This group of diseases include:
2. True pterygium.
It is a bilateral degenerative condition of old age characterized by a triangular yellowish nodule on the nasal side of limbus.
- It is always bilateral, but one eye precedes the other.
- It is present just nasal to the limbus.
- It is a yellowish triangle with its base touching the limbus.
- Never ulcerate.
It can be excised only if it is cosmetically bad.
2. TRUE PTERYGIUM
It is a degenerative diseases characterized by changes in the superficial corneal layers making them look like conjunctiva (not true encroachment of conjunctiva over the cornea).
Degeneration starts at the level of Bowman's membrane and superficial stromal layers of the cornea leading to invasion of the superficial corneal layers by vascular connective tissue derived from the conjunctiva. Then the corneal epithelium is replaced by epithelium similar to that of conjunctiva. It occurs on the nasal side.
Its exact cause is unknown, but it is related to chronic irritation by sun rays, fumes of petrochemical products and dust.
- Cosmetic disfigurement.
- Marked drop of vision if encroaches over the central area of cornea.
* Vascular fold of the conjunctiva is seen overlying over the cornea. It is triangular in shape consisting of:
- Apex over the cornea.
- Neck over the limbus.
- Body over the sclera.
* The progressive pterygium is thick, fleshy and vascular, while the atrophic pterygium is thin, membranous and less vascular.
D.D.: Pseudo pterygium:-
It occurs after a resistant corneal ulcer where a fold of conjunctiva becomes adherent to the ulcer either spontaneously or after conjunctivoplasty.
1. Recurrences are very common after pterygium excision.
2. Repeated excisions can cause symblepharon, thinning of the cornea and corneal opacities.
Indications of treatment:
1. Progressive pterygium.
2. Large pterygium extending over the pupillary area.
3. Cosmetically annoying the patient.
If it is small and stationary it is not removed.
A. The surgical procedure:
The pterygium is dissected form the cornea, then we do either:
1. Excision with bare scleral technique (D'Ombrian's technique):
The pterygium is dissected from the cornea till its base, then it is excised. The conjunctival edge is sutured to the episclera 4 mm from the limbus. This is to allow the corneal epithelium to cover the cornea before the conjunctival epithelium. Then beta irradiation is done.
2. Excision and lamellar keratoplasty: It is done if there is corneal thinning after multiple excisions of pterygium.
3. Excision and conjunctival grafting if there is symblepharon.
B. Beta irradiation:
* It is a beam of electrons obtained by a special applicator containing radio-active strontium 90.
* 3000 - 6000 rads are given in 3 - 5 sessions starting within 24 hours of surgery.
* It has the following advantages:
- Low penetration power (1 - 2 mm), so that it does not harm the intraocular structures.
- High selectivity to vascular endothelium with little damage to the collagen of stroma.
* It prevents growth of new vessels which are the cause of recurrence.
NB. There are recent techniques in treatment of pterygium to decrease its recurrence rate. For example application of antimetabolites and stem cell transplantation.