IlluminatedZoom: spatially varying magnified vision using periodically zooming eyeglasses and a high-speed projector

Spatial zooming and magnification, which control the size of only a portion of a scene while maintaining its context, is an essential interaction technique in augmented reality (AR) systems. It has been applied in various AR applications including surgical navigation, visual search support, and human behavior control. However, spatial zooming has been implemented only on video see-through displays and not been supported by optical see-through displays. It is not trivial to achieve spatial zooming of an observed real scene using near-eye optics. This paper presents the first optical see-through spatial zooming glasses which enables interactive control of the perceived sizes of real-world appearances in a spatially varying manner. The key to our technique is the combination of periodically fast zooming eyeglasses and a synchronized high-speed projector. We stack two electrically focus-tunable lenses (ETLs) for each eyeglass and sweep their focal lengths to modulate the magnification periodically from one (unmagnified) to higher (magnified) at 60 Hz in a manner that prevents a user from perceiving the modulation. We use a 1,000 fps high-speed projector to provide high-resolution spatial illumination for the real scene around the user. A portion of the scene that is to appear magnified is illuminated by the projector when the magnification is greater than one, while the other part is illuminated when the magnification is equal to one. Through experiments, we demonstrate the spatial zooming results of up to 30% magnification using a prototype system. Our technique has the potential to expand the application field of spatial zooming interaction in optical see-through AR.

Effect of multiple antireflection coatings on impact resistance of Hoya Phoenix spectacle lenses

PURPOSE

To investigate how the impact resistance of Hoya Phoenix spectacle lenses is affected by centre thickness and the application of a multilayer antireflection (MAR) coating.

METHODS

Four groups of plano lenses were tested: dress thickness with scratch resistant (SR) coating on both surfaces, dress thickness with SR and MAR, industrial thickness with SR and industrial thickness with SR and MAR. Lenses were edged to a clear circular aperture of 50 mm with a 0.5 mm hidden bevel and mounted in a specially-designed lens support. A pneumatic gun was used to propel a 6.35 mm steel ball at the centre of each lens. Impact speed was varied using the ZEST protocol to determine the threshold breakage speed.

RESULTS

The threshold breakage speeds of the dress and industrial thickness SR lenses were 55.1 and 63.2 m/s, respectively and the corresponding threshold breakage speeds for SR-MAR lenses were 50.1 and 54.7 m/s. All comparisons were statistically significant using Student's t-test with a rejection level of p < 0.005. Unlike polycarbonate lenses, dress thickness Phoenix lenses do not display 'oilcanning' deformation on high energy impact and therefore are less likely to be dislodged from their mountings.

CONCLUSIONS

We found that the mean impact resistance of the Phoenix lenses was greater than the level required of eye protector lenses by the standards AS/NZS 1337:1992, ANSI Z87.1-2003 and CSA Z94.3-02. Similar to CR39 and polycarbonate, the application of MAR to Phoenix lenses reduces their impact resistance, however, they provide an acceptable level of impact protection in industrial settings, where there is little danger of exposure to pointed or sharp-edged high-speed missiles.

Indicators for Assessing the Quality of Refractive Error Care

SIGNIFICANCE

Quality refractive error care is essential for reducing vision impairment. Quality indicators and standardized approaches for assessing the quality of refractive error care need to be established.

PURPOSE

This study aimed to develop a set of indicators for assessing the quality of refractive error care and test their applicability in a real-world setting using unannounced standardized patients (USPs).

METHODS

Patient outcomes and three quality of refractive error care (Q.REC) indicators (1, optimally prescribed spectacles; 2, adequately prescribed spectacles; 3, vector dioptric distance) were developed using existing literature, refraction training standards, and consulting educators. Twenty-one USPs with various refractive errors were trained to visit optical stores across Vietnam to have a refraction, observe techniques, and order spectacles. Spectacles were assessed against each Q.REC indicator and tested for associations with vision and comfort.

RESULTS

Overall, 44.1% (184/417) of spectacles provided good vision and comfort. Of the spectacles that met Q.REC indicators 1 and 2, 62.5 and 54.9%, respectively, provided both good vision and comfort. Optimally prescribed spectacles (indicator 1) were significantly more likely to provide good vision and comfort independently compared with spectacles that did not meet any indicator (good vision: 94.6 vs. 85.0%, P = .01; comfortable: 66.1 vs. 36.3%, P < .01). Adequately prescribed spectacles (indicator 2) were more likely to provide good comfort compared with spectacles not meeting any indicator (57.7 vs. 36.3%, P < .01); however, vision outcomes were not significantly different (85.9 vs. 85.0%, P = .90). Good vision was associated with a lower mean vector dioptric distance (P < .01) but not with comfort (P = .52).

CONCLUSIONS

The optimally prescribed spectacles indicator is a promising approach for assessing the quality of refractive error care without additional assessments of vision and comfort. Using USPs is a practical approach and could be used as a standardized method for evaluating the quality of refractive error care.

The Effect of Magnification Loupes on Dental Hygienists' Posture while Exploring

Purpose: The purpose of this study was to determine the effects of dental magnification loupes on posture during instrumentation.Methods: A convenience sample of 27 right-handed dental hygienists, with no prior history of injuries or disabilities of the head, neck, or trunk region, enrolled in the study. Baseline posture calibration was taken and tri-axial accelerometers were placed on four locations of the head and trunk (occipital region of head; cervical vertebrae C5; thoracic vertebrae T5; lumbar vertebrae L1) to measure acceleration and the orientation of the body to gravity. Participants were randomly assigned to wear self-supplied magnification loupes during either the first or second half of the session. Dental chair mounted typodonts, prepared with artificial calculus, were used to represent a simulated oral environment. Participants were asked to explore all areas of the mouth using an ODU 11/12 explorer. Mean accelerations of the three axes were used to compute average forward/backward (AP) and side to side (ML) tilt of each accelerometer recorded during the instrumentation sessions. An end-user opinion survey was completed by each participant at the conclusion of the session.Results: No statistically significant differences in posture were revealed between the sessions with the participants wearing their loupes and not wearing loupes. However, data from the end-user survey indicate that 74% of all the participants strongly agreed that magnification loupes made exploring easier and 67% strongly agreed that they felt that magnification loupes improved their posture.Conclusion: While the majority of participants perceived that their magnification loupes enhanced their posture and made exploring easier, data from this study provided little evidence to suggest that wearing loupes leads to improved body orientation. Future research needs to examine the declination angle of ergonomic loupes and its relationship to neck and trunk flexion.

Patient-Reported Spectacle Independence Questionnaire (PRSIQ): Development and Validation

PURPOSE

To develop a questionnaire quantifying spectacle independence following cataract surgery.

DESIGN

Questionnaire design and validation study.

METHODS

A literature review, expert clinical interviews, and patient interviews were undertaken to develop a patient-reported questionnaire assessing spectacle independence. Draft items were assessed and revised in a series of cognitive interviews where the instructions, recall period, and response categories were evaluated for understandability and consistency. The final draft items were evaluated in 2 quantitative studies. Confirmatory factor analyses, including item response theory calibration, were performed; reliability estimates were obtained; and validity analyses of the resulting scores were carried out.

RESULTS

Qualitative research demonstrated that patients often considered themselves spectacle independent yet, when probed, it was determined that the respondent actually wore correction for certain activities. Moreover, despite what the respondents claimed about needing to wear correction and their actual use of correction, there were various levels of function reported when carrying out activities at several different distances without the use of correction. Using the qualitative results, the Patient-Reported Spectacle Independence Questionnaire (PRSIQ) was developed to assess spectacle independence via items that assess what patients say and do, and how they function at various distances. All quantitative analyses (eg, discriminant and convergent validity correlations, known-groups analyses) conform to predictions and support the use of the PRSIQ as a measure of spectacle independence.

CONCLUSIONS

The PRSIQ is a patient-reported measure assessing spectacle independence following cataract surgery. The analyses conducted provide evidence for the use of the PRSIQ total score as a measure of spectacle independence.

Smart-Glasses: Exposing and Elucidating the Ethical Issues

The objective of this study is to provide an overview over the ethical issues relevant to the assessment, implementation, and use of smart-glasses. The purpose of the overview is to facilitate deliberation, decision making, and the formation of knowledge and norms for this emerging technology. An axiological question-based method for human cognitive enhancement including an extensive literature search on smart-glasses is used to identify relevant ethical issues. The search is supplemented with relevant ethical issues identified in the literature on human cognitive enhancement (in general) and in the study of the technical aspects of smart-glasses. Identified papers were subject to traditional content analysis: 739 references were identified of which 247 were regarded as relevant for full text examinations, and 155 were included in the study. A wide variety of ethical issues with smart-glasses have been identified, such as issues related to privacy, safety, justice, change in human agency, accountability, responsibility, social interaction, power and ideology. Smart-glasses are envisioned to change individual human identity and behavior as well as social interaction. Taking these issues into account appears to be relevant when developing, deliberating, deciding on, implementing, and using smart-glasses.

Contribution to the radiation protection for sunglasses standards

Literature establishes safe limits on the exposure of the eyes to ultraviolet radiation, for the range of 180-400 nm, including spectrally weighted and the total ultraviolet radiant exposure. Most standards for sunglasses protection only require ultraviolet protection in the spectral range of 280-380 nm to ensure the limits for effective spectrally weighted radiant exposure. Calculations of these limits were performed for 27 Brazilian state capitals, and they led to a change in the upper UVA limit to 400 nm on the 2013 review of the Brazilian standard. Moreover, because the sunlight irradiance in Brazil is quite high, integration over the 280- to 400-nm range yields an ultraviolet radiant exposure that is an average of 49% greater than that for the 280- to 380-nm range. These conclusions suggest revision on the standards.

Photochromic dynamics of ophthalmic lenses

We describe and characterize a straightforward test setup for characterizing temporal and spectral dynamics of photochromic spectacle materials. Three measurement examples of contemporary silicate and organic photochromic spectacles are provided. The setup showed a good absolute accuracy of ≤5% of the luminous transmittance (τ(v)) and repeatability of better than 3%. The samples showed different fading times. The sample with the highest dynamic range was the slowest and showed a noticeable change in the transmission spectra during deactivation. The silicate had the lowest dynamic range but also the most homogeneous transmission spectra throughout activation and deactivation. The proposed test device provided accurate results for spectral and temporal dynamics of photochromic materials under realistic conditions.

Quality control in the optical industry: From a work analysis of lens inspection to a training programme, an experimental case study

A cognitive work analysis of quality inspection in the optical industry has been carried out in order to devise a training programme. The task concerned the inspection of high quality human eyeglass lenses. We conducted an experimental investigation of defect detection and acceptability decision-making tasks in 18 experts and novice inspectors. Detection and decision-making were investigated together and separately in two experimental sessions. We showed the effect of expertise on reaction times and errors, and we described the cognitive processes of novice inspectors. On the basis of the processing differences between the two groups, a training programme for new inspectors was devised and described. Finally, training effects were tested.

Mapping of error cells in clinical measure to symmetric power space

During the refraction procedure, the power of the nearest equivalent sphere lens, known as the scalar power, is conserved within upper and lower bounds in the sphere (and cylinder) lens powers. Bounds are brought closer together while keeping the circle of least confusion on the retina. The sphere and cylinder powers and changes in these powers are thus dependent. Changes are depicted in the cylinder-sphere plane by error cells with one pair of parallel sides of negative gradient and the other pair aligned with the graph axis of cylinder power. Scalar power constitutes a vector space, is a meaningful ophthalmic quantity and is represented by the semi-trace of the dioptric power matrix. The purpose of this article is to map to error cells for the following: coordinates of the dioptric power matrix, its principal powers and meridians and its entries from error cells surrounding powers in sphere, cylinder and axis. Error cells in clinical measure for conserved scalar power now contain more compensatory lens powers. Such cells and their respective mappings in terms of most scientific and alternate clinical quantities now image consistently not only to the cells from where they originate but also to each other.

Angular and Linear Fields of View of Galilean Telescopes and Telemicroscopes

PURPOSE

The calculation of the angular fields of view (FOVs) of Galilean telescopes generally necessitates the calculation of the pupils and ports. This, in turn, requires knowledge of the optical design of the telescope, in particular, the focal lengths or powers of the objective and ocular lenses. Equations for finding the FOV that obviate the need to calculate pupils and ports, or even to know the lens powers of the telescope, are presented in this article. The equations can be used to find the FOVs in image space of real Galilean telescopes of known magnification, merely by measuring the distance between the objective and ocular lenses and the diameter of the objective lens. The equations include the effects of eye pupil diameter and eye relief. Linear FOVs (LFOVs) of Galilean telemicroscopes are similarly determined.

METHODS

Two image space angular FOV equations were derived: (1) an equation to determine the angular FOVs of a telescope with various amounts of vignetting and eye relief; and (2) an equivalent equation for the LFOVs of telescopes fitted with lens caps for near vision.

RESULTS

The FOV increases linearly with increasing vignetting. Increasing the eye relief results in a nonlinear decrease in the FOV, shown as a fraction of the normalized value for zero eye relief. Decrements in the FOVs with increasing eye relief as a fraction of the normalized field angle when the eye relief = 0 are shown to be constant regardless of the vignetting level. A transition of the objective lens from field stop to aperture stop occurs when the eye pupil diameter exceeds the diameter of the objective lens divided by the magnification.

CONCLUSIONS

Equations have been derived for Galilean telescopes and telemicroscopes that make it unnecessary to find pupils and ports, or to know the powers of the lenses. They provide a direct and simple evaluation of angular and LFOVs as functions of magnification, objective lens diameter, eye pupil diameter, eye relief, and vignetting, and enable comparisons of actual telescopes.

Brillengläser im Sport: Optimierung der Abbildungseigenschaften unter physiologischen Aspekten

The goal of correction spectacles is to create a sharp image on the retina by the combined optical system of the eye and the spectacle lens for a given ametropia. As a matter of principle, in this optical system an aberration free correction can be achieved in the optical centre of the spectacle lens, but not over the entire range of gaze angles. In spectacle optics large angles play an important role, different from paraxial optics where only rays close to the axis with small angles of incidence are relevant. This generates additional aberrations, the so-called oblique astigmatism, which can only be compensated at the expense of the spherical power. Therefore, every spectacle lens represents apart from the main visual point-, a more or less good compromise. For sports lenses in the currently used curved frames, an additional challenge arises from the fact that their orientation in front of the eye is generally not perpendicular to the principal gaze direction but tilted. In this article the imaging properties of such tilted sports lenses are discussed, and it is described why this results in a minor quality without a specific consideration of the obliqueness. The fact that tilted sports spectacles are also able to possess an improved correction behaviour for all gaze angles is due to individual mathematical optimization methods. The aim of the present article is, based on the underlying physical and physiological effects, to point out the advantages of individually optimized sports spectacle lenses in comparison to tilted lenses generated without applying this sophisticated computational method.

Prism adaptation in the rehabilitation of patients with visuo-spatial cognitive disorders

PURPOSE OF REVIEW

The traditional focus of neurorehabilitaion has been on the patients' attention on their deficit, such that they should become aware of their problems and gain intentional control of compensatory strategies (descending approach). We review prism adaptation as one of the approaches that emphasize ascending rather than descending strategies to the rehabilitation of visuo-spatial disorders. The clinical outcome of prism adaptation highlights the need for a theoretical reconsideration of some previous stances to neurological rehabilitation.

RECENT FINDINGS

Recent years have given rise to a growing body of experimental studies showing that the descending strategy is not always optimal, especially when higher-level cognition is affected by the patients' condition. Ascending approaches have, for example, used visuo-manual adaptation for the rehabilitation of visuo-spatial deficits. A simple task of pointing to visual targets while wearing prismatic goggles can produce remarkable improvements of various aspects of unilateral neglect.

SUMMARY

The neural mechanisms underpinning visuo-manual plasticity can be viewed as a powerful rehabilitation tool that produces straightforward effects not only on visual and motor parameters, but on visuo-spatial, attentional and higher cognitive neurological functions. The use of prism adaptation therapy in neglect and other visuo-spatial disorders has just started to reveal its potential, both at a practical and theoretical level.

Paraxial Optics of Astigmatic Systems: Relations Between the Wavefront and the Ray Picture Approaches

PURPOSE

The paraxial propagation of astigmatic wavefronts through astigmatic optical systems can be described by the augmented step-along method (ASAM). Its equivalence to the linear ray optics approach is considered in detail.

METHODS

The ASAM is exploited to derive paraxial ray paths through a general coaxial astigmatic system.

RESULTS

Starting from the information inherent in the ASAM all 2x2 submatrices rendering the general 4x4 transference of linear optics can be generated. This proves the complete equivalence of both approaches. Additionally, we show that the symplectic relations are automatically obeyed in the ASAM.

CONCLUSIONS

The ASAM offers a complete alternative to describe the paraxial optics of astigmatic optical systems. According to the ASAM, an optical system is fully characterized by the back vertex vergence and the angular magnification matrix. Hence, a complete description of the paraxial optics of an eye should not only report the state of refraction but the angular magnification matrix as well, although it is not yet very common. The magnification matrix might be important in cases of anisometropia or the design of progressive addition lenses. Yet, a simple clinical procedure to determine the angular magnification matrix is missing.

Principles and designs of the iseikonic lenses for near vision

PURPOSE

The purposes of this study were to find the problems of afocal iseikonic lenses as used for near vision and to elaborate the principles and designs of the ideal near iseikonic lenses.

METHODS

By analyzing the image-object relationship and imaging processes, the formulae were derived to quantitatively and qualitatively describe two errors of afocal iseikonic lenses as used for near vision: 1) inequality of accommodative demands to both eyes and 2) the difference between the actual and the nominal magnification. Formulae were derived to calculate and design the ideal near iseikonic lenses.

RESULTS

For iseikonic lenses now used for near vision, inequality of accommodative demands to both eyes and difference between the actual and nominal magnification increased as the magnification increased and the viewing distance decreased. Afocal iseikonic lenses have significant inequality of accommodative demands to both eyes with 3% magnification at a viewing distance of 25 cm or with 5% magnification at 40 cm. The ideal near iseikonic lenses were found to be flatter than the afocal ones. A series of the ideal near iseikonic lenses were designed with some practical considerations. The central thickness and the refractive index of the lenses affect magnification and lens shape. The thicker the lenses, the higher the magnification. The higher refractive index also gives higher magnification.

CONCLUSIONS

Iseikonic lens design is much different for distance and near vision. When the iseikonic lenses are used at a distance other than the designated distance, they will cause blurred vision and artificial aniseikonia as a result of inequality of accommodative demands to both eyes. In research as well as clinical settings, it is necessary to apply the ideal near iseikonic lenses for near vision.

Qualitätskontrolle bei der Rehabilitation sehbehinderter Patienten

BACKGROUND

Not only medical care and prescription of magnifying devices, but also social and professional rehabilitation are part of a complete interdisciplinary low vision service. This study provides quantitative data about the success of rehabilitation and the quality of the Low Vision Department's work.

PATIENTS AND METHODS

A sample of 105 visually disabled patients, who had already been provided with magnifying aids and other rehabilitation measures by the Low Vision Department, answered a questionnaire about quality control during a follow-up visit. The survey was carried out between May and October 2004. Patients were asked to rate the different rehabilitation measures and to comment on how frequently they used the different magnifying devices. Furthermore, they were asked to judge to what degree they coped with different life situations when using or not using the low vision aids.

RESULTS

The most frequently used aids were magnifiers (61%), glasses for near vision (34%), closed circuit television (20%), and monocular telescopes (20%). Of the 105 patients, 85 (81%) reported on frequent use of the devices, with just 3 patients (3%) reporting that they hardly ever used the aids. Only 2% of the patients could read newspaper text without the use of magnifying aids, while 51% were able to do this using the aids; 46% of the patients reported that they had profited from the social and professional rehabilitation measures.

CONCLUSION

Independently from the causal ophthalmologic diagnosis, patients were found to have benefited greatly from the rehabilitation measures provided by the Low Vision Department, enabling them to take part in more activities and participate more fully in social life, thereby greatly improving their quality of life. Frequent use of the low vision aids by the patient was ensured when offered alongside continued professional support.

Chronically mountable goggles for persistent exposure to single orientation

To examine the effect of experience on the developmental plasticity of functional maps in the visual cortex, we need to establish a method for a stable visual experience manipulation under the freely moving condition. For this purpose, we fabricated goggles that are chronically mounted stably on the animal's head, but easy to replace according to the animal's growth. Here we report the design of the goggles and the method of mounting them on the head of animals. By this method, combined with the intrinsic signal optical imaging technique, we were able to observe a rapid and robust reorganization of orientation maps.

Reabilitação visual em pacientes com retinose pigmentária

PURPOSE

To determine which low-vision aids could be useful to patients with retinitis pigmentosa and also the benefits that the rehabilitation program could provide based on visual acuity and/or daily visual tasks.

METHODS

A group of 30 patients with retinitis pigmentosa aged from 7 to 73 years were enrolled in this study. Visual acuity and visual function tests (visual field, full-field electroretinogram) was performed and low-vision aids tested. Information about the use of the remaining vision was obtained. After choosing the best optical or electronic devices and before their prescription, a low-vision training program was carried out.

RESULTS

The best corrected visual acuity varied from HM (hand movements) to 20/40 for distance and visual acuity better than 16M to 0.5M for near. 90% of the patients had optical devices prescribed: 13 for near, 9 for distance, 2 electronic devices and 3 filters. Three patients with extremely narrow visual field and very low visual acuity were referred to orientation and mobility.

CONCLUSIONS

The low-vision aids were useful for the retinitis pigmentosa patients: telescopes, hand-held magnifiers, stand magnifiers, half-eye base-in prism lenses, electronic devices and illumination control were beneficial to enhance visual acuity and visual efficiency. The prescription of low-vision aids was helpful in daily-life activities and a high level of satisfaction with the implemented visual rehabilitation program was reported.

Revisions to tolerances in cylinder axis and in progressive addition lens power in ANSI Z80.1-2005

BACKGROUND

ANSI Z80.1 (American National Standards Institute) is a voluntary standard that provides tolerance guidelines for ophthalmic lens parameters. The recently approved ANSI Z80.1-2005 changes tolerances for cylinder axis for all ophthalmic lenses and for distance power for progressive addition lenses (PALs).

METHODS

The ANSI Z80.1 committee analyzed the amount of unwanted residual cylinder created by rotating a cylinder axis away from its desired orientation for a range of cylinder powers. The limits of axis orientation error that keep the residual unwanted cylinder error within the tolerances for cylinder power were determined. For PALs, a tolerance for distance power error was sought that considers the currently followed standards for front surface power error and the tooling steps used for the rear surface.

RESULTS

Tolerances for cylinder axis error were changed to +/-14 degrees for 0.25 diopter (D) cylinders and to +/-7 degrees for 0.50 D cylinders. Tolerance for error in back vertex power of PALs was changed to +/-0.16 D for both sphere and cylinder.

CONCLUSION

Tolerances for cylinder axis for low cylinders have been made in ANSI Z80.1-2005 to be consistent with tolerances in cylinder power. Changes in tolerance for power errors in PALs have been made to recognize fabrication challenges.

Sequential Tilt and Tilted Power of Thin Lenses

PURPOSE

The purposes of this article were, for any sequence of tilts applied to a thin lens, to calculate an equivalent turn and single tilt, to show how to use the equivalent turn and tilt to calculate the tilted power of the lens, and, given the desired tilted power, to calculate the power of the untilted lens necessary to compensate for the effects of tilt. The untilted lens may be stigmatic (spherical) or astigmatic (spherocylindrical).

METHODS

The analysis makes use of rotation matrices to represent rotation in space and previous work in third-order optics on oblique central refraction.

RESULTS

Equations are presented for calculating the combination of turn and tilt that is equivalent to any sequence of tilts. They are specialized for the particular case of combinations of faceform and pantoscopic tilts and allow the decomposition of an arbitrary tilt into a combination of turn and pantoscopic and faceform tilts. The equations also lead to a procedure for calculating or compensating for the tilted power of a sequentially tilted thin lens.

CONCLUSIONS

Previous work on the effect of tilt on thin lenses has been generalized to handle combinations of arbitrary tilts.

The Effect of Multiple Antireflective Coatings and Center Thickness on Resistance of Polycarbonate Spectacle Lenses to Penetration by Pointed Missiles

PURPOSE

Previous work has shown that the impact resistance to blunt missiles is affected by coatings applied to either CR-39 or polycarbonate lenses. We investigated the effects of multiple antireflection (minimum angle of resolution [MAR]) coatings on the resistance of polycarbonate lenses to puncture on impact by sharp, high-speed missiles.

METHODS

Four groups of surfaced plano polycarbonate lenses were investigated. Two groups had a scratch-resistant (SR) coating applied to both surfaces. One of these groups had a 2-mm center thickness and the other had a 3-mm center thickness. The other two groups of 2-mm and 3-mm thick lenses had a MAR coating applied over the SR coating. The lenses were impacted by a missile consisting of an industrial sewing machine needle mounted in a cylindrical aluminum carrier.

RESULTS

The sharp missiles were able to pierce the lenses at speeds between 29.6 m/s and 46.2 m/s. Impact resistance was lowest for the thinner lenses and lenses with a MAR coating. The effect of the MAR and lens thickness was subadditive.

CONCLUSIONS

We have confirmed previous observations that polycarbonate lenses are more susceptible to penetration by sharp, high-speed missiles than blunt missiles. We have also found that reducing lens center thickness and applying a MAR coating further reduces the penetration resistance. Therefore, the use of 2-mm center thickness and MAR-coated polycarbonate lenses should be discouraged for industrial eye protectors where sharp missile hazards are possible.

Protection from ultraviolet radiation by spectacle lenses available in India: a comparative study

BACKGROUND

Exposure to ultraviolet radiation (UVR) can result in several ocular ailments. We studied the UV absorption (UV-A and -B bands) in 20 lenses (11 hard resin and 9 glass) commonly available in India as uncut lenses for the purpose of prescription as well as non-prescription wear.

METHODS

Using a UV-visible spectrophotometer (Thermo-Spectronic, UV-1 model, Thermo Electron Corporation, USA), the percentage transmittance was scanned between 190 and 400 nm, from which the results at 280, 320, 340, 360, 380 and 400 nm were analysed.

RESULTS

At 360 nm (UV-A), 75% of the lenses studied failed to offer 95% protection as recommended by the United States Food and Drug Administration (US FDA). At 280 nm (UV-B), 35% of the lenses failed to offer 99% protection against UV-B. Hard resin lenses showed a higher degree of variation in protection from UV-A.

CONCLUSIONS

Most of the lenses studied failed to meet the US FDA recommendations in terms of protection from UV-A. Glass lenses afforded better protection up to 320 nm compared with hard resin lenses. As the claims of lens manufacturers regarding UVR protection fall short of international standards, certification of UVR protection for different lenses should be introduced in India.

The effect of relative distance enlargement on visual acuity in the visually impaired

BACKGROUND

Prescribing magnification is typically based on distance or near visual acuity. This presumes a constant minimum angle of visual resolution with working distance and therefore enlargement of an object moved to a shorter working distance (relative distance enlargement). This study examines this premise in a visually impaired population.

METHODS

Distance letter visual acuity was measured prospectively for 380 low vision patients (distance visual acuity between 0.3 and 2.1 logMAR) over the age of 57 years, along with near word visual acuity at an appropriate distance for near lens additions from +4 D to +20 D. Demographic information, the disease causing low vision, contrast sensitivity, visual field and psychological status were also recorded.

RESULTS

Distance letter acuity was significantly related to (r = 0.84) but on average 0.1 +/- 0.2 logMAR better (1 +/- 2 lines on a logMAR chart) than near word acuity at 25 cm with a +4 D lens addition. In 39.8 per cent of patients, near word acuity was more than 0.1 logMAR worse than distance letter acuity. In 11.0 per cent of subjects, near visual acuity was more than 0.1 logMAR better than distance letter acuity. The group with near word acuity worse than distance letter acuity also had lower contrast sensitivity. The group with near word acuity better than distance letter acuity was less likely to have age-related macular degeneration. Smaller print size could be read by reducing working distance (achieved by using higher near lens additions) in 86.1 per cent, although not by as much as predicted by geometric progression in 14.5 per cent.

DISCUSSION

Although distance letter and near word acuity are highly related, they are on average 1 logMAR line different and this varies significantly between individuals. Near word acuity did not increase linearly with relative distance enlargement in approximately one in seven visually impaired, suggesting that the measurement of visual resolution over a range of working distances will assist appropriate prescribing of magnification aids.

[Analysis of anthropometry on head and eye for stipulating of children's spectacle frames]

OBJECTIVE

To investigate the normal value of six parameters of head and eye in Chinese children, including interorbit distance (IOD), interpupillary distance (IPD), superior otobasion-ectocochion distance (obs-ec), intersuperior otobasion distance (obs-obs), exophthalmos and nasal basis angle, for stipulating the sizes of children spectacle frames.

METHODS

The value of these six parameters in 10 171 children ages 5 to 17 years old were measured with caliper in four cities and the results were analyzed.

RESULTS

The IOD, IPD, obs-ec and obs-obs were increased and positively correlated with the age. The differences of these parameters among different ages were statistically significant (F = 0.97, P < 0.01), especially in IPD before 15, IOD before 13, obs-ec and obs-obs before 12 and exophthalmos before 12 years old. The fastest growth age in IPD, IOD, exophthalmos, obs-ec and obs-obs was 10, 11, 5, 7 and 11 years old, respectively. The growth period of IPD, IOD, exophthalmos, obs-ec and obs-obs was 5 - 15, 5 - 13, 5 - 8, 5 - 12 and 5 - 15 years old. The difference of these six parameters among children in 4 cities were statistically significant (t = 3.1, P < 0.01).

CONCLUSIONS

The most active growth period of IPD, IOD, obs-obs, obs-ec and exophthalmos lies between 5-15 years old in Chinese children 5-17 years old. Although the differences of these six parameters between male and female and among children in four cities are statistically significant, practically they are not important for stipulating the sizes of children's spectacle frames.

Inference of nested variance components in a longitudinal myopia intervention trial

This paper was motivated by a double-blind randomized clinical trial of myopia intervention. In addition to the primary goal of comparing treatment effects, we are concerned with the modelling of correlation that may come from two possible sources, one among the longitudinal observations and the other between measurements taken from both eyes per subject. The data are nested repeated measurements. We suggest three models for analysis. Each one expresses the correlation differently in various covariance structures. We articulate their differences and describe the implementations in estimation using commercial statistical software. The computer output can be further utilized to perform model selection with Schwarz criterion. Simulation studies are conducted to evaluate the performance under each model. Data of the myopia intervention trial are reanalysed with these models for illustration. The results indicate that atropine is more effective in reducing the progression rate, the rates are homogeneous across subjects, and, among the suggested models, the one with independent random effects of two eyes fits best. We conclude that model selection is a crucial step before making inference with estimates; otherwise the correlation may be attributed incorrectly to a different mechanism. The same conclusion applies to other variance components as well.

Impact resistance of common spectacle and safety lenses to airgun and rimfire projectiles

PURPOSE

To evaluate the penetration resistance of common spectacle and safety lenses to high-velocity projectiles and to examine the current recommendations regarding the use of such lenses.

METHODS

The penetration threshold of glass, high-index, and polycarbonate spectacle and safety lenses was determined by firing BBs, pellets, and 0.22-caliber projectiles. The mass, diameter, velocity, and energy of each projectile were measured, and the center thickness, mass, and refractive power of each lens were recorded. The penetration threshold for each lens type was calculated, and a comparison of impact resistance was made.

RESULTS

The maximum velocity of the BB was measured at 221 m/s; pellets at 210 m/s; CB.22 rimfire projectiles at 204 m/s; and 0.22 rimfire projectiles at 290 m/s. The BB penetration thresholds were as follows: glass lenses = 84.0 m/s (2.4 J) and high-index lenses = 107.7 m/s (4.09 J). Polycarbonate spectacle and safety lenses were not penetrated by BBs regardless of their velocity; however, these lenses were penetrated by CB.22 rimfire projectiles (89.2 J). Review of the penetrated lenses showed that center thickness and refractive power was comparable between the various groups of projectiles.

CONCLUSIONS

Polycarbonate offers a vastly superior degree of penetration resistance compared with other commonly used lens materials. The current recommendations regarding the use of polycarbonate in prescription and protective lenses, as endorsed by the American Academy of Ophthalmology and the American Academy of Pediatrics, must be reevaluated.

Identifying sources of verification errors in progressive addition lenses

BACKGROUND

Occasional disagreement over spectacle lens prescription accuracy between the optical laboratory and the practitioner is to be expected, especially with a progressive addition lens (PAL). The PAL continues to evolve in design, yet retains some unique, inherent problems. The purpose of this study was to determine if the source of these problems results from the lens design, laboratory error, or verification procedures.

METHODS

Six Varilux Comfort Orma Supra progressive addition lenses were surfaced to plano distance power, and then verified using manual and automatic lensmeters. The same lenses were then re-surfaced for various sphere and cylinder powers, and verified in the same manner. The results of each trial were spherocylindrically averaged, and compared to the desired result. The lenses were also verified by several incorrect methods to investigate positional tolerance during verification and possible verification errors.

RESULTS

The averages for the lenses surfaced to the "prescribed" power were not far from the expected power by all measurement techniques when measured at the central DRP location. Positional errors of as little as 2 mm from the DRP center, however, can lead to erroneous results.

CONCLUSION

Unless correct verification procedures are carefully followed, progressive lenses can be mistakenly identified as being in error when they are not.

Sunglasses and sunglass standards

Sunglasses and sunglass standards are reviewed from the point of view of the history of sunglasses and the development of sunglass standards. The need for eye protection from solar radiation is discussed and the provisions of the various national sunglass standards are discussed in relation to that need.

Head and eye movements in visual search using night vision goggles

BACKGROUND

Night-vision goggles (NVGs) provide only a restricted field of view and have other characteristics that may affect the head and eye movements used in visual search.

METHODS

We measured head scan patterns, the magnitude and duration of gaze saccades, and fixation duration as subjects searched computer generated imagery either with or without NVGs. Subjects searched for either a large (6 degrees) target on a low-detail background (high conspicuity condition) or a small (2 degrees) target on a high-detail background (low conspicuity condition).

RESULTS

All subjects displayed head-scan patterns that were qualitatively similar to those reported in the literature. Although both head-scan speed and amplitude were higher for the NVG condition as compared with the no-NVG condition, the difference was not statistically significant. Head-scan speed did vary significantly with target conspicuity, however. Gaze saccade amplitude varied with target conspicuity but only when NVGs were used. Fixation duration did not vary with either NVG use or target conspicuity. A two-parameter (exponent and scaling parameter) power function was fitted to the amplitude-duration data. The power-function exponents varied from about 0.30 to 0.44, but there was a concommitant variation in the scaling parameter, and the result was no significant difference in the form of the power functions fitted to the data.

CONCLUSIONS

NVG use did not significantly affect any of the individual head or eye movement variables involved in searching the computer-generated imagery studied here. However, the decrease in gaze-saccade amplitude with increased target conspicuity when NVGs were used is evidence of the sensitivity of the head and eye movement measurement techniques used here, and suggests that all available measures of response efficiency be considered when evaluating NVGs using complex stimuli.

Free surface nickel in CE-marked and non-CE-marked spectacle frames

Three hundred and ninety-five new frames were tested for evidence of nickel release using dimethylglyoxime and ammonia. For areas of CE-marked frames in direct contact with the skin a considerable improvement was found over the previous such survey by the authors, carried out before the widespread introduction of CE marking. However, free nickel was found in 6.5% of CE-marked metal frames (excluding titanium and titanium alloy) in such areas and a majority of half joints. Some titanium alloy frames also tested positive for nickel in areas in contact with the skin.

Comparing optical systems, and the concept of the converter system

The purpose of this article was to present a complete and general method for comparing the first-order optical character of optical systems. The method provides a common basis for quantifying the difference between systems of all kinds including thin lenses, ophthalmic prisms, eyes before and after accommodation, eyes before and after refractive surgery, etc. Systems may be astigmatic or stigmatic, coaxial or noncoaxial. In special cases, the method reduces to being equivalent in essence to ostensibly incommensurate comparisons implicit or explicit in current optometric and ophthalmological usage (difference in power for refractions, corneas, and thin lenses, difference in prismatic power for prisms, ratio of magnifications for afocal telescopes, etc.). The method uses the concept of a converter system that when placed in front of or behind one system, converts its first-order optical character to the equivalent of a second system. Equations are presented for the ray transferences of the anterior and posterior converter systems for pair-wise comparisons in general. For any two systems, the transferences of the converter systems always exist and are unique. Numerical examples are presented; they illustrate converter systems that may be thin in special cases but thick otherwise. The transference of a converter system embodies and quantifies the optical difference between systems or characterizes the change from one state of a system (presurgical or preaccommodative, for example) to another (postsurgical or postaccommodative). The method provides a rational and uniform methodology for research and clinical applications in many areas of optometry and ophthalmology.

Resistance of plastic ophthalmic lenses: the effect of base curve on different materials during static load testing

PURPOSE

This study was designated to evaluate, through a static load test, the influence of lens base curve on the fracture resistance of three common plastic materials.

METHODS

A JJ Lloyd load cell machine was used to test the fracture resistance of -4.00 D spherical lenses. The samples had a nominal center thickness of 2.0 mm and a base curve distributed in one of five groups (+0.50, +2.50, +4.50, +6.50, and +8.50 D). The lenses were manufactured in CR39, polycarbonate, and TL16, a high refractive index plastic (n = 1.599).

RESULTS

The lens base curve influenced fracture resistance for all materials. For these materials, resistance increased as the base curve varied from +0.50 to +8.50 D. The resistance of CR39, TL16, and polycarbonate lenses was found to be linearly dependent on lens base curve. The effect is stronger for polycarbonate. Fracture resistance was higher for TL16 than for CR39, and polycarbonate was much more resistant to breakage than the two other materials.

CONCLUSIONS

For a given power, the fracture resistance of an ophthalmic lens is reduced when its base curve has a low value. Consequently, the flattening of ophthalmic lenses for cosmetic purposes is not recommended as far as fracture resistance is concerned.

Light adaptation: night vision goggle effect on cockpit instrument reading time

BACKGROUND

Light adaptation to the intensified image provided by a night vision device may handicap pilots who have set cockpit instrument luminance too low.

METHODS

Under conditions simulating night flying, subjects adapted to an NVG image at 3 or 10 footlamberts (fL), then used a joystick to indicate the position of the horizon in an ADI illuminated by NVIS-compatible light at luminances 2 to 3.5 log units lower than the NVG image.

RESULTS

Response times increased no more than a few tenths of a second when the decrease in luminance was only 2 log units. Greater decreases produced correspondingly longer delays in response, reaching as much as 5.5 s for subjects in their twenties and 8-15 s for older subjects.

CONCLUSIONS

While a decrease of more than 2 log units is not likely to occur under most operational conditions, it is certainly possible, and pilots should be aware that significant risk can be incurred by setting cockpit instruments to luminance levels below 0.03 fL.

Verifying and evaluating progressive addition lenses in clinical practice

BACKGROUND

Despite the fact that more than 50% of multifocal lenses dispensed in the United States are progressive addition lenses, adequate methods for clinical verification of these lenses have been lacking. Using automated lens meter techniques, the author describes a simplified method for verification of these complex lenses.

METHODS

Thirty pairs of progressive lenses were measured in a modified method using a Humphrey 330 Lens Analyzer. Fifteen pairs were "premium-quality" progressive lenses: fifteen pairs were "non-premium-quality" progressives. Five criteria were assessed on each lens: Distance Zone Width (DZW). Intermediate Zone Width (IZW), Near Zone Width (NZW), Drop Distance (DD), and Maximum Astigmatic Distortion (MAD).

RESULTS

"Premium-quality" progressive lenses failed to demonstrate clear-cut superiority over "non-premium-quality" progressive lenses in the five specified criteria. Individual measurements indicate considerable product inconsistency affected every brand tested.

CONCLUSIONS

Premium- and non-premium-quality progressive lenses demonstrated similar performance characteristics in this study. Zone size variation in these lenses was found to be considerable, a characteristic that seemed to cut across brand lines. The AO Compact lens seemed to demonstrate a shorter drop distance than other lenses, which does enhance its suitability for use with small frames. A comparison of the Essilor Natural PAL to the Younger Image lens showed little difference in the categories measured, although peripheral distortions seemed closer to the reading zone in the image. A comparison of the MAD of lenses in this study to lenses tested in 1986 indicates a considerable improvement has been made in that important characteristic.

Deflectometric measurement of mechanical spectacle lens deformation

The warpage of a set of six hard resin spherical lenses was measured when they were compressed by means of the tangential force exerted by a metal frame. The technique employed to measure the lenses improves over previous work both because greater precision is achieved, and because radii of curvature are measured in two perpendicular meridians. In this work, a representative sample of lenses has been used in order to test the way in which deformation depends on lens power and base. It is found that the induced warpage is enough to move the tested lenses between different base families, spoiling the initial design of the manufacturer.

The impact of variable tint optics (Transitions Gray) on vision-related quality of life in normal volunteers: a randomized clinical comparison in a warm climate

PURPOSE

A randomized crossover comparison of Transitions Gray variable tint optics (VTO) vs clear and fixed-tint lenses was undertaken to evaluate the impact of VTO on vision-related quality of life (VRQOL) in a warm climate.

METHODS

Fifty-nine patients were randomized to one of four lens crossover groups: Transitions-->clear; clear-->Transitions; Transitions-->fixed-tint; fixed-tint-->Transitions. Each lens was worn for 30 days. VRQOL was measured using a newly developed and validated questionnaire instrument-the Transitions VRQOL. Changes in visual acuity were assessed by functional exam.

RESULTS

Overall, Transitions was associated with the greatest improvement in VRQOL relative to clear and fixed-tint lenses without compromise in acuity. Transitions proved statistically superior to clear lenses, most notably in vision comfort both indoors and outdoors. Seventy percent of all patients selected Transitions as their primary lens at the end of the study.

CONCLUSIONS

Transitions brand VTO offer patients significant and clinically meaningful improvements in VRQOL superior to clear lenses. VRQOL assessments provide clinicians with valuable information above and beyond visual acuity to help optimize lens product selection and enhance patient satisfaction.