Pterygium refers to any winglike triangular membrane occurring in the neck, eyes, knees, elbows, ankles or digits.
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In the eye, a pinguecula is called a pterygium if it invades the cornea.
The term comes from the Greek word pterygion meaning "wing".
Types
A pterygium grows in response to exposure to ultraviolet light. They are more common in light-skinned people living nearer the equator, particularly where outdoor activities are popular.
As the pterygium grows, it replaces the corneal epithelium, and erodes the superficial layers beneath it. These layers are Bowman's membrane, and the anterior corneal stromal lamellae. The pterygium pulls and distorts the cornea as it enlarges.
Effects
A pterygium reduces the vision in several ways:
- Distortion of the corneal optics. This begins usually when the pterygium is greater than 2mm from the corneal edge (limbus).
- Disruption of the tear film. The tear film is the first lens in the eye. Pterygia are associated with eyelid inflammation, called Blepharitis.
- Growth over the corneal centre, which leads to dramatic reduction of vision.
- Induced anterior corneal scarring, which often remains after surgical removal.
Surgical removal
Indications for surgery, in order of decreasing importance:
- Growth over the corneal centre.
- Reduced vision due to corneal distortion.
- Documented growth.
- Symptoms of discomfort.
- Cosmesis.
Surgery is usually performed under local anaesthetic with light sedation as day surgery. The pterygium is stripped carefully off the surface of the eye. If this is all that is done, the pterygium regrows frequently. The technique with the lowest recurrence rate uses an auto graft of conjunctiva from under the eyelid. This is placed over the defect remaining from the removed pterygium. The graft can be stitched in place, which is time consuming, and painful for the patient afterwards.
An alternative is the use of tissue adhesive fibrin glue, called Tisseel, which allows faster surgery and less pain post-operatively. A 3-year clinical study on the application of ologen collagen matrix as excision site grafts showed significantly improved surgery success rates.
The mechanism of the collagen matrix graft (commercially available as ologen®) works by promoting healthy cell growth into the matrix, thus preventing conjunctiva overgrowth that can cover the iris.
Natural history
A pterygium grows very slowly. Usually it takes several years or decades to progress.