Anthropometry for children's spectacle frames

Facial measurements of 154 Caucasian children aged 5-14 were taken, to provide statistical information for spectacle frame manufacturers. The main differences compared with adult measurements were in the following dimensions: temple width, head width, bridge height, projection, splay angle and front to bend. The range of the 'distance between rims' measurement of adults, was similar to that of children. A number of differences between this group and a small group of Afro-Caribbean children was encountered.

The sagitta and lens thickness: the exact solution and a matrix approximation for lenses with toric, spherical, and cylindrical surfaces

The exact equation for sagitta of spherical surfaces is generalized to toric surfaces which include spherical and cylindrical surfaces as special cases. Lens thickness, therefore, can be calculated accurately anywhere on a lens even in cases of extreme spherical and cylindrical powers and large diameters. The sagittae of tire- and barrel-form toric surfaces differ off the principal meridians, as is shown by a numerical example. The same holds for pulley- and capstan-form toric surfaces. A general expression is given for thickness at an arbitrary point on a toric lens. Approximate expressions are derived and re-expressed in terms of matrices. The matrix provides an elegant means of generalizing equations for spherical surfaces and lenses to toric surfaces and lenses.

[Protective sunglasses and color discriminating ability]

The influence on color vision of 4 kinds of sun-glasses with various characteristics of transparency and absorption of 25, 50, 75 p.c. was evaluated. Sixty persons with normal color discrimination took part in investigation. The selection of filters for professional drivers and railway engine-drivers was performed on the basis of Nagel's anomaloscope and Farnworth-Munsell's 100--Hue tests.

[Retinal protection using glasses filtering short wave lengths in patients with hereditary degenerative diseases. First electrophysiologic results]

The electrophysiological action of the ORMA RT glasses filtering the short and middle wavelengths are exposed through the first results of this work by retinitis pigmentosa patients. In 90% of the tested patients A.E.R.G. and V.E.P. are improved.

Pressure testing of ophthalmic safety lenses: the effects on different materials

The procedure of applying pressure to a lens until fracture occurs and the use of the fracture pressure as a measure of lens strength has been proposed as a quantitative alternative to the drop ball test. The fracture pressure or pressure resistance of untempered, thermally tempered, and chemically tempered glass lenses and CR39 lenses were compared. The results for the glass lenses were consistent with workplace experience and previous studies using the drop ball test. The results for glass and CR39 lenses showed the reverse to what was expected. In order to investigate the basis of this difference, a second procedure was followed in which the annulus supporting the lens and the steel ball applying the pressure to the lens were systematically changed. Glass lenses showed a highly statistically significant change in fracture pressure with decreasing ball size and a small but statistically significant change with annulus size. CR39 lenses showed no statistically significant change in fracture pressure with changing ball size but a highly statistically significant increase in fracture pressure with increasing annulus size. The mechanism of fracture is known to differ in the glass and plastics materials and it is concluded that this method should not be used to compare the performance of different materials.

A comparative study of the Seiko P-3 and Varilux 2 progressive addition lenses

Forty patients were selected to participate in a double-masked comparative study of the Seiko Plax 3 (P-3) and Varilux 2 progressive addition lenses. The study was designed to determine patient preference for either lens design. The patients wore each lens for 1 month. Following each period, a questionnaire relating to the patient's impressions of the lenses was completed. After both wearing periods, the patient's preference was determined. The results show that 89.7% of the patients preferred the Seiko lens over the Varilux. Further, 82.4% chose the Seiko lens and 44.1% chose the Varilux lens over their habitual multifocal design. The results of this study show that, in addition to a preference for the Seiko P-3 design, both progressive addition lenses are viable alternatives to the conventional multifocal lens.

Varifocal spectacle lens surface power measurement

An instrument is described for the assessment of varifocal lens surfaces based on a reflection technique. Results are also presented of measurements made on a series of lenses of the same design, illustrating some of the differences that exist between glass and plastics versions of the same lens.

The suitability of sunglasses used by patients following ingestion of psoralen

We have investigated the types of eyewear which patients on photochemotherapy have obtained, and determined their suitability for providing adequate protection. Fifty-eight pairs of sunglasses from 53 patients were assessed. Spectral transmission was measured between 200 nm and 800 nm at 10 nm intervals. Thirty-eight pairs of glasses (66%) were found to be satisfactory. Particularly high UV transmission was recorded in 11 cases (19%), highlighting the need for increased awareness of the problem of ensuring that suitable protective eyewear is used.

The effect of sunglasses on ocular exposure to ultraviolet radiation

Thirty-two pairs of inexpensive sunglasses were examined for their effectiveness in preventing ultraviolet radiation (UVR) from reaching the eyes. The transmission of UVB (290-310 nm) by all of the sunglass lenses was less than 2 per cent. However, in measurements performed with mannikins wearing the sunglasses, up to 14.1 per cent of the incident UVR passed through to the eyes. When the sunglasses were moved 6 mm from the forehead, the per cent reaching the eyes ranged from 3.7 to 44.8 per cent. Although sunglasses are somewhat more effective than untinted prescription eyewear in attenuating ocular exposure, the amount of attenuation is highly variable and depends mainly on their size, shape, and wearing position.

[Modified acetylcellulose etrols for molded frames of corrective eyeglasses]

The mode and cyclic pattern of tensions capable to disturb continuity of plastic frames and to change their shapes in long-term use are defined. The relations for their amplitudes are derived and limit values found. The process of filling a mould is studied as well as macrostructures and internal defects that develop in a casting. Creepage of the plastic frame is investigated when relaxation loading is applied. To assure prolonged strength and stability of the shape some criteria for optimizing the compositions of AC-etrols are proposed. Replacement of the AC and plasticization with low-molecular plasticizers are shown to affect the chosen criteria for which appropriate levels are ascertained. The optimum modifications of the AC-etrols used for mould frames are specified.

Legal aspects of prescribing for athletes and sportsmen

Eyewear for athletes and sportsmen must meet legally-recognized standards for impact-resistance. Negligence and product liability claims may result from a failure to observe these standards, which are intended to minimize the risk of ocular injury. Optometrists have a legal duty to warn athletes of the relative impact-resistance of ophthalmic materials, to dispense materials that offer adequate protection, and to verify all materials dispensed to ensure they meet the necessary standards.

[Centering of eyeglasses with special reference to aspheric single-power lenses]

In the positive power range, aspheric single-power lenses have clear advantages for the spectacle wearer over highly curved spherical lenses in terms of cosmetic appearance and comfort in wear. Correspondingly flat spherical lenses would not be acceptable, due to their dramatically poorer image reproduction properties. Only with an aspheric surface design is it possible to combine a flat lens with optimum image reproduction properties. In order to realize these advantages of aspheric surfaces, the lenses have to be centered in accordance with the ocular pivot point. Several examples are given to illustrate the effects of incorrect centering on the image reproduction properties of both spherical and aspheric single-power lenses. The negative effect of incorrect centering in accordance with the ocular pivot point is clearly far greater with the mathematically much more complex aspheric surfaces than with highly curved spherical lenses. Although the image reproduction quality of the aspheric lens is superior--at least on paper--when it is correctly centered, it is equally true that in practice these lenses quickly prove inferior if incorrectly fitted.

A critical view of presbyopic add determination

From a previous study at the Optometric Center of Fullerton, it was found that 17.5% of the review clinic population returned due to improper presbyopic reading adds. The population sample for the present study consisted of patients between 40-60 years of age who returned to the clinic between September 1983 and May 1985 due to improper add power. The add power originally prescribed was compared to each of four commonly used methods of add power determination. Our results indicate that the age expected add powers account for the fewest errors while the binocular cross cylinder the most. Upper and lower limits for an acceptable range of add powers versus age were determined.

Ocular phototoxicity: guidelines for selecting sunglasses

Within the last two decades appreciable laboratory and epidemiologic evidence has accumulated to support the notion that near ultraviolet radiation and lower wavelength visible light may be hazardous to the human lens and retina. However, a substantial number of commercially available sunglasses are being manufactured without apparent regard for these potential hazards. This review surveys the mechanism(s) for phototoxic damage to the eye, outlines persons at potentially greatest risk of injury, and summarizes recommendations for the selection of optimally efficient sunglasses.

[Aspherical single-strength eyeglasses with improved wearing comfort]

A new plastic single-vision lens series is presented with an aspherically designed front surface for the weak to medium-strength positive power range. With this lens the asphere is used to improve the non-optical properties and, at the same time, to maintain an image quality comparable to the high standard offered by regular spectacle lenses. The various factors which determine the optimization of so-called comfort in wear are discussed in detail.

NoIRs and low vision

Records of three hundred and eighteen low vision patients from three low vision centers were reviewed to determine patient preferences for NoIR light filters based on ocular disease and visual acuity. Eighty-nine percent chose the #101 and #102 filters. Patients with dry macular degeneration, chronic open angle glaucoma, and retinitis pigmentosa showed a greater preference for the #101 NoIRs. When visual acuity dropped below 20/400, no patients selected the darker filters (#108 & #109).

Characteristics and low vision corrections in Stargardt's disease. Educational and vocational achievements enhanced by low vision corrections

One hundred and sixteen patients with Stargardt's disease demonstrated the most useful optical aids that enabled them to obtain an education and employment. The most useful optical aid for distance was the 8X monocular focusable telescope. For near, high-add bifocals, tri-focals, half-eye binocular spectacle magnifiers, paperweight-type magnifiers and hand magnifiers were most useful. Optical aids were prescribed for 102 patients with a success rate of 96%. The progression of visual loss is generally gradual and symmetrical terminating within ten years after onset and not becoming worse than 20/800 (6/240). Academic success seems to be related more to intellectual ability than degree of visual impairment. Highly trained and educated individuals with Stargardt's disease were able to find employment and perform duties usually associated with normal vision.

Retinal image quality during oblique gaze through spectacle lenses: plastic vs. glass

The optical performance of standard plastic and glass spectacle lenses was compared at increasing angles of oblique gaze up to 40 degrees on either side of the optic axis of the lenses. For this purpose, the border enhancement method was used, a method which is suitable for monitoring small order changes in the retinal image. It was found that the enhancement band width increases with obliquity of gaze in all cases, signifying a deterioration in the retinal image. A glass lens will exaggerate this deterioration to some extent, whereas a plastic lens will exaggerate it to the greatest extent. It is shown that the relatively poorer performance of plastic is due to a relatively larger amount of narrow-angle scattering than is produced by glass.

Toward the design of an optimal filter for enhancement of dichromat monocular chromatic discrimination

Based on Farnsworth's theories of color confusion and discrimination, "rose-colored" or "pink" filters such as the X-Chrom material of 0.16 mm in thickness or the Kodak Wratten no. 30 filter act as monocular chromatic enhancers for red/green color deficients by virtue of colorimetrically lengthening color space in a direction perpendicular to the dichromatic axis of color confusion. Using derived formulas for dichromat colorimetry, a set of representative isoluminant-isochroma spectral hues, and interactive computer graphic colorimetric tools, it is possible to determine an optimum spectrophotometric filter curve. Such a filter has minimal middle wavelength transmission and is optimal in terms of providing maximal monocular chromatic clues for discriminative tasks involving confused colors.

Users' and nonusers' evaluations of the CPF 550 lenses

Thirty-six subjects completed questionnaires on their experiences wearing the CPF 550 lenses. Twenty-six subjects [21 with retinitis pigmentosa (RP)] were users of the 550's and 10 subjects (6 with RP) were nonusers who had rejected the 550's after a trial period. Subjects were asked about such factors as effects on adaptation time, ocular comfort, visual functioning, acceptability of tint strength in various lighting conditions, cosmetic appearance, effects of weather, and replacement intent. Users reported reduced adaptation time in changes of illumination, increased ocular comfort, improved visual functioning with the exception of poor color discrimination, and cosmetic acceptability. Satisfaction with tint strength varied with degree of illumination; usefulness in different types of weather also varied depending on the condition. Nonusers' responses were mixed; they were less likely to report improvements with the CPF 550 lenses compared to the users' group.