Validity of clinical measures of the AC/A ratio
The gradient stimulus and heterophoria stimulus measures of the accommodative convergence/accommodation (AC/A) ratio are simple and widely-used techniques. We compared these two clinical methods with the more accurate and objective gradient response AC/A ratio method. Twenty-three subjects, with ages ranging from 17 to 42 years and with normal binocular vision, were assessed. The response AC/A ratio was determined using a Canon AutoRef R-1 to measure accommodation and an IRIS eye movement monitor to measure eye movements. Stimulus AC/A ratios were determined by taking phoria measures with the presentation of lenses (gradient method) and by varying the working distance (heterophoria method), with the accommodation taken as dioptric value of each stimulus. The mean AC/A ratios were 4.37 ± 1.31 Δ/D (mean ± standard deviation), 3.49 ± 2.17 Δ/D, and 5.81 ± 1.03 Δ/D, for the gradient response, gradient stimulus and heterophoria stimulus AC/As, respectively. The gradient stimulus AC/A showed only moderate validity, as measures corresponded with the ratios of the response method mainly when identifying very high and very low AC/A ratios (r2 = 0.388). Inaccuracies in the gradient-stimulus AC/A arose because the accommodation often varied markedly from the value of the stimulus lenses. The heterophoria stimulus AC/A appeared to be invalid for the subjects tested, as no correlation was evident between it and the response AC/A (r2 = 0.003). Since the heterophoria technique is susceptible to both errors of focus and the influence of proximal vergence, it may reliably detect only very high AC/A ratios.
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|Item Type:||Journal Article|
|Additional Information:||For more information, please refer to the journal’s website (see link) or contact the author. Author contact details: email@example.com|
|Keywords:||accommodation, convergence, response AC/A ratio, stimulus AC/A|
|Subjects:||Australian and New Zealand Standard Research Classification > MEDICAL AND HEALTH SCIENCES (110000) > OPTOMETRY AND OPHTHALMOLOGY (111300)|
|Divisions:||Current > QUT Faculties and Divisions > Faculty of Health
Current > Institutes > Institute of Health and Biomedical Innovation
|Copyright Owner:||Copyright 1995 Optometrists Association Australia|
|Copyright Statement:||The contents of this journal from 1998 to 2005 can be freely accessed online via the journal’s web page (see link).|
|Deposited On:||28 Sep 2006|
|Last Modified:||15 Jan 2009 07:12|
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