Pterygium (conjunctiva)

Overview
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.

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.

The exact cause is unknown, but it is associated with excessive exposure to wind, sunlight, or sand. Therefore, it is more likely to occur in populations that inhabit the areas near the equator, as well as windy locations. Additionally, Pterygium are twice as likely to occur in men than women.

Some research also suggests a genetic predisposition due to an expression of vimentin, which indicates cellular migration by the keratoblasts embryological development, which are the cells that give rise to the layers of the cornea. These cells also exhibit an increased P53 expression likely due to a deficit in the tumor suppressor gene. These indications give the impression of a migrating limbus because the cellular origin of the pterygium is actually initiated by the limbal epithelium.

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. 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. 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.

Anatomically, the pterygium is composed of several segments:
 * Fuchs' Patches (minute gray blemishes that disperse near the pterygium head).
 * Stocker's Line (a brownish line composed of iron deposits).
 * Hood (fibrous nonvascular portion of the pterygium).
 * Head (apex of the pterygium, typically raised and highly vascular).
 * Body (fleshy elevated portion congested with tortuous vessels).
 * Superior Edge (upper edge of the triangular or wing shaped portion of the pterygium).
 * Inferior Edge (lower edge of the triangular or wing shaped portion of the ptyerygium).

As it is a benign growth, it requires no treatment unless it grows to such an extent that it covers the pupil, obstructing vision.

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.

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.

Symptoms
Symptoms of pterygium include persistent redness, inflammation, foreign body sensation, dry and itchy eyes. In advanced cases the pterygium can affect vision as it invades the cornea with the potential of induced astigmatism and corneal scarring.

Treatment
Today a variety of options are available for the management of pterygium, from β-irradiation, to conjunctival auto-grafting or amniotic membrane transplantation, along with glue and suture application. As it is a benign growth, pterygium typically does not require surgery unless it grows to such an extent that it covers the pupil, obstructing vision or presents with acute symptoms. Some of the irritating symptoms can be addressed with artificial tears. However, 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.

Conjunctival auto-grafting is a surgical technique that is effective and safe procedure for pterygium removal. When the pterygium is removed the tissue that covers the sclera known as the conjunctiva is also extracted, auto-grafting replaces the bare sclera with tissue that is surgically removed from the inside of the patients’ upper eyelid. That “self-tissue” is then transplanted to the bare sclera and is fixated using sutures, tissue adhesive, or glue adhesive.

Amniotic membrane transplantation is an effective and safe procedure for pterygium removal. Amniotic membrane transplantation offers practical alternative to conjunctival auto graft transplantation for extensive pterygium removal. Amniotic membrane transplantation is tissue that is acquired from the innermost layer of the human placenta and has been used to replace and heal damaged mucosal surfaces including successful reconstruction of the ocular surface. It has been used as a surgical material since the 1940s, and has been shown to have a strong anti-adhesive effect. Using an amniotic graft facilitates epithelialization, and has anti-inflammatory as well as surface rejuvenation properties. Amniotic membrane transplantation can also be fixated to the sclera using sutures, or glue adhesive. Amniotic membrane transplantation with Tisseel glue application and Mitomycin-C has shown excellent cosmetic outcomes with a surface free of redness, stitching, or patches which makes the ocular surface suitable for  vision correction surgery sooner.