Pressure at the limbus or inside the limbus on the cornea itself is without doubt the reason for discomfort from contact lenses in at least 90 per cent of the patients who complain of inability to wear them except for short periods. Any contact lens which rests on any portion of the cornea cannot be worn for more than one hour and often for a much shorter time.
Many contact lenses which have been judged as clearing the entire cornea have been proved, with a new method of observation, to rest on or inside the limbus. This is not surprising in view of the decided difficulty of observing the actual clearance as the edges of the cornea are approached. Part of this difficulty is due to the assumption that the corneal portion of the trial contact lens completely covers the cornea.
Recent observations from castings of 200 eyes, reported
Obrig TE. A COBALT BLUE FILTER FOR OBSERVATION OF THE FIT OF CONTACT LENSES. Arch Ophthalmol. 1938;20(4):657–658. doi:10.1001/archopht.1938.00850220129010
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