The misting characteristics of spectacle lenses

When a spectacle wearer enters a warm environment after having been in a cooler one, his/her spectacles may 'mist up' due to the formation of condensation on the lens surface. Both the physical properties of the spectacle lens and a number of environmental factors determine how long spectacles take to demist. The relative misting performance of crown glass, CR39 and polycarbonate spectacle lenses were assessed using a novel technique. A box in which the environmental conditions could be controlled was used first to cool the lens and then to warm it. This change in temperature caused condensation to form on the lens surface. By projecting the image of a grating through the lens onto a linear array of photodiodes it was possible to measure the contrast transmission of the spectacle lens as it demisted. Each lens type misted and demisted in a characteristic way. The polycarbonate lens demisted more rapidly than the CR39 lens which, in turn, demisted more rapidly than the glass lens. This indicates that polycarbonate spectacle lenses should be used in conditions where the adverse effects of spectacle misting need to be minimised.

Impact resistance of Transitions Plus spectacle lenses

Although it has been shown that photochromic glass industrial lenses do not provide adequate occupational impact protection, they are frequently requested by outdoor workers wanting sunglasses. The recent introduction of Transitions Plus (TP), a photochromic plastic lens, may meet the needs of these workers. The impact resistance of 60 TP lenses of dress thickness was studied using a ballistic test. Lenses were edged and mounted in metal industrial frames. The completed spectacles were placed on a headform for ballistic testing using a 6.5 mm (1/4 in) steel ball propelled from an airgun. The lenses were divided into test groups that received: (1) a single impact at the geometrical center by a ball traveling at 18 m/s (59 ft/s) and (2) 50 consecutive impacts at 18 m/s, or (3) a single impact at 46.5 m/s (152 ft/s). All lenses passed the single impact test at 18 m/s. Four lenses broke under repeated impact. All lenses subjected to the high-speed impact test failed, either breaking or being dislodged from the frame. These findings show that dress thickness TP lenses provide impact protection from small blunt missiles traveling at moderate speed, and that they are durable under repeated low energy impact. However, thicker lenses must be used when the wearer has a high risk of ocular exposure to small high-speed missiles in the workplace. It can be concluded that TP lenses may be used in occupational eyewear for many outdoor workers who want photochromic sunglass lenses, provided that other needs for vision and occupational safety are also satisfied.

The photic sneeze reflex as a risk factor to combat pilots

The tendency to sneeze upon exposure to bright light is autosomal dominant and affects 18-35% of the population. This uncontrolled sneezing may represent a danger to pilots during flight. Testing was conducted using Ditric narrow band (+/- 10 nm) interference filters. Wavelengths at 430, 532, and 560 nm were tested with a GE 500-W photoflood BCA #1 bulb at constant intensity. Subsequent testing of military and civilian aviation goggles and sunglasses was conducted using a Digikrom 240 monochromator. Repeated testing with interference filters in a clinical setting showed no effect on sneezing in a susceptible subject. The photic sneeze reflex does not appear to be mediated by specific wavelengths of light, but rather by the change in light intensity. This could trigger an unexpected sneezing episode during critical periods of flight. This is an unrecognized and previously unreported danger to fixed-wing and rotary aircraft pilots.

A ballistic evaluation of the impact resistance of spectacle lens materials

The impact resistance of chemically and thermally hardened glass lenses of 2.2- and 3.0-mm thicknesses was evaluated using a ballistic test. Each lens was edged and mounted into a spectacle frame, which was placed on a standard headform. A 6.5-mm steel ball was fired from an air gun at the center of the lens at increasing speeds until the lens broke. The multiple impact data were used to plot cumulative breakage curves. We found that heat-treated photochromic glass and heat-treated crown glass fail at similar missile speeds and that chemical treating considerably improves the impact resistance of crown glass but not of photochromic glass. The poorer performance of photochromic lenses indicates that they should not be prescribed when optimal impact protection is required. Plastic lenses show superior performance.

Comparison of the transmittance and coloration requirements of the four national sunglass standards

There are four national standards on nonprescription sunglasses and two international draft standards at different levels of development and activity. The variation in test specifications and pass/fail criteria among the national standards makes comparisons difficult and agreement on international standards slow. Arguments about the relative stringency of standards may be, as a consequence, ill-informed and self-defeating. In this study I compared the requirements of the four national sunglass standards and then the compliance of 253 sunglass and fashion spectacle lenses with the standards in the erythemal ultraviolet (UV), near UV, luminous transmittance, and coloration. The methods and criteria of the four standards vary quite substantially but the lenses failing to comply are frequently the same. The differences and similarities among the standards are clearly demonstrated. In the erythemal UV, the standards form two pairs in their stringency (Australian and British Standards as against German and U.S. Standards). In the near UV, the British Standard stands out as being more stringent. In the luminous transmittance region there is a basic agreement. In coloration requirements, even though there is extreme variation of methods, these too provide very similar results. The U.S. requirements on signal transmittance do not serve a useful function. Some comments on the differences in labeling requirements are made.

Eyeglasses and common complaints

About one-half of the population wear eyeglasses. For them, a pair of eyeglasses is a necessary aid and when properly fit, can provide clear and comfortable vision for a variety of daily activities.

Special spectacles facilitating débridement: a report of their use in 300 cases

Because the light reflected by tissues varies with the degree of viability, spectacles were made from glass transmitting light of a certain wavelength to help distinguish viable from non-viable tissue. They were used in wound débridement in 300 injured patients. The results showed that the quality of débridement was improved as shown by better and quicker healing. They can also be used to predict flap viability in plastic surgery.

Ready-to-wear reading glasses. American Academy of Ophthalmology

The purpose of the Committee on Ophthalmic Procedures Assessment is to evaluate on a scientific basis new and existing ophthalmic tests, devices, and procedures for their safety, efficacy, clinical effectiveness and appropriate uses. Evaluations include examination of available literature, epidemiological analyses when appropriate, and compilation of opinions from recognized experts and other interested parties. After appropriate review by all contributors, including legal counsel, assessments are submitted to the Academy's Board of Directors for consideration as official Academy policy.

Tinted lenses and the ANSI standards for traffic signal transmittances

The transmittance properties of 96 tinted lenses were examined to determine whether these lenses met the American National Standards Institute (ANSI) Z80.3 standards for traffic signal transmittances and color shifts. Transmission functions of the lenses were measured using a Zeiss Spectrophotometer, and the luminous transmittances and color shifts were calculated according to the ANSI guidelines. Approximately 50% of the sampled tinted lenses failed to meet at least 1 of the ANSI requirements. Lenses that failed to meet several ANSI requirements were often special purpose sun lenses. Although the special purpose tinted lenses do not have transmittance requirements for traffic signals, it is not always clear from the manufacturers' brochures that the lenses may be unsuitable for driving.

Special correspondence: vision standards

Physicians and ophthalmologists must know the vision standards for driving motor vehicles, as they are requested by patients to complete the necessary forms to obtain a restricted license. Physicians also should know why some standards are not in the best interests of their patients.

A comparative assessment of the ultraviolet radiation transmission of sunglasses for patients receiving photochemotherapy

The suitability of 75 sunglasses for use by patients receiving 8-methoxypsoralen photochemotherapy (PUVA) was assessed by measuring their ultraviolet radiation (UVR) transmission spectra and comparing the results with some published proposed spectral limits. The sunglasses were classified according to whether their lenses were polarised, photochromic, reflective, graduated tint or of a miscellaneous type. The UVR transmission of 39 of these sunglasses was also measured using a PUVA source and a UVA sensitive detector. There was a difference of a factor of x7 between the maximum PUVA source transmission of the sunglasses with satisfactory spectral transmission and the minimum PUVA source transmission of those with unsatisfactory spectral transmission. Values of PUVA source transmission values corresponding to hypothetical transmission spectra close to the spectral limits were derived by calculation. It was concluded that photochromic sunglasses could be rejected for patient use without recourse to measurement unless they were claimed to have low UVR transmission, and that the transmission of all other types had to be assessed individually. It was also concluded that the PUVA source method could be adopted for routine use with a maximum acceptable transmission of 0.2%.

The Sunglass Standard and its rationale

This paper reports on the 17-year development of the current Z80.3 Sunglass Standard. The dioptric tolerances of +0.125 to -0.25 D power, 0.125 D astigmatism, 0.25 delta prism, and 0.18 D power imbalance are based on research by optometry's leaders. The traffic signal and luminous transmittance requirements are the result of study of the literature and original research. There has been much misunderstanding regarding the UV transmittance specifications. They too were exhaustively researched and discussed. That work is reviewed in detail. New equations for calculating exposures are presented with sample spectra. Graphic evaluations of severe risk exposures are presented. They show that based on the accepted criteria, for reasonable assumptions the Standard offers a 10x margin of safety. Studies of retinal risk indicate the Standard provides ample protection. Some criteria need further study. Potential problems are based on the fact that some sunglasses are too dark for driving and that use of ordinary sunglasses for sports provides inadequate protection from injuries.

Does the ANSI Z80.3 nonprescription sunglass and fashion eyewear standard go far enough?

The recent public concern regarding sunglass protection from UV energy has sparked a significant debate among those in the research community and industry. This debate grows out of concern for the known effects of UV energy in producing or contributing to eye effects such as keratitis, cataract formation, and retinal damage. The ANSI Z80.3 Standard addresses itself to this issue by setting levels of UV energy that are permitted to be transmitted in various labeling categories for over-the-counter sunlenses. One important issue is that the ANSI Standard does not provide for an absolute block of UV energy in any category of these lenses. Because the technology to provide this sort of total UV block is currently available, it is argued that there should be at least one category of lens that is fully protective in the UV range.

Ultraviolet-absorbing spectacle lenses, contact lenses, and intraocular lenses

Optical materials that are available to the practitioner for protection of the eye against hazardous exposure to ultraviolet radiation (UVR) are discussed. Principles of protection, procedures for calculating safe ocular exposure duration, and transmittance curves of commonly prescribed spectacle lenses, contact lenses, and intraocular lenses are discussed. Suggestions are made to assist the practitioner in providing adequate protection for the patient.

[Ophthalmology and standardization]

The standards are the references for quality and safety of materials, instruments and devices in ophtalmological use. The French standardisation association, "Association Française de Normalisation" (AFNOR), drafts his standards in connection with the concerned professionals. The ophthalmologists are concerned by standards of diagnostic and therapeutic instruments, intraocular and orbital implants, contact lenses, spectacle frames and glasses, and ocular protectors.