Unfocused effect on the measurement of ocular aberrations.
OBJECTIVE
To evaluate the effect of unfocused measurement in the value of ocular aberrations.


METHODS
The present study was conducted at Siriraj Hospital, Mahidol University. Ocular aberrations of 20 eyes in 10 myopic patients (myopia less than -6.00 diopters (D) and astigmatism less than -2.00 diopters (D)) were analyzed by using Zywave aberrometer (Bausch and Lomb, USA). The measurements were done at the pupillary plane (focus) and 6 other different planes (unfocus); 5, 10 and 15 mm inside and outside pupillary plane respectively. The value of each measurement was analyzed to find the effect of unfocused measurement on ocular aberrations.


RESULTS
The magnitude of error (root mean square, RMS) of the spherical component of refraction at 5, 10, 15 mm inside and outside the pupillary plane was 0.16, 0.44, 0.57 D and 0.21, 0.38, 1.35D respectively. The RMS of astigmatic component of refraction inside and outside the pupillary plane at the same distance was 0.19, 0.50, 0.80 and 0.18, 0.52, 1.55 D respectively. The RMS of higher order aberrations inside and outside the pupillary plane at the same distance was 0.05, 0.13, 0.15 and 0.06, 0.1, 0.1 microns respectively.


CONCLUSIONS
There was more effect of outward unfocused measurement in the value of refraction (spherical and astigmatism) than inward unfocused measurement. Higher order aberration showed a similar error in both inward and outward defocus. The magnitude of error was 10 - 12% within 5 mm unfocused planes.
Srivannaboon
Sabong
S
Department of Ophthalmology, Faculty of Medicine, Siriraj Hospital, Mahidol University, 2 Prannok Rd, Bangkoknoi, Bangkok 10700, Thailand. sabong@pol.net
Adulbhan
Narisara
N