VASCULARIZATION OF CORNEA

Normal cornea is avascular except for small capillary loops which are present in the periphery for about 1 mm. In pathological states, it can be invaded by
vessels as a defence mechanism against the disease or injury. However, vascularization interferes with corneal
transparency and occasionally may be a source of irritation.

Pathogenesis
Pathogenesis of corneal vascularization is still not clear. It is presumed that mechanical and chemical factors play a role. Vascularization is normally prevented by the compactness of corneal tissue. Probably due to some vasoformative stimulus (chemical factor) released during pathological states, there occurs proliferation of vessels which invade from the limbus; when
compactness of corneal tissue is loosened (mechanical factor) due to oedema (which may be traumatic, inflammatory, nutritional, allergic or
idiopathic in nature).

 

Clinico-etiological features
Clinically, corneal vascularization may be superficial or deep.
1. Superficial corneal vascularization. In it vessels are arranged usually in an arborising pattern, present below the epithelial layer and their continuity can be traced with the conjunctival vessels (Fig. 1A). Common causes of superficial corneal vascularization are: trachoma, phlyctenular kerato-conjunctivitis, superficial corneal ulcers and rosacea keratitis. Pannus. When extensive superficial vascularization is associated with white cuff of cellular infiltration, it is termed as pannus. In progressive pannus, corneal infiltration is ahead of vessels while in regressive pannus it lags behind.

2. Deep vascularization. In it the vessels are generally derived from anterior ciliary arteries and lie in the corneal stroma. These vessels are usually straight, not anastomosing and their continuity cannot be traced beyond the limbus. Deep vessels may be arranged as terminal loops (Fig. 1B), brush (Fig. 1C), parasol, umbel (Fig. 1 D), network or interstitial arcade.

Common causes of deep vascularization are: interstitial keratitis, disciform keratitis, deep corneal ulcer, chemical burns and sclerosing keratitis and grafts.

Fig.1 Corneal vascularization : A, superficial
B, terminal loop type C, brush type D, umbel type

 

Treatment
Treatment of corneal vascularization is usually unsatisfactory. Vascularization may be prevented by timely and adequate treatment of the causative conditions. Corticosteroids may have vasoconstrictive and suppressive effect on permeability of capillaries. Application of irradiation is more useful in superficial than the deep vascularization. Surgical treatment in the form of peritomy may be employed for superficial vascularization.