NEUROPARALYTIC KERATITIS

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Neuroparalytic keratitis occurs due to paralysis of the sensory nerve supply of the cornea.
Causes

 
I. Congenital
1. Familial dysautonomia (Riley-Day syndrome)
2. Congenital insensitivity to Pain.
3. Anhidrotic ectodermal dysplasia.
II. Acquired
1. Following alcohol-block or electrocoagulation of Gasserian ganglion or section of the sensory root of trigeminal nerve for trigeminal neuralgia.
2. A neoplasm pressing on Gasserian
  ganglion.
3. Gasserian ganglion destruction due to acute infection in herpes zoster ophthalmicus.
4. Acute infection of Gasserian ganglion by herpes simplex virus.
5. Syphilitic (luetic) neuropathy.
6. Involvement of corneal nerves in leprosy.
7. Injury to Gasserian ganglion.

Pathogenesis
Exact pathogenesis is not clear; presumably, the disturbances in the antidromic corneal reflex occur due to fifth nerve paralysis. As a consequence
metabolic activity of corneal epithelium is disturbed, leading to accumulation of metabolites; which in turn cause oedema and exfoliation of epithelial cells followed by ulceration. Corneal changes can occur in the presence of a normal blink reflex and normal lacrimal secretions.

Clinical features   

1. Characteristic features are no pain, no lacrimation, and complete loss of corneal sensations.
2. Ciliary congestion is marked.
3. Corneal sheen is dull.
4. Initial corneal changes are in the form of punctate epithelial erosions in the inter-palpebral area followed by ulceration due to exfoliation of corneal
epithelium.
5. Relapses are very common, even the healed scar quickly breaks down again.

Treatment
1. Initial treatment with antibiotic and atropine eye ointment with patching is tried. Healing is usually very slow. Recently described treatment modality
include topical nerve growth factor drops and amniotic membrane transplantation.
2. If, however, relapses occur, it is best to perform lateral tarsorrhaphy which should be kept for at least one year. Along with it prolonged use of artificial tears is also recommended.

 ALLERGIC KERATITIS
1. Phlyctenular keratitis 
2. Vernal keratitis
3. Atopic keratitis