bluuebunny/crossref_metadata_2025 huggingface dataset:
A REVIEW OF THE THEORETICAL CONCEPTS, MEASUREMENT SYSTEMS AND APPLICATION OF CONTACT LENS OXYGEN PERMEABILITY
Authors: Brennan Noel A. , Efron Nathan , Holden Brien A. , Fatt Irving
Published: December 2007

Abstract— The interest in rigid gas‐permeable contact lenses for extended wear has prompted a re‐evaluation of the theoretical and practical aspects of the oxygen transport characteristics of contact lens materials. Oxygen permeability has been considered by some authors to be a parameter which is dependent upon the measurement conditions; however, this paper demonstrates that an intrinsic permeability coefficient may be derived for a given material when the basic principles of the transport mechanisms are considered. Two basic methodologies have been described for measuring oxygen permeability—dual‐chamber and electrochemical methods, the latter being the more popular. Although consistency in measured oxygen transmissibility of a given lens may be achieved among laboratories, current analytical techniques do not allow the intrinsic permeability coefficient of materials to be determined. Future research should be directed towards developing methods to fully correct for surface and edge effects, and to achieve standardization among laboratories.
SIMULATION OF A RETINAL SCOTOMA BY A STABILIZED RETINAL IMAGE
Authors: Foley‐Fisher J. A. , Murphy K. St. J.
Published: December 2007

Abstract— Two methods are described for simulating a retinal scotoma by means of a stabilized retinal image, hence allowing some aspects of the impairment of visual function associated with scotomas to be studied in observers with normal visual fields. In the first method, an optical lever arrangement is used to generate a small artificial scotoma at a controllable position with 15° field of view. The second, direct attachment, method uses a tight‐fitting scleral contact lens, to which is attached a very light, aluminium‐alloy tube. This carries a small piece of lightweight black card, the stabilized image of this card generating the scotoma. Although precise positioning of the scotoma is more difficult with the second method, the induced scotoma is absolute and the method is relatively cheap and easy to implement.
FIXATION DISPARITY IN BINOCULAR STRESS
Authors: Pickwell L. D. , Jenkins T. C. A. , Yetka A. A.
Published: December 2007

Abstract—Fixation disparity has been taken as a sign of stress on binocular vision because it is established that prism stress creates fixation disparity. This paper looks at the effect on fixation disparity of the stress caused by requiring subjects to read in inadequate illumination. It is found that the reduction in illumination does not in itself immediately change the magnitude of the fixation disparity. There is, however, an increase in the mean slope of the central part of the fixation disparity curve which suggests that when the effect of reduced illumination is added to prism stress, fixation disparity is increased. The stress created by asking subjects to read in reduced illumination for half an hour resulted in the mean associated heterophoria being increased, and over half the subjects reported symptoms of stress. It is concluded that fixation disparity is changed by this type of visual stress in some subjects, and in near vision is increased to a more marked degree of exo‐disparity. Most of this increase occurs in the first ten minutes.
RELIABILITY OF THE WETTING VALUE OF TEARS
Authors: Loran D. F. C. , French C. N. , Lam S. Y. , Papas E.
Published: December 2007

Abstract—The wetting value is the length of a S̀chirmer strip wetted in millimetres for a 5 min test period plus the length of time in seconds for dry spots to appear and has been suggested as a better prognostic test than its components in isolation (Fanti and Holly, 1980). Parameters of these procedures are examined and important shortcomings in the derivation of wetting value discussed. Reliability figures are presented for the Schirmer, tear break‐up and wetting value tests. The norms obtained for the tear break‐up test are substantially different from those usually assumed and we recommend that practitioners should therefore rely on their own norms rather than published values.
A SURVEY OF VISUAL DEFECTS ON TRISTAN DA CUNHA, 1984
Authors: Harwood K. A.
Published: December 2007

Abstract—This paper gives data, obtained during 1984, on the incidence of refractive error and ocular disease in the small, isolated island community of Tristan da Cunha in the South Atlantic. In general, despite inevitable consanguinity among the population of less than 300, ocular health is good.
THREE SOUTH AFRICAN STUDIES ON THE RELATION BETWEEN ROAD ACCIDENTS AND DRIVERS‘ VISION
Authors: Humphries Deryck
Published: December 2007

Abstracl—This report describes three studies of drivers' vision which have recently been carried out in South Africa. In the first, it was found that younger myopes constituted a substantial fraction of those drivers who failed to reach the acuity standards required for a South African driving licence: the acuity of almost all these drivers could be raised to an adequate standard by a proper refractive correction. In the second study, a comparison of the visual characteristics of a group of drivers who had been involved in accidents with those of a control group of accident‐free drivers suggested that the former had mean acuities and depth perception which were worse than those of the accident‐free group by small but statistically significant amounts. A third study, comparing the visual acuities of a group of randomly selected drivers with those of a group who had been involved in road accidents, showed that a higher proportion of the accident group had acuities which were below that required by the licensing authority.
TIME COURSE AND DECAY OF EFFECTS OF NEAR WORK ON TONIC ACCOMMODATION AND TONIC VERGENCE
Authors: Wolf Karen S. , Ciuffreda Kenneth J. , Jacobs Steven E.
Published: December 2007

Abstract Changes in tonic accommodation and tonic vergence were monitored before, during and immediately after a 45 min period of reading adult level text displayed on either a computer monitor or hard copy at 20 cm under binocular viewing conditions. Both tonic accommodation and tonic vergence gradually increased during the reading period, with changes in tonic accommodation occurring more rapidly. The average increases in tonic accommodation and tonic vergence following reading were 0.35 dioptres and 0.38 metre angles, respectively. Decay of both tonic components to the baseline in either light or total darkness occurred within the first 3 min. These results suggest that a moderate period of interrupted reading at a close distance can produce a transient increase in the tonic oculomotor levels.
ON THE USE OF SMALL ARTIFICIAL PUPILS TO OPEN‐LOOP THE ACCOMMODATION SYSTEM
Authors: Ward P. A. , Charman W. N.
Published: December 2007

Abstract Monocular accommodation responses to stimuli at vergences from 0 to‐4.5 D (i.e. effective object‐eye distances from infinity to 22 cm) were measured objectively using artificial pupils of 0.5,0.75, 1.0 and 3.0 mm diameters and a constant retinal illuminance of 7000 td. The slopes of the response/stimulus curves for the 0.75, 1.0 and 3.0 mm pupils agree with those reported previously. The 0.5 mm pupil produced open‐loop accommodation, no systematic change in accommodation being observed as the stimulus vergence was varied. However, the response drifted considerably with this pupil diameter.
The effect of mydriasis on the pupillary centration of the human eye
Authors: Walsh G.
Published: December 2007

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 have been derived for two eyes for centration changes of 0.2 mm. The importance of these changes in the formation of the retinal image, and hence on visual performance, is discussed.
Varifocal spectacle lens surface power measurement
Authors: Fowler C. W. , Sullivan C. M.
Published: December 2007

An instrument is described for the assessment of varifocal lens surfaces based on a reflection technique. Results are also presented of measurements made on a series of lenses of the same design, illustrating some of the differences that exist between glass and plastics versions of the same lens.
The spherical aberration of intra‐ocular lenses
Authors: Smith G. , Lu Cheng‐Wan
Published: December 2007

Seidel aberration theory shows that the spherical aberration of a spherically surfaced intra‐ocular lens cannot be made zero but only minimized and that the optimum shape is independent of the aberration of the rest of the eye (i.e. the cornea). The optimum shape of an intra‐ocular lens correcting for spherical aberration is almost plano‐convex with the more curved surface facing the cornea. The resulting total Seidel spherical aberration of the whole eye cannot be made zero unless the cornea has an asphericity much higher than the population mean.
Techniques and developments in automated perimetry: A review
Authors: Wild† J. M.
Published: December 2007

The development of automated perimetry represents one of the major opportunities for clinical advancement over the last 30 years. Compared with the data obtained from equivalent manual procedures, the technique now makes feasible a rapid and reliable static threshold investigation of the visual field and, as a result, has revolutionized the potential of the visual field examination in the diagnosis of ocular and neuro‐ophthalmic abnormality. Several perimeters are commercially available, each featuring a variety of stimulus parameters for investigating the visual field and a range of data reduction techniques and displays to aid the clinician in the interpretation of abnormality. The choice of stimulus, however, governs the format of the derived field and thus the efficiency of detecting and assessing a given field defect. In addition, patient‐specific variables also influence the visual field profile. This review outlines the techniques used in automated perimetry. In particular, the rationale is summarized for the choice of the major stimulus parameters employed by a given perimeter, such as stimulus type, adaptation level and testing strategy. The techniques available for data display and reduction are reviewed and the extraneous factors influencing the format of the normal differential sensitivity gradient are discussed.
Referrals and notifications by British optometrists
Authors: Port M. J. A. , Pope C.A.
Published: December 2007

1031 British optometrists completed a questionnaire to give information on their rates of referral and notification to the medical profession. Data were collected in relation to the conditions concerned, the age and sex of the patient, and the spectacle correction. Major causes of referral were cataract, glaucoma, fundus changes, headaches/migraine/eye pain and lowered visual acuity; 6.5% of all patients seen were referred to their general medical practitioner notified, and of this group it was estimated that 25–30% could have managed with reading glasses which comprised spherical lenses of equal power. If such glasses could be self‐selected, without reference to a medical practitioner or optometrist, a significant number of people would not would not benefit from the health screening aspects of the eye examination.
Reduced aniseikonia in axial anisometropia with contact lens correction§
Authors: Winn B. , Ackerley R. G. , Brown C. A. , Murray F. K. , Paris J. , John M. F. St.
Published: December 2007

Aniseikonia, although present in isometropia, is associated principally with anisometropia and is widely thought to be the result of differences in the retinal image size presented to each eye. This assumes that equating retinal image size results in congruous cortical images. To test this assumption 1 refractive and 17 axial anisometropic subjects were examined to determine the aniseikonia present when corrected with spectacles and contact lenses. Contrary to many previous predictions, based upon Knapp's Law, the presence of equal retinal images resulted in larger aniseikonias than observed when the eyes were presented with unequal retinal images. This suggests that non‐optical components have a significant role in the production of the cortical image, and this therefore requires a shift in the way the management of anisometropia is considered clinically. Contact lens correction maintains the aniseikonia at a minimum level in axial as well as refractive anisometropia and offers the clinician an acceptable practical alternative when prescribing for these patients.
Factors affecting the normal perimetric profile derived by automated static threshold LED perimetry. I. Pupil size
Authors: Wood J.M. , Wild J.M. , Bullimore M.A. , Gilmartin B.
Published: December 2007

The relationship between pupil size and perimetric sensitivity was investigated in group of clinically normal emmetropic subjects using the Dicon AP3000 computer‐assisted perimeter at bowl luminances of 10 asb and 45 asb. Pupil size was modified with the motic thymoxamine 0.5% and the mydriatic phenylephrine 10%; saline was used as the control. Perimetric sensitivity increased with an increase in pupil size. The effect was greatest for peripheral locations for both bowl luminances. The fluctuations in perimetric sensitivity increased with peripheral angle and with decrease in pupil size for both bowl luminances.
Sequential visual reaction times
Authors: Artigas J.M. , Felipe A. , Campbell F.W.
Published: December 2007

The reaction‐time to a series of successive digits was measured on two subjects. After practice, it was found that whilst the reaction time to the onset of the series was constant at 150 ms, the response time to additional digits became less and less to asymptote to a level of about 50 ms. The time course of this ‘chorus‐line’ phenomenon was studied in greater temporal detail by varying the interval in steps of 20 ms. The effect was greatest at 200 ms. Thereafter, it declined and for long intervals reached the value of a standard reaction time. On a third inexperienced subject, the learning period was established; this was about 300–400 presentations. The implications of these findings are discussed against the background of everyday visual motor behaviour.
A BASIC computer program for schematic and reduced eye construction*
Authors: O'Keefe L.P. , Coile D.C.
Published: December 2007

A simple computer program for calculating schematic and reduced eyes is presented. The user supplies distances from the front of the eye and radii of curvature of refractive surfaces (anterior and posterior cornea and lens), distance to retina, and refractive indices of ocular media (cornea, aqueous, lens, vitreous). These values are input to calculate the necessary parameters for construction of a schematic and reduced eye, using Gaussian formula and assuming a homogenous lens. The program produces powers of optical components and of the whole eye, cardinal points of the eye, and estimates of refractive state and retinal image size. These values may be printed in tabular form or plotted to scale with a graphics plotter. The program simplifies construction of schematic eyes by allowing rapid recalculation of the eye after changing one or more input parameters.
The use of accurate visual acuity measurements in clinical anti‐cataract formulation trials
Authors: Elliott David B. , Sheridan Michael
Published: December 2007

A standardized visual acuity technique is presented for use in anti‐cataract drug trials. Ferris Logmar charts were used in repeatability studies of vision, visual acuity and pinhole visual acuity measurements for twenty normal subjects (mean (±SD) age 64 ± 6.3 years). Visual acuity measurements were shown to be the most repeatable and thought to be the most suitable for monitoring cataract progression. Repeated visual acuity measurements were made on 29 cataractous eyes of 15 subjects (mean (±SD) age 67.8 ± 7.2 years). A Logmar score change of 0.1 (one line) was shown to be a statistically significant change. This value can be used in statistical analyses of drug efficacy. The normal data gives a mean Logmar visual acuity of 1.15 (Snellen equivalent 6/5). This indicates the inadequacy of using 6/6 as a norm value for visual acuity, even for older patients. As the possibility of reversal of cataract theoretically exists in the early stages of cortical and capsular cataracts, patients with small amounts of these types of cataract are ideal patients for anti‐cataract formulation trials. The normal visual acuity results indicate that the inclusion criteria for clinical trials can include patients with cataracts with visual acuity as good as 6/6.
The recognition and management of albinism
Authors: Abadi Richard , Pascal Eve
Published: December 2007

Albinism is not a single entity but represents a heterogenous group of inherited disorders of pigmentation. Despite a wide variety of manifestations, all forms of albinism are characterized by several ocular features, including: nystagmus, photophobia, reduced visual acuity and a lack of stereopsis. It is the intention of this review to describe and discuss the clinical implications of albinism with particular emphasis placed on these ocular features and their effects on visual performance. Various techniques that may be employed to aid the albino will also be described.
Influence of thymoxamine eye‐drops on the mydriatic effect of tropicamide and phenylephrine alone and in combination
Authors: Shah B. , Hubbard B. , Stewart‐Jones J. H. , Edgar D. F. , Turner P.
Published: December 2007

In a preliminary experiment in 12 healthy young volunteers, one drop of thymoxamine 0.5% instilled into the conjunctival sac completely reversed the mydriasis produced by phenylephrine 2.5%, 5% and 10% after 20 minutes. In a second study in eight volunteers, thymoxamine 0.5% completely prevented the mydriasis produced by phenylephrine 2.5% and produced a miosis. It also completely reversed the mydriasis produced by tropicamide 0.5%. The mydriatic effect of tropicamide 0.5% plus phenylephrine 2.5%, however, was not completely reversed by thymoxamine 0.5% over a period of 180 minutes. Phenylephrine, tropicamide and thymoxamine are freely available for use by registered optometrists.
Clinical evaluation of the Humphrey auto refractor
Authors: Yeow P.T. , Taylor S.P.
Published: December 2007

A study is made of the accuracy and repeatability of the Humphrey autorefractor (HAR) objective refraction for different refractive groups as measured against subjective refraction. The value of the autofogging mechanism in objective refraction for different refractive groupings is assessed.
The effect of accommodative hysteresis on apparent distance
Authors: Fisher S. K. , Ciuffreda K. J.
Published: December 2007

The influence of accommodative hysteresis on monocular distance perception was examined in 18 visually normal young adults. Tonic accommodation and apparent distance were measured immediately before and after a 10 minute period of sustained focus at either the accommodative nearpoint or farpoint. Separate sessions were used for the two sustained focus conditions. On each session, apparent distance was assessed for both a highly effective and a non‐effective accommodative target viewed at a constant optical distance of 3 D. Sustained focus at the nearpoint resulted in a significant increase in the apparent distance of the highly effective accommodative target, as well as in tonic accommodation. Sustained focus at the farpoint yielded a slight decrease in tonic accommodation, but no significant alteration in the apparent distance of the highly effective accommodative target. No tendency for change in the apparent distance of the non‐effective accommodative target was observed under either the nearpoint or farpoint condition. The results suggest that accommodative distance information is linked to the level of monocular blur‐driven accommodative innervation necessary for clarity of focus.
Multiple applications of the NCT: an assessment of the instrument's effect on IOP
Authors: Russell G. E. , Bergmanson J. P. G. , Godio L B.
Published: December 2007

The feasibility of the American Optical Non‐Contact Tonometer as an instrument for tonography was assessed. It was found that after 20 measurements in quick succession, there was a statistically insignificant change in IOP. Multiple intraocular pressure (IOP) readings with this instrument are helpful in determining an abnormally high IOP from an aberrant recording.
Axial chromatic aberration of the human eye: frequency or wavelength?
Authors: Pease Paul L. , Barbeito Raphael
Published: December 2007

The axial chromatic aberration of the human eye is nearly perfectly described by a linear function when expressed in terms of frequency rather than wavelength. Since linear functions are simple to work with and more readily understood, there are advantages for the expression of these data in terms of frequency.
Corneal asphericity and refractive error
Authors: Sheridan Michael , Douthwaite William Arthur
Published: December 2007

The relationship between corneal curvature measured by classical keratometry and refractive error raises the question of a possible systematic relationship between refractive error and the degree of corneal asphericity. A recomputation and analysis of previously published data leads to the conclusion that the different refractive groups have similar values of the parameter ‘p’ and differ only in the apical radius of the cornea.
The effect of pupil size on static and dynamic measurements of accommodation using an infra‐red optometer
Authors: Winn B. , Pugh J.R. , Gilmartin B. , Owens H.
Published: December 2007

The study examines to what degree the output of the Canon Auto‐ref R1 infra‐red (IR) optometer is affected by variations in pupil size for both static measurement of refractive error and for continuous recording of accommodation when switched to its modified mode of operation. In the normal static mode of operation the measurement of refractive state simply depends on the position of the peak photodetector output for each of three meridians: it does not depend on signal amplitude and hence pupil size. However, in continuous mode the actual output of a single photodiode is measured and the measurement is susceptible to changes in pupil size that occur within the area of the exit pupil utilized by the instrument. Using static and dynamic recording on model and human eyes the study shows that a 10% reduction in output signal relative to the maximum output level (for a constant stimulus) occurs for pupil sizes of 3.9 mm. The relatively small exit pupil has important advantages with regard to the use of mydriatic drugs and task‐induced changes in pupil diameter.
Causes of blindness and partial sight in the Bradford Metropolitan District from 1980 to 1985
Authors: Yap Maurice , Weatherill John
Published: December 2007

A retrospective review of the BD8 forms submitted for the period 1980–85 in the Bradford Metropolitan District was conducted to ascertain the incidence and causes of blindness and partial sight. A total of 1485 cases were registered in this period of which 755 (50%) were included in the Blind register and 730 (49.2%) in the Partially Sighted register. Age‐related macular degeneration was the most important cause of visual handicap, accounting for 43.9% of all registrations, followed by glaucoma (16.2%), diabetic retinopathy (6.3%), myopic degeneration (6.1%), optic atrophy (4.4%), cerebrovascular disease (3.8%), cataracts (3.6%), retinal vascular occlusive disease (3.2%), corneal opacities (3.0%), congenital anomalies (2.7%), retinitis pigmentosa/tapeto‐retinal degeneration (1.9%), retinal detachment (1.8%) and others (3.1 %). The ratio of female to male registrations was 1.8:1. Eighty‐four per cent of this sample population was above the age of 60 years at the time of registration.
Anthropometry for children's spectacle frames
Authors: Kaye Janice , Obstfeld Henri
Published: December 2007

Facial measurements of 154 Caucasian children aged 5–14 were taken, to provide statistical information for spectacle frame manufacturers. The main differences compared with adult measurements were in the following dimensions: temple width, head width, bridge height, projection, splay angle and front to bend. The range of the ‘distance between rims’ measurement of adults, was similar to that of children. A number of differences between this group and a small group of Afro‐Caribbean children was encountered.
Detection of change of size by young and old observers
Authors: Bowman Kenneth J. , Brown Brian
Published: December 2007

Thresholds for detecting change of angular size were determined for a range of angular separations in young and elderly observers. We found no differences in thresholds between these subject groups. Thresholds for detection of change of visual angle increased with angular separation in a power function relationship. Angular size change judgements based on successive views of a target are apparently not significantly affected by age.
Spatial summation in young and elderly observers
Authors: Brown Brian , Peterken Carolyn , Bowman Kenneth J. , Crassini Boris
Published: December 2007

We measured detection thresholds for targets over a range of sizes at both photopic and scotopic luminance levels in young and elderly observers, and used these data to estimate spatial summation areas 10 degrees in the retinal periphery. There were differences in detection thresholds between the young and old groups at photopic and scotopic luminances, but no differences in spatial summation areas at either background luminance level.
An analysis of three meridional keratometric measurement of the anterior corneal surface
Authors: Royston J. M. , Dunne M. C. M. , Barnes D. A.
Published: December 2007

Analysis of measurements taken in three meridians of a toroidal optical surface can produce a spherocylindrical result without having to locate the principal meridians. This technique is assessed for the anterior corneal surface using keratometry. Good agreement is found with measurements taken in the principal meridians making this a suitable method for the assessment of the eye's optical surfaces by Purkinje image measurement.
Visual conversion reaction in children
Authors: Barnard N. A. S.
Published: December 2007

Visual conversion reaction (VCR) is a psychosomatic illness that will occasionally be seen by optometrists and ophthalmologists. This paper discusses some of the possible aetiologies and manifestations of the condition. Investigation and management of children with suspected VCR is discussed. Four case histories are presented in which signs of VCR included amblyopia, reduced accommodation and a deterioration in handwriting. The visual field defects presented include a static quantitative anomaly. Such a defect has not previously been reported.

‘Just as you ought not to attempt to cure eyes without head or head without body, so you should not treat body without soul’ (Socrates)
The accommodative contribution to binocular vergence eye movements
Authors: Hesler Janet , Pickwell David , Gilchrist Jim
Published: December 2007

Forced vergence fixation disparity curves were generated for both with and without an accommodative stimulus (accommodative closed and open loop conditions respectively) for fifteen asymptomatic subjects. All subjects exhibited an exophoric shift in fixation disparity for the accommodative open loop condition at the forced convergence side of the curve. No corresponding bias was found at the forced divergence side of the curve. The findings are discussed in terms of the results of previous studies and the existing models of vergence eye movements.
A quasistatic study of pupil and accommodation after‐effects following near vision
Authors: Tsuchiya Kunihiko , Ukai Kazuhiko , Ishikawa Satoshi
Published: December 2007

The study examines the effect of a near task on immediate post‐task measures of pupil size and accommodative state. The method of quasistatic measurement of accommodation was used and pupillary changes elicited by the accommodative stimulus were simultaneously recorded using an infrared video‐pupillometer. This method requires a short (typically 2 minutes) but strong (up to 10 D in most subjects) near‐vision effort, with the accommodative and pupillary responses being recorded before, during, and after the task. The results show pupil after‐effects to be more pronounced than tonic accommodative after‐effects. Inter‐individual difference in after‐effects is large. The pupil after‐effect was dissociated from the tonic accommodation after‐effect and lasted in some cases for more than 15 minutes. The pupil after‐effect was not masked by darkness. It is proposed that monitoring the changes of pupil is valuable when assessing the after‐effects of sustained near vision.
The path to presbyopia: straight or crooked?
Authors: Charman W.N.
Published: December 2007

The non‐linear trends in the mean amplitude of accommodation with age that are observed in transverse studies as presbyopia is approached can be explained in terms of the summated effect of many individual linear trends. Increases in the near addition that may be required by patients after their early fifties are probably associated with an age‐dependent decrease in acuity, which necessitates a closer working distance to increase angular subtense, rather than with any continuing decline in accommodation.
Binocular summation in visually evoked responses and visual acuity
Authors: Heravian J. S. , Jenkins T. C. A. , Douthwaite W. A.
Published: December 2007

Monocular and binocular transient visually evoked responses (VER) were recorded on 50 adult subjects using a pattern reversal stimulus (check size 5.5 min arc). The peak‐to‐trough amplitude of the VER wave was measured and compared with the subjective visual acuity (Landolt C). The binocular amplitude enhancement over the monocular amplitude was around 26% across the acuity range studied, whereas the mean binocular subjective visual acuity improvement was around 11.3%, but this varied from 1% at the high acuity end to 17% at the low acuity end of the range.
Effect of illuminance on the directions of chromostereopsis and transverse chromatic aberration observed with natural pupils
Authors: Simonet Pierre , Campbell Melanie C. W.
Published: December 2007

The direction of chromostereopsis observed with a natural pupil and the direction of the monocularly perceived disparity between coloured targets (F and C lines—486 and 656 nm) have been measured in a sample of 30 subjects at 10 and 1000 lx. At both illumination levels approximately equal numbers of subjects perceived positive and negative chromostereopsis. When the ambient illumination was increased, a reversal in the direction of the chromostereopsis occurred for 16 subjects. For six of them a change from a positive to a negative chromostereopsis was observed, a pattern not reported in previous studies. In most cases at both high and low illuminance, there was an absence of perception of a monocular disparity (transverse chromatic aberration), although chromostereopsis was reported, indicating that binocular information can be obtained from sub‐threshold monocular disparities. At low illuminance, the lack of correlation between the direction of chromostereopsis and transverse chromatic aberration (TCA) may indicate that there may be a supplementary binocular factor in chromostereopsis.
Differences in the legibility of letters at contrast threshold using the Pelli‐Robson chart
Authors: Elliott David B. , Whitaker David , Bonette Lorraine
Published: December 2007

One disadvantage of using high‐contrast letters as test objects when measuring visual acuity is the fact that they are not of equal legibility. A number of charts are now commercially available that assess contrast sensitivity using letter targets. This study attempted to assess the legibility of letters at contrast threshold on the Pelli‐Robson letter contrast sensitivity chart by determining the percentage of correct responses for each of the ten Sloan letters at contrast threshold. Results of 493 contrast sensitivity measurements taken in optometric practice indicated that there is a definite difference in legibility between letters at contrast threshold as for letters at acuity threshold. The data suggest that the probability of correctly identifying two out of a group of three letters at threshold on the Pelli‐Robson chart varies between 67% and 97% due to letter type alone. Because of the very regular and pronounced miscalling of the letter C as an O, we suggest that this should be accepted as a correct call during threshold measurements on the Pelli‐Robson chart. This helps to balance the legibility of different groups of letters.
Concurrent visual conversion reaction and simulated colour vision defects in a 12‐year‐old child
Authors: Barnard N. A. Simon , Birch Jennifer , Wildey Helen
Published: December 2007

Visual conversion reaction (VCR) is a psychosomatic anomaly which occasionally manifests in children, most commonly in the form of reduced vision and visual field defects. Malingering or conscious simulation for secondary gain would appear to be rare in children but occasionally VCR and simulation coexist. A case history is presented of a 12‐year‐old child with behavioural and reading difficulties who manifested reduced vision most probably attributable to VCR and severe colour deficiency, which was best explained in terms of simulation or malingering.
Meibomian gland dysfunction: some clinical, biochemical and physical observations
Authors: Ong B. L. , Larke J. R.
Published: December 2007

Dysfunction of the meibomian glands resulting from contact lens wear has recently been recognized. This study shows that 30% of lens wearers develop some degree of meibomian gland dysfunction after 6 months of wear whereas only 20% of non‐lens wearers have similar problem. Thirty‐three per cent of the male wearers have dysfunctioning glands compared with 28% of female wearers. The incidence does not depend on the type of lenses worn. There was no detectable differences between the composition of the abnormal fluid secreted by the dysfunctioning glands and the clear fluid coming out of the normal unblocked glands, as shown by thin layer chromatography. On studying the melting point of the lipids, we found that material from abnormal glands melted at approximately 3°C higher than the normal fluid.
Accommodative responses to naturalistic stimuli
Authors: Ciuffreda Kenneth J. , Rosenfield Mark , Rosen Jay , Azimi Abbas , Ong Editha
Published: December 2007

Steady‐state accommodative responses to a wide range of commonly encountered textural and graphic stimuli were investigated in 12 young, visually normal subjects. Details of two experiments are described. In the first experiment, stimuli were varied in terms of size, contrast, spatial frequency, colour and intellectual demand. In the second experiment, only the colour of the targets was systematically altered. In both experiments the stimulus demand was maintained at 3 D, and accommodation was measured subjectively using a Hartinger coincidence optometer. No significant difference in mean accommodative response was observed between the widely differing targets adopted in either experiment. These findings suggest that an overall threshold exists for accommodative stimuli, with supra‐threshold targets of low to moderate contrast being capable of initiating and sustaining an appropriate accommodative response.
An evaluation of techniques for measuring stereopsis in infants and young children
Authors: Broadbent Helen , Westall Carol
Published: December 2007

Demonstrating stereopsis is valuable in vision screening of infants and toddlers, since its presence rules out the possibility of profound visual deficits. We assessed the performance of 55 infants and young children on three clinically available tests, the Lang, the Frisby and the TNO. The results were compared with those found using a computerized dynamic random dot stereogram.

Most of the children tested were under 3 years of age and 10 were aged under 1 year. The Lang test was passed by 74%, including 50% of those under 1 year. The Frisby test was passed by 65%, but by only 20% of infants under 1 year. Forty‐nine per cent passed the TNO test; none were under 1 year. The computerized stereogram was passed by 42.5% of those tested, including 100% of those over 3 years old. Both this test and the TNO presented difficulty in testing infants between 8 months and 2 years because of the increased likelihood that these children would reject the red/green glasses.

We recommend that the most appropriate stereotest is largely based on whether the child will tolerate red/green glasses. We would use the dynamic random dot test for infants under 8 months of age, the Lang or Frisby stereotest for infants from 8 months to 30 months, and the TNO or dynamic random dot stereogram after this age.
The reliability of the Pelli‐Robson contrast sensitivity chart
Authors: Elliott David B. , Sanderson Kay , Conkey Alison
Published: December 2007

Normative contrast sensitivity (CS) data were obtained using the commercially available Pelli‐Robson chart from the dominant eye of 30 young (mean (±SD) age 22.5 ± 4.3 years) and 42 older (mean (±SD) age 70.2 ± 6.7 years) subjects with normal healthy eyes. The majority of young subjects were found to have a CS of 1.80 log units or above. The majority of the older subjects were found to have a CS of 1.65 log units or above. CS results were obtained using both sides (A and B) of the Pelli‐Robson chart from 30 (15 young and 15 older) of these subjects. These measurements were repeated under identical conditions, 2 weeks later. There was no significant difference between the results from sides A and B of the chart. The CS scores were shown to be repeatable to within ±0.15 log units or ±1 step. Therefore a significant change in CS score is +2 steps or 0.30 log units. Slight improvements in reliability could be obtained by more careful permutation of letters on each step and a smaller step size. The restriction against these changes is the ensuing increased chart size.
The aspherizing of intra‐ocular lenses
Authors: Lu Chengwan , Smith George
Published: December 2007

While a spherically surfaced intra‐ocular lens cannot be designed to give zero spherical aberration for the whole eye, aspherizing one surface of an intra‐ocular lens can produce zero Seidel spherical aberration in a pseudophakic eye or set it to any desired level provided the corneal asphericity is known and this does not change with the operation. Equations for determining the asphericities are given. Asphericities for five lens shapes; the minimum spherical aberration lens and its reverse form, the equi‐biconvex lens, the plano‐convex lens and its reverse form are determined. The Seidel aberrations of eyes with aspherized intra‐ocular lenses were compared with that of eyes with spherical intra‐ocular lenses. While aspherizing eliminates the Seidel spherical aberration, some residual higher order spherical aberration exists and the amount of this residual spherical aberration depends upon the lens shape. However, this residual aberration can be reduced but not made zero by modifying the asphericity. For currently used plano‐convex lenses, only the curves surface can be aspherized. The effect of variations in the anterior corneal asphericity on the necessary lens asphericity was also investigated.
Prism adaptation and viewing distance
Authors: North Rachel V. , Sethi Begum , Owen Katharine
Published: December 2007

Previous studies have shown that subjects with normal binocular vision adapt to prism‐induced phorias. However, there are conflicting reports as to the amount of adaptation shown to horizontal prisms. Some investigations found a greater amount of adaptation to base out prisms compared with base in, whilst others found the reverse and one study found no adaptation to base out prism at all. This study investigated the adaptation response to horizontal prisms at distance and near in a larger number of subjects (n = 40). The results confirmed our previous findings and showed that at distance the adaptation responses are asymmetrical, there being a significantly greater amount of adaptation to base out prism compared with base in, whilst at near the responses are virtually symmetrical. Possible reasons for these findings are discussed.
Use and non‐use of low vision aids by visually impaired children
Authors: Leat Susan J. , Karadsheh Sahar
Published: December 2007

The results of this study indicated that children do use and benefit from low vision aids and that the child's need for near low vision aids can be predicted from their age, unmagnified reading performance, and visual field characteristics. The use of distance monoculars is less easily predicted. However, many visually impaired children both in mainstream special units and in schools for the blind are not being supplied appropriate low vision aids (LVAs). Many have not had an LVA assessment within 1 year and others are experiencing difficulties with LVAs that could be eliminated or reduced.
Aniseikonia: a method of objective assessment in pseudophakia using geometric optics
Authors: Snead M. P. , Lea S. Hardman , Rubinsteint M. P. , Reynolds K. , Haworlh S. M
Published: December 2007

There have been various reports in the literature regarding the limits that separate acceptable from disturbing aniseikonia. A criterion value of 5% is often quoted but actual values in pseudophakia may vary from 2% to 10%, depending on the type and position of implant used. En the accompanying paper we have reported a method by which image size can be calculated in the pseudophakie eye. Using this method a series of patients with anterior and posterior chamber implants were analysed and the image size for both eyes of each patient determined. This was compared with the patient's subjective appreciation.
A tint to reduce eye‐strain from fluorescent lighting? Preliminary observations
Authors: Wilkins Arnold J. , Wilkinson Peter
Published: December 2007

The rapid modulation of light from fluorescent lumps is responsible for eye‐strain and headaches. The modulation is greater at certain wavelengths than at others, and it can therefore be reduced by wearing tinted spectacles. A lint was designed: (11 to minimize the luminous pulsation of light from conventional halophosphate fluorescent lumps; (2) lo avoid as much as possible any concomitant increase in the pulsation from triphosphor lamps: (3) to interfere with colour perception as little as possible; and |4| to have a cosmetically acceptable colour appearance. The four design criteria conflict. A compromise design is described, together with case histories of patients who appear lo have benefited from the use of the tint.
Sjögren–Larsson syndrome: case reports of two brothers
Authors: Simon Barnard N. A. , Patel Chaya , Barnard Rachel A. M.
Published: December 2007

Sjögren‐Larsson syndrome (SLS) is an autosomal recessively inherited disorder characterized by the triad of congenital ichthyosis, spastic diplegia or tetraplegia and menial retardation. SLS is also often associated with a variety of other anomalies, including signs that are of interest to optometrists and ophthalmologists. Two case histories are presented. Both patients exhibited maculopathies and uncorrected astigmatism. The reduced visual acuities in one case appeared to be caused at least partly by astigmatism and the associated astigmatic amblyopia.
Influence of transiently altered retinal vascular perfusion pressure on rod/cone contributions to scotopic oscillatory potentials
Authors: Lovasik John V. , Kergoat Hélène
Published: December 2007

The oscillatory pntentials (Ops) are sensitive to vascular disturbances in the retina. Rods in man are more susceptible than cones to ischaemia. The findings in a recent study showed that the while flash OPs had a heightened sensitivity to altered retinal vascular perfusion pressure (RVPP), compared with earlier OPs and the h‐wave. In the present study, a comparison was made of the sensitivity of scotopically matched blue and red flash OPs to dim white flash OPs, to transient stepwise changes in the RVPP, in 10 healthy young adults. After 30 minutes of dark adaptation, two consecutive 0.3 Hz Hash groups (n= 20) were filtered and averaged to obtain 100 ms flash ERGs and OPs simultaneously via DTL, fibre electrodes For white, blue, and red flashes. To minimize any earn‐over effects across flash colour, or repeated testing, the retinal responses to each of these stimuli were measured in separate test sessions several hours to days apart. The RVPP was increased or decreased by 20% and 40% non‐invasively by body inversion and scleral suction respectively. For the flash intensities used, blue and red Hash OPs appeared more variable than white flash OPs. The OP index increased or decreased across all flash colours when the RVPP was increased, with blue OPs showing the greatest spread of data. Retesting in five subjects using white and red flashes against a blue background disclosed the input of both rods and cones to the while flash scotoptc OPs. The provocative test conditions described here offer a potentially profitable approach for studies attempting to differentiate the effects of vascular disorders on rod versus cone function.
The distribution of dioptric power: ellipsoids of constant probability density
Authors: Harris W. F. , Malan D. J. , Rubin A.
Published: December 2007

A Sample from a population of dioptric powers may be used to estimate the distribution of dioptric powers in the population itself. This paper describes the method and shows further how one can obtain a graphical representation of the distribution. The graphical representation takes the form of ellipsoids of constant probability density. The centroid of each ellipsoid estimates the mean of the population while the size shape and orientation Show the extent and nature of the spread of the population, For illustrative purposes the theory is applied to measurements of refractive status before and after radial keratotomy. The ellipsoids are presented as stereo‐pairs. They are useful for comparative and predictive purposes. Thus the ellipsoid that contains 95% of the population after surgery defines the set of refractive errors within which the refractive error of a particular eye can be expected to fall with a probability of 95%.
A practice based study of factors influencing intra‐ocular pressure
Authors: McCaghrey F. E. , McCaghrey G. E.
Published: December 2007

Many factors are claimed to influence the pressure measured by the tonometer. This study analyses Ultra‐ocular pressure data collected over 10 years on 500 ‘normal’ individuals using a non‐contact tonometer. It attempts to analyse which patient variables are relevant and considers the effects of age, sex, laterality and refractive status on intra‐ocular pressure, using various statistical techniques. No significant relationship was found for age, sex or refractive error, but axis of astigmatism and laterality were found to be significant factors.
Referrals for vascular hypertension in a group of 45‐64‐year‐old patients
Authors: Barnard N. A. Simon , Allen Richard J. , Field Andrew F.
Published: December 2007

Two hundred and ten consecutive 45‐66‐year‐old patients underwent a routine eye examination and a decision was made whether to refer each patient on the basis of fund us appearance and other non‐sphygmomanometric criteria. Blood pressure was then measured and the referral decision was reviewed. Of the 33 (15.7%) patients finally referred, only 5 (2.4%) would have been referred on the non‐sphygmomanometric findings. It is suggested that optometrists include a protocol of blood pressure measurement as part of the eye examination routine.