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Biomedical subjects

T Grosvenor

Publications and source records attributed to T Grosvenor.

At least 37 records · Page 2Linked to original sources
PubMed1989

Use of silicone-acrylate contact lenses for the control of myopia: results after two years of lens wear.

Although a number of reports have been published concerning the use of polymethyl methacrylate (PMMA) contact lenses for the control of myopia, there have been no reports of the use of gas permeable contact lenses for this purpose. In the study reported here, 100 myopic children between the ages of 8 and 13 years were fitted with Paraperm O2 plus silicone-acrylate contact lenses to be worn for a period of 3 years. Lenses were fitted by the alignment method, most lenses having diameters from 8.5 to 9.0 mm. At the end of 2 years 60 subjects remained in the study, 53 of whom were wearing their lenses on a regular basis and the other 7 were irregular wearers. Mean increases in myopia during the 2-year period were found to be 0.28 D for the subjects who wore their lenses regularly and 0.93 D for the irregular wearers, compared to 0.80 D for a group of 31 age-matched single vision spectacle lens wearers. Mean corneal refracting power was found to decrease (the cornea flattened) 0.33 D for the regular wearers as compared to an increase of 0.14 D for the irregular wearers and a decrease of 0.13 D for the spectacle wearers. Mean changes in axial length were an increase of 0.1 mm for the regular wearers, an increase of 0.4 mm for the irregular wearers, and an increase of 0.6 mm for the spectacle wearers.(ABSTRACT TRUNCATED AT 250 WORDS)

Acrylates↗
PubMed1989

Myopia: what can we do about it clinically?

Methods that have been used by vision practitioners for the control of myopia include visual training, biofeedback training, undercorrection, overcorrection, the use of bifocal lenses, the use of contact lenses, the instillation of atropine, and refractive surgery. With some exceptions the use of these methods has achieved only limited success. The lack of success with the less-invasive methods--which are based on the supposition that myopia is caused by accommodation--may be due to the fact that they are used for eyes that are already myopic and therefore have already undergone axial elongation and scleral stretching. If it were possible to predict which children were at risk for the development of myopia, vision practitioners would be able to institute procedures for the control of myopia when only a minimum of scleral stretching has occurred. Risk factors that warrant investigation include the axial length/corneal radius ratio and the resting state of accommodation.

Accommodation, Ocular↗
PubMed1988

Refraction and its components in Melanesian schoolchildren in Vanuatu.

Refraction and its components were measured on 788 Melanesian children and 39 children of other races, aged 6 through 19 years, in the South Pacific island nation of Vanuatu. Of the 788 Melanesian children, 766 (97.2%) were found to have uncorrected visual acuity of 6/6 or better, and 763 (96.8%) were found to have a spherical equivalent refraction between -0.25 and +1.00 D. Only 23 (2.9%) Melanesian children were found to have myopia greater than 0.25 D, only 2 (0.3%) were found to have hyperopia greater than 1.00 D, and only 2 (0.3%) were found to have refractive astigmatism greater than 1.00 D. Mean corneal refracting power was greater for girls than for boys, at all ages, but did not appear to change in any regular manner with age. Mean axial length and mean vitreous length were greater for boys than for girls, at all ages, each increasing approximately 1.0 mm from age 6 and 7 years to age 18 and 19 years. Although the low prevalence of ametropia may be considered to be due mainly to genetic factors, the possibility of environmental factors cannot be excluded.

Adolescent↗
PubMed1988

High axial length/corneal radius ratio as a risk factor in the development of myopia.

Results of refractive component measurements have shown that eyes of Melanesian schoolchildren living in Vanuatu, almost all of whom are emmetropic, have relatively short axial lengths and relatively flat corneas in comparison to emmetropic eyes of children examined in England. Evidence is presented to suggest that the relation between the axial length of the eye and corneal radius--the axial length/corneal radius (AL/CR) ratio--may be a useful predictor of future refractive state. Mean axial length/corneal radius ratios for 6- to 19-year-old Melanesian school children were found to be 2.88 for boys and 2.86 for girls, as compared to mean AL/CR ratios for 6- to 19-year-old British schoolchildren of 3.05 for boys and 3.04 for girls. It is proposed that an eye having a high AL/CR ratio is at risk for the development of myopia, and that such an eye has maintained its state of emmetropia by virtue of a compensatory flattening of the crystalline lens. In order to test the proposition that an increase in axial length occurs as a precursor to the development of myopia, a prospective longitudinal study of a group of 6- to 7-year-old schoolchildren is proposed.

Adolescent↗
PubMed1988

Myopia in Melanesian school children in Vanuatu.

Visual acuity, refraction, and the components of refraction were measured in 788 Melanesian children in the South Pacific island nation of Vanuatu. Of the 788 children, 97.2% were found to have uncorrected visual acuity of 6/6, 96.8% were found to have a spherical equivalent refraction between -0.25 and +1.00 D, 2.9% were found to have myopia of 0.50 or more, 0.25% were found to have hyperopia of 1.25 D or more, and 0.25% were found to have refractive astigmatism of 1.25 D or more. The low prevalence of ametropia may be considered to be due mainly to genetic factors; however, the possibility of environmental factors cannot be ruled out.

Child↗
PubMed1988

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.

Adolescent↗
PubMed1987

A review and a suggested classification system for myopia on the basis of age-related prevalence and age of onset.

Systems for the classification of myopia are usually based on etiological dichotomies such as hereditary vs. environmental, physiological vs. pathological, structural vs. functional, or axial vs. refractive. The purpose of this paper is to propose a system for the classification of myopia based not on assumed etiological factors but on readily available and easily verifiable information, including age-related prevalence and age of onset. The proposed system classifies myopia into four categories: congenital, youth-onset, early adult-onset, and late adult-onset. Paradoxically, such a classification, being devoid of etiological assumptions, may help to make possible a better understanding of the etiology of the various categories of myopia.

Adolescent↗
PubMed1987

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.

Adolescent↗
PubMed1987

Reduction in axial length with age: an emmetropizing mechanism for the adult eye?

Mechanisms accounting for the fact that the eye tends to become and remain emmetropic have been proposed for the developing eye, but no such mechanisms have been proposed for the adult eye. In the study reported here, refractive component data published by Sorsby and his co-workers were reanalyzed in terms of the variations in these components with age. Included in the analysis are component data for one eye of each of 271 subjects from age 4 to age 70 years, whose ocular refraction was between plano and +2.00 D. The results of this analysis show that the axial length of the eye appears to decrease during the adult years of life, concurrently with a decrease in anterior chamber depth and an increase in the refractive power of both the cornea and the lens. It is proposed that a reduction in the axial length of the adult eye serves as an emmetropizing mechanism, occurring in harmony with the increase in the refracting power of the eye, which would otherwise cause the refraction of the eye to move in the myopic direction.

Adolescent↗
PubMed1985

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.

Adolescent↗
PubMed1985

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.

Adult↗
PubMed1985

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.

Accommodation, Ocular↗
PubMed1985

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.

Adolescent↗
PubMed1984

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.

Accommodation, Ocular↗
PubMed1983

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.

Child↗
PubMed1983

How to write an abstract of a paper or a report to be presented at the annual meeting of the American Academy of Optometry.

Although the General Papers Program (held on Saturday, Monday and Tuesday afternoons at the Annual Meeting of the Academy) has expanded to a format in which 20-minute papers and 10-minute reports are presented simultaneously in 4 or 5 rooms the committee continues to receive abstracts for approximately 25 percent more papers and reports than the program can accommodate. The committee's task of selecting papers and reports is complicated by the failure of many writers of abstracts to include sufficient and pertinent information in their abstracts. This presentation lists the essential elements of an acceptable abstract, and tabulates the reasons for non-acceptance of abstracts.

Abstracting and Indexing↗
PubMed1982

A comparison of clinical refractive data obtained by three examiners.

Clinical refractive data were obtained on 32 subjects by each of three examiners, each examiner using standard subjective refraction procedures with an endpoint criterion of "maximum plus for best visual acuity." The results of the three examiners were compared in terms of spherical equivalent refraction, spherical power, cylinder power, cylinder axis, and anisometropia. In addition, results were compared to those of previous studies involving both clinical refraction and the American Optical Corporation's SR III Subjective Refraction System.

Adolescent↗