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Frederick M Kapetansky; BUBBLE-FREE GONIOSCOPY?. Invest. Ophthalmol. Vis. Sci. 2017;58(8):2072.
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© ARVO (1962-2015); The Authors (2016-present)
Accurate gonioscopy is necessary for the diagnosis and the treatment of glaucoma.The gold standard for indirect gonioscopy has been the Goldman lens.The design of this lens requires gel as the optical coupling agent between the corneal surface and the goniolens. The presence of this gel obviates any further testing on the eye at that time.The design of an ideal lens would not only eliminate the need for gel, but would at the same time solve the problem of a bubble of air trapped under the lens.The goal of this study was to identify the factors involved in designing the goniolens which would met the needs of the clinician.
Currently, the design of a gonio-lens has been guided by two basic parameters:1) the diameter of the corneal contact surface and 2) the base curve of this surface.When the diameter of the contact surface of the lens matches or exceeds that of the cornea, and the base curve of the lens is steeper than that of the cornea, a potential space is created between the lens and the cornea, which needs to be filled with an optical coupling gel. When the diameter of the corneal contact surface is less than that of the cornea, this space can be filled with tears, provided that the base curve of the lens matches that of the cornea. The clinical advantage of the tears as the coupling agent is that further testing of the eye can be carried out at the same visit.
This study involved several lens on the market (Zeiss, Volk, Sussman, Goldman to name a few).It appears that the critical parameter to eliminate the need for gel and achieve "bubble-free" gonioscopy was the flattening of the base curve of the lens i.e. from 7.45mm to 8.4mm. The area of contact of the original Goldman lens (12.25mm) and down to the area of contact for 4 and 6 mirror lenses (8.4mm) was not a factor in eliminating the need for gel, as long as the base curve was flattened at the same time.
Our stated goal of eliminating the need for gel as a optical coupling agent as well as bubble-free gonioscopy was dependent on the base curve of the area of contact and not on the area of contact. When the base curve of the area of contact of the goniolens approached that of the base curve of the cornea, then our goal was achievable no matter what the size of the area of contact was. This observation may have significant applicability for re-designing some of our current lenses which require gel as an optical coupling agent.
This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.
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