Corneal hypoxia

Transcorneal and transscleral iontophoresis, at the same conditions, can produce different toxicity levels due to the significant differences between cornea tissue and sclera. Any damage to the corneal surface immediately affects the vision and comfort of the patient, which is less pronounced when applied to the sclera. The clarity of the cornea is essential for interaction with light whereas the sclera is not relevant for light interaction. The cornea is an avascular and highly innervated tissue, unlike the sclera, and thus very sensitive to pain and hypoxia. On one hand, transcorneal iontophoresis endangers the front window of the eye, but on the other hand transscleral iontophoresis threatens the retina underneath the application site, which is essential for visual image formation. 

Epithelial microcysts are an abnormal corneal response at the cellular level to chronic hypoxia from contact lens wear. When present, they tend to be observed in soft contact lens wearers, particularly those wearing extended-wear lenses. A hypoxic state can result in the development of microcysts due to such causes as... 

A change in refraction at high altitude, and thus transient myopia, can occur through osmoticaUy altered vitreous volume or altered curvature of the lens secondary to edema or cihary muscle spasm. The authors pointed out that altitude-related hypoxia (causing corneal swelling) and dehydration (associated with both exercise and inadequate fluid intake) could have contributed in this case. Drugs that can cause transient myopia include aspirin [4 ], chlortalidone [5 ], co-trimoxazole [6, 7 ], dapsone [8 ], hydrochlorothiazide metronidazole [10, ... 

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