A pterygium (plural is pterygia) is a wing like triangular sheet of fibro-vascular tissue which originates in peri-limbal conjunctiva within the palpebral fissure (opening of the eyes between the eyelids) with progressive involvement of the cornea. The lesion involves nasal side of limbus (junction between cornea and conjunctiva) more frequently as compared to temporal limbus. Rarely, it affects the temporal limbus alone.
Pterygium is usually bilateral, may be asymmetrical, among elderly patients.
Pterygium can vary from small, atrophic quiescent lesion to a large, aggressive, rapidly growing lesion that can distort corneal surface. In advanced cases, it can obscure optical center of the cornea and may affect vision.
Basak Samar K, Atlas of Clinical Ophthalmology, 2nd ed. Jaypee Brothers Medical Publishers (P) Ltd, 2013, New Delhi, P. 57-59.
Kanski,Jack J. Clinical Ophthalmology, A Systematic Approach .Third Edition.UK. Butterworth Heinemann, 1994. P 96 - 97.
Patients with pterygium may be asymptomatic or may present with following symptoms in eyes:
- Elevated lesion in eye.
- Blurring of vision due to induced astigmatism or obscuration of visual axis.
- Restriction of movement with double vision.
Cause for pterygium is not known.
A genetic predisposition to development of pterygium may be apparent in certain families.
Risk factors for pterygium include:
- Increased exposure to ultraviolet (UV) light, including living in subtropical and tropical climates near equator.
- Environmental micro-trauma.
- Engaging in occupations that require outdoor activities.
- Dry and hot climates.
- A higher incidence in males may reflect higher rate of exposure to ultraviolet radiation.
Recurrent pterygium may be related to surgical trauma than ultraviolet radiation as avoidance of UV radiation has not affected the incidence of recurrence.
Diagnosis of pterygium is based on typical clinical appearance.
A pterygium causes fibro-vascular change on the surface of conjunctiva and cornea. It is more common for the pterygium to be present on the nasal conjunctiva and then to extend onto the surface of cornea, although it can present temporally, as well as in other locations.
Clinically, pterygium can present in different fashion:
Slow growing Pterygium:
Pterygium present as flat, slow growing lesion with minimal proliferation and a relatively atrophic appearance. Pterygium on surgical excision has a relatively lower incidence of recurrence.
Rapidly growing pterygium:
Pterygium present as significantly elevated fibro-vascular, rapidly growing lesion. It is progressive and fleshy with prominent vessels. Pterygium has a more aggressive clinical course and a higher incidence of recurrence following surgical excision.
- Primary double pterygium: Primary double pterygium involves both nasal and temporal limbus.
- Recurrent pterygium: Recurrent pterygium shows more scarring and is sometimes much wider.
- Malignant pterygium: Malignant pterygium is a recurrent pterygium with symblepharon formation (adhesion of eyelid to the eyeball) and may be associated with restriction of ocular movement in opposite direction.
Recurrence sometimes may be associated with pyogenic granuloma formation.
Primary pterygium may undergo cystic changes with or without corneal dellen (thinning of cornea) and an eyelash may be present underneath the pterygium.
Typical findings of pterygium include:
- Wing like triangular shaped fibro-vascular conjunctival growth within palpebral fissure with apex or head extending onto the cornea.
- Vascular straightening in the direction of advancing head of pterygium on the corneal surface.
- May be a thin translucent membrane or significantly thickened and elevated gelatinous tissue.
- It may be present on nasal and/or temporal limbus of one or both eyes.
- It may be white or pink lesion depending upon the vascularity.
- Advanced cases may show involvement of visual axis.
- A pigmented epithelial iron line called Stocker’s line may be present in long standing and non progressive pterygium.
- Pinguecula (yellowish triangular deposit on conjunctiva near limbus) may be present in ipsilateral or contra-lateral eye.
- Restriction of ocular movement with diplopia (often seen in recurrent pterygium with conjunctival loss and scarring).
Morphology of pterygium:
Various parts of pterygium are labelled as:-
- Head: Head is the part which rests on cornea.
- Neck: Neck is the constricted portion seen at the limbus.
- Body: Body is the remaining bulk of mass.
- Cap: Cap is a semi-lunar infiltrating portion in front of head of pterygium showing opaque spots (Fuch’s spots). It is suggestive of progression.
- Corneal topography: Corneal topography may be useful in assessing the degree of irregular astigmatism being produced by advanced pterygium.
- External photography: External surface photography may be done for pterygium to follow its progression over the time.
Pterygium is characterised by elastotic degeneration of collagen and fibro-vascular proliferation, with an overlying epithelial covering. Vermiform or elastotic degeneration refers to wavy worm-like appearance of the degenerated fibers. Epithelium is usually normal, but may be acanthotic, hyperkeratotic or even dysplastic and often exhibits goblet cell hyperplasia. Typically, there is destruction of Bowman’s layer and superficial stroma by fibro-vascular in-growth.
Pterygium shows an accumulation of degenerated sub-epithelial tissue which stains basophilic with a characteristic slate grey appearance on Haematoxylin and Eosin (H&E) staining. This tissue also stains with elastic tissue stains, but it is not true elastic tissue, in that it is not digested by elastase.
Pterygium should be distinguished from:
- Pseudo-pterygium: A pseudo-pterygium results from corneal inflammation due to chemical or thermal burns, trauma, marginal corneal disease, corneal ulcer or corneal perforation with reparative process leading to adhesion of a fold of conjunctiva to peripheral cornea.
Pseudo-pterygium is differentiated from true pterygium by history of inflammation in affected eye, location may be other than horizontal meridian, configuration not resembling wing structure, usually unilateral, non progressive and ability to pass probe (probe test) under the neck of pterygium.
- Neoplasia: Neoplasia such as carcinoma in situ or squamous cell carcinoma should be excluded.
- Pinguecula: Pinguecula is an actinic lesion confined to the peri-limbal conjunctiva that does not extend onto the cornea. Pinguecula are commonly occurring, usually small and asymptomatic, often yellow, raised nodules appearing on the bulbar conjunctiva. These are found commonly on the nasal side, but can also be present on temporal aspect of limbus. Pinguecula can occasionally undergo inflammation with symptoms of itching, burning or mild pain. Pinguecula show mild to moderate focal thickening of conjunctival stroma with elastotic degeneration of collagen.
- Pannus formation.
- Terrien’s marginal degeneration.
- Stevens-Johnson syndrome.
- Neurotrophic keratitis.
- Limbal dermoid.
Management should be carried out under medical supervision.
Management of pterygium involves medical and surgical therapy.
Corneal extension of pterygium should be measured and followed periodically every one to two years to determine the rate of growth toward the visual axis. Patient should be observed for symptoms of significant redness, discomfort or changes in visual function.
Medical therapy includes:
- Use of UV light blocking glasses: Patients who are at risk of developing pterygium because of a positive family history or because of extended period of exposure to UV light should use UV blocking glasses. Patient should avoid direct sunlight, wear goggles or may use cap to reduce ocular exposure.
- Use of tear substitutes: Use of tear substitutes may be considered to minimise effect of environmental micro-trauma in those who are exposed to it. Lubricating drops and ointments may be used to alleviate symptoms of inflamed pterygium.
- Vasoconstrictor drugs: Inflammation of pterygium may cause irritation, foreign body sensation and tearing and these symptoms may be relieved by use of vasoconstrictor eye drops.
Pterygium can be removed for cosmetic reasons, as well as for any functional abnormality of vision or any symptoms of ocular discomfort.
Indications for surgical treatment of pterygium are:
- Encroachment upon pupillary area and blocking visual axis, thereby causing diminution of vision.
- Distortion of vision due to high astigmatism being induced by pterygium extending onto cornea.
- Recurrent inflammation.
- Evidence of progression like absence of Stocker’s line.
- Restriction of ocular movement with diplopia.
- Cosmetic removal.
- Rarely, for any suspected metaplastic change in pterygium.
Surgical modalities are:
- Pterygium excision with simple closure of wound.
- Bare sclera technique of excision.
- Transplantation of pterygium by suturing head of pterygium to its body or to the inferior fornix (junction between bulbar and palpebral conjunctiva).
- Conjunctival autograft (CAG) with or without the use of Mitomycin C (Mitomycin C prevents recurrence). Due to increased occurrence of scleral complications, beta irradiation and thiotepa to reduce recurrence of pterygium, are seldom used today.
- Amniotic membrane transplantation.
- Use of fibrin glue with conjunctival or amniotic membrane transplantation.
- Lamellar keratoplasty in conjunction with pterygium surgery.
- Early laser treatment of recurrences may help in preventing progression.