Ophthalmic & physiological optics : the journal of the British College of Ophthalmic Opticians (Optometrists)
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Ophthalmic Physiol Opt · Jul 1999
Clinical TrialBoth coloured overlays and coloured lenses can improve reading fluency, but their optimal chromaticities differ.
Some individuals read more fluently when the text is coloured: i.e., when coloured sheets of plastic (overlays) are placed upon the page, or when coloured lenses are worn. Overlays provide a surface colour whereas lenses mimic a change in the colour of a light source. The neural mechanisms that underlie colour constancy ensure that the chromaticity of overlays and lenses is processed differently by the visual system. ⋯ The aids increased reading rate significantly only in conditions (2) and (4). There was no significant improvement when lenses matching the overlay colour were used, and under this condition the reading rate was significantly poorer than in conditions (2) and (4). The colour of a lens will improve reading only if it is selected under conditions that mimic a change in the colour of a light source: coloured overlays give no clinically reliable guide to optimal lens colour.
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Ophthalmic Physiol Opt · Jul 1997
Double-pass measurements of retinal image quality in monofocal contact lens wearers.
The double-pass method is applied to determine the optical image quality in monofocal contact lens (CL) wearers. This is an objective non-invasive technique that permits in vivo testing of the optical performance of CL wearers' eyes. Retinal image quality was measured for three subjects wearing two types of monofocal CLs: a rigid gas permeable (RGP) CL and a soft contact lens (SL), for pupil diameters of 3 mm and 5 mm. ⋯ In eyes presenting corneal astigmatism, the best results are obtained when wearing RGP CLs, because the lens compensates the corneal astigmatism. The modulation transfer function (MTF) is considerably smaller when no lens or soft lenses are worn, even for small amounts of astigmatism (0.5 D). When the astigmatism is corrected, the retinal image quality obtained with both types of CLs and with no lens is similar.
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Ophthalmic Physiol Opt · Jul 1996
A preliminary investigation into the aetiology of Meares-Irlen syndrome.
A recent double-masked placebo-controlled trial has confirmed that some children experience a reduction in symptoms of eyestrain and headache when they read through individually prescribed coloured filters and has shown that this benefit cannot be solely attributed to a placebo effect. People who are helped by coloured filters in this way have been described as having "Meares-Irlen syndrome'. We investigated the mechanism of this benefit by studying the optometric and visual perceptual characteristics of the children in the double-masked study. ⋯ However, these factors seemed to be correlates of Meares-Irlen syndrome rather than the underlying cause. Pattern glare, a sensitivity to striped patterns (e.g. lines of text), was prevalent in our sample and was significantly associated with the subjects' symptoms. The spatial contrast sensitivity function was normal.
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Ophthalmic Physiol Opt · Jan 1996
Elimination and minimization of the spherical aberration of intraocular lenses in high myopia.
By applying Seidel aberration theory we have studied the spherical aberration of intraocular lenses in place (SIL), and the total spherical aberration of pseudophakic eyes (S(IT)). The optimum lens shapes for zero SIL and S(IT) or for minimum SIL and S(IT) of 12 schematic, highly myopic eyes were investigated. ⋯ If the power of the intraocular lens is negative, the total Seidel spherical aberration of the whole eye can be made zero, and one of the optimum lens shapes would be meniscus with the convex surface towards the retina. In addition to improving the quality of the image, the lens has advantages from the physiological point of view, since it helps to maintain the structure of the eye.
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Ophthalmic Physiol Opt · Sep 1995
Case ReportsA new protocol for the optometric management of patients with reading difficulties.
Research by Evans et al. (Ophthal. Physiol. Opt. 15, 481-487, 1995) has demonstrated a correlation between visual processing and ocular motor factors in people with specific reading difficulties (dyslexia). ⋯ With the second patient, ocular motor functions were found to be within acceptable limits and relief of symptoms was obtained by the prescribing of lenses of a specific chromaticity. For the third patient, both orthoptic intervention and the use of specifically tinted lenses were necessary to relieve the visual difficulties that were being experienced. By taking advantage of recent research and developments in optometric instrumentation, it is possible for some of those with dyslexia to receive considerable benefit from optometric intervention.