Pterygium, from the Greek pterygos meaning “wing”, is a common ocular surface lesion originating in the limbal conjunctiva within the palpebral fissure with progressive involvement of the cornea. The lesion occurs more frequently at the nasal limbus than the temporal with a characteristic wing-like appearance.
The etiology is unknown. An increased incidence is noted in latitudes nearer the equator and in individuals with a history of increased UV exposure. Some studies have shown a slightly higher incidence in males than females, which may only reflect a higher rate of UV radiation.
UV radiation, proximity to the equator, dry climates, outdoor lifestyle.
Histologically, pterygia are an accumulation of degenerated subepithelial tissue which is basophilic with a characteristic slate gray appearance on H&E staining. Vermiform or elastotic degeneration refers to the wavy worm-like appearance of the fibers. Destruction of Bowman layer by fibrovascular ingrowth is typical. The overlying epithelium is usually normal, but may be acanthotic, hyperkeratotic, or even dysplastic and often exhibits areas of goblet cell hyperplasia.
The American Academy of Ophthalmology's Pathology Atlas contains two virtual microscopy images of tissue samples with Pterygium:
The large number of theories that exist to explain the pathogenesis of pterygium growth underscores the uncertainty of the etiology. The increased prevalence in hot dry climates and regions nearer to the equator suggest a role of environmental factors such as UV radiation and dryness. Actinic changes seen on histopathology similar to actinic keratoses on the skin also supports the role of UV radiation. It has been suggested that radiation activated fibroblasts may result in excessive production of material resulting in pterygia. Other proposed theories include choline deficiency, inflammation, disregulation of angiogenesis, immune system abnormalities, tear film abnormalities, as well as the possible role of a viral stimulus. <be> Coronea MT proposed that pterygium occur due to albedo concentration in the anterior eye (albedo's hypothesis). Light entering the temporal limbus at 90 degree is concentrated at medial limbus and this is responsible for predominance of medial pterygia.
As UV radiation is believed to play an important role in the pathophysiology, avoidance of UV exposure is important to primary prevention. Ocular surface lubrication may also help.
The diagnosis is made by slit-lamp examination of the wing-shaped limbal growth at the characteristic location within the palpebral fissure. The diagnosis is most often clear clinically, but histopathologic confirmation is performed routinely, as there can be associated dysplasia of the overlying tissue.
A complete eye exam should be performed on all patients with apparent pterygia focusing on assessment of visual and refractive impact as well as the exclusion of less common alternate diagnoses.
- Visual acuity with current correction and manifest refraction
- External examination (lids, lashes, lacrimal apparatus)
- Examination of bulbar and palpebral conjunctiva as well as fornices
- Slit lamp biomicroscopy of the ocular surface and anterior segment
- Corneal Topography
- Motility Exam
- The remainder of a comprehensive eye exam to include pupil exam, visual fields, intraocular pressure, and dilated funduscopic exam
The diagnosis of pterygium is based on the clinical appearance of the lesion. Typical findings include
- Fibrovascular conjunctival growth within the palpebral fissure extending onto the corneal surface
- triangular or trapezoidal shape with the apex, or head, extending onto the cornea
- vascular straightening in the direction of the advancing head of the pterygium on the corneal surface.
- It may affect the nasal and temporal limbus of both eyes or only a single location.
- Raised lesion, white to pink in color depending on vascularity
- Ranges from a fine transparent area with very mild elevation, few vessels, and minimal corneal involvement in the early stages to a thick opaque vascular growth extending to the visual axis in later stages
- Pinguecula are often present in the ipsilateral or contralateral eye
- A pigmented epithelial iron line (Stocker’s line) adjacent to a pterygium is evidence of chronicity.
It is unusual for pterygia to deviate from the characteristic locations of three and nine o’clock within the palpebral fissure. Pterygioid lesions in other locations should elevate suspicion for alternate diagnoses.
Though frequently asymptomatic, pterygia can become inflamed and cause ocular surface irritation. Many patients will disclose their dislike of the appearance of the pterygium when questioned directly. As the lesion progresses, vision may be affected by induction of astigmatism or obscuration of the visual axis.
Diagnosis is based on the typical clinical appearance
Assessment of visual acuity, changes in manifest refraction, and corneal topography can aid in determining the visual impact of pterygia. Histopathologic confirmation is routine for excised lesions and can be important in verifying atypical cases.
- Limbal stem cell deficiency
- Conjunctival Intraepithelial Neoplasia (CIN)
- Terrien’s marginal degeneration
- Symblepharon secondary to chemical, thermal, or mechanical injury
- Stevens Johnson Syndrome
- Limbal dermoid
- Neurotrophic keratitis
- Fuchs' Superficial Marginal Keratitis
A number of potential therapeutic options exist for the management of pterygia ranging from conservative management with lubrication to surgical excision with conjunctival autografts. Due to the potential for recurrence of a more aggressive lesion, as well as other surgical risks, the surgical removal of pterygia should not be undertaken casually.
Inflamed pterygia may cause irritation, foreign body sensation, and tearing which, in many cases, can be alleviated with over the counter vasoconstrictor drops, lubricating drops and ointments.
Medical follow up
Initially, the corneal extension of the pterygium should be measured and followed every 1 to 2 years to determine the rate of growth toward the visual axis.
Excision: simple excision or simple conjunctival closure will result in a recurrence rate as high as 80% and is now considered unacceptable.
Excision together with adjunctive therapies such as mitomycin C or 5-fluorouracil can reduce the risk of recurrence to approximately 10%. However, the use of mitomycin C and 5-fluorouracil can increase the risk of corneal or scleral melt postoperatively.
Excision with conjunctival flap or autograft: this approach carries an approximate rate of recurrence of 5-10% with minimal risk of complications. However, it is a lengthier and more technically challenging procedure than the methods described above. Results reported with a modification the standard conjunctival autograft technique, involving extensive Tenon's resection and suturing of the conjunctival autograft (referred to as P.E.R.F.E.C.T. for pterygium) indicate a further decreased recurrence rate (as low as 1 in 1000 in one series).
Surgical follow up
Topical steroids are often utilized in the initial postoperative period. Patients should be followed to monitor for recurrence. 97% of all recurrences occur in the first year after surgery.
- Corneal scarring
- Corneal perforation
- Non-healing epithelial defect (esp with mitomycin C)
- Scleral melt (esp with mitomycin C)
Recurrence rate can be as low as 1 in 1000 depending on surgical approach. Defects in Bowman layer often result from surgical excision due to the involvement of Bowman layer by the lesion, and mild residual astigmatism may be present despite successful surgery. Visual prognosis is typically very good and only limited by the cornea if the excised lesion involved the visual axis.
- Boyd K, Lipsky SN. Pinguecula and Pterygium. American Academy of Ophthalmology. EyeSmart® Eye health. https://www.aao.org/eye-health/diseases/pinguecula-pterygium-list. Accessed March 21, 2019.
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