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S. Luque, M. Aldaba, F. Diaz-Douton, V. Lapuente, J. Pujol; Objective Measurement of Amplitude of Accommodation Using a Double Pass Based System. Invest. Ophthalmol. Vis. Sci. 2008;49(13):4554.
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The aim of our study was to objectively measure the amplitude of accommodation using a double pass commercial device (OQASTM, Visiometrics, SL). The response was tested by stimulating accommodation as in Sheard and Donder’s methods and the result compared to subjective techniques.
The measurement of the amplitude of accommodation was carried out using a modified double pass system. A periscope was incorporated to the commercial device to get a stronger stimulation of the accommodation. The stimulation was obtained by adding negative lenses up to 4 diopters or bringing the object nearer to the patient and defocus was measured at 780 nm with OQASTM. In all the cases the subject's sphere and cylinder were corrected. When negative lenses are added the subject accommodates to cancel the generated defocus. Therefore, while accommodation acts the measure remaining defocus corresponds to the accommodative lag. When the object is presented at different positions instead of using lenses, the measured defocus is the accommodation produced. A group of 14 people, 10 normal and 4 pseudophakic, were measured using both negative lenses and proximal object methods. The age ranged from 25 to 60 (mean age 35) and the spherical refraction from -3.5 to 2 D (mean value -1.25 D). The measurements were correlated using the same ways of stimulation while subjective techniques were applied.
We did not find statistically significant differences between the two ways of stimulation when measured objectively. This might confirm that the differences found between Donder and Sheard method when measure subjectively are due to the change of the image size on the retina while the stimulation of accommodation is in both cases similar. The observed differences between object position and defocus measured may be explained by chromatic differences between target illumination and the wavelength used by the instrument. Statistically significant differences (0.75 D ± 0,3; p<0.05) were found between subjective and objective methods which are ascribed to pseudo-accommodation since pseudophakic eyes also showed similar differences.
We have shown the possibility of using a modified double pass commercial device to measure the amplitude of accommodation. The technique presented the advantage of avoiding pupil effect found in subjective methods which enhances the amplitude of accommodation results because of pseudo accommodation. Furthermore, the pupil size is not critical and pseudo accommodation can be also objectively estlimated and included to compute an expected subjective range.
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