A pterygium is an elevated, superficial, external ocular mass that usually forms over the perilimbal conjunctiva and extends onto the corneal surface. Pterygia can develop on the nasal and/or temporal limbus and can affect either or both eyes. Pterygia can vary from small, atrophic quiescent lesions to large, aggressive, rapidly growing fibrovascular lesions that can distort the corneal topography, and, in advanced cases, they can obscure the optical center of the cornea.[1, 2]
The pathophysiology of pterygium is characterized by elastotic degeneration of collagen and fibrovascular proliferation, with an overlying covering of epithelium. Histopathology of the abnormal collagen in the area of elastotic degeneration shows basophilia with hematoxylin and eosin stain. This tissue also stains with elastic tissue stains, but it is not true elastic tissue, in that it is not digested by elastase.[1, 2]
United States
The incidence of pterygium within the United States varies with geographical location. Within the continental United States, prevalence rates vary from less than 2% above the 40th parallel to 5-15% in latitudes between 28-36°. A relationship is thought to exist between increased prevalence and elevated levels of ultraviolet light exposure in the lower latitudes.[3, 4]
International
Internationally, the relationship between decreased incidence in the upper latitudes and relatively increased incidence in lower latitudes persists.
A pterygium can cause a significant alteration in visual function in advanced cases. It can become inflamed, resulting in redness and ocular irritation.
Pterygium is reported to occur in males twice as frequently as in females.
It is uncommon for patients to present with pterygium prior to age 20 years. Patients older than 40 years have the highest prevalence of pterygia, while patients aged 20-40 years are reported to have the highest incidence of pterygium.
The visual and cosmetic prognosis following pterygium excision is good. The procedures are well tolerated by patients, and, aside from some discomfort in the first few postoperative days, most patients are able to resume full activity within 48 hours of their surgery. Those patients who develop recurrent pterygia can be retreated with repeat surgical excision and grafting, with conjunctival/limbal autografts or amniotic membrane transplants in selected patients.[5, 6]
Patients with pterygium should reduce exposure to ultraviolet light whenever possible. Methods of reducing ultraviolet exposure include wearing ultraviolet-blocking sunglasses, wearing a cap with a wide brim, and seeking shade from direct sunlight.
Patients who are at high risk of the development of pterygium because of a positive family history of pterygia or because of extended exposure to ultraviolet irradiation need to be educated in the use of ultraviolet-blocking glasses and other means of reducing ocular exposure to ultraviolet light.
Patients with pterygia present with various complaints, ranging from no symptoms to significant redness, swelling, itching, irritation, and blurring of vision associated with elevated lesions of the conjunctiva and contiguous cornea in one or both eyes.
A pterygium can present as any of a range of fibrovascular changes on the surface of the conjunctiva and the cornea. It is more common for the pterygium to present on the nasal conjunctiva and to extend onto the nasal cornea, although it can present temporally, as well as in other locations.
The clinical presentation can be divided into 2 general categories.
One group of patients with pterygium can present with minimal proliferation and a relatively atrophic appearance. The pterygia in this group tend to be flatter and slow growing and have a relatively lower incidence of recurrence following excision.
The second group presents with a history of rapid growth and a significant elevated fibrovascular component. The pterygia in this group have a more aggressive clinical course and a higher rate of recurrence following excision.
Risk factors for pterygium include (1) increased exposure to ultraviolet light, including living in subtropical and tropical climates,[7] and (2) engaging in occupations that require outdoor activities.
A genetic predisposition to the development of pterygia appears to exist in certain families.
A predilection exists for males to develop this condition in significantly higher numbers than females, although this finding may represent an increased exposure to ultraviolet light in this portion of the population.[7]
Complications of pterygium include the following:
Extensive involvement of the extraocular muscles may restrict ocular motility and contribute to diplopia. In patients who have not yet undergone surgical excision, scarring of the medial rectus muscle is the most common cause of diplopia. In patients with pterygia who have previously undergone surgical excision, scarring or disinsertion of the medial rectus muscle is the most common cause of diplopia.
In patients with significantly elevated pterygia, focal drying and subsequent thinning of the adjacent cornea may rarely occur.
Postoperative complications of pterygium repair can include the following:
Late postoperative complications of beta radiation of pterygia can include scleral and/or corneal thinning or ectasia, which can present years or even decades after treatment. Some of these cases can be quite difficult to manage.
In some cases, adjunctive use of topical MMC at and after pterygium surgery has been reported to cause similar ectasia or melting of the sclera and/or the cornea.[9, 10, 11]
The most common complication of pterygium surgery is postoperative recurrence. Simple surgical excision has a high recurrence rate of approximately 50-80%. The rate of recurrence has been reduced to approximately 5-15% with use of conjunctival/limbal autografts or amniotic membrane transplants at the time of excision.[12, 13, 14, 15]
On rare occasion, malignant degeneration of epithelial tissue overlying an existing pterygium can occur.
Corneal topography can be very useful in determining the degree of irregular astigmatism induced by an advanced pterygium.
External photography can assist the ophthalmologist in following the progression of the pterygium.
Multiple different procedures have been advocated in the treatment of pterygium. These procedures range from simple excision to sliding flaps of conjunctiva with and without adjunctive external beta radiation therapy and/or use of topical chemotherapeutic agents, such as mitomycin C (MMC).[9, 17]
Using free grafts of conjunctiva (with or without limbal tissue) at the same time as primary excision of the lesion has been widely advocated as the preferred treatment modality for aggressive pterygia. For moderate-to-severe pterygia, some corneal surgeons use amniotic membrane transplants. Both the conjunctival autografts and the amniotic membrane transplants may be sutured onto adjacent conjunctiva and subjacent cornea. Some corneal surgeons seal the graft tissue onto the underlying sclera with the aid of fibrin tissue glue rather than with sutures.[18, 19, 20, 21, 12, 22]
A study by Kheirkhah et al found that conjunctival inflammation was much more common with amniotic membrane transplantation than with conjunctival autograft after pterygium surgery. However, with control of such inflammation and intraoperative application of mitomycin C, both techniques brought about similar final outcomes.[23]
Patients with pterygium can be observed unless the lesions exhibit growth toward the center of the cornea or the patient exhibits symptoms of significant redness, discomfort, or alterations in visual function. Pterygia can be removed for cosmetic reasons, as well as for functional abnormalities of vision or discomfort.[24]
Surgery for excision of a pterygium is usually performed in an outpatient setting under local or topical anesthesia with sedation, if necessary.
A prospective, randomized, interventional study by Kheirkhah et al assessed 56 patients who underwent pterygium excision with MMC application and an amniotic graft.[25] Of those 56 patients, 28 received MMC on the perilimbal bare sclera from 1-5 minutes, whereas 28 other patients received MMC under the conjunctiva. Endothelial cell studies revealed loss of 3.4% of cells in the bare sclera group compared with 4.8% in the subconjunctival group at 6 months. No complications were observed in either group; however, the study was small.
A prospective, nonrandomized study by Bahar et al examined the risk of endothelial cell loss in 43 subjects following pterygium surgery with MMC and conjunctival autograft.[26] The study included a control group who had a primary pterygium excision without MMC. Although the number of patients in each group was small, the patients who received MMC experienced a 4% reduction in endothelial cells at 3 months, compared with no loss in the control group. This suggests that MMC can affect the endothelial cell counts in patients undergoing pterygium excision.
Despite the relatively small sample sizes, both studies reported statistically significant decreases in corneal endothelial cell counts (P values ≤0.05) as long as 3 months after surgery. The authors note that placement of MMC at the limbus can be a risk factor for scleral melts. Thus, the authors advise placement of MMC only in the area of the fibrovascular conjunctival tissue.
Hirst initiated a prospective nonrandomized study of an evolution of previous pterygium surgical techniques involving extensive excision of overlying conjunctiva and underlying Tenon fascia in the vicinity of the pterygium, combined with a large, limbal-sparing autograft harvested from the superior conjunctival surface.[27] Hirst subsequently published his longer-term results after more than 1000 surgeries, including 806 primary pterygia and 194 recurrent pterygia. The author had a follow-up of longer than 1 year in 99% of those patients, with a mean follow-up of 616 days. The author reported only one recurrence among those 1000 patients, significantly lower than has been previously reported for both primary and secondary pterygium surgeries.[28]
This technique did not require the use of antimetabolites and it spared limbal stem cells at the site of conjunctival autograft harvesting. In addition to a reduction in expected recurrences, Hirst also reported a lower rate of postoperative complications with fewer than expected postoperative granulomas and fewer than expected conjunctival inclusion cysts.
In a prospective chronological study of 60 eyes in 53 patients, Yin, et al found a statistically significant reduction in recurrence with the use of interferon (IFN) alpha-2b eye drops, 4 times per day for 3 months postsurgery. After 12 months, the recurrence rate in control eyes was 33.3%, compared with a recurrence rate of 7.4% in the treatment group. The difference between the two groups was statistically significant (P = 0.048). The recurrence rates at the end of 18 months were the same. Adjunctive interferon alpha-2b eye drops in the postoperative period may be a useful addition to present therapy. The study is limited by the 18-month follow-up period.[29]
Postoperatively, the eye is generally patched overnight, and it is treated subsequently with topical antibiotics and anti-inflammatory drops and/or ointments.
Theoretically, minimizing exposure to ultraviolet radiation should reduce the risk of development of pterygium in susceptible individuals. Patients are advised to use a hat or a cap with a brim, in addition to ultraviolet-blocking coatings on the lenses of glasses/sunglasses to be used in areas of sun exposure. This precaution is even more important for those patients living in tropical or subtropical areas or for those patients who are engaged in outdoor activities with a high risk of ultraviolet exposure (eg, fishing, skiing, gardening, outdoor construction work).
Postoperatively, after pterygium excision, the topical steroids are slowly tapered. Patients on topical steroids need to be observed to reduce the risk of related problems, such as elevated intraocular pressure and cataracts.[30]
Medical treatment of pterygium consists of over-the-counter (OTC) artificial tears/topical lubricating drops (eg, Refresh Tears, GenTeal drops) and/or bland, nonpreserved ointments (eg, Refresh P.M., Hypo Tears), as well as occasional short-term use of topical corticosteroid anti-inflammatory drops (eg, Pred Forte 1%) when symptoms are more intense. In addition, the use of ultraviolet-blocking sunglasses is advisable to reduce the exposure to further ultraviolet radiation.
Clinical Context: Artificial tears provide topical ocular surface lubrication in patients with irregular corneal surfaces and irregular tear films. These conditions are very common in the setting of pterygium.
Clinical Context: A relatively more viscous lubricant for the ocular surface. These thicker preparations tend to blur the vision temporarily; therefore, they are generally used at night, except in patients with severe discomfort.
Clinical Context: A topical corticosteroid suspension used to reduce inflammation in the eye. Use should be limited to eyes with significant inflammation not relieved by topical lubricants.
To reduce inflammation on the ocular surface and other ocular tissues. Corticosteroids can be helpful in the management of inflamed pterygia by reducing the swelling of the inflamed tissues of the ocular surface adjacent to the lesions.