to surgery to help the eyelids to close. Rarely, the eyelids need to be sutured together on a temporary basis to prevent immediate complications.
  • Computed Tomography Scan (CT scan) :
    Imaging frequently used to assess orbital disease. The scan takes a few minutes and may involve an intravenous injection of contrast to outline any changes around the eye in more detail. The patient lies on a couch and passes through a large open ‘ring’ which is the scanner, and patients do not tend to feel claustrophobic. The results are usually available within an hour, and the images are subsequently interpreted and reported by a radiologist (doctor). The CT scan can be copied onto a CD for subsequent review. CT imaging exposes the patient to a very small small amount of radiation, and this is always taken into account when considering the scan, particularly in children. Where possible, other imaging techniques, such as ultrasonography, can be performed first, and may obviate the need for CT scanning. Another commonly used imaging modality is magnetic resonance imaging – this is more useful where details of the optic nerve and cranial structures (brain) are required.
  • Crocodile tears : 
    See ‘Gustatory epiphora’
  • Cup-to-disc ratio (CDR) : 
    An estimation of the width of the optic cup (the central area of the optic nerve seen end on, this area containing no nerve fibres)relative to the overall diameter of the optic disc. ‘Normal’ values vary considerably, although in glaucoma, in which retinal ganglion nerve fibres have decayed, the CDR increases, and the cup becomes deeper.


  • Dacroadenitis :
    Inflammation of the lacrimal gland. Dacrodenitis is typically viral in origin. Where this does not settle completely within a few months on oral non-steroidal anti-inflammatory tablets (NSAIDs, such as Froben), a biopsy of the lacrimal gland is required to exclude unusual inflammations and very rare cancerous changes.
  • Dacrocystitis :
    Inflammation of the lacrimal sac (this lies in the inner corner of the eyelids against the bone of the side of the nose). See also mucocoele.
  • Dacrocystorhinostomy (DCR) :
    An operation to allow the tears to drain more directly into the nose, thereby bypassing any resistance in the nasolacrimal duct. This can be achieved either with a small incision on the side of the nose (the external approach), or using an endoscope and operating only on the internal aspect of the nose. Each technique has advantages and disadvantages, although the external technique currently has the highest success rate in experienced hands.
  • Dermis fat graft :
    Transferred from the abdomen or buttock, fatty tissue with its overlying tougher bonding layer (the dermis, this being the layer immediately beneath the skin) can be used to increase the volume around the eye or in the eye socket. A similar technique involves aspirating the fat through fine incisions in the skin (a form of liposuction) and, after removing unwanted fluid and oil by centrifugation, injection of the fatty cells in or around the eye socket (Coleman fat injection).
  • Dermolipoma :
    This congenital ‘fatty’ lesion is rarely encountered on the outer surface of the eye between the two eyelids. It may be debulked for aesthetic reasons, although surgery carries a very small risk of surface dryness and double vision.
  • Diplopia :
    Double vision occurs when the eyes are not each orientated towards the same intended visual target. This is known as a squint, or strabismus. All individuals have a tendency for an eye to drift either inwards or outwards, but this is subconsciously controlled in order to maintain single vision. If the vision in one eye is poor, then there is a higher risk of strabismus developing, although double vision will not be appreciated (because of the reduced vision in the eye). Causes for diplopia include neurological impairment (impairment of the 3rd, 4th, and/or 6th cranial nerves which control eye movements), disease of the muscle (such as myasthenia gravis), orbital diseases (such as thyroid eye disease) and orbital or ocular injury. Patients with double vision should always seek medical attention.
  • Droopy eyelid :
    See ‘ptosis
  • Dry eye :
    A much misused term. True dry eye, as a diagnosis, is due to a very rare systemic immunological disorder called Sjögren’s syndrome. As a symptom, a ‘dry’, or ‘gritty’, eye is usually due to instability of the tear film (also called evaporative dry eye), and is typically due to blepharitis. See tear film below.
  • Duction :
    Ocular duction – referring to movement of the eye.


  • Ectropion :
    This describes an ‘out-turning’ of the eyelid from the surface of the eye, and has different causes, including age-related laxity of the tissues, impaired facial nerve function (such as Bell’s palsy) and contracture of the skin of the lower eyelid.
  • Endoscopy (nasal) :
    Examination of the nasal space can be done with a rigid endoscope in the clinic after a small amount of anaesthetic spray to the nose. This examination can provide valuable information on the natural tear drainage into the nose in patients who have had previous lacrimal drainage surgery, as well as identify other intra-nasal pathology which can reduce the natural flow of tears from the eyelids into the nose. Endoscopy is sometimes necessary when removing a tube after DCR surgery.
  • Enophthalmos :
    A ‘sunken’ eye relative to the other side. This can be due to an orbital fracture, or a collapsed maxillary sinus (‘imploding antrum syndrome’), or due to true proptosis of the other side (due to swelling or a growth in behind the eyeball).
  • Entropion :
    Frequently with a similar aetiology (cause) to ‘ectropion’, entropion describes an ‘in-turning’ of the eyelid towards to surface of the globe, and may account for a red, watery and uncomfortable eye.
  • Epiphora :
    The medical term for a watery eye, implying overflow of tears onto the cheek.
  • Exenteration :
    Removal of all the contents of the socket, including the eye and its muscles, the fatty tissue, and the eyelids. Usually performed to remove a life-threatening eyelid or orbital tumour where less invasive options could compromise life expectancy.
  • Exophoria :
    A tendency for the eye to drift outwards when under cover, or asleep. This is a common finding among healthy individuals.
  • Exophthalmometry :
    The measurement of the position of the eyes in the ‘axial’ plane. An eye that is relatively set forward is described as exophthalmic, or proptosed. An eye that is set back in the socket, is described as ‘enopthalmic’.
    An ‘exopthalmometer’ is the instrument used to measure the distance between the anterior corneal surface and the lateral orbital rim. Note, this does not measure ‘non-axial’ proptosis (where the globe may be displaced vertically, or towards or away from the bridge of the nose).
  • Exophthalmos :
    A forward movement of the eye relative to its normal position within the socket. Also termed ‘proptosis’. Measured with an exophthalmometer.
  • Eyelid :
    A multi-layered structure which both protects the cornea and produces meibomian secretions – a component of the tear film. Any distortion of the eyelid can cause ocular discomfort, and may require surgical correction. The function of the eyelid is also dependent on normal innervation by the facial nerve, hence the laxity of the lower eyelid which can occur after complete or partial paralysis (for example Bell’s palsy).


  • Facial canal : 
    The facial canal (or ‘fallopian’) canal is located within the middle ear region and runs from the internal acoustic meatus through the temporal bone and terminates at the stylomastoid foramen. Being about 3 centimeters long, it is the longest osseous canal for a nerve in the human. It contains the facial nerve (also known as the seventh cranial nerve) whose chief role is to provide innervation to the muscles of facial expression.
  • Facial nerve :
    The facial nerve (the seventh of twelve cranial nerves) innervates the muscles of facial expression, and injury to the nerve (including facial trauma, Bell’s palsy, surgery to the parotid gland or for an intracranial tumour such as an acoustic neuroma) can cause weakness of the orbicularis muscle. Depending on the severity, this can cause drooping of the side of the face and an inability to close the eye fully, particularly when asleep. Symptoms include a dry burning eye (due to ocular exposure), and also a watery eye (due to reflex watering and failure of the lacrimal ‘pump’ which propels the tears into the nose.)
  • Filler :
    Typically in the form of Hyaluronic acid gel, this material can be injected under the skin to provide more volume where there has been a volume deflation due to ageing or injury.
  • Fluorescein :
    A fluorescent orange dye which absorbs from the blue spectrum and emits in the green/yellow spectrum. Normally blinked off the corneal surface, any irregularities in the cornea (such as punctuate erosions – as seen in a dry eye, a scratch, injury or foreign body) can readily be detected by the instillation of fluorescein onto the eye. It is not permanent and is readily wiped off the skin. Fluorescein also has other applications, such intravenous angiography to examine the integrity of blood vessels within the eye itself.
  • Fornix :
    Used in the context of ‘conjunctival fornix’, this refers to the redundant peripheral conjunctival tissue (between the eyelids and the eyeball) which allows the eye to move freely to all positions of gaze.


  • Ganglion :
    A ‘relay’ centre for peripheral nerves. In the neck, the sympathetic nerves travel upwards through a number of ‘ganglia’ to reach their target organs. In 80% of individuals, the inferior cervical and first thoracic ganglion are fused to form the stellate ganglion, which lies close to the first rib.
  • Glaucoma :
    Glaucoma is a form of optic neuropathy. It has many different causes but all lead to a gradual loss of retinal nerve fibres in the back of the eye, this resulting in visual field defects and, if untreated, eventual loss of vision. It is the second most common cause of visual loss in the industrialized world, and, as of 2013, accounts for 12% of all global blindness with over 4.5 million people affected. The most common cause of glaucoma is primary open-angle glaucoma (POAG), this representing over 90% of all forms of the disease, and occurs in up to 2% of the general population. The main risk factors for POAG are age, family history, vascular factors (including blood pressure in some populations), and raised intraocular pressure, although glaucoma can occur even if the pressure is not raised (‘normal tension glaucoma’, NTG). Increasingly effective medical treatments (in the form of drops) are available, although frequently different drops, or combinations of drops, are required to stabilise the visual field. Where drops are ineffective, surgery (‘trabeculectomy’) to allow the fluid in the front of the eye (the aqueous humor) to be absorbed away from the eye can also be effective in controlling the intraocular pressure. In certain complex or resistant cases, a microscopic drainage tube is placed in the front of the eye to improve fluid absorption. Because there are no symptoms until a visual field defect is well established, patients with a family history of glaucoma (there are hereditary factors) should have a regular eye test and intraocular pressure check. Although the visual field loss is irreversible, medical and surgical treatments are typically effective in slowing or stabilising the disease.
  • Goldman tonometry :
    Assessment of the intraocular pressure in primary position using an applanation tonometer after the instillation of topical anaesthesia and fluorescein. Considered to be more accurate than non-contact (‘air-puff’) tonometry. A normal intraocular pressure lies between 10mmHg and 21 mmHg, although higher of lower values are normal in a small percentage of the population. Raised intraocular pressure with evidence for secondary ocular change(s) (e.g., in the visual field, optic nerve or retinal nerve fibre layer) is called glaucoma.
  • Gustatory epiphora (‘crocodile tears’) :
    This is a particular form of aberrant reinnervation occurring after a facial nerve injury. Also called an ‘autonomic synkinesis’ it occurs when recovering parasympathetic fibres destined to innervate the salivary glands are misdirected to the lacrimal gland, this resulting in excess watering of the eye. This can occur because the normal facial nerve contains fibres to innervate both the facial muscles, the salivary glands, and the lacrimal gland; following injury, regrowth of fibres can be misdirected to any of the other structures.


  • Horner’s syndrome :
    Due to interruption of the sympathetic nerve chain, Horner’s syndrome may cause hemifacial anhydrosis (lack of sweating), hemifacial erythema, a smaller pupil (this typically being more apparent in a dark environment), and mild upper eyelid drooping (because the sympathetic supply to the lid plays a small role in elevating the eyelid). More central interruptions (i.e. closer to the brainstem, also termed ‘pre-ganglionic) cause a greater number of symptoms and signs, whereas more peripheral disease (e.g. disease in the neck, ‘post-ganglionic), cause only pupil asymmetry and ptosis.
  • Hypotropia :
    Describing an eye orientated in down-gaze relative to the fellow eye.
  • Hypertropia :
    Describing an eye orientated in up-gaze relative to the fellow eye.


  • Inferior scleral show :
    The amount of visible sclera, measured in millimetres, between the lowest part of the cornea and the edge of the lower eyelid. Typically there is no, or minimal scleral show, although occurs in some patients with naturally ‘prominent’ eyes. Any orbital disease resulting in proptosis (such as thyroid eye disease), or where there has been previous lower eyelid surgery or skin removal can also increase the inferior scleral show.
  • Injected :
    When used to describe the eye, this signifies a redness (engorged blood vessels – episcleral and scleral) over the white coat of the eye.
  • Intraconal space :
    The conical space behind the eyeball contained within the extraocular muscles, this containing fat pads, fibrous septae, blood vessels and nerves, including the optic nerve.
  • Itchy eye :
    An itchy eye is commonly due to allergic eye disease, this more prevalent in sufferers of hayfever, and other allergic disorders. Blepharitis can cause an instability of the tear film, which can also cause itchy and ‘burning’ eyes.


  • Keratopathy :
    Disease of the anterior (front) surface of the eye. ‘Exposure keratopathy’ refers to irregular wetting, or drying, of the anterior surface with secondary abnormalities in the superficial corneal epithelium, or deeper substance (stroma) of the cornea. This can occur in thyroid eye disease (due to upper lid retraction and proptosis), and with any structural abnormalities of the eyelid.


  • Lacrimal gland :
    Situated alongside the outer upper aspect of the eye, and immediately behind the bony rim of the orbit, the lacrimal gland produces the aqueous (watery) component of the tear film and can become enlarged due to infection (dacroadenitis) and systemic inflammatory disorders (e.g. sarcoidosis).
  • Lacrimal sac :
    Situated under the skin at the inner corner of the eyelids, and collecting the tears from the surface of the eye via the puncti and canaliculi, the lacrimal sac drains via the nasolacrimal duct into the nose. If the duct becomes narrowed or occluded, the sac (which is ‘upstream’) can become distended, or inflamed, and becomes apparent as a swelling (a mucocoele) at the inner corner of the eyelids against the side of the nose (the medial canthus).
  • Lagophthalmos :
    The inability to close the eyelids fully with minimal effort (e.g when asleep).
  • Lateral canthus :
    The lateral, or outer corner of the upper and lower eyelids.
  • Levator function :
    Describing the maximum upper eyelid excursion (measured in mm) from down to upgaze, (and examined with gentle pressure on the eyebrow to stop brow elevation), ‘levator function (‘LF’) gives an indication of the efficacy of the levator muscle (levator palpebrae superioris) in raising the upper eyelid. Normal levels lie between ~12 and 20 mm. Levator function is reduced in the following forms of ptosis: congenital (e.g.congenital levator dystrophy), neurological (e.g. third nerve palsy) and myopathic (e.g.myaesthenia gravis). LF can also be reduced following trauma, or adhesions with other eyelid or orbital structures. LF is usually normal, or minimally reduced in age-related ptosis.
  • Levator Palpebrae Superioris :
    The strap-like muscle which, together with the Mullers muscle, elevates the upper eyelid. The muscle originates at the back of the eye socket, and passes above the superior rectus muscle and over the eye to insert by means of a broad collagenous ‘aponeurosis’ into the top and front of the tough ‘tarsus’ of the eyelid. Drooping of the eyelid can occur with advancing years (ptosis) and is generally amenable to surgical correction. The levator muscle is controlled by the third cranial nerve, and rare neurological disorders can also cause ptosis.
  • Lester Jones tube (LJT) :
    Also known as a lacrimal bypass tube, this glass tube allows the tears to drain from the eye into the nose, and can be highly effective where other lacrimal operations have been unsuccessful. To be effective, insertion of such a drainage tube requires a previous dacrocystorhinostomy (DCR).


  • Macula :
    The central area of the retina which corresponds to the central visual field.
  • Media :
    The clear structures of the eye – the cornea, anterior chamber, natural crystalline lens, and vitreous cavity.
  • Medial canthus :
    A term describing the inner corner of the eyelids and side of the nose. The medial canthus contains numerous structures, these including the upper and lower medial (inner) lids, the canaliculi of the lids (tear drainage channels), the anterior and posterior limb of the medial canthal tendon (this securing the eyelids at the medial canthus), the lacrimal sac, and sensory nerves to this region. Medial canthal injuries can be complicated by tearing because the various delicate structures in this region play important roles in conducting the tears away from the eyes.
  • Medial rectus muscle :
    A strap-like muscle which begins at the back of the eye socket and which runs forwards along the inner aspect of the socket, inserting into the white of the eye approximately 5 – 6 mm from the limbus (the beginning of the clear cornea). Contraction of the muscle turns the eye inwards towards the nose. When changing gaze from a distant to a near object, the medial rectus muscles on both sides contract to turn the eyes inwards.
  • Meibomian cyst :
    A Meibomian ‘cyst’ is not a ‘true’ cyst histologically, but rather contains retained oily secretions produced within the Meibomian glands in the eyelid. A ‘cyst’ (also referred to as a chalazion) can also become inflamed (causing a red uncomfortable pea-sized lump within the eyelid), and even cause generalised eyelid inflammation or infection. Many chalazia resolve spontaneously and need no treatment. Others require local hygiene and antibiotic ointment to the lid margins, and some require release of the inflammatory contents under local anaesthesia.
  • Meibomianitis :
    The Meibomian glands are orientated vertically within the upper and lower eyelids, and open onto the eyelid margin immediately behind the eyelashes. Inflammation of these glands can cause an irregular tear film, and consequently an uncomfortable ocular surface. Treatment includes local warm compresses to improve the flow of the oily glandular secretions, and frequently topical antibiotic preparations.
  • Mohs’ micrographic surgery :
    Named after Dr Mohs, this surgery involves excision of a surface cancer (such as basal cell carcinoma or squamous cell carcinoma) and immediate (peroperative) identification of any residual tumour on the cut surface of the specimen. This permits accurate localisation of persistent tumour and further excision of residual tumour from this area with great precision. Mohs’ micrographic surgery offers higher accuracy than standard paraffin sectioning and is associated with a low (1:1000) rate of tumour recurrence. It is particularly valuable for lesions around the eyelids where it is desirable to remove an absolute minimum of normal tissue, or where there has been previous surgery or treatment for a similar lesion.
  • Morphoeic BCC :
    These infiltrative BCCs, which can present as flat or depressed yellow-white waxy patches, tend to have poorly defined edges and can extend more widely than suspected on clinical examination.
  • Mucocoele :
    A dilation of a mucosal-lined cavity, mucocoeles may occur in the air sinuses (sinus mucocoele), and lacrimal sac (lacrimal sac mucocoele). The latter occurs with narrowing of the nasolacrimal duct and is associated with a watery eye, gummy discharge from the eye, sticky eyelids (particularly on waking), and/orinflammation of the walls of the mucocoele (dacrocystitis). Surgery (DCR) offers a cure for a sticky eye in over 98% of patients.


  • Nasolacrimal duct :
    This duct drains tears from the lacrimal sac into the nose. Narrowing or closure of the lower end is a common cause of a watery or sticky eye, and can lead to a swelling (mucocoele) at the inner corner of the eyelids.
  • Neuropraxia :
    Impaired function of a nerve, usually due to a blunt injury.


  • Ocular cicatricial pemphigoid (OCP) :
    Ocular manifestation of mucous membrane pemphigoid (MMP), an autoimmune disease in which surface inflammation can lead to scarring over the front of the eye. Prompt recognition and systemic immunosuppression are essential, and typicaly involves corneal and eyelid specialists. Surgery can be required to correct eyelid entropion and deepen the conjunctival fornices to allow full closure of the eyelids.
  • Omega oil :
    Considered to improve the consistency of the Meibomian gland secretions, Omega oils are often taken as a dietary supplement as an adjunctive treatment in blepharitis.
  • Optic nerve :
    The second of 12 ‘cranial nerves’, the optic nerve relays visual information from the eye to the brain.
  • Optic disc :
    The ‘end-on’ view of the optic nerve at the back of the eye when viewed with a specialised lens or ophthalmoscope.
  • Optic neuropathy :
    This describes reduced function of the optic nerve, which can cause reduced colour sensitivity, blurred vision, loss of visual sensitivity in different parts of the visual field. Loss of optic nerve function can be inherited or acquired, and reversible or irreversible, depending on the cause and duration of disease.
    External pressure on the nerve (such as may occur in severe thyroid eye disease, or orbital haemorrhage) can lead to reduced function and therefore blurred vision. This is usually reversible but treatment should not be delayed. Orbital injury can also result in direct injury to the nerve (traumatic optic neuropathy), and this tends to be irreversible. Other acquired causes of optic neuropathy include glaucoma, nutritional diseases, vascular disease (inadequate blood supply to the nerve), and inflammation of the nerve (optic neuritis).
  • Orbicularis muscle :
    The flat ‘purse-string’ muscle within the upper and lower eyelids which is responsible for closing the eyes on blinking and with voluntary effort.
  • Orbital floor implant : 
    Synthetic or host donor material used to address either an orbital fracture, or to give more volume to the socket of a patient with post-enucleation socket syndrome (PESS). Typically, either a Medpore ® sheet or a fashioned block of silicone is used.
  • Orbital fracture :
    Blunt or sharp trauma may result in fracture of the bony wall(s) of the eye socket. Associated injury to the eye must be excluded. A fracture does not always require surgery, unless there is persistent double vision or a sunken appearance to the eye. Prompt examination by an eye doctor is always required.
  • Orthophoria:
    The term relates to the balance of the two eyes when fixating an object. It indicates the correct natural ocular alignment such that a single image is seen (no diplopia), and that each eye remains in the correct position without a tendency to drift out of alignment, even if each is temporarily occluded. Such temporary occlusion is performed by the ‘cover-uncover’ test, which dissociates the visual axes, removing the fusional stimulus to retain a single image.
    Orthophoria can refer to a near target (‘orthophoria for near’) or a distant target (‘orthophoria for distance’).
    An esophoria indicates the tendency of an eye to drift inwards when the eyes are dissociated by the cover-uncover test. An exophoria refers to a drift outwards, and so on for ‘vertical phorias’.
    A ‘phoria’, therefore, indicates that although no manifest squint is present (see below, orthotropia), nevertheless an eye has a tendency to drift out of alignment IF the eyes are dissociated by alternately covering one eye then the other – the cover-uncover test.
  • Orthotropia:
    This term indicates the absence of a manifest squint. A patient with a horizontal squint is describes as being ‘esotropic’ (with the eye turning inwards), or exotropic (with the eye turning outwards).


  • Palpebral aperture :
    The horizontal or vertical opening of the eyelids, measured at rest, in millimetres. The vertical aperture typically measures 8 – 10 mm, and the horizontal aperture approximately 27 – 30 mm.
  • Parasympathetic nerve supply :
    An ‘involuntary’ nervous system with many systemic effects. Is also responsible for ocular pupil constriction (has the opposite effect on the eye to the sympathetic nervous system).
  • Perimetry :
    Assessment of the width, height and sensitivity of the over all visual field (see visual field).
  • Phthisis :
    Also referred to as ‘phthisis bulbi’. Describes a severely diseased eye which has become shrunken and is usually blind, or may perceive light at best. Such a residual eye has no potential for improved vision, and is often associated with other severe intraocular disease such as a retinal detachment. Common cause for phthisis bulbi include ocular injury and inoperable retinal detachment.
  • Posterior vitreous detachment (PVD) :
    See under ‘vitreous’
  • Post enucleation socket syndrome (PESS) * :
    After the loss of an eye (either through severe injury or surgery to remove the eye), the volume of the eye should be replaced with a similar volume implant to prevent an overall volume deficiency of the socket. This volume is usually replaced in the form of a ball implant, either at the time of surgery (primary placement) or at a later date (secondary placement). Typically, an acrylic ball implant is placed, these having the best track record in terms of tolerability and stability.
    In the absence of a deep socket implant, or where the implant is too small (or where there is an unaddressed orbital fracture), the characteristic clinical features, together known as post enucleation socket syndrome, or ‘PESS’, can occur. These can include the need for an increasingly large (and therefore) heavy artificial eye, poor movement of the artificial eye, a sagging lower eyelid, a droopy upper eyelid, and a ‘hollowness’ to the socket and the upper sulcus (lid).
    Corrective surgery typically involves placing a secondary ball implant (or exchanging the implant for a larger one), then, if volume remains an issue, to place an implant beneath the fibrous floor (periosteum) of the socket. Finally, if despite these measures, the upper lid sulcus remains hollow, this can be addressed by placing a fat graft into the region of hollowness. Following any of these measures, a new artificial eye will be needed, this likely to be lighter and with better movement.* NB, the term was first described when enucleation was the preferred surgery for removal of an eye, Generally, evisceration surgery is now preferred.
  • Primary repair :
    The first surgery performed on a damaged eye to address the most significant injuries and to closed any defects in the coats of the eye. Subsequent ‘secondary repair(s)’ may be required to address other less urgent defects (such as lid abnormalities, cataract surgery, etc).
  • Proptosis (Exophthalmos) :
    A forward movement of the eye within its socket caused by structural changes behind the eye. The commonest cause (affecting one or both eyes) is thyroid eye disease.
  • Prosthesis :
    Literally meaning an ‘attachment’, an ocular prosthesis can be an acrylic or glass artificial eye which is worn in the socket and can be removed for cleaning (used after evisceration or enucleation surgery). More complex spectacle-borne (or magnet fixating) silicone prostheses are required for patients who have had undergone extensive surgery such as an exenteration. A well-crafted prosthesis has a good colour-match with the fellow eye, and to the observer can even be indistinguishable from a real eye.
  • Ptosis :
    Upper eyeliddrooping, or ptosis, may be congenital (due to an abnormal eyelid levator muscle), or acquired (typically age related, in which the tendon of this muscle becomes ‘stretched’, or due to a generalised muscle weakness). In its most severe form, the visual field can become obscured. Correction of ptosis depends on its cause.
  • Punctate epithelial keratopathy (PEK) :
    In a number of conditions the tear film (see definition) may be abnormal or inadequate. In others, the natural lubrication of the ocular surface may be defective due to lid malposition (such as entropion), or irregular eyelashes (trichiasis). The resultant effect on the corneal ‘epithelial’ surface is localised trauma and damaged or missing epithelial cells (PEK). Clinically, this causes an uncomfortable, often ‘fiery’, ocular surface discomfort, and is detectable as irregular surface ‘pinpoints’ after instilling 2% fluorescein onto the eye and examining with a blue cobalt light. Treatment is directed at the underlying condition and improving the quality and volume of the tear film, typically with forms of topical hyaluronate which is known for its water-retaining property.
  • Punctum :
    The opening of the canaliculus at the inner aspect of the upper and lower eyelids. Narrowing of the punctum (punctual stenosis), or ectropion (in which the punctum is turned away from the eye) are causes of a watery eye. Where there is no other identifiable cause for watering, opening of the punctum under local anaesthesia (punctoplasty) can relieve the symptoms.


  • Relative afferent pupillary defect : 
    Also known as an ‘RAPD”, this describes in difference in the degree to which the two pupils react to the same intensity light (also known as the ‘swinging light test). Where there is such a difference, the finding indicates impaired function of the optic nerve (optic neuropathy). In such cases, the pupil on the involved side subtly dilates when a focussed examination light is swung from the good side to the side in question. The test should be performed with a bright light in a darkened room.
    If there is impaired optic nerve function on both sides, a RAPD may be difficult to demonstrate because the test only compares the function of one optic nerve with the other.
  • Retraction :
    Usually in relation to the upper lid, and most commonly due to thyroid eye disease or facial weakness in facial nerve palsy (for example, Bell’s palsy).
  • Rosacea :
    A common inflammatory skin disorder typically affecting the periocular region and cheeks, and associated with blepharitis. Often treated with a 3- month course of low dose antibiotic (such as doxycycline or lymecycline) to reduce the irritant effect of the normal skin flora (microbes).


  • Sarcoidosis :
    A systemic inflammatory disease which can cause inflammation within the eye (uveitis), lead to enlarged lacrimal glands (noted as a fullness in the outer aspects of the upper eyelids), and which can also impede tear drainage through the nasolacrimal duct. Sarcoidosis can also lead to troublesome systemic problems such as skin rashes, swelling of the lymph glands, joint pain and respiratory symptoms, and frequently requires treatment with an immunosuppressant such oral prednisolone.
  • Schirmer’s test :
    A simple test to determine the quantity of tears produced at rest. A strip of filter paper is folded over the lower eyelid, and the degree of wetting is measured with a ruler after 5 minutes. Reduced tear production, which is rare, occurs in true dry eye, a form of autoimmune disease of the lacrimal gland (see also Sjögren’s syndrome).
  • Sclera :
    The strong outer white ‘coat’ of the eye ball. Inflammation of this structure is called scleriti; inflammation of the fine episcleral tissues overlying it is called episcleritis.
  • Sebaceous keratosis :
    A non-cancerous, benign waxy skin growth, which can occur anywhere on the body and which becomes more common with age.
  • Skin crease :
    The eyelid skin creases on itself on up-gaze, this occurring between 6 to 9 mm above the eyelashes. The position of the skin crease may help to determine the cause of ptosis, being higher than normal in cases of age-related ptosis. Surgery on the upper eyelid or orbit can often be performed via the skin crease to minimise any visible scarring. Surgery to lower the upper eyelid in cases of thyroid eye disease can sometimes result in a troublesome visible secondary skin crease.
  • Sjögren’s syndrome :
    An autoimmune disease which results in loss of lacrimal gland and salivary tissue, causing the so-called ‘sicca symptoms’, which include a dry eye (keratoconjunctivitis sicca) and a dry mouth( xerostomia). Such patients are at risk of corneal infections, thinning and even perforation and require very frequent topical lubrication.
  • Smoking and eye disease :
    Smoking is a serious global public health concern, referred to by some authors as the “20th century’s silent epidemic.” Indeed, of the 1.3 billion smokers in the world, some 6 million die each year from tobacco-related diseases. The toxic byproducts from smoking are thought to lead to an increase in ‘free radicals’ and a decrease in ‘antioxidants’, this leading to cellular stress and tissue damage. Smoking is also considered to play a key role in the deterioration of the tissues of the eye, and is known to be a risk factor for ocular diseases such as age-related macular degeneration (ARMD), diabetic retinopathy, glaucoma, and optic neuropathies.
  • Snellen visual acuity :
    A universal measurement of visual acuity, the Snellen chart consists of text lines of diminishing size, these labelled as ‘60’, ‘36’, ‘24’, ‘18’, ‘12’, ‘9’, ‘6’, and ‘5’, the number indicating the distance in metres at which the letters would always appear to be the same size – i.e, at 6 meters the ‘6’ line would appear the same size as the ‘60’ line read at 60 metres. By convention the measurement is taken at 6 metres (20 feet in the US), and the smallest line of letters is recorded. Acuity is recorded as a/b, with ‘a’ being the distance from the chart (6 metres), and ‘b’ indicating the smallest (labelled) line that can be read. In order of increasing visual acuity, these measurements are: 6/60 (at which only the large single top letter of the chart is seen), 6/36 (the top two lines can be seen), 6/24, 6/18, 6/12, 6/9, 6/6 and 6/5. A patient with normal vision would see 6/6 or better, and, if positioned closer to the cart, would see smaller lines of text.
  • Socket :
    Refers to the eye socket either after removal of an eye, or with a sunken non-seeing eye (phthisical eye, or congenital microphthalmia or anopthalmia).
  • Stickler’s syndrome : 
    A group of genetic disorders affecting connective tissue, specifically collagen, which can facial abnormalities, ocular problems, hearing loss, and joint problems. Ocular complications can include myopia, cataract, glaucoma, and retinal detachment
  • Sticky eye :
    A sticky eye has many causes, including nasolacrimal duct occlusion with an associated mucocoele, allergy, or any socket disease (e.g., a poorly-fitting prosthesis causing irritation of the socket lining.)
  • Sulcus :
    Referring to the hollow depression above the upper eyelid, the sulcus becomes more prominent with age, and where there has been contracture of the orbital contents. A deep upper sulcus can occur with age, or where the socket contains insufficient volume following loss – or shrinkage – of an eye after severe injury.
  • Superior oblique muscle : 
    Supplied by the IVth cranial nerve, the superior oblique muscle essentially moves the eye downwards when viewing a near object – this action being of particular importance when reading. The IVth cranial nerve has the longest intra-cranial course, and can be damaged in closed contusional head injuries.
  • Superior rectus muscle :
    One of six strap-like muscles which moves the eye. The superior rectus elevates the eye and enables upgaze. It originates at the back of the eye socket, and passes under the levator muscle to insert into the tough coats of the eyeball approximately 7 – 8 mm from the superior corneal limbus.
  • Sympathetic endophthalmitis :
    Very rarely, inflammation can occur in an eye following a previous injury to the same or the fellow eye. The inflammation results from exposure of the immune system to intraocular antigens (self-proteins) during the initial injury (or surgery) with a secondary inflammatory response against such proteins which can occur days to decades later.
  • Sympathetic nerve supply :
    An ‘involuntary’ nervous system with many systemic effects. The sympathetic nervous supply to the eye is responsible for involuntary upper eyelid elevation and dilation of the pupil (occurring with emotion, e.g. fear, excitement). Interruption to this nervous chain leads to Horner’s syndrome.


  • Tarsorrhaphy :
    A temporary or permanent, complete or partial, closure of the eyelids performed to protect the cornea where there is exposure keratopathy. Facial palsy is one indication for a tarsorrhaphy, although is only rarely required in Bell’s palsy.
  • Tear film :
    Tears are a complex 3-layer ‘sandwich’ composed of:

    1. a fine mucus layer to enable the tears to adhere to the ocular surface,
    2. the watery, or ‘aqueous’ component which also contains nutrients and antibacterial agents (immunoglobulins) to protect the cornea, and
    3. the superficial oily layer – produced from the sebaceous glands in the eyelids – to reduce evaporation of the aqueous component.
  • Temporomandibular joint (TMJ) :
    Also known as the jaw joint, the TMJ is located on both sides of the face, and is formed of a synovial articulation between the lower jawbone (or mandible) and temporal bone, which is part of the skull.
  • Thyroid eye disease :
    A constellation of symptoms and signs usually (but not always) associated with abnormal activity of the thyroid gland, in which anti-thyroid antibodies cross-react with orbital structures and lead to orbital inflammation. This can cause ocular irritation, and swelling of the normal muscles and fatty cushions around the eye. In more severe cases, proptosis (bulging of the eye), double vision and even loss of vision (optic neuropathy) can occur. Please see further information on this website on thyroid eye disease.
  • Trichiasis :
    Aberrant eyelashes, either in terms of their position, or direction of growth, and which may abrade the surface of the eye. Typically occur following lid injury or inflammation.
  • Trigeminal Nerve (The fifth cranial nerve) :
    The sensation of the face is subserved by the trigeminal nerve. This has three branches, the frontal nerve (for sensation above the eyelid and including the upper lid), the maxillary division to include sensation of the cheek to the angle of the mouth, and the mandibular division which provides sensation over the jaw and under the chin.
  • Tubes’ :
    In the context of lacrimal surgery (DCR), ‘tubes’ refer to the fine silicone stent, or ‘string’, typically left in place until 3 – 4 weeks after surgery. The tubes are thought to influence healing in the nose, although are probably not required in all patients.
  • Tumour :
    A tumour refers to a new growth, and can be benign (implying limited growth with no distant spread), or malignant (implying an ability to grow, to invade and replace adjacent structures, and to spread to other parts of the body – or ‘metastasise’). The character of malignant tumours can vary from those which take many years to grow (and with little metastatic potential), to those which grow rapidly (and which can even metastasise before the primary tumour is discovered). Most tumours around the eyelids are basal cell carcinomas (BCCs) – these do not spread elsewhere, but require treatment, usually by complete excision and reconstruction of the eyelid.


  • Ultrasound (USG) :
    A form of non-invasive imaging and without irradiation, ocular ultrasonography is able to detect abnormalities within the eyelids, globe, and anterior one-third of the orbit. USG is particularly good at detecting the interface between two different structures (such as sclera and vitreous, vitreous and free blood, cystic structures, etc) and can be used to detect the integrity of the globe and the presence of intraocular haemorrhage after injury. Ocular ultrasonography is also an accurate method to detect abnormal vessels within the orbit, such as a change in flow in the superior ophthalmic vein in a dural fistula, and unusual collections of blood vessels, such as a congenital capillary haemangioma.
  • Upper lid show :
    The vertical distance in millimetres of lid skin between the eyelashes and the skin crease with the patients looking directly ahead (primary position).
  • Upper lid skin :
    The length of skin, measured in millimetres, between the eyelashes and the lowest part of the eye brow. Where the amount of skin is reduced, as can occur with previous injury or surgery, lagophthalmos (incomplete eyelid closure with minimal effort) and exposure keratopathy can occur.
  • Upper lid skin crease :
    The eyelid skin creases on itself when the eyelid moves upwards on up-gaze. This crease, or fold, runs parallel to the eyelid margin and typically occurs between 6 – 9 mm above the eyelid margin.
  • Upper lid sulcus :
    Refers to the hollow between the upper lid and the eyebrow (which overlies the orbital rim)


  • Visual field :
    The field which an individual is visually aware of, either using one eye (monocular field of view) or two eyes (binocular field of view). For each eye, the normal visual field extends from about 60 degrees nasally from the midline to 100 degrees temporally from the midline, and about 60 degrees above and 75 beneath the horizontal. Various methods exist to measure the extent and sensitivity of the visual field, and depend on the patient detecting either moving targets of different sizes, or a static targets of increasing intensity. The visual field can be reduced in either or both eyes due to ocular disease (e.g., glaucoma), or to other disorders which affect the optic pathways within the brain (e.g., a stroke).
  • Vitreous cavity : 
    The vitreous cavity is the space within the eye behind the lens and in front of the retina and the optic nerve. It contains about 4.5 ml of vitreous humor.
  • Vitreous humour :
    The gel which fills the posterior segment and which is attached to the retina at the ora serrata (the vitreous base) and to the disc. ‘Detachment’ of the vitreous from its attachment at the disc (due to trauma, surgery, or spontaneously) is termed ‘posterior vitreous detachment’ (PVD). This does not require intervention, but a PVD can also be associated with traction and retinal tears at the vitreous base, and this requires intervention to prevent progression of the detachment. The symptoms of a PVD can include painless photopsia (‘flashing lights’), ‘floaters in the visual field, and/or reduced vision if there is any associated haemorrhage in the eye.


  • Watery eye :
    Essentially occurring as a result of over production of tears (for any reason) and/or under-drainage of tears (for any reason). ‘Epiphora’ refers to over-flow of tears from the corner(s) of the eyes, or onto the cheek.


  • Xanthelasma :
    Deposition of fatty deposits in the eyelid skin, typically the inner aspect of the lids, and is sometimes an indication of raised cholesterol in the blood stream. Recurrence or development of new xanthelasmata can occur after excision.