Introduction It has been shown in a 6 month non-randomised clinical trial that patients with both diabetic macula oedema and obstructive sleep apnoea (OSA) improved vision by one line on the logMAR chart if they used CPAP for more than 2.5 hours/night, compared to those using for less than 2.5 hours/night. However there are many potential explanations for this improvement, including reduced sleepiness leading to increased effort to read the logMAR chart, rather than any direct improvement in retinal function. We are assessing if non-visually impaired patients, treated for OSA, also improve their ability to read visually degraded words, thus simulating impaired vision.
Methods A specially designed computer programme repeatedly presents five-letter words for three seconds, with one second intervals between. Progressively, the bottom halves of the letters making up the words are removed, making them harder and harder to read. The point at which only 50% of the words are correctly recognised is ‘hunted’ by increasing and decreasing the % revealed, analogous to a hearing test that hunts the auditory threshold. Preliminary tests on normal subjects established that a 10 minute training period, followed by a 10 minute rest, and then by a 10 minute trial period, produced stable results with little or no learning effect over several weeks. 23 symptomatic patients with OSA have been tested pre CPAP, and so far only 5 have been re-tested approximately 2 weeks post CPAP.
Results The average % of words needing to be revealed to allow 50% correct recognition in the 23 subjects was 35% (range 23 to 64%). In the 5 restudied so far this was 37% pre CPAP, and 40% post.
Conclusions Although the study is not yet finished, the preliminary results are not supporting the hypothesis that improved vision in patients with diabetic macular oedema post CPAP treatment is likely to be due to reduced sleepiness, improved vigilance or improved enthusiasm for reading the logMAR chart.
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