ISSN:1040-5488    

出版商:OVID    

年代:2002

数据来源: OVID

ISSN:1040-5488    

出版商:OVID    

年代:2002

数据来源: OVID

ISSN:1040-5488    

出版商:OVID    

年代:2002

数据来源: OVID

ISSN:1040-5488    

出版商:OVID    

年代:2002

数据来源: OVID

ISSN:1040-5488    

出版商:OVID    

年代:2002

数据来源: OVID

ISSN:1040-5488    

出版商:OVID    

年代:2002

数据来源: OVID

摘要:

Purpose.To determine whether the degree of myopia affects the optical quality of the retinal image after appropriate correction, monochromatic aberrations of the human eye were measured as a function of the degree of myopia.Methods.Using a modified Hartmann-Shack method, a population of 27 myopic (up to −9.25 D) and 7 emmetropic optometry students (18–32 years) were objectively evaluated before and after pupil dilation. We then identified for each subject the most influential aberration types, and we calculated the profile of wavefront aberration. To study the behavior of aberration as a function of the degree of myopia, we determined the maximum value of aberration as well as the root mean square (rms) value.Results.It turned out that aberration increases with the refractive error in a quasi-linear relationship for pupil diameters of 5 and 9 mm. This result is valid for both rms and maximum values.Conclusions.We objectively showed that optical quality decreases as myopia increases and as the pupil gets larger. Coma is more frequent in high myopia, and spherical aberration occurs more frequently for dilated pupils.

ISSN:1040-5488    

出版商:OVID    

年代:2002

数据来源: OVID

摘要:

We compared retrospectively the distribution of refractive errors in a sample of adolescent and adult albinos (n = 19) with that in persons with idiopathic congenital nystagmus (CN) (n = 46), whose eye movements are similar to those of albinos but whose visual acuity is better. The distribution of spherical-equivalent refractive errors is more broadly distributed and slightly less myopic in albinos than in persons with idiopathic CN. On average, albinos also have more astigmatism (primarily with-the-rule), than persons with idiopathic CN. Unlike the leptokurtic distribution of refractive error that characterizes the normal adolescent and adult population, the distributions of refractive error for albinos and for persons with idiopathic CN exhibit no significant kurtosis. Moreover, neither group of subjects exhibits significant kurtosis for refractive errors in the vertical meridian, which corresponds to the retinal-image orientation with the least motion smear during horizontal nystagmus. The absence of significant leptokurtosis in the refractive-error distributions of young-adult albinos and persons with idiopathic CN suggests that the presence of nystagmus may interfere with normal refractive development.

ISSN:1040-5488    

出版商:OVID    

年代:2002

数据来源: OVID

摘要:

Purpose.This study investigated the effect of myopic axial elongation on pulsatile ocular blood flow (POBF) in young normal subjects. A regression equation was derived to quantify the effect. The effect of posture in POBF for eyes with different axial lengths was studied to determine if axial myopia, with different ocular volumes, would result in a change in POBF with various postures.Methods.Seventy-nine normal subjects (38 males and 41 females) with different refractive errors were recruited. The mean age of the subjects was 22 years, and only the right eye was used for analysis. The axial length (AL) was measured, followed by Perkins intraocular pressure (IOP) and POBF with an OBF tonometer (OBF Labs [UK] Ltd) in a sitting posture. An “erected arm” blood pressure (BP) was measured with an automatic sphygmomanometer for the calculation of ocular perfusion pressure (OPP), using the formula: mean BP − IOP, where the mean BP was calculated as one third of the systolic blood pressure plus two thirds of the diastolic blood pressure. The measurements of IOP, POBF, and BP were repeated in a supine posture.Results.The POBF was negatively correlated with AL (r = −0.57, p < 0.01). The regression line was in the form of POBF (&mgr;l/min) = −78.5 × AL (mm) + 2655.7. There was a significant reduction (17%) in POBF in a supine posture (p < 0.01). The reduction was not significantly correlated with AL. The pulse amplitude also demonstrated a 10% reduction from postural variation (p < 0.01). The OPP increased significantly (33%) in the supine posture (p < 0.01).Conclusions.The POBF was significantly influenced by AL. Therefore, AL should be measured in determining the POBF, especially in young myopic subjects. The amount of postural variation in POBF was similar to previous studies with young subjects and was not affected by AL.

ISSN:1040-5488    

出版商:OVID    

年代:2002

数据来源: OVID

摘要:

Background.Very small high-resolution displays (SVGA, 800 × 600 pixels) worn near the eye and imaged to create a virtual image have potential as alternatives to traditional computer displays.Methods.Twenty-two subjects performed text-based tasks on five displays: monocular virtual, binocular head-mounted virtual, hard copy, flat panel, and a small format portable display. Outcome measures included performance speed, symptoms, visual acuity, and heterophoria. In a second experiment, subjects performed a proscribed routine of head and body movements designed to elicit motion-related symptoms.Results.Performance speed on monocular virtual was generally comparable with performances on flat panel and hard copy. Overall, performance speeds on the binocular virtual display were about 5% slower than normalized performances, 6.75% slower compared with the traditional flat panel and hard copy displays. Symptoms of eyestrain and blurry vision were significantly higher on monocular virtual than on other displays. No significant changes in visual acuity or heterophoria occurred with any of the displays. Motion-related symptoms with the head mounted near-eye display were not significantly different than with other displays tested.Conclusions.Performance and comfort on the near-eye displays in this study was more similar to traditional displays than in many previous studies with head mounted displays. This is likely due to lack of task movement, partial instead of full immersion, better display resolution, and concordance of the accommodative and vergence stimuli.

ISSN:1040-5488    

出版商:OVID    

年代:2002

数据来源: OVID