Visual discrimination training improves Humphrey perimetry in chronic cortically induced blindness

Abstract

Objective: To assess if visual discrimination training improves performance on visual perimetry tests in chronic stroke patients with visual cortex involvement.

Methods: 24-2 and 10-2 Humphrey visual fields were analyzed for 17 chronic cortically blind stroke patients prior to and following visual discrimination training, as well as in 5 untrained, cortically blind controls. Trained patients practiced direction discrimination, orientation discrimination, or both, at nonoverlapping, blind field locations. All pretraining and posttraining discrimination performance and Humphrey fields were collected with online eye tracking, ensuring gaze-contingent stimulus presentation.

Results: Trained patients recovered ∼108 degrees² of vision on average, while untrained patients spontaneously improved over an area of ∼16 degrees². Improvement was not affected by patient age, time since lesion, size of initial deficit, or training type, but was proportional to the amount of training performed. Untrained patients counterbalanced their improvements with worsening of sensitivity over ∼9 degrees² of their visual field. Worsening was minimal in trained patients. Finally, although discrimination performance improved at all trained locations, changes in Humphrey sensitivity occurred both within trained regions and beyond, extending over a larger area along the blind field border.

Conclusions: In adults with chronic cortical visual impairment, the blind field border appears to have enhanced plastic potential, which can be recruited by gaze-controlled visual discrimination training to expand the visible field. Our findings underscore a critical need for future studies to measure the effects of vision restoration approaches on perimetry in larger cohorts of patients.

Figure 1. Effects of discrimination training on Humphrey visual field (HVF)–derived metrics

(A) Area of the HVF that improved by ≥6 dB in trained and untrained participants. (B) Area of the HVF that worsened by ≥6 dB in trained and untrained participants. (C) Change in perimetric mean deviation (PMD) averaged across the 2 eyes, computed from 24-2 HVF. (D) Positive correlation between the area of the HVF that improved by ≥6 dB (from A) with the change in PMD (from C). Values in A–C are means ± SEM.

Figure 2. Effect of visual discrimination training on Humphrey visual fields (HVFs)

(A) Composite HVFs with circles indicating the size and location of training stimuli. (B) Difference HVF maps on the same patients as in A with red hues indicating locations of significant improvement in luminance sensitivity (i.e., ≥6 dB of improvement). Number of training sessions and number of locations trained are listed for each trained patient. Details of how the maps were created are provided in appendix e-1.

Figure 3. Effect of patient demographics on Humphrey visual field (HVF) improvements

Both trained and untrained patients were included in these analyses. (A) The age of the patient at the time of recruitment did not correlate with the area of HVF improvement (≥6 dB). (B) The size of the HVF-defined deficit at the time of enrollment did not correlate with the area of improvement. (C) The time between stroke and enrollment also failed to correlate with improvement. CB10 was removed as an outlier from this analysis (time since lesion was 226 months, area of improvement = 184.79 degrees²). (D) The number of training sessions correlated strongly with the area of improvement measured on HVFs, as did (E) the number of locations trained. R²s and equations are presented after removing 2 outliers. Including these outliers generates R² values of 0.114 for D and 0.116 for E.

Figure 4. Humphrey visual field (HVF) changes inside and outside trained locations

(A) Area of the visual field that improved ≥6 dB inside and outside of the trained blind field locations in CB1–CB16. (B) Area of the visual field that worsened by ≥6 dB inside and outside of the trained blind field locations in CB1–CB16. (C) Area improved as a function of distance from training locations (light data points) and the pretraining blind field border (black data points). Distance was binned in 5-degree increments. (D) Plot of the average magnitude of improvement in each 5-degree distance bin. (E) Pretraining visual sensitivity in areas of the Humphrey field that improved by ≥6 dB posttraining in CB1–CB16. Area improved in each bin is expressed as a percentage of the total area improved. (F) Pretraining visual sensitivities in areas of the blind field covered by training stimuli (expressed as % of total area trained) in CB1–CB16. Bins are greater than the lower number and ≤ greater number. Zero bin encompasses only locations with 0 dB sensitivity. Values are means ± SEM.