Vol 57: april • aVril 2011
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Canadian Family Physician•Le Médecin de famille canadien447
Ophthaproblem
Answer to Ophthaproblem
continued from page 4432. Pterygium
Pterygium is an ocular surface disorder characterized by a fibrovascular growth of the conjunctiva that invades the superficial cornea. Exposure to UVB light is considered to be the most important risk factor for the development of pterygia.1 Oxidative stress caused by exposure of the ocu- lar surface to UVB light results in mutagenic changes to limbal stem cells. These changes induce overexpression of certain cytokines, inflammatory modulators, and growth factors, resulting in a hyperproliferation of degenerated conjunctival cells with subsequent fibrovascular ingrowth into the Bowman layer of the cornea.1 Other risk factors for the development and progression of pterygia include exposure to dry, dusty, and windy environments; dry eye syndrome; and any ocular surface inflammation. The prev- alence of pterygia varies geographically, with rates as high as 29% in certain equatorial regions.2
Pterygia are often asymptomatic. In some cases, they might cause ocular surface irritation. Large pterygia are capable of affecting vision, either by inducing corneal astigmatism or by obstructing the visual axis. In severe cases, ocular motility can be restricted.3
Several conditions can be mistaken for pterygia.
Pingueculae, which can be precursors to pterygia, are yel- lowish in appearance, do not invade the cornea, and do not affect vision. They can occur in either the nasal or tempo- ral interpalpebral regions, whereas pterygia typically occur nasally. Pingueculae might cause ocular surface irritation;
symptomatic patients often find relief with lubricating eye drops. Corneal ulcers are acute, painful infections of the cornea associated with a corneal epithelial defect and cor- neal opacification. They do not involve the conjunctiva.
The most important condition to rule out in a patient presenting with a conjunctival lesion is conjunctival squamous cell carcinoma (SCC). These lesions might be mistaken for pterygia because of their location and appearance. Conjunctival SCC lesions typically present with redness and irritation, and often originate at the lim- bus. They are usually elevated and pink-gray in colour, with a translucent gelatinous surface. The presence of large, engorged, and tortuous surrounding feeding vessels helps to distinguish conjunctival SCC from pterygia, which are usually associated with straight conjunctival vessels of normal caliber that are dragged by the pterygium lesion.4 Wide local excisional biopsy with cryotherapy is indicated for conjunctival or limbal lesions exhibiting the aforemen- tioned atypical characteristics of conjunctival SCC.4
Management
As most pterygia are asymptomatic and prog- ress very slowly, these lesions can typically be mon- itored clinically. Patients should be advised to use UV-protection sunglasses outdoors to help prevent
further progression. Symptoms of ocular surface irritation can be treated with lubricating artificial tear drops.
Pterygium excision is indicated in a number of circum- stances. Patients with substantial ocular surface irritation who do not get adequate relief with lubricants might be candidates for excision. More important, if the pterygium is inducing clinically meaningful astigmatism, or encroach- ing close to the visual axis (as in the case presented), exci- sion is warranted. Finally, some patients opt for surgical excision for cosmetic reasons.3,5
Several techniques of pterygium excision have been described. The simplest technique involves simple bare sclera excision. Unfortunately, this method is fraught with an extremely high recurrence rate (almost 80% in some stud- ies) and is therefore not recommended.5 Using an adjunctive agent, such as mitomycin C, an antimetabolite, can reduce recurrence rates to around 10%.5 Excision followed by place- ment of a sliding or rotational conjunctival flap can also be performed. The most commonly performed technique, how- ever, is pterygium excision with free conjunctival autograft, which is typically harvested from the superior conjunctiva of the same eye. The free autograft can be fixed into place with dissolvable sutures or glued using tissue fibrin adhesives.6 This technique is more technically challenging but is asso- ciated with a lower recurrence rate of around 5%. Although allografting with amniotic membrane has also been used with good success, it is more costly to perform.7
The surgery is generally performed under topical anes- thesia; subconjunctival lidocaine is injected around the pterygium and at the site of autograft harvesting. It is rec- ommended that all excised pterygia be sent for pathologic examination. This is important because actinic-induced neoplasms, particularly conjunctival intraepithelial neopla- sia and conjunctival SCC, can mimic pterygia in appear- ance and clinical behaviour.4
Recommendations
Patients with pterygia should be referred to ophthalmolo- gists nonurgently for assessment. In certain cases, patients might benefit from surgical excision. Suspicious lesions should always be biopsied to rule out malignancy.
Mr O’Brien is a postgraduate diploma student in the Division of Medical Sciences at Harvard University in Cambridge, Mass. Dr Jesudasan is a graduate of Kasturba Medical College in Manipal, India. Dr Noble is a clinical retina fellow in the Department of Ophthalmology at Harvard Medical School in Boston, Mass.
Competing interests None declared references
1. Bradley JC, Yang W, Bradley RH, Reid TW, Schwab IR. The science of pterygium. Br J Ophthalmol 2010;94(7):815-20. Epub 2009 Jun 9.
2. West S, Muñoz B. Prevalence of pterygium in Latinos: Proyecto VER. Br J Ophthalmol 2009;93(10):1287-90. Epub 2009 Jun 30.
3. Hirst LW. The treatment of pterygium. Surv Ophthalmol 2003;48(2):145-80.
4. Abeloff M, Armitage J, Niederhuber J, Kastan M, McKenna WG, editors. Abeloff’s clini- cal oncology. 4th ed. Philadelphia, PA: Churchill Livingstone; 2008.
5. Alpay A, Ugurbas SH, Erdogan B. Comparing techniques for pterygium surgery. Clin Ophthalmol 2009;3:69-74. Epub 2009 Jun 2.
6. Panda A, Kumar S, Kumar A, Bansal R, Bhartiya S. Fibrin glue in ophthalmology.
Indian J Ophthalmol 2009;57(5):371-9.
7. Park JH, Jeoung JW, Wee WR, Lee JH, Kim MK, Lee JL. Clinical efficacy of amniotic membrane transplantation in the treatment of various ocular surface diseases. Cont Lens Anterior Eye 2008;31(2):73-80. Epub 2008 Jan 30.
