Alkali burns
These are among the most severe chemical inju ries known to the ophthalmologists. Common al kalies responsible for burns are: lime, caustic potash or caustic soda and liquid ammonia (most harmful).
Mechanisms of damage caused
1. Alkalies dissociate and saponify fatty acids of the cell membrane and, therefore, destroy the structure of cell membrane of the tissues.
2. Being hygroscopic, they extract water from the cells, a factor which contributes to the total necrosis.
3. They combine with lipids of cells to form solu ble compounds, which produce a condition of softening and gelatinisation.
The above effects result in an increased deep penetration of the alkalies into the tissues. Alkali burns, therefore, spread widely, their action con tinues for some days and their effects are diffi cult to circumscribe. Hence, prognosis in such cases must always be guarded.
Clinical picture
It can be divided into three stages:
1. Stage of acute ischaemic necrosis. In this stage,
i. Conjunctiva shows marked oedema, con gestion, widespread necrosis and a copious purulent discharge.
ii. Cornea develops widespread sloughing of the epithelium, oedema and opalescence of the stroma.
iii. Iris becomes violently inflamed and in se vere cases both iris and ciliary body are re placed by granulation tissue.
2. Stage of reparation.
In this stage conjunctival and corneal epithelium regenerate, there occurs corneal vascularization and inflammation of the iris subsides.
3. Stage of complications.
This is characterised by development of symblepharon, recurrent corneal ulceration and development of compli cated cataract and secondary glaucoma.