Pterygium

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 by Nambi Nallasamy, MD on March 21, 2020.



Disease Entity

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.

Etiology

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.

Risk Factors

UV radiation, proximity to the equator, dry climates, outdoor lifestyle.

General Pathology

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:

Pterygium histopathology. H&E stain exhibiting elastotic degeneration.

Pathophysiology

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.

Primary prevention

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.

Diagnosis

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.


Physical examination

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
  • Keratometry
  • Corneal Topography
  • Motility Exam
  • The remainder of a comprehensive eye exam to include pupil exam, visual fields, intraocular pressure, and dilated funduscopic exam

Signs

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.

Symptoms

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.

Clinical diagnosis

Diagnosis is based on the typical clinical appearance

Diagnostic procedures

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.


Differential diagnosis

  • Pannus
  • 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

Management

General treatment

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.

Medical therapy

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.

Surgery

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.

Complications

  • Recurrence 
  • Corneal scarring
  • Corneal perforation
  • Strabismus
  • Non-healing epithelial defect (esp with mitomycin C)
  • Scleral melt (esp with mitomycin C)

Prognosis

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.

Additional Resources

References

1: Hirst LW. Recurrent pterygium surgery using pterygium extended removal followed by extended conjunctival transplant: recurrence rate and cosmesis. Ophthalmology. 2009 Jul;116(7):1278-86.

2: Hirst LW, Axelsen RA, Schwab I. Pterygium and associated ocular surface squamous neoplasia. Arch Ophthalmol. 2009 Jan;127(1):31-2.

3: Hirst LW. Prospective study of primary pterygium surgery using pterygium extended removal followed by extended conjunctival transplantation. Ophthalmology. 2008 Oct;115(10):1663-72. Epub 2008 Jun 16.

4: Hirst LW. Mitomycin C in the treatment of pterygium. Clin Experiment Ophthalmol. 2006 Apr;34(3):197-8.

5: Troutbeck R, Hirst L. Trends in beta irradiation for pterygium in Queensland. Clin Experiment Ophthalmol. 2003 Dec;31(6):545.

6: Hirst LW. The treatment of pterygium. Surv Ophthalmol. 2003 Mar-Apr;48(2):145-80. Review.

7: Jaros PA, DeLuise VP. Pingeculae and pterygia. Survey of Ophthalmology 1988;33:41-49.

8. Nemesure B, Wu S, Henis A, Leske MC, Barbados Eye Studies Group. Nine-year incidence and risk factors for pterygium in the Barbados Eye Studies. Ophthalmology 2010;115:2153-2158.

9. Detorakis ET, Spandidos DA. Pathogenetic mechanisms and treatment options for opthalmic pterygium: Trends and perspectives (Review). International Journal of Molecular Medicine 2009;23:439-447.

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.