bluuebunny/crossref_metadata_2025 huggingface dataset:
Modification of the Canon Auto Ref R1 for use as a continuously recording infra‐red optometer
Authors: Pugh J.R. , Winn B.
Published: December 2007

The Canon Auto Ref R1 has been modified to allow continuous recording of accommodation while retaining its capacity to record in ‘single‐shot’ static mode. Possible alternative principles of modification are discussed with emphasis placed on the method used in this paper. Preliminary results are presented for both a novel dynamic model eye and an emmetropic real eye. The system described provides a useful research tool in the study of ocular accommodation dynamics.
Referrals and notifications by optometrists within the UK: 1988 survey
Authors: Port M.J.A.
Published: December 2007

In a survey of nearly 75000 eye examinations, 6% of patients were referred to a medical doctor and the doctor was notified in a further 2% of cases. The level of referral was 2% higher than in 1986; 70% of referrals were the result of reminders or periodic attendances, and 80% of those referred were over 40 years of age. The general pattern of referral was broadly in agreement with a survey conducted in 1986 but indicates that some categories of eye conditions are being referred at a higher rate.
The effects of 0.025% hyoscine hydrobromide eyedrops on visual function in man
Authors: Morrison J.D. , Reilly J.
Published: December 2007

Instillation of three drops of 0.025 % hyoscine hydrobromide into one eye at 5 min intervals caused a mydriasis and cycloplegia of rapid onset and of 4–6 days' duration; this was similar to the previously reported actions of concentrations of up to 0.5%. After refraction for the working distance of the experiments, contrast sensitivity to stationary oscilloscope‐generated grating patterns of 10 and 20 c/deg was unaffected despite the mydriasis. Also, contrast sensitivity to laser interference fringes of 10 and 20 c/deg observed in the Maxwellian view, in which the effects of the ocular media are bypassed, was unaffected. Contrast sensitivity to a 3 cydeg phase‐reversed grating pattern was, however, transiently reduced by 40% after hyoscine. A second series of experiments showed a deleterious effect of hyoscine on contrast sensitivity to both stationary and phase‐reversed grating patterns of 2, 3 and 5 c/deg while contrast sensitivity at 10 c/deg was not consistently affected. These results were explained by a direct deleterious action of hyoscine at the level of the retina, specific to channels that detect low spatial frequencies.
Computed extraocular muscle activity during blinks
Authors: Boylan C. , Clement R.A.
Published: December 2007

The rotations and retractions of the eyeball due to co‐contraction of the extraocular muscles are investigated using a model of the mechanics of the orbital plant. The hypothesis that the rotational movements are secondary to globe retraction is not supported.
The bandage lens in bullous keratopathy
Authors: Andrew N.C. , Woodward E.G.
Published: December 2007

One of the most common indications for the fitting of therapeutic contact lenses is bullous keratopathy, a painful condition often iatrogenic in origin and more usually encountered in elderly patients. A retrospective study of 30 patients fitted with therapeutic lenses for the condition and followed up for at least a year showed that the symptoms of bullous keratopathy were reduced in most cases. There was a higher incidence of suppurative keratitis (13 per cent) than has been reported in previous series. The prescribing of prophylactic antibiotics was haphazard in the series, and the authors suggest further study is needed to determine their precise role.
A comparison of three methods for the measurement of progressive addition lenses
Authors: Fowler C.W. , Sullivan C.M.
Published: December 2007

Three methods of measuring aberrational astigmatism in progressive addition spectacle lenses are described. Measurements are presented from each method made on an Essilor Varilux 2 lens, which illustrate the small differences between the methods for low power lenses.
Presbyopia correction and the accommodation in reserve
Authors: Millodot Michel , Millodot Susan
Published: December 2007

One method of determining the additional correction for presbyopia suggests leaving a percentage of the amplitude of accommodation in reserve. The rationale for this assumption seems logical because using all of the available accommodation is not sustainable without discomfort. However there is no empirical evidence indicating what percentage of the amplitude of accommodation should actually be left in reserve. Common figures adopted have been one‐half and one‐third. In this investigation the percentage of accommodation used is deduced mathematically after having determined the following:

1. The ‘add’ by the direct subjective clinical method.

2. Measured the amplitude of accommodation.

3. Measured the reading distance in 305 presbyopes ranging from 40 to 83 years of age.

The results showed a small decline in the amplitude of accommodation up to the age of 52, after which age the measurements were scattered about a steady level. This finding suggests that after the age of 52 the results are based on the depth‐of‐focus of the eye. Females had slightly greater accommodation than males of the same age. The power of the add was significantly correlated to the age of the subject. The mean percentage of accommodation used for the 305 subjects was found to be 50.7%, thus confirming the rule of leaving half of the accommodation in reserve, although there were large variations: there were differences between males and females and with age the percentage of measured accommodation used, after having determined the correct add, diminished. Similarly the percentage of accommodation also decreased for shorter reading distances.
Human tear film pre‐rupture phase time (TP‐RPT)‐A non‐invasive technique for evaluating the pre‐corneal tear film using a novel keratometer mire
Authors: Hirji Nizar , Patel Sudi , Callander Murchison
Published: December 2007

A non‐invasive method of assessing the stability of the human pre‐corneal tear film is described using a novel keratometer mire designed in the form of a grid pattern (HIR‐CAL Grid). In a laboratory environment, the technique measures with ease and little variability the time taken for the tear film to loose stability and enter the pre‐rupture phase (TP‐RPT) before rupturing (BUT). This technique may prove useful in evaluating the stability or otherwise of the pre‐corneal tear film of prospective contact lens wearer and the pre‐contact lens tear film stability on differing current and new contact lens materials.
A review of the clinical applications of the pattern electroretinogram
Authors: Hull B. M. , Thompson D. A.
Published: December 2007

The pattern electroretinogram (PERG) has recently been introduced as a clinical procedure. It has been thought by many to represent activity of the retinal ganglion cells, although this is still a matter of contention. The exciting prospect of a selective test of ganglion cell function led to the application of the PERG in a variety of ophthalmological conditions. In the course of these investigations the PERG was found to be diminished in cases of maculopathy, optic atrophy, optic neuritis, toxic optic neuropathy, neurotransmitter disorders, glaucoma and ocular hypertension and in retinal vascular disorders such as diabetes. It was also affected in some cases of amblyopia. This paper briefly describes the techniques used to record the PERG and reviews current literature pertaining to its clinical application.
Binocular accommodation reaction and response times for normal observers
Authors: Heron G. , Winn B.
Published: December 2007

Accommodation was recorded from right and left eyes of visually normal observers in both binocular and monocular viewing. Reaction and response times were similar in monocular and binocular viewing and are not influenced by eye dominance. Far‐to‐near responses were significantly quicker than near‐to‐far responses. The origin of this difference may be a feature of the elastic properties of the accommodation mechanism. Limited data are presented that indicate that the slowing of accommodation speed with age affects the near‐to‐far response disproportionally. Errors in the initial direction of response were fewer in binocular viewing in comparison with monocular viewing.
A longitudinal study of the changes in the static accommodation response
Authors: Ramsdale C. , Charman W.N.
Published: December 2007

The results are described of a 10‐year study of the longitudinal changes in the static response of an individual subject during the approach to absolute presbyopia. The amplitude of accommodation declines linearly with age. A new finding is that the magnitude of the slope of the linear portion of the response/stimulus curve also reduces with age, as does the level of tonic accommodation.
Peripheral visual acuity and age
Authors: Collins Michael J. , Brown Brian , Bowman Kenneth J.
Published: December 2007

We measured the peripheral visual acuity of a group of eleven older subjects (mean age 54.2 years) and a group of seventeen young subjects (mean age 22.1 years). Peripheral visual acuity was measured using Konig bars with critical detail subtending 2.4 and 4.8 minutes of arc. The older group showed a substantial reduction of peripheral visual acuity.
Congenital pit of the optic nerve
Authors: Barnard N. A. S.
Published: December 2007

Congenital pit of the optic nerve is a rare condition which can lead to serous retinal detachment. A case history of a patient with a small pit of the optic nerve is presented and management by the optometrist is discussed.
Does target orientation influence the accommodative response?
Authors: Rosenfield Mark , Ciuffreda Kenneth J.
Published: December 2007

A number of studies have demonstrated that visual responsivity is optimum when viewing either horizontal or vertical stimuli but is significantly reduced when viewing an obliquely oriented object of regard. Accordingly this study examined the accommodative response in 10 subjects to targets oriented at 45, 90, 135 and 180 degrees to the horizontal. Stimuli were located at distances of 1, 3 or 5 D, and steady‐state accommodation was measured subjectively from the right eye using a Hartinger coincidence optometer. The data indicate that, for high contrast, supra‐threshold targets, variation in target orientation did not produce any significant change in accommodative response. These results suggest that neural sensitivity for monocular blur‐driven accommodation is orientation independent. This finding would imply that accommodation and contrast detection are mediated by dissimilar processes.
Do long wavelength pass filters improve low vision performance?
Authors: Leat Susan J. , North Rachel V. , Bryson Heather
Published: December 2007

It has been suggested that the wearing of band‐pass tints may improve the contrast performance in certain ocular conditions. We examined this by measuring grating visual acuity (VA) for targets of various contrasts. The benefits of Corning CPF 511, 527 and 550 lenses, and neutral density (ND) filters were examined with and without the presence of glare.

Generally, patients with anterior sector conditions showed improved performance with band‐pass filters (not with ND filters). It is suggested that the filter reduces the scatter within the ocular media. People with retinitis pigmentosa or diabetic retinopathy rarely benefited. The CPF 511 most frequently improved VA followed by CPF 527 and 550 respectively. We suggest that a condition of glare is incorporated when assessing suitability with tints.
Efficiency in reading with closed‐circuit television for low vision
Authors: Lowe J. B. , Drasdo N.
Published: December 2007

A closed circuit television (CCTV) magnifier was used to measure the reading rates of nine fluent low‐vision subjects. Performance was found to be dependent on field width, character size, and the number of characters displayed in line. A field width of 70 degrees and a mean of 24 characters were commensurate with the fastest reading rate. The optimal character size that elicited the fastest reading was determined for each subject. In seven of the nine subjects, this differed from the character size selected by chance at their initial CCTV sessions, prior to these experiments. A clinical procedure is recommended, which avoids inappropriate choice, and guides the examiner in achieving directly the most efficient CCTV reading conditions for each individual patient.
Ocular dimensions and refractive power in Malay and Melanesian children
Authors: Garner Leon F. , Meng Chung Kah , Grosvenor Theodore P. , Mohidin Norhani
Published: December 2007

A cross‐sectional study of 753 Melanesian children in Vanuatu and 904 Malay children in Malaysia included measurement of refractive error and ocular dimensions. All children were between the ages of 6 and 17 years. The prevalence of myopia in Malay children was 4.3% at 7–8 years and 25.6% at 15–16 years with corresponding figures of 0.8% and 4.3% for Melanesian children. The range of refractive error was greater for Malay children at all ages. Mean refractive error for Malay children showed greater hypermetropia, together with a shorter axial length at 6 years, than Melanesian children, but at 17 years the situation reversed and Malay children had more myopia and longer axial lengths than their Melanesian counterparts.
A gradient‐index ophthalmic lens based on Wood's convex pseudo‐lens
Authors: Fowler C. W. , Pateras E. S.
Published: December 2007

Although the Varilux type varifocal has been and still is very popular, research has been carried out on other methods of providing a progressive addition lens. This paper deals with the field of gradient‐index optics. It includes a review of the literature related to the production of a gradient‐index element and the theoretical analysis of concentric varifocals. A procedure is described to construct a varifocal lens, after that described by Wood in 1905, to produce lenses known as ‘non‐homogeneous cylinders’ or ‘pseudo‐lenses’. The method is based on a diffusion process, taking place in half of the lens, and creates steps in the refractive index of the material. Experimental data are also given on the change of the spherical and cylindrical power, which indicate that the lens constructed is an optical system having a rotational symmetry in power, around a fixed point.
The Ed ridge‐Green Lecture Vision at low light levels: role of spatial, temporal and contrast filters*
Authors: Hess R. F.
Published: December 2007

One of the most impressive features of our vision is the fact that we see with good sensitivity over such a large range of light levels. This process is usually termed light adaptation by which it is meant that the sensitivity of individual neurones within the retina automatically adapts to suit the prevailing lighting conditions. Although this is usually thought about in terms of single neurones, its effectiveness is greatly enhanced by the fact that individual neurones have distinctive properties. The fact that individual neurones can be considered as acting as neural filters along the dimensions of size, time, orientation and contrast means that visual information is distributed across the whole neuronal population which in turn plays an important role in extending our dynamic range. In this paper the distributed nature of visual processing is emphasized and its role in extending the range of light levels over which we can see is highlighted.
Joint hypermobility in keratoconus
Authors: Woodward E. G. , Morris M. T.
Published: December 2007

There are several reports linking keratoconus and connective tissue disorders, such as Ehlers‐Danlos syndrome, osteogenesis imperfecta and mitral valve prolapse, suggesting that keratoconus may be the result of a localized dysfunction in collagen metabolism. In view of this the incidence of hypermobility of the joints among a group of patients with keratoconus was compared with a normal (matched) control group. Eighty‐four patients were examined using the Beighton modification of the Carter and Wilkinson scoring system. A control group matched for sex, age and ethnic group was also assessed. No statistically significant difference between the groups was found for the trunk or knees; a difference was found for the metacarpo‐phalyngeal and wrist joints. The findings support the theory that keratoconus is a localized manifestation of a mild connective tissue disorder. Also, it can be stated that patients with keratoconus are five times more likely to show hypermobility of the metacarpo‐phalyngeal and wrist joints.
Age‐related maculopathy. I: A review of its morphology and effects on visual function
Authors: Swann P. G. , Lovie‐Kitchin J. E.
Published: December 2007

Age‐related maculopathy (ARM) is a leading cause of permanent vision loss in elderly people. ARM therefore constitutes an important public health problem which will increase in magnitude as the number of aged people in the general population becomes greater. The consequences of this condition are exacerbated by the fact that treatment, especially of the atrophic form of the disease, is ineffective. While laser photocoagulation may be helpful in the exudative form of ARM, there is often an inexorable progression towards severe vision loss in these patients. Therefore considerable attention needs to be paid to the aetiology of ARM, the potential for its prevention or delayed onset and its recognition through functional disturbances. This is the first of three papers dealing with ARM and its effects on visual function. We review its morphology and the visual disturbances that may ensue. The second and third papers will discuss the nature and detection of the central visual field loss due to ARM.
The effect of monocular defocus on binocular contrast sensitivity
Authors: Pardhan Shahina , Gilchristt Jim
Published: December 2007

The monocular contrast sensitivity loss with defocus is well known. We measured binocular contrast sensitivity of sinewave gratings of 6 c/deg in the presence of different levels of monocular defocus. In the absence of defocus, the binocular sensitivity was about 42% higher than monocular. With increasing monocular defocus, the binocular sensitivity decreased steadily until it reached a level below the monocular, showing binocular inhibition. The clinical implications of binocular inhibition with monocular defocus are discussed.
Binocular contrast sensitivity with monocular glare disability
Authors: Pardhan Shahina , Gilchrist Jim
Published: December 2007

Glare disability plays an important part in the investigation and assessment of cataract. We investigated the effect of monocular glare disability on binocular contrast sensitivity. The magnitude of binocular summation was measured at different degrees of monocular glare disability. In the absence of glare, maximum binocular summation was shown. With increasing glare disability, the degree of binocular summation decreased steadily until binocular inhibition was produced. Binocular inhibition is defined as a reduction in binocular sensitivity to reach a level below the monocular. The clinical implications of binocular inhibition with monocular glare disability are discussed.
Comparison of the standard and Adams desaturated D‐15 tests with congenital colour vision deficiencies
Authors: Dain Stephen J. , Adams Anthony J.
Published: December 2007

The Adams desaturated D‐15 was designed to be administered to patients with acquired colour vision defects by simply reducing the chroma of the Munseli colours by 2 for each cap in the test. In this study, the performance of the Adams desat D‐15 in the assessment of congenital colour vision deficiencies is evaluated. The standard D‐15 and Adams desat D‐15 tests were administered to 75 congenital red‐green colour deficient subjects who had been diagnosed on the basis of their performance on the Nagel anomaloscope Mark 1. The results were analysed in terms of the direction, extent and specificity of errors and compared with the diagnosis on the Nagel anomaloscope. Of the 13 colour‐deficient subjects who made no errors on the standard D‐15, 1 failed the Adams desat D‐15 and 2 made single crossings. No colour‐deficient subject who failed the standard D‐15 made anything less than a simple inversion of adjacent caps on the Adams desat D‐15. The Adams desat D‐15 did not perform as well as the standard D‐15 in identification of the type of defect in dichromats. On the basis of these data, it is predicted that about 5% of dichromats will be mis‐classified by the Adams desat D‐15 whilst under 0.1% will be mis‐classified by the standard D‐15. However, with the anomalous trichomats, more crossings were made on the Adams desat D‐15, particularly by the milder anomals, and a diagnosis was possible in more cases. Where a diagnosis was possible, it was also correct more often with the Adams desat D‐15. The Adams desat D‐15 provides a useful sub‐classification of those who pass the standard D‐15. A choice of Munseli colours lying on confusion lines rather than by a simple universal reduction of chroma by two steps should provide a more reliable diagnosis of type of hereditary red‐green colour deficiency.
Vision screening of children: a review of methods and personnel involved within the UK
Authors: Bishop A. M.
Published: December 2007

The validity or vision screening of children for amblyopia, squint and significant degrees of ametropia is reviewed. The suitability of the tests used in screening, the age at which they are applied and the personnel involved is assessed. Some suggestions for improvement are made with particular reference to the optometrist's role, especially in view of the proposed child health surveillance scheme to be undertaken by selected general medical practitioners.
Referrals for suspected glaucoma: an International Glaucoma Association survey
Authors: Tuck M. W.
Published: December 2007

In a survey covering 275600 eye examinations by optometrists. 0.55% resulted in a referral to a medical practitioner for suspected glaucoma. Some 85 90% of the referred patients subsequently attended For examination by a consultant ophthalmologist. Of these, rather more than a third wore confirmed as having glaucoma, almost a third were discharged as not having the disease, and the diagnosis was borderline for the remainder. The survey's results imply that optometrists detect about 20000 eases of glaucoma in England and Wales each year.
Tear production and evaporation in the normal eye
Authors: Tomlinson Alan , Trees Gerald R. , Occhipinti Joseph R.
Published: December 2007

The volume of tears in the eye depends on ihe rate of production and the rate of elimination by drainage and evaporation. A mechanism for the regulation of tear production mediated through changes in tear tonicity has been suggested. High evaporation of tears with a patent drainage system has been thought to be related to reduced tear volume, increased tonicily and an eventual stimulus to production. In this study no significant correlation was found between tear evaporation, measured by a modified evaporimeter system, and tear production, as measured by the turnover rate with a scanning fluorophotometer. This result suggests that regulation of tear production through the mechanism of tonicity change may not be the only, or principal, mechanism in the normal eye.
Effect of a topical beta‐adrenergic receptor antagonist on the dynamics of steady‐state accommodation
Authors: Owens H. , Wrnn B. , Gilmartin B. , Pugh J. R.
Published: December 2007

The ocular accommodation response to a stationary near target exhibits microfluctuations which arc characterized by two dominant components of activity: a low‐frequency component (LFC: < 0.5 Hz) and a high‐frequency component (HFC: 1.0–2.2 Hz). We have shown recently that there is a significant correlation between the frequency of arterial pulse (AP) and the peak frequency of the HFC. If the mechanisms by which AP induces the HFC are intraocular they are likely to involve both rhythmic variations in choroidal blood flow and intraocular pressure (IOP) pulse: the former inducing changes in ciliary ring diameter from pulsatile blood volume changes in the ciliary body, the latter producing changes in effective lens power following small shifts in lens position or, with each drop in IOP. reduced resistance to inherenl lens substance and capsule elasticity. In addition to its well‐known ocular hypotensive effect, topical instillation of the beta‐ad renergic receptor antagonist timntol maleate has been shown to reduce significantly the magnitude of the IOP pulse, an effect that has been attributed to the vasoconstrictive action of the drug on the choroidal vasculature. Using li modified Canon IR optometcr we report on the effect of 0.5% timolol maleate on the accommodative microfluctuations for a group of 10 emmetropic subjects viewing a target monocularly at a distance of 25 cm. Following a double‐blind protocol against a saline control, timoloi was shown to reduce the rms for both LFCs and HFCs. An experiment to separate local from systemic effects involved four subjects whose treated and untreated eyes were examined to determine the effects of the consensual reduction in IOP: the results on microfluctuations in the untreated eyes were equivocal but the correlation between arterial pulse frequency and location of the peak frequency of HFC was maintained. The results show that factors relating to IOP and vasculature will affect the magnitude of accommodative microfluctuations.
Approximate matrix expression for the thickness of any lens generalized to allow for prism
Authors: Harris W. F. , Abelman H.
Published: December 2007

A single approximate matrix expression is derived that gives the thickness at any point on any lens. The lens may have dioptric power or prism power or both. The expression gives, amongst other things, the equation for lines of constant thickness.
Some visual, optometric and perceptual effects of coloured glasses
Authors: Wilkins Arnold , Neary Catherine
Published: December 2007

We examined 20 individuals who had worn coloured glasses (Irlen filters) for a period of at least 3 months and who claimed to find them beneficial. Sixteen had a history of reading difficulties. The performance of a variety of visual tasks was compared (1) using the coloured lenses; (2) using neutral density filters of similar photopic transmittance; and (3) using trial lenses to correct any residual refractive error. The coloured lenses appeared to reduce discomfort and susceptibility to a anomalous perceptual effects upon viewing grating patters. They also improved the speed of visual search by a small amount. The lenses had idiosyneratic effects on ocular muscle balance and acuity. They did not affect contrast sensitivity at a spatial frequency of 4 c/deg.
Dysthyroid eye disease masquerading as glaucoma
Authors: Currie Z. I. , Lewis S. , Clearkin L. G.
Published: December 2007

Intraocular pressure (IOP) screening by optometrists is increasingly prevalent. Although a raised IOP usually signifies glaucoma there can be other causes, notably dysthyroid eye disease, which those screening should be aware of The patients in the four cases presented were presumed to have glaucoma on the basis of raised IOPs, and three of them actually received medication. Because their optic nerves and visual fields showed no abnormalities this diagnosis was questioned and the cause shown to he dysthyroid eye disease. Thyroid eye disease causes raised IOP on upgaze due to a thickened inferior rectus identing the globe: however, in the primary position the IOP is normal, A misleadingly raised IOP can thus be found if tonometry is inadvertently done in upgaze, either because of poor patient positioning or Bell's phenomenon. Although some patients will have a past medical history of thyrotoxicosis, dysthyroid eye disease can occur in the absence of systemic or biochemical abnormalities. The important clinical signs are lid lag, lid retraction, raised IOP on upgaze and proptosis, the first three being the most common. Tonometry should thus always be done in the primary position and if raised IOPs are found without any of the other features of glaucoma, other causes particularly dysthyroid eye disease, should be considered.
Distance and near readings of associated heterophoria taken on 500 patients
Authors: Pickwell L. D. , Kayet N. A. , Jenkins T. C. A.
Published: December 2007

Distance and near readings of associated heterophoria were taken, using standard Mallett units, on 500 patients passing consecutively through an optometric practice and any symptoms, connected with distance and near vision, were noted. Complete sets of results were obtained on 383 people. Distance readings, either in size or direction, did not appear related to symptoms and such readings did not appear helpful in patient management. For near vision a fair degree of association existed between readings of associated phoria and symptoms and it was possible in the under 40 years and 40–59 years age groups to express clinically useful rules regarding the relationship. Over 60 years of age such a relationship was complicated by the fact that high degrees of exophoria readings existed in both symptomatic and asymptomatic patients and it is suggested that this may be related to the quality of binocular vision.
The suppression effect of simulated anisometropia
Authors: Simpson Trefford
Published: December 2007

Although there is evidence that differential interocular image clarity degrades binocular performance (for example, reducing stereo sensitivity) little is known about how this sensitivity reduction occurs, As there is evidence that suppression scotomas are induced in the more defocused eye. the presence and approximate size of suppression scotomas induced with uni‐ocular defocus was investigated in live binocularly normal subjects. The targets comprised a fusional lock and a suppression check For each eye and the task of each subject was to report the presence of the suppression check with varying amount of defocus. There was a range of simulated anisometropia over which suppression did not occur (approximately ± 0.50 DS). Thereafter the probability of suppressing a small foveal target increased approximately linearly until (the target was always suppressed. Greater amounts of simulated anisometropia produced larger suppression scotomas. However, less anisomeiropia was required to produce an equivalent sized suppression scotoma if greater amounts of fusional detail were provided. These results suggest that the decrement in binocular performance which accompanies simulated anisomeiropia may occur because of localized inhibition in the more defocused eye and is not solely due to loss of resolution in that eye.
The optical modelling of the human lens
Authors: Smith G. , Pierscionek B. K. , Atchison D. A.
Published: December 2007

The effect of varying lens shape factors and refractive index distribution on two lens performance characteristics (equivalent power and spherical aberration) are considered, using a mathematical model of the human lens which is based upon ellipsoidal iso‐indical contours. Values of radii of curvature based on the work of various authors are used to determine asphericity and these inferred values compared with previous measurements. Discrepancies are found and although asphericity has no effect on equivalent power, it does affect the spherical aberration. Based on preliminary findings of the refractive index distribution in the equatorial plane of human lenses, the index distribution is described by a polynomial in the Y (the distance from the optical axis in the equatorial plane), the coefficients of which are polynomials in Z (the distance along the optical axis). The shape of the index profile was found to have a, significant effect on the equivalent power and spherical aberration of the lens. The results indicate that more information on surface asphericity and accurate measurement of the index profile in the sagittal plane are required for more accurate modelling of the human lens.
Protection from acute exposure to ultraviolet radiation by ultraviolet‐absorbing RGP contact lenses*
Authors: Dumbleton† Kathryn A. , Cullen‡ Anthony P. , Doughty Michael J.
Published: December 2007

One eye in each of 12 female pigmented rabbits was irradiated with UVB while wearing an EqualensR I rigid gas‐permeable contact lens. The other eye served as a control. The irradiance level was 625 μ W cm ‐2 (285‐315 nm total band pass) with exposure times up to 2364s. Eyes evaluated 24 h and 48 h after exposure by biomicroscopy and pachometry, and later by scanning electron microscopy (SEM). The contact lens was found to protect the central cornea from radiant exposures up to 60 times threshold. The exposed areas of cornea showed characteristic ultraviolet damage with an arc of demarcation indicating the position of the lens. With time the area formed a ridge of damaged cells (confirmed by SEM). At radiant exposure over 0.75 J cm ‐2 some oedema was seen in the ‘protected’ region, apparently by extension rather than as a direct effect. These findings suggest that in the human being exposed to ultraviolet radiation this ultraviolet‐obsorbing RPG lens would permit nasal and temporal photoketatitis with sparing of the central cornea and provide some protection of more posterior ocular structures.
Influence of peripheral degradation on the identification of eccentric targets (revised)
Authors: Semmlow John L. , Pedrono Claude , Bonnin Thierry
Published: December 2007

When the peripheral Held is degraded, or ‘modulated', as occurs with certain corrective lenses, identification of a peripheral image requires combined head and eye movements to place the image within a relatively clear section of the Held. In such cases the time required to identify a peripheral object increases systematically. Previous experiments involving severely restricted peripheral fields (slit viewing) have indicated that the increase in identification lime is primarily determined by the dynamics of the head movement. Head movement characteristics, in turn, are related to the nature of the peripheral distortion. To describe more complex peripheral distortions, a ‘modulation’ function is developed which provides a realistic, quantitative measure of the deficit induced by a given distortion. Modification in head movement can be traced directly to the influence of this modulation function.
How optometrists screen for glaucoma: A survey
Authors: Strong N. P.
Published: December 2007

All optometrists registered and practising in Leicestershire were surveyed to find out what facilities they have for glaucoma screening, how patients are selected for screening, what tests are performed, and the criteria used for referring patients to the hospital ophthalmic service. All respondents examine the optic disc of all patients: Wu have tonometry available, but most use it selectively, on the basis of age family history and disc appearance. Although 88% have field testing apparatus, this is usually not of a type likely to be effective in screening a general population: 38% have automated or semiautomated perimetry. The criterion level of IOP at which 80% of respondents would refer was 27 mm Hg in the absence of disc cupping, falling to 24 mm Hg if cupping was suspected. Over 80% would refer any patient with a field defect irrespective of IOP.
Psychophysical measurement of the size and shape of the human foveal avascular zone
Authors: Bradley Arthur , Applegate Raymond A. , Zeffren Bernard S. , van Heuven W. A. J.
Published: December 2007

We have examined two psychophysical procedures for assessing the size and shape of the human foveal avascular zone (FAZ). Both procedures used a Maxwellan view system with a rotating beam to create a high contrast enioptie view of the retinal vasculature. Most subjects readily report a clear avascular zone surrounding their fixation point. The size of this FAZ was measured by (a) reducing the circular Maxwellian view field stop until it appeared to coincide with the edge of the FAZ, and (b) by tracing the boundary of the FAZ with a point source. Consistent with earlier angiogntphic and anatomical studies, the first method (N= 34 eyes) showed a mean FAZ diameter of 0.736 mm (area 0.42 mm2). FAZ diameter ranged from 0.46 to 1.13 mm (area 0.166–1.00 mm2) and the FAZ from the right and left eyes of each individual subject were very similar (r2= 0.863). The tracing technique (n= 24 eyes) showed that FAZ's were generally not spherical but well lit by ellipses with, on average, a major axis 17% longer than the minor axis. The maximum diameters of the FAZ tracings were very similar and significantly correlated with the circle diameters matched to the FAZ in experiment 1.
The use of colour difference vectors in diagnosing congenital colour vision deficiencies with the Farnsworth—Munsell 100‐hue test
Authors: Vingrys Algis J. , Atchison David A. , Bowman Kenneth J.
Published: December 2007

Colour difference vector analysis provides useful and meaningful information in scoring the Farnsworth–Munsell (FM) 100‐hue test. However, the FM 100‐hue test is limited in its ability to diagnose type and severity of congenital colour vision defect. Type classification for all subjects is incorrect in 21% of cases, and for deuteranomals the misclassification rate is 38%, Visual inspection of the plots yields a similar misclassification rate and classification of plots with few errors (under 180) is generally less reliable. The FM 100‐hue test has a limited ability to separate dichromats from anomalous trichromats. A test protocol based on joint DI5 and FM 100‐hue tests should pass 36% of anomalous trichromats and 26% of all colour defectives yet fail all dichromatic observers. We conclude that administering the FM 100‐hue test is of less value than a combination of D15 panels (Standard D15 and L'Anthony's desaturated D15) in the clinical diagnosis of congenital colour defective observers. Our results for the FM 100‐hue panel are similar to those reported previously by other investigators.
New method based on random luminance masking for measuring isochromatic zones using high resolution colour displays
Authors: Birch J. , Barbur J. L. , Harlow A. J.
Published: December 2007

A new method of measuring normal hue discrimination ellipses and dichromatic zones using a high resolution colour monitor is described. The lesl involves the detection of chromatic bars on a grey background (x= 0.305, y= 0.323) having a luminance of 34 cd m−2. Elements of the background matrix of square cheeks are varied randomly in luminance in space and time to provide random luminance masking (RLM) which compensates for differences in the relative luminous efficiency of different observers. The measurement technique provides a rapid and comprehensive colour vision test. Typical results are presented for normal trichromats. protanopes and deuteranopes without RLM and with the RLM sel of 25%. The size of the discrimination ellipse in normal observers is the same in both viewing conditions, hut the use of the RLM technique reveals the extent of the isochromatic zones in colour deficient observers.
Pupillary responses to stimulus structure, colour and movement
Authors: Barbur J. L. , Harlow A. J. , Sahraie A.
Published: December 2007

Pupillary responses to stimuli which favour the preferential stimulation of neural mechanisms invoked in the detection of visual attributes such as colour, spatial structure, movement and light flux changes on the retina have been measured and compared. Pupil responses in a decrement m stimulus luminance (i.e., a flash of darkness), suggest that at least three components are involved in this response, their relative contribution being determined largely by stimulus size. contrast and presentation time. A comparison of pupil responses to gratings of equal and lower space‐averaged luminance shows that the amplitude of pupillary constriction at grating onset for the equal luminance condition is about twice that measured with similar gratings in the lower luminance condition. Pupillary responses to chromatic isoluminant gratings are in general of longer latency when compared to responses of similar amplitude elicited by achromatic gratings. Small pupillary constrictions elicited by the onset of coherent movement in dynamic, random dot patterns are also demonstrated under stimulus conditions which eliminate pupillary responses to sudden light flux changes on the retina. The results support an earlier hypothesis which suggests that the onset of sudden changes in neural activity in the visual cortex when a visual stimulus is presented to the eye causes an overall perturbation which weakens transiently the regulatory inhibitory input to the pupillomotor nucleus. This, in turn, results in a transient increase in the efferent parasympathetic innervation of the iris sphincter muscle and hence the observed constriction of the pupil. The characteristics of the pupillary response reflect the properties of the mechanisms and the number of neurones which participate in the detection of each simulus attribute.
Non‐linear processes in perceived region segregation: orientation selectivity of complex channels
Authors: Graham Norma , Sutter Anne , Venkatesan Charu , Humaran Maria
Published: December 2007

Models incorporating linear spatial‐frequency‐ and orientation‐selective channels explain many aspects of visual texture segregation. The inability of such models to fully explain texture segregation results, indicates that non‐linear processes are also involved. One non‐linearity that has been suggested is complex channels consisting of two stages of linear filtering separated by a rectification‐type non‐linearity (much like cortical complex cells). Here we further demonstrate the usefulness of complex channels in explaining texture segregation results and investigate the orientation‐selectivity of the first stage of such complex channels. Our results suggest that the first stage is much more selective for orientation than are lateral geniculate nucleus cells, but that the first‐stage orientation bandwidth is rather wide with some interaction occuring between perpendicular orientations.
Geometrical optical analysis of photorefractive methods
Authors: Bobier W. R. , Campbell Melanie C. W. , McCreary C. R. , Power A. M. , Yang K. C.
Published: December 2007

Photorefractive methods allow rapid measures of the refractive and accommodative state of infants and young children whose brief attention and co‐operation limit the use of more traditional methods such as retinoscopy and autorefraction. Three methods have been defined: orthogonal, isotropic and eccentric, We provide a common geometrical optical analysis for these three methods where the photorefractive pattern is defined at the plane of focus of the camera. Since this plane is conjugate with the detector plane of [he camera then the critical optical parameters can be defined without reference to the design of the camera by simply determining the relative magnification of the projected image of an object photographed at the camera's plane of focus. Specifically the pattern width CF(mm) over a photorefractor's working range can be defined for the isotropic and orthogonal methods as:

image

and for the eccentric method as:

image

where
K is a myopic refractive error of the eye (dioptres)(K < 0)
P the distance of the flash source to the eye (dioptres)
L the distance in front of the eye of the camera's plane of focus (dioptres) (L < 0)
GH the pupil diameter (mm)
e the electricity of the flash source from the camera aperture (mm)
M magnification of the image measured relative to the camera plane of focus
Facilitation of pattern recognition by cuing foveation with the luminance centroid as origin of the frame of reference
Authors: Pavlovskaya M. , Vol I. , Blum B.
Published: December 2007

The strategy for visual information processing must vary with the specific situation. We assume that in recognition of pre‐learnt letter‐like patterns under time‐pressure conditions, mechanisms of selective intention arc involved. We propose that, with simple stimuli, foveation is to the luminance centroids of such patterns, and if normally the latter has to he computed by the brain, cuing such information should improve performance. This assumption was tested on three subjects with live stimuli. In confirmation of the working hypothesis, we found significant improvements in performance (p= 0.01 or better) for each of the stimuli, with cuing to ‘relevant’ as compared with ‘irrelevant’ sites, and also when the point of foveation was nearer to the ‘nodal’ site. It is concluded that in pattern recognition processes, nodal regions are computed, the luminance centroid for example, for simple pattern stimuli.
Binocular chromatic rivalry and single vision
Authors: Kulikowski J. J.
Published: December 2007

Depth perception is known lo be impaired for chromatic equiluminam patterns. To investigate this phenomenon I have compared the effects of hinocularly presented stimuli in the form of stripes, which contain only luminance information with similarly presented stimuli which contain on to chromatic information. Observations of the reported percepts for the two conditions demonstrate that mechanisms of colour vision tan impede stereopsis based on binocular fusion when the chromatic stripes are at, or even near, equiluminance, provided that their saturation is high. This observation is consistent with inhibitory interactions within the chromatic‐sensitive neuronal groupings in the visual cortex.
Visual evoked electrical and magnetic response to half‐field stimulation using pattern reversal stimulation
Authors: Harding G. F. A. , Armstrong R. A. , Janday B.
Published: December 2007

The visual evoked magnetic response to half‐field stimulation using pattern reversal was studied using a d.c. SQUID coupled to a second order gradiometer. The main component of the magnetic response consisted of a positive wave at around 100ms (P100M). At the lime this component was present the response to half‐field stimulation consisted of an outgoing magnetic field contralateral and extending lo the midline. When the left half Held was stimulated the outgoing field was over the posterior right visual cortex and when the right half field was stimulated it was over the left anterior visual cortex. These findings would correctly identify a source located in the contralateral visual cortex. The orientation of the dipoles was not that previously assumed to explain the paradoxical lateralization of the visual evoked potential. The results are discussed in terms of both electrical and magnetic models of the calcarine fissure.
Rules for colour constancy
Authors: McCann J. J.
Published: December 2007

Colours of objects lend to he constant regardless of the colour of the illuminam, therefore, regardless of the quanta catch of the retinal cones. Various mechanisms lor this including context recognition, adaptation of retinal sensitivities and independent processing by receptor types have been proposed. These present experiments test the hypothesis that colours are determined by the normalized relationship between all colours in the field of view. In this hypothesis, colours are constant in classical experiments simply because changes of the illuminant do not disrupt the relationship between quanta catches across the field of view. The experiments consist of making sets of colour displays: each with the same relative quanta catches, bui different absolute reflectances. ‘Colour tautomi’ arrays of five colour patches were printed using controlled amounts of yellow, magenta, cyan and black toners. The experiment began with a control ‘colour tautomi’ array of reflectances with measured relative quanta catches. New arrays of colours were then chosen that increased (or decreased) the reflectances, and quanta catches, a constant amount for the entire array. These changes were done independently for each receptor type. When these ‘colour tautomi’ are viewed in the room, each array has a different set of colours. When viewed in a restricted field of view, all arrays appear the same. In a further experiment new areas such as white are added lo the display. Colour constancy is a field phenomenon controlled by the relative quanta catches in the field of view. Absolute colour constancy is controlled by the relative quanta catches in the field of view and the absolute quantum catches of the receptors.