摘要:

Chronic and acute exposure to ultraviolet (UV) radiation has been shown to have deleterious effects on all layers of the human eye. As a consequence, appropriate protective measures have been advocated with respect to exposure to this form of radiation. Among suggested actions are spending less time in the sun and wearing protective visual aids such as those containing UV-absorbing materials when exposed to sunlight. To investigate the protective ability of currently available contact lens materials we measured the transmittance characteristics of 11 different types of soft and rigid contact lenses in the UV and visible range from 280 to 500 nm with a Zeiss model DM4 Dual Beam Spectrophotometer. Our findings indicate that lenses not treated with UV absorbers transmitted most of the UV radiation. Lenses containing UV absorbers provided excellent UV protection and transmitted significantly less UV radiation than the untreated lenses (Student's t-test with Bonferoni's correction, N = 10, p < 0.001). Based on our findings, we recommend that contact lenses with UV absorbers be considered as a viable option for providing UV protection, especially for aphakic patients, patients taking photosensitizing pharmaceutical agents, and those patients who spend a great deal of time outdoors.

ISSN:1040-5488    

出版商:OVID    

年代:1994

数据来源: OVID

摘要:

The legibility of three selected sets of optotypes: (1) letters; (2) Snellen E; and (3) KOLT test have been compared to the Landolt ring in a study based on the German Standard DIN 58220, Part 2 and the International Standard ISO 8597. The letters were printed in the standard typeface used on German street signs (sans serif Linear-Antiqua, Typeface B). The main results are: 1. A set of letters can be selected in such a way that the differences in legibility displayed between different letters in the set are smaller than the ISO/DIN allowance of 0.05 logarithmic units of the visual angle, although the letters are not constructed according to the traditional 5 by 5 or 5 by 4 construction principles. 2. The eight letters C, D, E, K, N, P, U, Z are proposed for standardized visual acuity tests because of their almost equal legibility. 3. The height of the typeface used for this selected set of letters should be 5% less than the diameter of the Landolt ring in order to achieve the same legibility as the latter. 4. Both shape optotypes (Snellen E and KOLT test) must be approximately 15% smaller than the diameter of the Landolt ring in order to obtain comparable visual acuity scores.

ISSN:1040-5488    

出版商:OVID    

年代:1994

数据来源: OVID

摘要:

We looked for the earliest signs of the onset of myopia in 194 emmetropic (-0.25 to +0.75 D) eyes by following them for 1 to more than 2 years. Visual acuity examination, cycloplegic retinoscopy, and A-scan ultrasonography were performed at intervals of 6 to 12 months. Of the 194 eyes 64 became myopic during the observation time. Our results show that during the progression from emmetropia to myopia the change in visual acuity is not a good indicator of the onset of myopia. When visual acuity decreased to below 6/6 (20/20) cycloplegic retinoscopy showed that most of the 64 eyes had become truly myopic and A-scan ultrasonography revealed a significant increase in vitreous chamber depth and axial length as compared to the nonmyopic eyes. In the early stage of myopia development the anteroposterior diameter of the eye elongates. However, changes in anterior chamber depth and lens thickness did not differ between the myopic and nonmyopic group. Our results suggest that routine ocular refraction should be conducted in addition to the school vision screening. For those who have visual acuity 6/6 (20/20) and ametropia of -0.25 0 or more minus we would like to be able to prevent or at least retard the development of myopia.

ISSN:1040-5488    

出版商:OVID    

年代:1994

数据来源: OVID

摘要:

Background. Exposure to ultraviolet radiation (UVR) and blue light has been shown to cause retinal damage in animals. In humans, it has been argued that the loss of short-wavelength (S) cone sensitivity during normal aging may be related to chronic light exposure. Methods. We measured sensitivity to blue and yellow lights presented on bright yellow backgrounds at several retinal eccentricities in both eyes of an observer with long-standing unilateral aphakia. Results. For yellow lights, where media absorption is not a major factor, there was a 2-fold loss in sensitivity of long (L) and medium (M) wavelength cone mechanisms in the aphakic eye relative to the phakic eye. For blue lights detected by S-cones, there was a 10-fold loss of Scone mechanism sensitivity in the aphakic eye, after differences in ocular media density were taken into account. Conclusions. Our findings strongly support the hypothesis that chronic exposure to short wavelength radiation impairs S-cone function.

ISSN:1040-5488    

出版商:OVID    

年代:1994

数据来源: OVID

摘要:

Javal's rule and Grosvenor's simplification of it are commonly used formulas for predicting spectacle astigmatism from keratometric measurements. We assessed the accuracy of these two rules. Spectacle astigmatism was estimated using both rules from measurements of corneal astigmatism on 100 eyes of 100 subjects. These estimates were then compared to the subjectively determined spectacle astigmatism. Grosvenor's simplification of Javal's rule gave slightly more accurate assessments than the original rule. However, only 66% of results gave estimates within 0.50 D, and 7% differed by more than 1.00 D. This can be compared to previous reports on the accuracy of autorefractors, where approximately 95% of cylinder results were within 0.50 D of the spectacle astigmatism. These results indicate that using Javal's rule or Grosvenor's simplification of it to determine spectacle astigmatism from corneal cylinder readings is of limited clinical value.

ISSN:1040-5488    

出版商:OVID    

年代:1994

数据来源: OVID

摘要:

Background. The structural and elastic properties of the cornea play an important role in the outcome of corneal refractive surgery. A way to describe the elastic properties is to calculate Young's modulus. The tangent Young's modulus (Elt) represents the first part of the viscoelastic response of the intact cornea due to intraocular pressure increase. Method. The tangent Young's modulus (Elt) of the central cornea of 16 fresh enucleated intact bovine eyes determined from the immediate response was calculated by means of holographic interferometry. The stress was an increase of the intraocular pressure. In 16 eyes the change of intraocular pressure was 10 Pa (group I), starting with an intraocular pressure of 1340 Pa (about 10 mm Hg). In 6 of these 16 eyes there was a second pressure increase of 20 Pa starting at the same intraocular pressure of 1340 Pa (about 10 mm Hg) (group II). Results. The mean value for the Young's modulus in group I was 1.58 x 10s Pa. For group II the Young's modulus was 1.60 x 10s Pa. The difference was not significant. The values for the Young's moduli of the cornea of intact eyes are about 100 times smaller than calculations based on experiments with strips of the cornea. Conclusion. It is necessary to consider the localization of the corneal tissue to avoid influences of corneal hydration or dehydration and to define the existing intraocular pressure if Young's modulus of the cornea is to be calculated.

ISSN:1040-5488    

出版商:OVID    

年代:1994

数据来源: OVID

摘要:

Other investigators have provided normal values of facial and ocular dimensions of subjects of different ethnic backgrounds. Our main reason for carrying out this study was to provide a data base of similar measurements for the male Arab (Saudi) population. A projected photographic technique was used. Measurements from the photographs were transformed to real life distances by multiplying by a constant factor. The results of our investigations show that Japanese have wider inter-outer canthal distance (IOCD) than Arabs and Caucasians, both of whom have similar IOCD. Arabs have wider inter-inner canthal distance (IICD) than Caucasians. African-Americans and Japanese have wider inter pupillary distance (IPD) than Arabs. Percentile values of the measured distances will aid in syndrome diagnosis among male Arabs.

ISSN:1040-5488    

出版商:OVID    

年代:1994

数据来源: OVID

摘要:

Purpose. The latency of adaptation of the human vergence system to a change in convergence or divergence forced upon it by a prism was investigated in this pilot study. Methods. Adaptation was stimulated by a 5–s period of binocular vision through a prism of 0 Δ, –8Δ, or 8 Δ. Immediately thereafter and for a further period of 45 s, lateral heterophoria was monitored subjectively by an automated version of Duane's screen and parallax test. Adaptation was calculated from the phoria 40 s after the end of binocular vision. Tests were performed at 0.4 m. In the first test session, there was screening during the binocular period to test for flaws in the screening method. In the second session, there was no screening during the binocular period and phoria measurement was started without changing the power of the prism. In the third session, the prism was restored to 0 Δ after the period of binocular vision. Immediately after the last 5–s test, tests were repeated with 1 s of binocular vision. The subject had excellent visual acuity, stereoacuity, and stereolatency. Results. The test functioned correctly and showed good repeatability. The greatest adaptation to 8 Δ was 59%. This was obtained with only 1 s of binocular vision. There was adaptation to – A with 5 s of binocular vision but it was obscured by adaptation to 0 Δ or 8 Δ which persisted from previous tests. Discussion. The reason why the subject's latency was not found more precisely is explained. Additional evidence is presented in support of the finding that prism adaptation can take place within 1 s (perhaps less) of binocular vision, and the persistence and dominance of adaptation to base-out prism at near is pointed out. Guidelines are proposed for the experimental measurement of prism adaptation latency.

ISSN:1040-5488    

出版商:OVID    

年代:1994

数据来源: OVID

摘要:

The clinical performance of a portable ultrasonic pachometer was compared with a modified optical pachometer on a group of normal subjects. The mean central corneal thickness according to optical pachometry using the "edge-to-edge" method of optical doubling was 0.553 mm (SD=±0.022). The mean central corneal thickness using the ultrasonic device was 0.506 mm (SD=±0.039). The differences between the means was statistically significant (at 1% level of probability). Based on the light distribution within the corneal optical section viewed during optical pachometry a hypothesis is derived supporting the notion that optical pachometry tends to overestimate corneal thickness rather than ultrasonic pachometry underestimating corneal thickness.

ISSN:1040-5488    

出版商:OVID    

年代:1994

数据来源: OVID

摘要:

This retrospective study examined the interview scores, admission grades, and optometry grades of students who received one of two types of admission interviews. The INDIV-BLIND group (N=36) represented those students who had received an individual interview (i.e., one interviewer) for which the interviewer had no access to the candidate's file. The PANEL-ACCESS group (N=21) was made up of those students who had received a panel interview (i.e., two interviewers) for which the interviewers had access to the candidate's file. The two groups were compared using two admission grades and seven optometry grades. Both t-test and Wilcoxon Score statistical procedures were used to test the null hypothesis (Ho) that there were no significant grade differences (p <0.05) between the INDIV-BLIND and PANEL-ACCESS groups. The Ho was accepted. There were no indications that the homogeneity of grades in the two groups was a function of the admission process. When the interview scores in each group were considered, Spearman Correlation Coefficients showed that the interview scores of the PANEL-ACCESS group significantly correlated (p <0.05) with six of the academic grades such that better scores were associated with higher grades. No such correlations were found for the INDIV-BLIND group. The results were interpreted as evidence that interviewers can be unduly influenced in their scoring of the interview by the candidate's written file. The difference in skills reflected by the interview score and the clinic grade was suggested as an important factor in accounting for the lack of correlation between these two measures. The limitations of the study and the implication of the findings on admission decisions are discussed.

ISSN:1040-5488    

出版商:OVID    

年代:1994

数据来源: OVID