Plasticity of fixation in patients with central vision loss

Abstract

The aim of this study was to explore the plasticity of fixation in patients with central vision loss. Most of these patients use preferred retinal loci (PRLs) in the healthy eccentric part of the retina to fixate, but fixation stability and retinal location are not always optimal for best visual performance. This study examined whether fixation stability and a new PRL location can be trained and whether these changes in ocular motor control transfer into better reading performance. Six patients with age-related macular degeneration participated in the study. Fixation stability measurements, microperimetry, and auditory biofeedback training were performed with the MP-1 microperimeter. The auditory biofeedback was used during five 1-h long training sessions to improve fixation and relocate the PRL. Fixation location and stability were recorded while viewing four different targets: a cross, a letter, a word, and a nine-cycle radial grating. Visual acuity was assessed with the Early Treatment Diabetic Retinopathy Study (ETDRS) chart and reading performance with the MNRead test. The results showed that all patients developed a new PRL in an optimal location for reading, and they were able to use it consistently while viewing different targets. Fixation stability improved 53% after training. Learning transferred to the old PRL even though fixation stability at this location was not trained. All these improvements in ocular motor control translated into better reading performance: reading speed improved 38% and reading acuity and critical print size gained two lines. We conclude that the ability of the ocular motor system to fixate is flexible in patients with central vision loss: a new PRL can be trained, fixation stability can be improved, and learning transfers to an untrained location. These gains in ocular motor control result in better visual performance. This property can be successfully used to optimize the residual vision of patients with central vision loss.

Changes in Retinal Sensitivity in Geographic Atrophy Progression as Measured by Microperimetry

“…Previous investigators have shown that although MP-1 parameters for fixation may grossly correlate with reading speed, measurements of fixation with the bivariate contour ellipse formula may correlate better. 37,38 Despite this limitation, the fixation quantification method used by the MP-1 microperimeter provides a rapid recording of fixation ability that agrees with previous measurement methods 39 and an accessible method for detecting progressive change in fixation ability. Our results indicate that fixation quality may indeed decline progressively during GA progression, although refinements in methodology and further validation may be necessary to establish this as an outcome measure in GA.…”

Clinical and Microperimetric Predictors of Reading Speed in Low Vision Patients: A Structural Equation Modeling Approach

“…12,14,17,18,26 Another study 30 using MP1 microperimetry in patients with wet or dry AMD found that PRL eccentricity was a predictor of RS. The authors argued that the PRL used by patients during a fixation task is also preferentially used during a reading task or is used at least in some critical periods of the reading process.…”

“…Previous research has identified several predictors of reading performance in low vision patients, including reading and letter CS, 6,7 the presence of a deep scotoma in the retinal reading area, 5,[8][9][10][11] fixation features (such as eccentricity, usually related to scotoma size), [12][13][14] and fixation stability. [15][16][17] Although microperimetry has increasingly been used in low vision research, 9,10,13,[18][19][20] Micro Perimeter 1 (MP1; Nidek Technologies Inc., Padova, Italy) retinal sensitivity has not been compared with other psychophysical measures as a predictor of reading ability in low vision patients to the best of our knowledge. Moreover, we have recently introduced Reading Explorer (REX) charts to directly measure the effect of reading material contrast on RS, finding that the impact of reduced contrast on reading is undervalued, 7 and we expanded on this finding in a larger, multicenter study.…”

Feasibility of Macular Integrity Assessment (MAIA) Microperimetry in Children: Sensitivity, Reliability, and Fixation Stability in Healthy Observers

“…This means that excessive fixation instability is still likely to affect sensitivity estimates. In future studies it would therefore be instructive to see whether children's fixation stability can be improved, either through practice, instruction, reward, or the use of a more engaging fixation target, and whether, as has been found in some adults, 45,46 improvements in fixation stability lead to improvements in estimated visual sensitivities.…”