The effects of spectacle frames on field of vision

Spectacle frames with thick frames and wide and low-set temples were obtained from an optical goods distributor. Peripheral visual fields were mapped with a Goldmann Projection Perimeter to determine if there was evidence of a safety hazard. A novel way of displaying visual fields was employed. Frame fronts caused more obstruction than temples, which were not found to be a particular problem. Large lenses and thin frames are still recommended for aviator's spectacles and sunglasses. Unusually wide, solid temples should not be worn while flying or driving.

Clinical trial with commercial aspheric aphakic lenses

A clinical trial with 11 subjects was conducted to compare the Armorlite Multiple Drop, the Signet Hyperaspheric, the Sola Hi-Drop, and the American Optical Fulvue types of aspheric aphakic lenses. Reasonable off-axis visual acuities were obtained with the Signet, Sola, and Fulvue types, but poor visual acuities were found with the Armorlite type. Similar visual field limits were found with the armorlite, Signet, and Sola types. Considerably larger limits were found with the Fulvue type than with the other types. However, subjects failed to appreciate these larger limits; this was attributed to the extremely poor image quality near the edge of the visual field with this lens type. Some subjects disliked the poor off-axis image quality with the Armorlite lens type, and it had poor acceptance relative to the other types. Concerning subjective perception of weight, cosmetic appearance, and visual field size, and subjective evaluation of performance of everyday activities, there were no significant differences between lens types. It was concluded that reducing lens off-axis power errors, corresponding to the rotating eye, should remain the most important principle of aphakic spectacle lens design.

Development of quantitative tools for filter-aided dichromats

Historically, there has been little quantitative rationale for the prescription of colored filters for color deficients . A formal prediction of the effects of any filter on dichromat luminance and chromatic discrimination is presented; these predictions were generated by using colorimetric concepts and related derived formulas to create four interactive computer-graphic tools. In addition to predicting performance of presently available commercial filters, such tools can be used to describe, classify, and even design new filters.

An experimental test of filter-aided dichromatic color discrimination

Using derived formulas for dichromat colorimetry and related computer graphic colorimetric tools, predictions of color discrimination performance are made for a deuteranope and protanope standard observer for each of three commercial color deficiency "treatment" filters. Five deuteranopes and five protanopes then participated in two experiments. They were asked to order the caps of the D-15 test, and in a second experiment arrange color pairs (from the D-15 test) in order of difference. Predictions and subject performance reveal that although X-Chrom aided dichromats gain both luminous and chromatic information, all dichromats used predominantly chromaticity information in discrimination tasks. The colorimetric tools correctly predicted that protanopes would derive less useful luminous information from the X-Chrom filter compared with deuteranopes , and correctly predicted an increase in discrimination of blues and purples for both classes of red-green color deficients .

Considering the ocular motor system in the treatment of anomalous retinal correspondence

For over fifty years optometrists have treated anomalous retinal correspondence with techniques which may owe much of their success to an effect on the motor system. This paper will review a sample of these techniques and speculate on how considering the motor system may enhance strabismus therapy.

Overcorrection as a means of slowing myopic progression

Thirty-six subjects (18 males and 18 females) ranging in ages from 7.38 to 15.82 years received an overcorrection of 0.75 D over the power required to correct their myopia exactly. These 36 experimental subjects were matched by control subjects selected at random from the files of the Indiana University Optometry Clinics. The criteria used in matching were sex, beginning age, beginning refractive error, and duration of time covered by the record. The mean rate of change of refractive error for the experimental group was (minus indicating increase of myopia) -0.49 D/year (range, +0.37 to -1.95 D/year) on retinoscopy and -0.52 D/year (range, +0.21 to -1.32 D/year) on subjective refraction. The mean rate of change for the control group was -0.47 D/year (range, +0.06 to -2.03 D/year) on retinoscopy and -0.47 D/year (range, +0.28 to -1.72 D/year) on subjective refraction. Rates for the experimental and control groups were not significantly different. The results of this study do not support the hypothesis that an overcorrected myope has a lower rate of increase of myopia than a myope wearing a conventional spectacle correction.

The effects of caffeine on near point plus acceptance

Forty-two university students participated in a study of reading with +0.50 sphere or yokes prism base down for overconvergence and base up for underconvergence. Sixty-four percent of the group improved with a mean of +10.79 wpm. The level of coffee consumption of each student was recorded. A negative correlation existed between the intake of caffeine and reading improvement, r = -.81, p less than .001. Two students reduced their coffee consumption and transformed their loss in words per minute to a significant gain. A double-blind protocol was used in this study. A placebo lens (plano) controlled for subject and investigator bias. The relationship between caffeine and accommodation was investigated by means of a monocular test through a +4.D sphere. The location of the blur point was indicative of the state of tonicity of the ciliary system. Pre- and post-tests of the blur point for 14 subjects who were tested before and after consuming 150 mg of caffeine showed a significant change. The experimental group showed an increase of -0.52D while the control group showed a change of +0.36D. r = .781, p less than .01.

Plus lens, prism, and bifocal effects on myopia progression in military students, Part II

Military academies routinely lose a percentage of their pilot-qualified students to myopia during the 4-year academic program. This study investigated the progression of myopia during such a program and evaluated the usefulness of reading glasses to prevent myopia progression and subsequent acuity loss. A group of students at the United States Naval Academy comprised three randomly divided groups: a placebo group (no. 1 pink tint), a plus with prism group (+1.25 D with 2 delta base-in each eye), and a bifocal group (+1.50 D near addition). All the lens powers were relative to the experimental subject's distance refraction and were for use full-time when reading. The pre- and post-test refractive errors at distance were determined using 1% tropicamide HCl. At the end of 4 years, the tropicamide refraction showed approximately -0.25 D of myopic shift in all groups. There were no significant differences between the myopic shifts in the controls and experimental groups.

Magnification for a series of K spherical coaxial refracting surfaces

This paper reviews the theory of magnification for a series of K spherical coaxial refracting surfaces. It considers the magnification contributed by each component surface of the series.

Bioptic telescopic spectacle is a hazard for operating a motor vehicle

The primary purpose of the bioptic telescopic spectacle is to permit the driver to pass the visual requirement to operate a motor vehicle. It is paradoxical that a driver can pass the vision test only by the use of a telescope but that he cannot drive while looking through the telescope. Rather, he must drive with his limited vision (sometimes legal blindness) while looking through the carrier lens. He can use the telescope only for reading a sign or for distinguishing an object, and even then he must lower his head to look through it. This is hazardous: he becomes thus "blind" to the traffic while reading the sign through the telescope. Such a driver could never pass a peripheral vision test due to the blind areas created in the peripheral field. It is more humane and reasonable to grant a waiver for the impaired vision than to compel a handicapped person to purchase a bioptic telescopic spectacle to pass the visual requirement.

Distortion by ophthalmic lenses calculated at the farpoint sphere

Distortion by ophthalmic lenses has generally been calculated with respect to an ideal flat image surface. This results in improper distortion values as the ideal image surface for the mobile eye is the farpoint sphere. Results of distortion calculations for lenses ranging from +20 to -24.65 D are given for point focal lenses (corrected for oblique astigmatism), Percival lenses (designed to place the circle of least confusion on the farpoint sphere), minimum astigmatism and minimum distortion lens forms. Distortion of point focal Ostwalt lenses of powers +6.60 to -24.65 D range from 4.45 to -28.31% when computed at the flat image surface. Referred to the farpoint sphere the corresponding distortion values are +0.85 to -13.54%. Similarly, the distortion of the minimum astigmatic forms of lenses ranging in power from +20 to +7 D are +27.31 to 4.64% at the flat image surface but decreased to +16.38 to 0.84%, respectively, at the farpoint sphere. If the rotations of the unaided ametropic eye that are required to fixate two points in the field are compared with the necessary rotations with a spectacle correction (+20 to -24 D), it is found that the corrected eye rotation errors at the flat image surface range from 14.87 to -4.53%, but drop to +0.87 to -1.88% when referred to the farpoint sphere. It is concluded that distortion at the farpoint sphere is a more valid measure of distortion for the mobile eye than the classical measurement of distortion. This has implications for the study of space perception through lenses.

Congenital hereditary downbeat nystagmus

This report describes an 8-year-old boy with congenital hereditary downbeat nystagmus, the youngest person with downbeat nystagmus in the literature to date and the first to have an apparently congenital form. He had tended to keep his chin down since birth and had had difficulty reading since starting to attend school. His 28-year-old mother manifested a subclinical combined rotatory-downbeat nystagmus only in oblique downward gaze. Neither the child nor the mother demonstrated evidence of spinocerebellar degeneration. Homologous base-up prisms incorporated into glasses eliminated his chin-down head posture, improved his vision in primary position and "cured" his so-called learning disability.

A functional interpretation of the visual fields of low vision patients

The importance of using visual field information when evaluating low vision patients is often overlooked. The authors present some clinical discussions of various types of field losses and their functional implications.

Aspheric high positive power lenses and third order theory

To correct third order (primary) oblique astigmatism of thin spectacle lenses outside an approximate lens power range of -22 D to +7 D, one surface must be aspherized. Aspherizing is of particular importance in the high positive power range used for the correction of aphakia. Graphs are presented showing the required front surface asphericities and power drops required to correct oblique astigmatism in this range. The results are a guide to the required asphericities in thick lenses.

Optical characteristics of Transpaseal as a partial occluder

The acuity degradation produced by Transpaseal, a typical adhesive scattering material applied to spectacle lenses to produce partial occlusion during orthoptic treatment, is studied by measuring the angular characteristics of the scattering and its effect upon the visual contrast sensitivity function. Whereas in general the material acts as a low-pass spatial frequency filter, it is shown that the scattering function is not symmetrical and hence that the visual degradation produced varies with the orientation of the detail observed.

Reliability of power measurement of toric soft contact lenses

We studied the reliability of lensometer measurements of hydrated toric soft contact lenses in air and compared them to similar measurements of toric hard contact lenses and a spherocylindrical spectacle lens. Twenty measurements were made of each of five soft lenses, three hard lenses, and one spectacle lens. One-half of the measurements used an eyepiece lensometer and one-half a projection lensometer. The reliability of the technique was found to be lower for soft lenses than for hard lenses and highest for the spectacle lens. Reliability was sufficiently high for hydrated toric soft lenses with either type of lensometer to support recommendation of a standard tolerance of +/-0.25 D when applied to the mean of five measurements.

Retinitis pigmentosa--an overview

Retinitis pigmentosa is a retinal pigment dystrophy of multiple genetic inheritance patterns affecting approximately .5% of the world population. It may be recognized clinically by observing specific ophthalmoscopic changes, as well as through psychophysical and electrodiagnostic testing. It may also be associated with several other genetic conditions. Basic research indicates that while there is no specific cure, certain precautions may prevent rapid acceleration of the disease process. This article presents an overview of retinitis pigmentosa, including its diagnosis and genetic patterns, and discusses various auxiliary aids and filters that may be helpful in protecting and increasing visual function in R.P. patients.

Iseikonia and accommodation in the fellow eye in monocular IOL implantation

In unilateral implantation of an intraocular lens (IOL), the main goal, for both distant and near vision, is iseikonia. After monocular IOL implantation, when the normal fellow eye accommodates for different distances, the changed magnification will result in aniseikonia. We have derived formulas for calculating the power of an iseikonizing IOL and of corresponding spectacles for both distant and near vision. Using the formulas, we can predict the degree of aniseikonia produced by accommodation in the normal eye. We suggest that accommodation in the fellow eye be avoided by using reading glasses.

The low vision aphakic patient

This paper gives a comprehensive overview of the care of the low vision aphakic patient. Included is a discussion of the psychological considerations in dealing with this patient, the examination procedures, a summary of the categories of low vision aids available, lighting considerations, accessory aids, training and follow-up care, and the use of outside agencies for referral.

Clinical evaluation of vertical fixation disparity. Part One

The successful prescribing of vertical prism for the individual patient requires that (1) the deviation be measured in the presence of horizonal fusion, (2) the deviation be determined with distance and near fixation in the straight ahead and down-gaze positions, and (3) the ability to adapt to the prism be assessed. This study addresses the first requirement by evaluating the measurement of fixation disparity of asymptomatic patients using a readily available clinical procedure. The results indicate that the vertical fixation disparity varies directly and in a consistent manner with forced vertical vergence in patients with no vertical fixation disparity as well as in those with a vertical fixation disparity with zero forced vertical vergence. The implication of this information for the prescription of vertical prism is discussed.