THE EFFECT OF THE VOLK QUADRASPHERIC WIDE FIELD CONTACT LENS ON RETINAL PHOTOCOAGULATION

Holly Meyers

Abstract

The benefits of retinal photocoagulation for various retinal pathologies such as proliferative diabetic retinopathy are well known. A variety of contact lenses are commonly used for pan-retinal photocoagulation including the Goldmann 3-Mirror Universal lens and the Volk QuadrAspheric lens. Because of its wide field of view, the Volk QuadrAspheric lens has been described as a convenient and effective lens in the delivery of pan-retinal photocoagulation. However, the wide field characteristic of this lens causes a beam spread of approximately 40%, hence producing burns of a larger diameter but with a lower energy density. This is a study of how the threshold for retinal burn might be altered by this beam spreading effect. Subjects were Dutch Belted rabbits which were anesthetized with an IM ketamine-xylaxine mixture. After dilation, a Volk QuadrAspheric and a Goldmann 3-mirror lens were used to produce an intensity series (ie: 50, 100, 150, 200, 250, and 300 mW) of retinal burns at both 100 and 200 msec duration. The burns were made with a MIRA green argon laser (514.5 nm) in a homogeneous area of the retina. Goldmann lesions were made using a 500 micron spot and QuadrAspheric lesions were made with 250 and 500 micron spot sizes. The resultant burns were assessed and documented using a Nikon Photoslitlamp immediately and at 48 hours. Effective burns were obtained with either lens at all intensities used. As expected the burn diameter did enlarge with the wider field lens. The burns created with the Volk lens were, therefore, more diffuse when compared to those formed by the Goldmann lens. Reducing the projected beam diameter to 250 u while using the Volk lens tended to compensate for the spreading of the beam, thus making these lesions appear more equivalent to the Goldmann 500 u burns. This work is significant to the practitioner performing retinal photocoagulation in light of the many different fundus lenses available.

Details

Year: 1992

Program Number: Poster 25

Author Affiliation: n/a

Co-Authors: Felix Barker

Co-Author Affiliation: n/a

Room: Great Hall