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Cone– and rod–mediated retinal function before and after multiple laser therapies in age–related macular degeneration

Centre for Health Research, School of Optometry, Queensland University of Technology, Brisbane, Australia

Commercial Relationships: B. Feigl, None; J. Lovie–Kitchin, None; B. Brown, None.

Grant Identification: none

Abstract

Aim: To study the cumultative effect of laser treatments with photodynamic therapy (PDT) and transpupillary thermotherapy (TTT) on retinal function in eyes with age–related macular degeneration (AMD).

Methods: Seven eyes of seven AMD subjects were investigated before and 4 weeks after each laser treatment during a follow up period of 6 months. Three eyes underwent three PDT treatments and two eyes underwent two PDT treatments. One eye was treated with two TTTs and another eye underwent one PDT and one TTT. We studied subjective macular function by testing visual acuities (VA), central visual fields (VF), contrast sensitivity (Pelli–Robson) and colour vision (sat–D15) as well as cone– and rod–mediated mfERGs (VERIS). The mfERG stimulus for the cones consisted of 103 scaled hexagons and we used the conventional method for deriving the responses. For the rod–mediated mfERG we used a 61 hexagon unscaled stimulus with 3 blank frames, a Wratten 47B filter and reduced the luminance and stray light influence by adding a neutral density filter (1.5 ND) and a surround respectively. For analysis of the mfERG amplitude and implicit time a computer fitting method was applied (Matlab). We compared each of the 103 and 61 local first–order kernel mfERG responses after treatment with those before treatment.

Results:Four eyes showed stabilisation in some of the vision measures and three eyes showed impairment in all the psychophysical tests after the second treatment. This was significantly reflected in the cone–mediated mfERG in two eyes (p<0.01). Cone–mediated mfERG function significantly deteriorated in three eyes (p<0.01), improved in one (p<0.01) and remained stable in three eyes after all treatments. Rod–mediated function was significantly impaired in only one eye (p=0.02) and did not show any further deterioration in the other eyes after two treatments. Both eyes treated with TTT showed a significant cone–mediated amplitude reduction greater than 40% which was reflected in reduced subjective function tests in only one eye. Data collection is continuing.

Conclusion:Consistent with previous studies with the mfERG after one PDT treatment, subjective and objective function measured by the mfERG appears to be stabilized after multiple PDT treatments. Similarly rod–mediated function seems not to be further compromised. In contrast TTT treated eyes showed greater cone–mediated functional deficits.

Keywords: electrophysiology: clinical • photodynamic therapy • age–related macular degeneration

© 2004, The Association for Research in Vision and Ophthalmology, Inc., all rights reserved. For permission to reproduce any part of this abstract, contact the ARVO Office at arvo{at}arvo.org.