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Publications
Publications (51)
To determine if simple, robust spectacle mounted devices are feasible for the replacement of the mirror boxes currently used in the rehabilitation of patients suffering from phantom limb pain, complex regional pain syndrome and stroke.
Four devices, using three different optical systems were produced: plane mirror, astronomical telescope using cyli...
The theoretical transmittances at the installation angle of the windscreens of the ten best-selling cars in the UK in 2008 are investigated. The data show that the ten most popular cars on the UK roads have a windscreen rake that reduces transmittance to a value close to or below that specified in International Standards for normal incidence. Briti...
The current international standard for spectacle frames recommends that frames weighing up to 25 g should have a minimum nose-pad contact area of 200 mm(2) and that those weighing over 25 g should have a minimum contact area of 250 mm(2). It is shown that these recommendations are being almost universally ignored for frames with separate pads on ar...
Tungsten filament lamps are rapidly being displaced from the market-place by compact fluorescent lamps. Although the colour temperature and total luminous output of a fluorescent lamp may be similar to that of an incandescent lamp, the output spectrum is very different. The peaks of the mercury vapour spectrum at 365.4nm (UV) and at 435.8nm (blue)...
To investigate the effect of windscreen rake angle on effective transmittance and the contribution of spectacle lenses to the total transmittance of the system.
Theoretical analysis has been carried out using the Fresnel reflectance equations.
Windscreen rake can reduce effective transmittance significantly at angles present on modern aerodynamic v...
To investigate if jump or diplopia is experienced at the dividing line of bifocal lenses and if the belief in jump may be, in part, the result of leading questions.
Ten subjects were asked an open question and 10 a closed question relating to jump for six bifocal lenses and three eye movement conditions.
All subjects failed to see any effects other...
The variation in the measurement of an inter-pupillary distance and monocular centration distance by 54 registered practitioners using a 'pd rule' was investigated. Their estimate of the repeatability of the measurement was also recorded, as was any correction for their own inter-pupillary distance. There was found to be considerable variation betw...
The evidence for the basic optometric function of optical dispensing is discussed in terms of the basic principles of scientific debate. The degree of rigour applied to product testing and evaluation of most other medically related areas is lacking in the dispensing of spectacles. There has been much debate on the place of religious faith in our so...
Visual field testing of subjects wearing a niqab was carried out using the approved (Esterman) test on a Humphrey perimeter to determine if visually normal subjects met the European driving standard. Measurement of aperture dimensions of the niqab when worn was recorded. When wearing the niqab, all subjects achieved a visual field adequate to satis...
To build a simple, low cost, variable-power prism with a linear scale.
A sliding lens system, using the prismatic effect of ophthalmic lenses, was constructed.
The system functions well at low powers using conventional curved form ophthalmic lenses.
The sliding lens variable prism is a useful alternative to the conventional rotating variable-power...
The materials that have been reported as causing allergic contact dermatitis within spectacle frames are identified, and their most likely location on the frame is highlighted. The lack of any real control over spectacle frame quality and content is indicated to be a problem, as is the difficulty in determining the true source of many frames. Much...
A technique by which a ptosis crutch can be fitted in minutes, using readily available and inexpensive materials and tools, is described. No specialist skills are needed and the device can be fitted to existing frames and lenses.
The calculation of the extent of the ring scotoma around positive lenses, as conventionally taught to students of clinical optics, indicates that the scotoma is of a significant size. Using knife-edge lenses this study shows that the calculations are invalid due to the finite size of the eye's entrance pupil and in many instances the scotoma is sho...
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 wa...
The groove of a spectacle frame is responsible for lens retention. It also tends to fill with unsightly dirt which cannot be readily removed by our patients. The results of this investigation would suggest that both loose spectacle lenses and dirt accumulation may often be due to poor quality control in the frame industry. The data also suggests th...
Fifty "used" and 373 new spectacle frames were tested for evidence of nickel release using dimethylglyoxime and ammonia. Nearly all the "used" frames (96%) tested positive. A lower proportion (24.5%) of new frames showed evidence of nickel leaching. It is suggested that this is evidence of non-conformance with the current British Standard although...
Fifty “used” and 373 new spectacle frames were tested for evidence of nickel release using dimethylglyoxime and ammonia. Nearly all the “used” frames (96%) tested positive. A lower proportion (24.5%) of new frames showed evidence of nickel leaching. It is suggested that this is evidence of non-conformance with the current British Standard (British...
Patients with diabetes mellitus often have ophthalmic dysfunction, as diabetic eye disease can affect the majority of the ocular structures. The present study investigated contrast sensitivity (experiment 1) and glare sensitivity (experiment 2) using Pelli-Robson and Bailey-Lovie charts in normal and diabetic patients with a range of degrees of isc...
We assessed the reliability and validity of a new computer-assisted crossed-cylinder aberroscope technique which measures the monochromatic optical aberrations of the human eye.
Intra-image variability, the variability occurring when the same image is repeatedly measured, and inter-image variability, the variability occurring when different images...
An investigation was carried out into the thickness and standard of application of the plating and lacquer coatings applied to three metal spectacle frames. All conform to BS 6625 (1991) for plating thickness, but there was considerable variation in regularity and porosity.
British Standards specify a very small number of screw sizes as being acceptable for use in spectacle frames. We have measured the screw sizes of 50 frames, selected at random from the stock of Glasgow Caledonian University Clinic and have shown that very few of the screws used conform to these standards.
The purpose of this research was to determine if a clinically significant variation in corneal curvature occurs with the menstrual cycle. The EyeSys Corneal Analysis System (CAS) was used to measure corneal curvature of a test group of three normally menstruating female subjects over three cycles and compared with a control group of three males, fo...
One male and one female subject wore a selection of ten current spectacle frames in random order. Monocular visual fields were assessed using an Aimark perimeter in accordance with UK Driver and Vehicle Licensing Authority (DVLA) guidelines. Of the ten frames, seven plastic frames produced an absolute scotoma intruding into a 120 degrees x 40 degre...
The aim of our study was to evaluate the performance of both the Keeler Pulsair 2000 and the American Optical (AO) MkII non-contact tonometers (NCT) and compare these to the reference Goldmann standard using the same group of patients. Forty-five patients (89 eyes) receiving medical treatment for primary open angle glaucoma had their intraocular pr...
The aim of our study was to evaluate the performance of both the Keeler Pulsair 2000 and the American Optical (AO) Mkll non-contact tonometers (NCT) and compare these to the reference Goldmann standard using the same group of patients. Forty-five patients (89 eyes) receiving medical treatment for primary open angle glaucoma had their intraocular pr...
We have developed a video-based system for the acquisition and analysis of images produced by an aberroscope. The aberroscope uses a helium-neon laser to project a shadow image of a grid onto the retina. The retinal image is, in its turn, imaged onto a CCD video camera. As the grid forms a shadow image, the position of each grid intersection at the...
We have developed a video-based system for the acquisition and analysis of images produced by an aberroscope. The aberroscope uses a helium—neon laser to project a shadow image of a grid onto the retina. The retinal image is, in its turn, imaged onto a CCD video camera. As the grid forms a shadow image, the position of each grid intersection at the...
One hundred consecutive patients who underwent bilateral pan-retinal photocoagulation (PRP) for proliferative diabetic retinopathy were assessed in accordance with the UK Driver and Vehicle Licensing Agency (DVLA) guidelines. Visual acuity was documented, and visual fields were assessed using the Esterman test. Among the 30% of patients who failed...
Experiments are described in which the steady-state accommodation response versus stimulus curve was measured with an infrared autorefractor for high-contrast stimuli having a 100% square-wave temporal modulation of luminance in the frequency band 1-200 Hz. Slightly more accurate responses were found at frequencies approximately 50-100 Hz, i.e. abo...
For circular pupils of diameters < or = 2 mm the optical performance of the eye in monochromatic light is effectively diffraction-limited, so that its modulation transfer function (MTF) is essentially independent of grating orientation and its phase transfer function (PTF) is close to zero. For larger pupils, however, the wave aberration of the eye...
Small periodic (0.25-40 Hz) changes in the contrast of suprathreshold, spatially sinusoidal (0.8-10.5 c/deg) grating test objects were generated on an oscilloscope screen. It was found that the minimum temporal modulation in spatial contrast which could be detected subjectively was approximately proportional to the mean contrast of the grating duri...
The variation with defocus in the contrast and phase of the retinal image of a grating stimulus is computed from a knowledge of the measured wavefront aberration of individual eyes. Contrast or modulation transfer is generally lower than in the aberration-free, diffraction-limited case, even at a pupil size of 3 mm, and marked spatial phase shifts,...
We show that normally a spherocylindrical lens will correct the local refractive error of any small area of the pupil. In general, however, the correction varies with position across the pupil. Plots are given to illustrate this variation for 2 typical individual eyes and for the average of 11 eyes, as calculated from the corresponding wavefront ab...
Measurements were made of the ability of observers, whose accommodation had been paralysed, to detect the small changes in contrast resulting from sinusoidal, oscillatory changes in the dioptric focus of test objects, as a function of the mean position of focus. Variables studied included the form and wavelength composition of the test object, the...
The change in pupil centration occurring as the human eye pupil dilates, both naturally in darkness and following the use of a mydriatic drug (cyclopentolate HCl, 1%), has been measured photographically. In both cases, changes in centration of up to 0.4 mm have been found. Using available ocular wavefront aberration data, modulation transfer curves...
The variation in sphero-cylindrical refractive error with position in the human eye pupil is derived from the wavefront error of two subjects. The modulation transfer function is also calculated for 1, 2 and 3 mm pupils decentred 1 and 2 mm nasally and temporally. Whilst decentration causes relatively little difference in the M.T.F. at the smaller...
The design of alternating andsimultaneous-vision bifocal contact lenses is discussed in relation to the form of the geometrical point images (spot diagrams) that they produce on the retina. Examples are given to show that the effects of variations in lens decentration and in the diameter of the entrance pupil of the eye depend upon the lens design...
An objective variation of Howland and Howland's subjective crossed-cylinder aberroscope method of estimating ocular aberration is described. An ophthalmoscopic arrangement allows the distorted retinal image of the aberroscope grid to be directly photographed for later analysis. Results for 10 subjects show that the ocular wavefront aberration near...
An objective variation of Howland and Howland's subjective crossed-cylinder aberroscope method of estimating ocular aberration is described. An ophthalmoscopic arrangement allows the distorted retinal image of the aberroscope grid to be directly photographed for later analysis. Results for 10 subjects show that the ocular wavefront aberration near...
The subjective crossed-cylinder aberroscope method of Howland and Howland [ J. Opt. Soc. Am. 67, 1508 ( 1977)] has been modified by the addition of a beam splitter and a camera to permit direct photographic recording of the distorted retinal image of the aberroscope grid. The ocular aberration can then be deduced from direct measurements of the gri...
This article gives an introduction to binocular vision.