Pterygium_(conjunctiva)

Pterygium usually refers to a benign growth of the conjunctiva. A pterygium commonly grows from the nasal side of the sclera. It is associated with, and thought to be caused by ultraviolet-light exposure (e.g. sunlight), low humidity, and dust. The predominance of pterygia on the nasal side is possibly a result of the sun\'s rays passing laterally through the cornea where it undergoes refraction and becomes focused on the limbic area. Sunlight passes unobstructed from the lateral side of the eye, focusing on the medial limbus after passing through the cornea. On the contralateral side, however, the shadow of the nose medially reduces the intensity of sunlight focused on the lateral/temporal limbus.Coroneo, MT (November 1993). "Pterygium as an early indicator of ultraviolet insolation: a hypothesis". Br J Ophthalmol 77 (11): 734-9. PMID 8280691. 

Pathology

Pterygium in the conjunctiva is characterized by elastotic degeneration of collagen and fibrovascular proliferation. It has an advancing portion called the head of the pterygium, which is connected to the main body of the pterygium by the neck. Sometimes a line of iron deposition can be seen adjacent to the head of the pterygium called Stocker\'s line. The location of the line can give an indication of the pattern of growth. As it is a benign growth, it requires no treatment unless it grows to such an extent that it covers the pupil, obstructing vision. Some patients may also choose surgery if the growth becomes too unsightly. The exact cause is unknown, but it is associated with excessive exposure to wind, sun, or sand. Wearing protective sunglasses with side shields and/or wide brimmed hats and using artificial tears throughout the day may help prevent their formation or stop further growth. For surfers and other water-sport athletes, they should wear eye protection that block 100% of the UV rays from the water.

Occasionally it is found as an incidental finding in middle aged patients who spend a lot of time in the sun. Pterygiums are also among younger men and women who surf, wakeboard, and kiteboard due to excessive exposure to UV rays bouncing off of the water. It was also seen in NASCAR drivers who did not wear goggles due to dust irritation to the sclera. Skiiers and snowboarders protect their eyes on the snow so athletes participating in water sports also need to take heed of the UV rays and protect their eyes.

Treatment

While patients can be symptomatically treated w/ artificial tears, no reliable medical treatment exists to reduce or even prevent pterygium progression. Definitive treatment is achieved only by surgical removal. Long term follow up is required as pterygium may recur even after complete surgical correction. If there is recurrence after surgery or if recurrence of pterygium is thought to be vision threatening, it is possible to use strontium (⁹⁰Sr) plaque therapy.

⁹⁰Sr is a radioactive substance that produces beta particles which penetrate a very short distance into the cornea at the site of the operation. It suppresses the regrowth of blood vessels that occur with return of the pterygium. The treatment requires some local anaesthetic in the eye and is best done at the time of, or on the same day as the pterygium excision.

The ⁹⁰Sr plaque is a concave metal disc about 1-1.5cm in diameter which is hollow and filled with an insoluble strontium salt. The side placed on the eye is a very thin and delicate silver film that will contain the strontium but allow the beta particles to escape. The dose of radiation to the conjunctiva is controlled by the time that the plaque is left in contact with the surface. The integrity of the plaque surfaces is paramount to prevent exposure to patients and so is wipe tested to see if radioactive matter is escaping. Obviously this test must be done very very gently.

See also

• List of eye diseases and disorders
• Pinguecula

External links

• Facts About the Cornea and Corneal Disease The National Eye Institute (NEI)

References

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