Answer: Can you identify this condition?

2. 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 ocular 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 prevalence 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 yellowish in appearance, do not invade the cornea, and do not affect vision. They can occur in either the nasal or temporal 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 corneal 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 limbus. 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 aforementioned atypical characteristics of conjunctival SCC.⁴

Management

As most pterygia are asymptomatic and progress very slowly, these lesions can typically be monitored 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 circumstances. 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 encroaching close to the visual axis (as in the case presented), excision 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 studies) 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 placement of a sliding or rotational conjunctival flap can also be performed. The most commonly performed technique, however, 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 associated 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 anesthesia; subconjunctival lidocaine is injected around the pterygium and at the site of autograft harvesting. It is recommended that all excised pterygia be sent for pathologic examination. This is important because actinic-induced neoplasms, particularly conjunctival intraepithelial neoplasia and conjunctival SCC, can mimic pterygia in appearance and clinical behaviour.⁴

Recommendations

Patients with pterygia should be referred to ophthalmologists nonurgently for assessment. In certain cases, patients might benefit from surgical excision. Suspicious lesions should always be biopsied to rule out malignancy.