Critical Subjective Measurement of Amplitude of Accommodation
The use of fixed print size to measure amplitude of accommodation by the push-up method will result in a range of angular sizes of the print at the nearpoint for patients with different amplitudes. We investigated the effect of this on measured amplitude of accommodation in 60 subjects aged 25 to 45 yeas. We designed a near-vision chart, based on the Bailey-Lovie near-vision charts, but for which the letter sizes on adjacent lines are varied so that the difference between the inverse of letter sizes is constant (dioptric scale) rather than the geometric ratio between letters on adjacent lines being constant (logarithmic scale). Using this new chart, we compared the amplitudes obtained using N5 print (N5 Blur method) and with two critical methods for which the print of interest was always close to threshold acuity. This was achieved by having patients’ attention drawn to a smaller line of letters every time the chart was moved closer in half-diopter steps. The N5 Blur method gave considerably higher amplitude measures than the two critical methods, but the mean differences decreased markedly as age increased: 1.8 to 2.2 D for a 25- to 29-year-old group to 0.7 to 0.8 D for a 40- to 45-year-old group. We believe that the use of fixed size print for measuring amplitude of accommodation by the push-up method gives overestimations that are more marked the higher the amplitude. This occurs because smaller measuring distances that accompany the higher amplitudes will increase angular size and consequently depth-of-focus (in dioptric terms). A critical method of measuring amplitude of accommodation in clinical practice is described. A comparison of our results with those of previous, large scale studies leads to the conclusion that these studies overestimated amplitude in young subjects relative to those of older subjects.
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|Item Type:||Journal Article|
|Additional Information:||The contents of this journal can be freely accessed online via the journal’s web page (see link) 12 months after publication. For more information, please refer to the journal’s website (see link) or contact the author. Author contact details: firstname.lastname@example.org|
|Keywords:||amplitude of accommodation, nearpoint, push, up method, test chart|
|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 1994 Lippincott Williams & Wilkins|
|Deposited On:||28 Sep 2006|
|Last Modified:||15 Jan 2009 07:12|
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