Abstract
Purpose: :
To assess the feasibility of macular vision testing using a novel rotation optical illusion in patients with AMD.We hypothesise the test may be sensitive to paracentral visual loss which commonly occurs with macular degeneration but is usually hard to detect in elderly age groups. This approach has never been tried.
Methods: :
21 adults with diagnosed or suspected AMD were randomly selected from medical retina outpatient clinics.The freezing rotation optical illusion adopted from Dürsteler (2007) by Aslam onto a computer programme with various adjustable variables.Testing was done at standard comfortable distance from the patient for near viewing (~12 inches).The illusion consists of a central regularly rotating sentence that the patient is asked to concentrate on. Around it are many small dots that mostly rotate with the central sentence but then occasionally change to the opposite direction. At that point, perception of the paracentral dots causes in most people the illusion that the central rotating sentence slows down.Initially, the illusion was demonstrated with a maximum number of dots (500) to assess whether it was perceived at all. The test then restarts with only 10 dots in the paracentral area. If the illusion is not perceived, the number of dots was increased incrementally by 20 until the illusion is observed.The threshold where the minimum amount of dots needed for the illusion to be observed (five or more times consecutively, counter-checked by examiner) was recorded. This is known as RIT score. Test is repeated on the other eye.
Results: :
Many individual patients provided encouraging results:Patient with poor acuity (6/24) due to bilateral foveal scarring but apparent intact remainder of maculae. On illusion test best possible score of 10 was achieved.Patient with poor macular appearance from dry AMD, but intact foveal acuity (6/9). During test, illusion was not observed.Patients with unilateral disease, where one eye had macular involvement and the other none, scored worse with the former eye.
Conclusions: :
Most patients in the elderly age group were able to perceive the illusion and do the test.Objective evidence was found where patients had disease with expected paracentral vision loss, the illusion effect was indeed less easily seen, even when they had good central vision. As hoped, macular unrelated general loss of vision did not affect the test as much.This feasibility study propose the illusion could be a useful measure for paracentral vision loss to screen patients with new or established macular degeneration. Nevertheless, further work is needed in refinement of the test based on user experience and formal testing for reliability and validity.
Keywords: age-related macular degeneration • aging: visual performance • clinical (human) or epidemiologic studies: systems/equipment/techniques