Dark adaptometry, FST and PAT tests

Introduction

The examination of dark adaptation evaluates the recovery of light sensitivity after exposure to bright light.
It presents several clinical applications:
• the functional evaluation of processes that affect directly the eye (retinitis pigmentosa, ..). Responses can often be obtained with the psychophysical exam of dark adaptation whereas the electroretinogram is extinct,
• when a metabolic process is suspected (vitamin-A deficiency),
• the functional evaluation of subjects working under low luminance conditions,
• the evaluation of subjects who complain of visual difficulties at night.

The Full Field Stimulus threshold test (FST) measures the threshold of light sensitivity with full field stimulations after dark adaptation.
It is used during clinical research studies, for example for retinitis pigmentosa. The use of full field stimulations allows measurements even when fixation is not stable (nystagmus).

The Photoaversion test (PAT) measures the threshold of discomfort of photophobic subjects.

Methodology

The program for dark adaptometry starts with a light adaptation phase of typically 5 minutes duration followed by a dark phase.
Tests for false positives are included to evaluate the patient's reliability.
The curve here-by shows a typical result. The ordinate scale is given in dB with a 0 dB level set at 318 cd/m2 (reference of the Goldmann perimeter).

The program for the FST test begins right after dark adaptation and measures the sensitivity threshold to full field light stimulations with a staircase strategy starting from the lowest luminance level.

In the PAT test luminance increases gradually, in steps of 1 dB, the patient having to press the response button when he/she can no longer bear the level of luminance. The test is repeated several times for a pre-programmed duration and the final threshold is the average of the responses obtained during this time. The video is recorded throughout the duration of the examination and the lid opening can be measured from this video.

Specifications

This program is available on several models of the Vision Monitor:
- MonCvONE for clinical research. It includes the FST tests (full field stimulus threshold), the PAT tests as well as tests with several wavelenths and several locations,
- MonPackONE or - MonColor for standard clinical exams and
- MonCv3 for screening exams.
For detailed specification,refer to the PDF brochure.