|Classification and external resources|
- 1 Disease Entity
- 2 Diagnosis
- 3 Management
- 4 Additional Resources
- 5 References
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 degenerate fibers. Destruction of Bowman’s 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, an inflammatory disorder, disregulation of angiogenesis, immune system abnormalities, tear film abnormalities, as well as the possible role of a viral stimulus.
Recurrent pterygia appear to be more related to surgical trauma than UV radiation as avoidance of UV radiation has not been shown to affect the incidence of recurrence. The actinic damage noted histologically on primary pterygia is characteristically absent from recurrent pterygia, supporting this theory.
As UV radiation is believed to play an important role in the pathophysiology, avoidance of UV exposure is probably important to primary prevention. Ocular surface lubrication may also help.
The diagnosis is made by slit-lamp examination of the typical limbal growth at the characteristic location within the palpebral fissure. The diagnosis is most often clear clinically, but histopathologic confirmation is performed routinely.
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 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.
- May be a thin translucent membrane or significantly thickened with an elevated mound of gelatinous material.
- 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.
- Conjunctival Intraepithelial Neoplasia (CIN)
- Terrien’s marginal degeneration
- Symblepharon secondary to chemical, thermal, or mechanical injury
- Stevens Johnson Syndrome
- Limbal dermoid
- Neurotrophic 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 radiotherapy, mitomycin and 5FU: the use of these adjunctive agents will reduce the 80% recurrence of simple excision to about 10% but bring with them some visually threatening complications. The only real advantage of these methods is the simplicity and speed of the surgery.
Conjunctival Flap/Graft : this is considered the Gold Standard of care and carries an approximate rate of recurrence of 5-10% with minimal complications. However, it is a lengthier procedure and technically slightly more complicated than those methods above. Recently a major modification of a routine autograft, known as P.E.R.F.E.C.T. for PTERYGIUM, has reduced the recurrence rate to 1/1000 and results in a cosmetic result where the appearance of the eye after this procedure is indistinguishable from that of a normal eye.
Surgical follow up
Intensive postoperative topical steroids may be required. Patients need to be followed for one year if a recurrence is to be identified. 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 1/1000 with complications being very uncommon.
- American Academy of Ophthalmology. Pterygium and pinguecula Practicing Ophthalmologists Learning System, 2017 - 2019 San Francisco: American Academy of Ophthalmology, 2017.
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10. The Wills Eye Manual, 5th Edition. Ehlers and Chirag. Lippincott, 2008.
11. Ocular Pathology Atlas. American Academy of Ophthalmology Web site. https://www.aao.org/resident-course/pathology-atlas. Published 2016. Accessed January 4, 2017.