To the naked eye, corneal oedema might not be obvious but careful inspection will reveal a lack of luster when the affected cornea is compared with that on the other side. The normal sparkle of the eye is no longer evident and the iris becomes less well defined. Microscopically, a bedewed appearance is seen, minute droplets being evident in the epithelium. When the stroma is also involved, this can seem misty and might also be infiltrated with inflammatory cells, which are seen as powdery white dots. When the oedema is long-standing, the droplets in the epithelium coalesce to produce blisters or bullae.
The more important causes of corneal oedema are as follows:
• Acute narrow-angle glaucoma
• Virus keratitis
• Contact lenses
• Fuch's endothelial dystrophy.
When the intraocular pressure is suddenly raised from any cause, the cornea becomes oedematous. The normal cornea needs to be relatively dehydrated in order to maintain its transparency, and the necessary level of dehydration seems to depend on active removal of water by the corneal endothelium, as well as an adequate oxygen supply from the tears. The mechanism is impaired not only by raising the intraocular pressure, but also by infection or trauma. Senile degenerative changes might also be the sole underlying cause because of failure of the endothelial pumping mechanisms. Contact lenses, if ill fitting and worn for too long a period, can prevent adequate oxygen reaching the cornea, with resulting oedema.
The management of corneal oedema depends on the management of the underlying cause. Oedema due to endothelial damage can respond, in its early stages, to local steroids and sometimes a clear cornea can be maintained by the use of osmotic agents, such as hypertonic saline or glycerol. Chronic corneal oedema tends to be painful and often acute episodes of pain occur when bullae rupture leaving exposed corneal nerves. In such cases, it can be necessary to consider a tarsorrhaphy, or in some instances, a corneal graft can prove beneficial. The pain of corneal oedema is a late symptom and in its early stages, oedema simply causes blurring of the vision and the appearance of coloured haloes around light bulbs. This is simply a "bathroom window" effect. Patients with cataracts also see haloes, so that defects in other parts of the optical media of the eye might give a similar effect.
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