Quick measurements of contrast sensitivity in the peripheral visual field

Abstract

 

Purpose

 

Measuring the contrast sensitivity function (CSF) in the periphery is complicated. The long measurement time has precluded all but the most determined subjects. The aim of this study was to implement and evaluate a faster routine, based on the quick-CSF method (qCSF, Lesmes et al. 2010), that works in the periphery. Additionally, normative data is presented on neurally limited CSFs in different peripheral field directions.

 

Methods

 

Precision and accuracy of the modified qCSF was tested for a total of six conditions (subject 1 at 20 degrees, subject 2 at 10, 20 and 30 degrees and subject 3 at 20 degrees with and without 2 D of defocus). Precision was evaluated using 8 qCSF measurements with 200 trials at each condition. Accuracy was estimated by comparing the qCSF results with those of a more traditional way to measure the CSF. In the second part of the study, we collected CSFs for six persons in the 20 degrees nasal, temporal, inferior and superior visual field using three qCSF measurements with 100 trials at each location. All measurements were performed in an adaptive optics system running in continuous closed loop (Rosén et al. 2011).

 

Results

 

A peripheral qCSF measurement using 100 trials can be performed in three minutes. On average, it has a precision of 0.12 log units for estimates of contrast sensitivity at individual spatial frequencies. This can be decreased to 0.07 log units if three qCSF measurements are taken. Average accuracy compared to the traditional way of measuring CSF was 0.08 log units, with no systematic error. An example of the precision and accuracy estimates for one of the measurement conditions can be seen in Figure 1. The results of the second experiment are shown in Figure 2. Tukey HSD test showed significant differences (p<0.05) between all field directions, except between nasal and temporal field. Contrast sensitivity was higher in the two horizontal field directions. In the vertical directions, the inferior field had a better CSF than the superior.

 

Conclusions

 

The modified qCSF method gives a precise and accurate way to measure the peripheral CSF, substantially decreasing the measurement time needed. This allows hitherto unfeasible studies using more subjects.

 

 

Figure 1. Precision and accuracy for one of the testing conditions, subject 2 at 20 degrees.

 

 

Figure 2. Average CSF in the different field directions at 20 degrees for the six subjects.

 

Keywords: 478 contrast sensitivity • 758 visual fields • 626 aberrations