摘要:

Purpose.To investigate how bifocal contact lenses, when combined with the aberrations of the eye, will affect visual performance. Also, to investigate the relationship between the patient’s predicted and actual visual benefit with bifocal contact lenses.Methods.The monochromatic aberrations of 16 subjects were measured and used to simulate visual quality with three bifocal contact lens designs. Actual and computed visual benefit was compared for an Acuvue bifocal contact lens in 5 of the 16 subjects.Results.Subjects were predicted to have either a bifocal response or an increase in depth of focus for all lens designs. Our subjects were predicted to have a decrease in visual benefit for distance viewing and a gain in visual benefit at near compared with not wearing a contact lens. We found a statistically significant association between our subjects’ predicted and actual visual benefit with the Acuvue Bifocal contact lens (r = 0.685, p = 0.008).Conclusions.Bifocal contact lens designs, when combined with the aberrations of the eye, will not always provide bifocal vision. Visual quality with a bifocal contact lens can be predicted based on a patient’s ocular aberrations.

ISSN:1040-5488    

出版商:OVID    

年代:2003

数据来源: OVID

摘要:

Purpose.This study evaluated interexaminer agreement in the measurement of tear volume using the phenol red thread (PRT) test on Hong Kong-Chinese subjects. The effect of an intensive training session on interexaminer agreement was also investigated.Methods.Three postgraduate students without an optometry background were introduced to the use of the PRT test. After a general introduction (including a demonstration and some practice among themselves), the examiners collecting the first set of data from 38 subjects. They were then given an intensive 30-min training that involved strict standardization of instructions/procedures and practice. PRT values were collected from 27 subjects (four subjects participated in both phases of the study) after the intensive training.Results.Significant differences were found among the examiners before and after the intensive training, which was mainly due to examiner 1, who consistently obtained relatively lower mean PRT values in both testing sessions. The intraclass correlation values estimated for all examiners were 0.35 and 0.58 before and after the training session, respectively. The 95% limits of agreement after the training session ranged from −14.8 to 8.0 mm/15 s between examiners 1 and 3, who showed the largest difference, and from −8.8 to 9.3 mm/15 s between examiners 2 and 3, who showed the smallest difference. The latter pair also showed the most significant increase in agreement after the intensive training (intraclass correlation value increase from 0.29 to 0.65), although no significant differences in the PRT results were found between the two examiners before and after training.Conclusions.Our results suggest that the interexaminer agreement of PRT results is influenced by both examiner- and training-specific factors. Intensive training is important for ensuring the highest consistency among examiners. The moderate interexaminer agreement suggests that clinicians should seek a substantial difference in tear volume when making decisions regarding interventions for their Hong Kong-Chinese patients.

ISSN:1040-5488    

出版商:OVID    

年代:2003

数据来源: OVID

摘要:

Purpose.Disruption of the anterior refracting surface of the eye reduces visual performance. In the case of a contact lens wearer, this surface is the prelens tear film. This study determined whether artificial tears stabilize the tear film in contact lens wearers and maintained optimal visual performance for a prolonged period.Methods.Five normal subjects all in good general and ocular health and adapted to contact lens wear were fitted with Acuvue lenses. A temporal, two-alternative, forced-choice paradigm was used to measure contrast sensitivity. The stimuli were vertically oriented sine-wave gratings (between 0.5 and 14 cpd) presented for 16.67 ms. The stimuli were presented at two different times after blink detection: 2 s after blink detection (i.e., before tear layer break-up) or 4 s after tear film break-up. Three conditions were investigated at 4 s after tear layer break-up: (1) without artificial tears added, (2) with Clerz2 (Ciba Vision) instilled, and (3) with Sensitive Eyes (Bausch & Lomb) applied. The artificial tears were instilled at 10-min intervals during the experimental run.Results.High spatial frequency contrast sensitivity was found to be reduced after tear film break-up and was not enhanced by either tear solution.Conclusions.This study indicates that there is no effect of Clerz2 or Sensitive Eyes in maintaining or improving visual performance beyond the normal prelens tear film break-up time in normal subjects wearing Acuvue lenses.

ISSN:1040-5488    

出版商:OVID    

年代:2003

数据来源: OVID

摘要:

Purpose.To assess the validity and reliability of the Convergence Insufficiency Symptom Survey (CISS) in children aged 9 to 18 years. The CISS is the primary outcome measure for a pilot study evaluating two different treatments for convergence insufficiency (CI).Methods.Children with CI were given the CISS twice to assess reliability. CISS scores for the first administration were also compared with scores from children with normal binocular vision to assess the validity of the CISS.Results.Forty-seven children with CI and 56 children with normal binocular vision participated in the study. Reliability was assessed using intraclass correlation and 95% limits of agreement for the children with CI. For children with CI, the intraclass correlation was 0.77 (95% confidence interval, 0.613 to 0.873), and the 95% limits of agreement were −10.2 to +12.1. The mean (±SD) CISS score was 30.8 ± 8.4 for the children with CI and 8.4 ± 6.4 for the children with normal binocular vision. These means were significantly different (p < 0.0001). Good discrimination (sensitivity, 96%; specificity, 88%) was obtained using a score of ≥16.Conclusions.Children with CI showed a significantly higher CISS symptom score than children with normal binocular vision. The results of the study indicate that the CISS is a valid and reliable instrument to use as an outcome measure for children aged 9 to 18 who are enrolled in clinical research concerning CI.

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

摘要:

A focimeter is one of the basic clinical instruments used in every optometric practice, and verification of the accuracy and calibration of the instrument are of the utmost importance. Calibration is accomplished using special test lenses. These lenses must be of high quality and of nominal ophthalmic power that is known with high accuracy. The standard ISO 9342:1996Optics and Optical Instruments: Test Lenses for Calibration of Focimetersimposes stringent requirements on permitted deviation from nominal ophthalmic power of test lenses. In this study, the influence of tolerancing and uncertainties in design and production of standard test lenses for calibration of focimeters was analyzed. Two approaches were used. First, the paraxial approximation was used to relate the lens parameters with ophthalmic power and to calculate the uncertainty budget. Second, exact ray tracing using a professional optical design program and tolerancing sensitivity analysis in conjunction with Monte Carlo simulation were used to evaluate the uncertainty budget and balance the required tolerances. The results of both approaches are compared and discussed in detail. The customary uncertainty budgeting based on simple paraxial approximation does not guarantee the compliance with the requirements of the ISO 9342:1996 standard. Consequently, such an approach is inadequate for characterization and tolerancing of test lenses for calibration of focimeters.

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