摘要:

Background.Autorefractors are increasingly used in myopia research because they are convenient tools to investigate aspects of the accommodation response. The degree to which the autorefractor measures are affected by ocular aberrations has been highlighted by studies that have shown changes in aberration levels through different parts of the pupil and with accommodation. We have compared accommodative accuracy as measured with a Shin-Nippon SRW 5000 autorefractor with wavefront error as measured with a Hartmann-Shack wavefront sensor to investigate how factors such as accommodation demand, ocular aberrations, and pupil size can influence autorefractor measures.Methods.Accommodation stimulus-response curves were determined (using negative lenses) for 30 young healthy subjects (20 myopic [−0.75 to −6.00 D] and 10 emmetropic). Accommodation levels ranged from 0 to 4 D in 1 D steps. Wavefront aberrations were also determined for the same accommodation levels using a Hartmann-Shack wavefront sensor for both the subjects’ natural pupil sizes and for a 2.9-mm pupil.Results.For all subjects, there was a consistent increase in negative spherical aberration with increases in accommodative stimulus. However, there was no consistent change in paraxial spherocylindrical refractive correction with accommodation stimulus. For the emmetropic subjects, accommodation error as measured with the autorefractor was statistically similar to the total spherocylindrical correction for the eye as estimated by the Hartmann-Shack wavefront sensor, but only for a 2.9-mm pupil (the pupil size utilized by the autorefractor). For the myopic subjects, accommodation error as measured with the autorefractor was statistically similar to the higher-order aberrations, but only when measured for a natural pupil size.Conclusions.The relationship between the accommodation accuracy as measured with the autorefractor and the total wavefront aberration as measured with a Hartmann-Shack wavefront sensor is largely influenced by the higher-order (fourth and above) aberration levels. For the emmetropic subjects, the errors measured by the two methods agree when adjusted to measure at similar pupil sizes. For the myopic subjects with similar pupil sizes, however, the Hartmann-Shack wavefront sensor underestimates the accommodation error at higher accommodation levels (2 to 4 D) compared with the autorefractor.

ISSN:1040-5488    

出版商:OVID    

年代:2003

数据来源: OVID

摘要:

Purpose.To investigate the effects of eyelid pressure on corneal shape and corneal aberrations during reading.Methods.Twenty young subjects with normal ocular health were recruited for the study. The experiment was conducted early in the morning, with subjects instructed not to perform any prolonged reading before the experiment. Corneal topography of one eye was measured with a videokeratoscope before reading and then again after a 60-min reading task. The natural position of the eyelids was photographed in primary gaze and during the reading task.Results.Twelve of the 20 corneas showed significant changes in central topography immediately after reading. The location of the changes corresponded closely to the position and angle of the subject’s eyelids during reading. The change in shape was best described as a wave-like distortion that significantly altered some corneal wavefront Zernike coefficients. There was a significant correlation between the changes in primary vertical coma and trefoil (along 30°). Within the central 6 mm of the cornea, there were significant changes in the root mean square error, overall refractive power, and astigmatism.Conclusions.The changes we observed in corneal topography appear to be directly related to the force exerted by the eyelids during reading. Because the cornea is the major light-refracting surface of the eye, the optical characteristics of some eyes can be significantly changed during reading by the force of the eyelids. These findings may have important implications for the definition of refractive status and may also aid in the understanding of the relationship between reading and the development of refractive errors.

ISSN:1040-5488    

出版商:OVID    

年代:2003

数据来源: OVID

摘要:

Purpose.To evaluate the optical quality of the eye before and after the insertion of an Artisan phakic intraocular lens for the treatment of high myopia.Methods.Consecutive patients implanted with the Artisan lens by a single surgeon between June 2001 and April 2002 were enrolled prospectively. One eye per subject was tested. The wavefront aberration was calculated from images recorded with a Hartmann-Shack sensor. This wavefront aberration was expressed as a Zernike polynomial expansion from the third up to the seventh order. Root mean square wavefront error was used as a parameter of optical quality. Point-spread function and modulation transfer function were also computed from the wavefront aberration.Results.The mean age of the four patients (four eyes) was 46 ± 11 years. The preoperative mean spherical equivalent was −14.13 ± 3.19 D (range, −20.50 to −9.75 D), with a best-corrected visual acuity of 20/25 or better in three of the four eyes. No complications were encountered. Postoperatively, the mean spherical equivalent was −0.22 ± 0.30 D (range, −0.75 to +0.38 D). An uncorrected visual acuity of 20/40 or better was observed in three eyes. Overall, for each combination of order (third, fourth, and fifth to seventh) and pupil size (3, 4, and 5 mm), the mean postoperative root mean square values for the four subjects were lower than the mean preoperative values. However, because of the small size of the study population (four patients), this improvement did not reach a statistically significant level.Conclusion.Preliminary data using the Hartmann-Shack wavefront sensor have not revealed a tendency toward deterioration of the optical performance after the insertion of an Artisan lens for the treatment of high myopia. The Hartmann-Shack sensor was a useful tool for the objective assessment of the image optical quality of eyes with a phakic intraocular lens.

ISSN:1040-5488    

出版商:OVID    

年代:2003

数据来源: OVID

摘要:

Because diffraction and aberration affect the performance of the optical system, a new metric is advanced that emphasizes the link between these three aspects. In general, the modulation transfer function is used as a measure for contrast sensitivity reduction, whereas the root mean square error is often used to quantify the optical quality of the system. However, for a given object, wavefront aberrations can alter the output image very differently even though they have the same root mean square error and modulation transfer function profile. A distinction between coherent and incoherent illumination is made, and a new measure, called optical transfer error, is defined to characterize optical performance complementarily to root mean square and modulation transfer function. The optical transfer error measures the optical excellence in terms of the shape of the wavefront as well as the theoretical performance results. Several illustrations are presented to better discuss optical performance.

ISSN:1040-5488    

出版商:OVID    

年代:2003

数据来源: OVID

ISSN:1040-5488    

出版商:OVID    

年代:2003

数据来源: OVID