The subjective and objective effects of tinted spectacle lenses on visual performance
- Authors: Moore, Linda A.
- Date: 2012-08-17
- Subjects: Eye -- Protection , Ophthalmic lenses , Visual acuity
- Type: Thesis
- Identifier: uj:2608 , http://hdl.handle.net/10210/6056
- Description: M.Phil. , Tinted spectacle lenses have long been worn to provide ocular protection from harmful electromagnetic radiation during recreational activities. Controversy exists surrounding the colour of the spectacle tints and the environmental conditions under which these tints are worn. There is little scientific evidence to substantiate the many opinions of authors on the effects of tinted spectacle lenses on visual skills and, ultimately, on overall performance in recreational situations. This study serves to provide scientific data concerning the effects of tinted lenses on static visual acuity, contrast sensitivity, colour vision, stereopsis and visual evoked potential (VEP). These results are related to the visible spectrum transmission curve for each experimental lens. recommendations are then made concerning the environmental conditions under which each lens tint should be worn. The HOYA ULT-2000 Light Transmission Metre was used to establish the percentage of visible light being transmitted through each of the experimental lenses. The DMS 80/90 Visible Spectrophotometer was used to generate a visible spectrum transmission curve for each of the 8 experimental lenses used in this study. 30 subjects (Group A) were randomly selected from the RAU student population for the assessment of the effects of tinted lenses static visual acuity, contrast sensitivity, colour vision and stereopsis. 10 students (Group B) were then randomly selected from the RAU student population for the assessment of the effects of tinted experimental lenses on visual evoked potential (VEP). The ametropic subjects in Groups A and B all wore their habitual spectacle or contact lens corrections throughout the testing procedure. The following lens tint colours were used: clear, black, grey, yellow, green, blue, red and pink. The subjects were evaluated binocularly without any tinted lens being worn, then through each of the 8 tinted experimental lenses (randomly presented). Results of the visual skills and VEP testing were analysed as follows: Group A: An average score was calculated for the results achieved on the static visual acuity, contrast sensitivity, colour vision and stereopsis tests when no experimental lenses were worn. This average was then compared to the average static visual acuity, contrast sensitivity, colour vision and stereopsis scores for each of the 8 experimental lenses. Group B: An average score was calculated for each of the amplitude and latency components of the VEP waveforms generated when no experimental lenses are worn. This average was then compared to the average amplitude and latency components generated when each of the 8 experimental lenses (as for Group A) are worn. Static visual acuity was assessed using a Snellen visual acuity letter chart at 6m. Contrast sensitivity was assessed using a Vistech VCTS 6500 Contrast Sensitivity Chart at 3m. Colour vision assessment was performed using the lshihara Colour Vision Test and the City University Colour Vision Test. The Random Dot Near Stereo Test was used to assess stereopsis. The Nicolet Pathfinder II was used to assess visual evoked potentials (VEPs). The results of this study show that the black, grey, yellow, green, blue, red and pink tinted lenses have a statistically significant influence on visual efficiency only when subjective methods (i.e. static visual acuity, contrast sensitivity, colour -vision and stereopsis) of visual efficiency assessment are used. The tinted lenses had little effect on visual efficiency when an objective means (i.e. VEP) of assessment was used, as there were no statistically significant differences between the lenses. The results of this research project indicate that the colour of the lens tint has little real effect on visual efficiency, when measured objectively. The effect of the lens tint is shown to be highly subjective. Tinted lens selection would therefore be based on personal preference and the amount of protection that the lens provides from harmful electromagnetic radiation. It can be concluded that no single lens tint is therefore suitable for all individuals under the same environmental conditions.
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Surfaces of constant visual acuity in symmetric dioptric power space
- Authors: Rubin, Alan
- Date: 2012-08-28
- Subjects: Visual acuity , Eye -- Accommodation and refraction , Multivariate analysis , Refraction
- Type: Thesis
- Identifier: uj:3290 , http://hdl.handle.net/10210/6695
- Description: D.Phil. , Visual acuity and refractive state probably are the two most basic or fundamental quantities that concern optometry, ophthalmology and vision science. Both of these variables are complicated and their mathematical and statistical use in research and other activities has been poorly understood. During particularly the last decade, modern statistical multivariate methods have become available to optometry and ophthalmology and this has assisted with the understanding of concepts such as refractive state (and its underlying nature, namely, dioptric power). It is now possible to transform measurements of refractive state from the conventional notation that is commonly used in the fields of optometry and ophthalmology to an orthodox mathematical form that can be understood by scientists and mathematicians. With this matrix form of refractive state it then is possible to use appropriate methods of linear algebra and multivariate statistics. Other theoretical approaches and analytical procedures or methods also have become accessible or have been developed recently as a consequence of this significant shift in thought as regards the fundamental nature of dioptric power. On the other hand, the scientific understanding of visual acuity (that is, the measurement of the resolving ability of the eye) perhaps has been somewhat neglected. Certainly there has been an abundance of research involving visual acuity and there also has been discussion concerning some of the difficulties that become apparent when measuring or attempting to interpret results from studies involving visual acuity. Visual acuity, unlike refractive state, can be represented by means of a single number and thus univariate, rather than multivariate, statistical methods are appropriate. And, of course, univariate statistics is less complicated than the multivariate form. But there are various difficulties with the understanding and researching of visual acuity. Some of these difficulties are relatively simple and thus can be solved more easily. For example, visual acuity measurements can be obtained from charts designed according to a logarithmic scale, or measurements from other charts can be transformed to a logarithmic scale. And thereby the ordinal nature of the basic or more common visual acuity scale is avoided and certain statistical methods become available that otherwise would not be possible. But more fundamentally visual acuity probably cannot truly be considered without the subject from which the measurement is obtained and, more particularly, the refractive state of the eye concerned. So the visual acuity and refractive state of an eye, perhaps, should be more appropriately regarded as a unitary concept that ideally should not be separated into two distinct parts. Thus to truly understand the relationship between visual acuity and refractive state we need to understand the 4-dimensional (mathematical) nature of the particular relationship involved. It follows then that the relationship between visual acuity and refractive state is a multivariate problem and that multivariate methods are best suited to its consideration. If we then begin to take into account other variables such as age or the ocular health, or say, iris aperture diameter of the eye then the complicated multivariate nature of the situation becomes even more obvious. In this dissertation an attempt is made to consider the possibilities of a modern multivariate approach to studies involving visual acuity, refractive state and other variables. The methodology used in this dissertation differs from those used in previous studies involving visual acuity and refractive state and other related variables. For example, here Jackson crossed cylinders are used extensively to produce dioptric blur or defocus in experimental subjects (positive and negative spheres also are used to a more limited extent). In previous published studies spherical or, less commonly, cylindrical lenses were used instead. Another difference between this dissertation and previous research studies is that the visual stimulus that the subjects observed, generally but not always, was a meridionally-independent or non-directional letter 0. The reasons for this choice is explained in the dissertation but in other research an enormous variety of visual stimuli have been used depending upon the interests of the researchers. But even more essentially this dissertation differs significantly from that of previous studies in terms of the manner in which the various experimental and other results (for instance, that from earlier researchers such as HB Peters) are presented. Entirely new, and largely unpublished, methods are used in many parts of this dissertation that probably represent a paradigmatic transition in understanding of visual acuity and its relation to refractive state. New terms such as decompensation and accompensation surfaces of constant visual acuity and antistigmatic ellipses are defined herein. (Briefly, one imagines starting from a state of compensation (of the refractive state of, say, an eye viewing a stimulus).
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Inter-and intra-subject variation of contrast visual acuities
- Authors: Sukha, Anusha Yasvantra
- Date: 2015-07-15
- Subjects: Visual acuity
- Type: Thesis
- Identifier: uj:13766 , http://hdl.handle.net/10210/14030
- Description: D.Phil. (Optometry) , The measurement of Contrast Visual Acuities (contrast VA) is recognised in various studies as an important psychophysical measure of visual function, and contrast VA is often used to understand visual limitations or functional disability. Contrast VA is also useful for monitoring the effects of disease modifying therapies. High and medium contrast levels are generally used in studies to evaluate contact lens performance, the outcomes of surgical procedures and for assessing activities of daily living. Measurement of stimuli with low contrast levels are also sometimes applied in diagnosing, monitoring and evaluating disease processes and their management, especially where high contrast visual acuity remains intact. This is believed to be the first study that comprehensively investigates the reliability (or repeatability) of four contrast levels using the computerized Thomson Test Chart 2000 XPert. (A similar study with four contrast levels and both univariate and multivariate analysis as applied in this thesis has not been performed elsewhere). Although the main emphasis of this study was to explore various issues relating to short-term repeatability of contrast VA, both within and across individuals, both univariate and multivariate statistical analyses were also used in this thesis to investigate age and gender related changes in measurements of contrast VA. Together the results from this thesis provide test and re-test contrast VA reliability measures and some basic or preliminary statistical normative contrast VA values, which should aid clinicians to confidently detect abnormal measurements which, in turn, promotes good clinical practice. For this thesis and within a clinical environment to investigate inter-subject variation in contrast VA, two measurements of contrast VA at four specified contrast levels (100%, 10%, 5% and 2.5%) at a 6 metre distance were obtained for the right eyes only of 155 healthy participants. Thus, at each contrast level 155 test and re-test contrast VA measurements were determined using the computerized Thomson Test Chart 2000 XPert. All measurements were determined through the optimal refractive compensation for each right eye of the 155 participants concerned. In a subset of ten subjects or participants, samples of thirty consecutive measurements of contrast VA at each of the four contrast levels were also obtained to explore short-term intra-subject variation in contrast VA. A simple questionnaire was administered to all subjects to obtain biographical, general and ocular health histories. Visual assessment included II subjective clinical refraction, stereopsis, colour vision, direct ophthalmoscopy and biomicroscopy to understand the eyes of the participants and exclude possible factors that could cause ocular or neurological changes in the retina or in vision thereby influencing contrast VA in a detrimental fashion...
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