Not Medical Advice: One possible cause is epithelial erosion, common to patients with Map-dot-fingerprint dystrophy.
Epithelial erosions alter the cornea's normal curvature, causing periodic blurred vision. They may also expose the nerve endings that line the tissue, resulting in moderate to severe pain lasting as long as several days. Generally, the pain will be worse on awakening in the morning.
This condition usually happens bilaterally in adults from 40-70 years of age when the basement membrane of the corneal epithelium fails to develop properly resulting in sloughing off of the epithelial cells to stick to the basement membrane.
Map-dot-fingerprint dystrophy is normally recurrent, occurring every few years then resolving completely with no loss of vision and in fact, many cases are not severe that patients fail to recognize that there is something wrong.
You can get more info about the cornea and corneal disease at National Eye Institute.
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