The Hirschberg test: correlation with corneal radius and axial length.

The results of this study indicate that the axial length is not strongly associated with the Hirschberg formula, and therefore the axial length does not have to be considered when measuring an ocular deviation with the Hirschberg test. This study does demonstrate an association between the radius of curvature of the cornea and the Hirschberg formula. For patients with keratometer readings below 46 D, the use of the standard Hirschberg formula, 1 mm = 22 delta, is appropriate. For patients with keratometer readings greater than 46 D, and with deviations greater than about 30 delta, the use of the Hirschberg formula, 1 mm = 27 delta, is more appropriate. When performing the Hirschberg test on infants up to about 2 months of age, the use of the higher Hirschberg formula would probably be more appropriate because this age group often has higher keratometer readings.

Predicting refractive astigmatism: a suggested simplification of Javal's rule.

In the period of almost 100 years since Javal proposed an empirically determined rule for the prediction of refractive astigmatism on the basis of corneal astigmatism, many authors have made suggestions for the modification of "Javal's Rule." These modifications, rather than being based on clinical data, have been based on concepts of mechanisms that can contribute to refractive astigmatism, but in most cases the modifications do nothing more than complicate the process of predicting refractive astigmatism, with the result that only Javal's original rule is widely used. In this paper, keratometric and refractive data for three groups of subjects are used to demonstrate that a simplified version of Javal's rule is more effective in predicting refractive astigmatism than is Javal's rule itself.

Entoptic phenomena and reproducibility of corneal striae following contact lens wear.

Vertical corneal striae distributed across the posterior cornea are one of the objective signs of clinically unacceptable corneal swelling (greater than 6%) resulting from contact lens wear. This study reports that corneal striae are repeatable both in configuration and location with different levels of hypoxia. In most instances entoptic phenomena result from the presence of these lines. The results suggest that the healthy, avascular, transparent cornea has certain localised areas in its anatomical structure which may give rise to bundles of collagen fibres being made visible objectively and subjectively during conditions of corneal swelling.

Houston Myopia Control Study: a randomized clinical trial. Part II. Final report by the patient care team.

In a randomized clinical trial designed to test the efficacy of bifocal lenses for the control of juvenile myopia, each of 207 children between the ages of 6 and 15 years wore single vision lenses, +1.00 D add bifocals, or +2.00 D add bifocals for a period of 3 years. For the 124 subjects who completed the study, the mean changes in refraction were found to be -0.34 D per year for subjects wearing single vision lenses, -0.36 D per year for those wearing +1.00 D add bifocals, and -0.34 D per year for those wearing +2.00 D add bifocals. These differences were not statistically significant. When subjects in all three treatment groups were combined, it was found that the rate of progression tended to be the most rapid for subjects who entered the study at an early age with a large amount of myopia, and tended to be the least rapid for subjects who entered the study at a later age with a small amount of myopia. It was also found that subjects having with-the-rule astigmatism progressed more slowly than those having no astigmatism or against-the-rule astigmatism.

Houston Myopia Control Study: a randomized clinical trial. Part I. Background and design of the study.

The Houston Myopia Control Study is a 3-year randomized clinical trial in which each of 213 myopic children was placed in either a single vision (standard treatment) group, a +1.00 D add treatment group, or a +2.00 D add treatment group, on the basis of a randomized procedure. Subjects for the three treatment groups were matched on the basis of sex, age, and the initial amount of myopia. The study involves two groups of investigators: an evaluation team, whose task has been to evaluate candidates before entering the study and to reevaluate each subject on a yearly basis for the 3-year period, and a patient care team, whose task has been to prescribe glasses for each subject as well as to counsel subjects and their parents in the correct use of the glasses and to provide a follow-up examination every six months for the duration of the study. Once the glasses had been prescribed, members of the evaluation team were not permitted to know which subjects wore single vision lenses and which wore bifocals. In the interest of good patient care, members of the patient care team knew which subjects wore single vision lenses and which wore +1.00 D add or +2.00 D add bifocals. In this report, the authors discuss theories concerning the etiology of myopia, methods that have been used in an attempt to control the progression of myopia, and the design of the current study. Further reports will present the results of the study on the basis of the data collected by each of the two study teams.

The Houston myopia control study: a preliminary report by the patient care team.

The Houston Myopia Control Study is a 3-year randomized clinical trial designed to test the efficacy of bifocal lenses for the control of myopia. Each of 213 myopic subjects, between the ages of 6 and 15 years, was placed in either a single vision (standard treatment) group, a +1.00 D. add group, or a +2.00 D. add group, by means of a table of random numbers. Subjects in each of the 3 groups were matched on the basis of sex, age, and the amount of myopia. Subjects were accepted into the study during an 18-month period ending in September, 1982, so all subjects will have completed the study by September, 1985. The purpose of this preliminary report is to inform optometrists of the existence of the study and to discuss the factors that must be taken into consideration when designing a randomized clinical trial making use of bifocal lenses for the control of myopia.

Comparison of refractive findings obtained by the Bausch and Lomb IVEX and by conventional clinical refraction.

The Bausch and Lomb IVEX (Integrated Vision Examination System) is a computerized refractor, designed for both subjective and objective refraction and binocular vision testing. Using a double-masked protocol, subjective refraction findings were obtained on 40 subjects by means of both IVEX and conventional clinical refraction. Although for most subjects IVEX spherical equivalent findings varied by no more than 0.25 or 0.50 D from conventional refractive findings, for some subjects IVEX findings yielded more minus or less plus than conventional refractive findings by as much as 1.00 or 1.25 D.

Three-way comparison of retinoscopy, subjective, and Dioptron Nova refractive findings.

On the basis of routine clinical findings taken on a group of 100 patients serving as subjects in the Houston Myopia Control study, a three-way comparison was made between retinoscopy, subjective, and Dioptron Nova refractive findings. Retinoscopy and subjective findings compared very favorably, mean differences being -0.01 D for spherical equivalent power and -0.05 D for cylinder power. Dioptron and retinoscopy findings differed by -0.30 D for spherical equivalent power and -0.13 D for cylinder power, whereas Dioptron and subjective findings differed by -0.33 D for spherical equivalent power and -0.18 D for cylinder power.

Comparison of Dioptron Nova refractive data with conventional refractive data.

Refractive data obtained by means of the Dioptron Nova Diagnostic Eye Computer were compared to data obtained by conventional clinical refraction on a group of 236 clinic patients. Spherical equivalent power data were found to average -0.32 D more for Dioptron Nova data than for clinical data, whereas spherical power data averaged -0.25 D more for Dioptron Nova data than for clinical data, and cylinder power averaged -0.12 D more for Dioptron Nova data. Dioptron and clinical data were found to be within +/- 0.50 D of each other for 74% of eyes for spherical equivalent power, for 83% of eyes for spherical power, and for 91% of eyes for cylinder power. Cylinder axis data were found to be within +/- 10 degrees for the two methods for 78% of eyes.

Comparison of American optical SR-IV refractive data with clinical refractive data on a group of myopic children.

Previous studies involving the American Optical SR-III Subjective Refraction System have indicated that refractive data for adults and for populations of mixed age groups compare favorably with conventional refractive data. However, no data concerning children, as a group, have been available. As a part of a 3-year Myopia Control Study being conducted at the University of Houston, 131 myopes between the ages of 6 and 15 years have been refracted by means of both the redesigned SR-IV Programmed Subjective Refractor and conventional clinical procedures. The results indicated that for the majority of subjects, the refractive data obtained by means of the SR-IV differed by no more than 0.25 D from data obtained by conventional procedures. SR-IV and clinical refractive data were also compared for a group of 30 second year optometry students, and agreement for the two methods was found to compare favorably with agreement of clinical refractive data obtained by two or more examiners.

A clinical evaluation of the american optical SR III subjective refractor.

The American Optical SR III Subjective Refraction System is a recent addition to the vision care field. Subjective refractions were performed, using the SR III, on 275 eyes of 139 subjects (clinic patients, optometry students, staff members, and faculty members) and the results were compared to clinical refractive data. Although subjective refraction results were found to compare favorably to the clinical results, the instrument was found to be limited to the extent that there is no provision for binocular vision testing and no provision for near vision testing.