INTRODUCTION — A pterygium is a triangular wedge of fibrovascular conjunctival tissue that typically starts medially on the nasal conjunctiva and extends laterally onto the cornea (picture 1). "Pterygium" refers to the shape of the tissue, which looks like an insect wing. The plural form of pterygium is pterygia.
A pterygium is sometimes thought of as a trivial problem because it is unlikely to threaten visual acuity unless it approaches the visual axis. Nevertheless, it can be a cause of concern to patients because of the abnormal appearance it confers upon the eye and the irritation that is often associated with it. Although benign in the sense that pterygium is not cancerous, it can have important adverse effects on vision if proliferation approaches or reaches the visual axis.
This topic will focus on the clinical presentation, diagnosis, and treatment of pterygium. Some conditions that may occasionally be confused with pterygium are discussed in detail elsewhere. (See "Conjunctivitis" and "Blepharitis" and "Episcleritis" and "Photokeratitis".)
EPIDEMIOLOGY — Worldwide prevalence of pterygium varies from 1 to 25 percent, depending on the population studied [1-6]. Pterygium occurs more commonly in tropical regions, although the exact mechanisms for this are not well known [7-9]. The prevalence of pterygium is associated with chronic sun exposure  and specifically to ultraviolet (UV) light [11-13], which may partly explain the geographic variation in prevalence.
Several population-based studies have found higher rates of pterygium to be associated with older age, male sex, fewer years of education, and outdoor job location [2,6,14-16]. In the Barbados Eye Study, approximately one-fourth of the Black participants had pterygium, a frequency that was 2.5 to 3 times higher than among White participants in this study . Lower rates were associated with always using sunglasses outdoors and using prescription glasses [1,16]. One study in Australia found a higher rate of pterygium in rural areas compared with urban areas (6.7 and 1.7 percent, respectively), partly as a result of ocular sun exposure .
PATHOGENESIS — Although pterygium is classified as a corneal degenerative disorder, it may be considered more of a proliferative condition that has several possible inciting factors . Ultraviolet (UV) light , abnormal conjunctival expression of tumor suppressor gene p53 , presence of angiogenesis-related factors , human papillomavirus (HPV) infection , and abnormal human leukocyte antigen (HLA) expression  have all been proposed as pathogenic factors. In particular, UV radiation may trigger events that produce damage to cellular DNA, RNA, and extracellular matrix composition [21,22]. Hereditary factors may also contribute to pathogenesis and therefore to varying prevalence rates among populations .
One model of epithelial cell production suggests that light-induced alteration of limbal stem cell function can account for the classic wedge shape of pterygium, which starts at the limbus (junction of the cornea and sclera) (figure 1) .
NATURAL HISTORY — The natural history of pterygium is poorly understood. One general observation is that pterygium, when active, can grow over a period of several months to years. Activity is marked clinically by redness and localized thickening, which probably represent active inflammation. When inactive (white and flat), pterygium may remain static for decades with no measurable increase in size or clinical significance. It is unclear how pterygium converts from active to inactive, or if it can be reactivated.
CLINICAL PRESENTATION — The most common symptoms caused by pterygium are redness and irritation. Visual impairment is less common. In the absence of symptoms, patients may also report a change in the appearance of their eye, or pterygium may be noted incidentally on physical examination.
Although common, the redness and irritation associated with pterygium is usually mild. Most patients may not seek treatment initially. When patients do seek treatment, it is typically for worsening symptoms of discomfort and foreign body sensation, which impairs their daily activities.
Mild visual impairment caused by pterygium may be ignored initially, although some patients present with visual compromise due to pterygium that significantly affects daily function. A pterygium extending more than a few millimeters onto the cornea can impair vision on the basis of induced astigmatism. Astigmatism is a refractive error in which a warped corneal surface causes light rays entering the eye along different planes to be focused unevenly. At low magnitude, astigmatism causes little subjective blur. A pterygium larger than 3.5 mm, and therefore more than halfway to the center of the pupil in a typical cornea of 11 to 12 mm, is likely to cause blurring of vision . Once a threshold is crossed of 45 percent of the corneal radius, or within 3.2 mm of the visual axis, the astigmatism may increase significantly . A pterygium that extends further centrally may directly affect the visual axis, with the resultant opacity blocking vision (picture 2 and picture 3). (See "Visual impairment in adults: Refractive disorders and presbyopia", section on 'Astigmatism'.)
An uncommon manifestation of pterygium is restricted eye movement. This occurs following multiple attempts at excision when the resulting inflammation over the pterygium causes the conjunctiva and overlying eyelid to stick together, preventing the eye from moving properly.
In the absence of symptoms, patients may report a growth over the clear cornea, which sits anterior to the iris (figure 1). Pterygium is often unnoticed by the patient or clinician until the pterygium appears white against the background of the colored iris (picture 1 and picture 4 and picture 2) or until there is a significant vascular component causing redness of the pterygium to contrast with the conjunctiva (picture 2 and picture 5).
DIAGNOSIS — The diagnosis of pterygium is made by the classic clinical appearance of a wedge-shaped growth extending onto the cornea (picture 1). However, pterygium does not always manifest in its classic form, and other conditions may have a similar appearance.
Pterygium is typically soft, varying from nearly flat, white, and amorphous to thick, pink/red, and fibrovascular. Pterygium is also more likely to be bilateral than unilateral. The pictures each show a typical pterygium (picture 1 and picture 2 and picture 3 and picture 4 and picture 5).
Differential diagnosis (malignant and premalignant lesions) — Several features help to distinguish pterygia from squamous cell carcinoma of the conjunctiva and its premalignant precursor, conjunctival intraepithelial neoplasia (CIN):
●Malignant lesions are usually more vascular than pterygia and may have a prominent feeder vessel.
●Malignant lesions are more likely to have nodular or leukoplakic features and to be irregular in consistency.
●CIN and malignant lesions are less likely to have the characteristic triangular insect wing shape of pterygium (picture 1 and picture 2 and picture 3 and picture 4 and picture 5) and may be more fan-like in morphology (picture 6).
●CIN and malignant lesions are more likely to be unilateral and often occurs in axes other than the horizontal plane.
Conjunctival neoplasms that may be confused with pterygium are:
●Ocular surface squamous neoplasia (OSSN) including:
•Conjunctival squamous cell carcinoma (SCC)
•CIN (picture 6)
●Melanoma of the conjunctiva, particular amelanotic variant
OSSN is associated with sun exposure, HIV/AIDS, and HPV . Increased incidence of conjunctival melanoma parallels that of cutaneous melanoma and may be related to exposure to sunlight . Pterygia that are atypical or lesions with suspicious features should be referred to an ophthalmologist with appropriate expertise to determine whether excisional biopsy is warranted.
Differential diagnosis (benign lesions) — Pinguecula is a degenerative eye condition that is often confused with pterygium. A pinguecula is a yellowish, slightly raised conjunctival lesion arising at the limbal conjunctiva (picture 7). Unlike a pterygium that arises from the limbus and progresses onto the cornea, a pinguecula arises from the limbus and remains confined to the conjunctiva without corneal involvement. The tendency to extend onto the corneal surface is the main distinguishing factor of a pterygium, compared with a pinguecula. There is usually space between the pinguecula and the edge of the cornea (picture 8). Unlike pterygium that more likely appears on the nasal conjunctiva, a pinguecula may appear on the nasal conjunctiva, temporal conjunctiva, or both.
Other conditions that can mimic pterygium include localized conjunctivitis, pseudo-pterygium (corneal pannus, a proliferative response to chronic blepharitis, allergy, contact lens wear, or other insult) (picture 9), and episcleritis (picture 10 and picture 11). Other clinical findings for these conditions will help distinguish from pterygium. These conditions can also cause lesions outside the horizontal axis, unlike pterygium. (See "Conjunctivitis" and "Blepharitis" and "Episcleritis".)
Finally, symblepharon after chemical, thermal, or mechanical injury, or related to cicatrizing disease such as Stevens-Johnson syndrome, mucous membrane pemphigoid, fibrosis after surgery near the limbus, and limbal dermoid may have findings that mimic pterygium.
TREATMENT — Patients with a small pterygium can be treated symptomatically for redness and irritation with artificial tears or other ocular lubricants. The management of patients with larger lesions that impair visual acuity or eye movement usually involves surgical excision of the pterygium. The decision to perform surgical excision also varies based on the rate of documented growth and degree of induced astigmatism. Surgery should be avoided for cosmetic reasons alone, as pterygium may recur, often times with irritative symptoms.
Correction of visual impairment due to refractive error, including astigmatism, is discussed in detail elsewhere. (See "Visual impairment in adults: Refractive disorders and presbyopia", section on 'Treatment'.)
There are few randomized trials of pterygium that help to direct management, particularly for medical treatments . Clinical practice varies widely based on individual patient and clinician preferences.
Medical therapy — Medical treatments are for symptomatic relief and have not been shown to stop progression or cause regression of a pterygium. Patients with pterygium that does not affect vision or eye movement may be treated symptomatically with topical lubricants including drops, ointments, and gels, all of which are available over-the-counter. Artificial tears are the most frequently utilized topical lubricant for pterygium and may help to reduce symptoms . They can be given 1 to 2 drops to affected area three to four times daily. Preservative-free preparations should be used in patients who have irritative symptoms with preservatives or who need to use lubrication more than four times per day. Preservative-free preparations are more expensive.
Treatment with topical decongestants, nonsteroidal antiinflammatory drugs (NSAIDs), and glucocorticoids may also be effective for symptomatic relief of pterygium [30,31], but are all associated with adverse effects which limit their use. Topical decongestants can be used to treat redness and irritation not relieved by artificial tears and are often associated with significant tachyphylaxis. The most common side effects of topical decongestants are increased intraocular pressure, high systemic blood pressure, palpitations, and headache. Topical NSAIDs should be prescribed only by an ophthalmologist, as they can cause keratitis as well as increased lacrimation and a transient burning sensation. Topical glucocorticoids should also be prescribed only by an ophthalmologist because these can exacerbate infection and cause glaucoma and cataracts with long-term use. These agents should be avoided if the patient is asymptomatic. Any of these medications taken chronically can lead to tachyphylaxis as well as cause "rebound" symptoms when discontinued.
Vascular endothelial growth factor (VEGF) inhibitors have been proposed to block angiogenesis responsible for pterygium formation . Small cases series found that intralesional bevacizumab, but not ranibizumab, injections help to decrease size of primary pterygium [33-35]. It is unclear whether VEGF inhibitors improve symptoms related to pterygium or affect long-term prognosis.
Follow-up of pterygium with medical management varies based on the degree of pterygium inflammation, growth, and proximity to the visual axis. If there is no visual impairment, restriction of eye movement, encroachment on the pupil, or other concerning signs/symptoms, monitoring at 6- to 12-month intervals is reasonable.
Surgery — Surgery generally involves excision of pterygium, often with adjuvant medical and surgical treatments to help lower rates of recurrence. Limited data are available on surgical outcomes for pterygium, as there are few randomized trials with large numbers of patients and long-term follow-up. Excision usually corrects pterygium-induced astigmatism and visual impairment from a visual axis opacity . However, recurrence of pterygium is common.
Indications — Surgery for pterygium is indicated in the following situations :
●Induced astigmatism that causes visual impairment
●Opacity in the visual axis
●Documented growth that is threatening to affect the visual axis via astigmatism or opacity
●Restriction of eye movement
●Significant cosmetic impact or intractable irritation
Recurrent pterygium, which may occur after surgery, can be more symptomatic and problematic to eliminate than primary pterygium. These are factors that should be taken into consideration when surgery is contemplated for small pterygium, irritation, or for cosmetic reasons alone.
Operative approach — Surgical excision is straightforward from a technical perspective. The excision procedure typically lasts about half an hour and is done on an outpatient basis under local anesthesia, with or without intravenous (IV) sedation.
Simple "bare sclera" excision is associated with high recurrence rates, so excision should be combined with adjunctive measures [37-39]. These include conjunctival autografts, topical or subconjunctival medications, or irradiation [28,38,40-50]. A meta-analysis of 24 trials involving 1815 eyes found that the most effective adjuvant treatment to prevent recurrence after surgery was the combination of a conjunctival autograft and cyclosporine eye drops . A 2019 report of an international survey of cornea specialists found resection with autologous conjunctival or limbal-conjunctival graft as the preferred technique, with 61 percent using that technique preferring fibrin glue over sutures .
Follow-up — The ophthalmologist typically follows the patient closely after surgery, treating pain, monitoring for ocular complications, and documenting visual outcome. The progression of pterygium can be documented photographically or with video keratography, which is a form of topographic mapping of the corneal surface.
Postoperative pain due to the surgical abrasion of the corneal surface may require opioids for several days after surgery, although elimination of bare sclera technique and advances such as the use of grafts secured by fibrin glue rather than sutures reduce the likelihood of postoperative pain requiring opioids. Photophobia usually lasts a few weeks. Pain and photophobia, rather than any anatomic healing complications, limit patient activity in the early postoperative period. Patients are typically prescribed postoperative topical antibiotics for a few days or weeks, and topical glucocorticoids for a few weeks or months. Patients should be monitored by the ophthalmologist while glucocorticoids are prescribed due to possible side effects, including infection and secondary glaucoma.
Complications — Intraoperative complications are rare for pterygium removal as the procedure is extraocular; however, complications include ocular perforation or inadvertent extraocular muscle damage as well as possible retinal detachment or endophthalmitis that might occur as a result of inadvertent perforation of the globe.
Corneal ulceration is a rare complication associated with the use of adjuncts that have anti-metabolic effect.
Repeated excisions tend to lead to corneal scarring, irregular astigmatism, fibrotic restriction of extraocular movements leading to diplopia, and formation of symblepharon (adhesions of eyelid to ocular surface of globe). All of these can contribute to an abnormal appearance of the globe and can interfere with visual function.
Recurrence — Recurrence rates for simple surgical excision to bare sclera are high, varying between 30 to 80 percent of cases , and reported as high as 88 percent in certain subpopulations . The high recurrence rate, even when adjunctive measures are used with excision, is the main reason that surgery is not recommended for a small pterygium, for irritation, or for cosmetic reasons alone.
The recurrent lesion may also be more inflamed or grow larger than the initial lesion. Recurrent pterygium has a higher rate of recurrence after excision than primary pterygium , creating a vicious cycle of excision and recurrence. Recurrences and repeated excisions can lead to disruption of the ocular surface and subsequent complications. Increasing patient age is associated with lower risk of recurrence . When there is recurrence, it is typically apparent by four months after surgery. If the pterygium has not recurred after one year, it is not likely to recur .
PREVENTION — The efficacy of prevention measures for pterygium is unknown. Exposure to ultraviolet (UV) light is an important risk factor for development of pterygium. (See 'Pathogenesis' above.)
Several population-based studies suggest that the use of sunglasses and hats may help prevent primary pterygium [1,55,56]. It is not yet established that any specific measures reduce the progression once pterygium, primary or recurrent, has appeared. Lubrication and protection with a hat and/or UV blocking spectacles that fit closely, wrap around, or have side shields against potentially adverse factors of UV exposure are sensible approaches in the absence of evidence.
INFORMATION FOR PATIENTS — UpToDate offers two types of patient education materials, "The Basics" and "Beyond the Basics." The Basics patient education pieces are written in plain language, at the 5th to 6th grade reading level, and they answer the four or five key questions a patient might have about a given condition. These articles are best for patients who want a general overview and who prefer short, easy-to-read materials. Beyond the Basics patient education pieces are longer, more sophisticated, and more detailed. These articles are written at the 10th to 12th grade reading level and are best for patients who want in-depth information and are comfortable with some medical jargon.
Here are the patient education articles that are relevant to this topic. We encourage you to print or e-mail these topics to your patients. (You can also locate patient education articles on a variety of subjects by searching on "patient info" and the keyword(s) of interest.)
●Basics topic (see "Patient education: Pterygium (The Basics)")
SUMMARY AND RECOMMENDATIONS
●A pterygium is a triangular wedge of fibrovascular conjunctival tissue that extends onto the corneal surface (picture 1). Pterygium can cause local symptoms of redness and irritation and can also impair vision by inducing astigmatism or by directly affecting the visual axis. (See 'Clinical presentation' above.)
●Pterygium should be differentiated from other ocular conditions, including conjunctival neoplasia and pinguecula, as treatments for these differ. (See 'Diagnosis' above.)
●Indications for surgical removal of pterygium include:
•Astigmatism leading to visual impairment
•Opacity in the visual axis
•Documented growth that is threatening to affect the visual axis via astigmatism or opacity
•Restriction of eye movement
•Significant cosmetic impact or intractable irritation
Recurrent pterygium, which is common after surgery, can be more symptomatic and problematic to remove than primary pterygium. These factors should be taken into consideration when surgery is contemplated for a small pterygium, associated irritation, or cosmetic reasons alone. (See 'Indications' above.)
●Exposure to ultraviolet (UV) light is an important risk factor for development of pterygium, and the use of sunglasses and hats may help prevent it. However, it is not clear that any specific measures reduce the progression of pterygium. Lubrication and protection with a hat and/or UV-blocking spectacles that fit closely, wrap around, or have side shields are sensible approaches in the absence of evidence. (See 'Prevention' above.)
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