bluuebunny/crossref_metadata_2025_split huggingface dataset:
The ChromaGen contact lens system: colour vision test results and subjective responses
Authors: Swarbrick Helen A. , Nguyen Phuong , Nguyen Tuyen , Pham Phuong 
Published: March 2003

SummaryThe ChromaGen lens system is designed to enhance colour perception in colour vision deficiency (CVD). To investigate its efficacy, 14 CVD subjects were prescribed ChromaGen contact lenses. Colour vision tests (Ishihara, Farnsworth Munsell D‐15, Farnsworth Lantern) were administered at baseline, lens dispensing, and after a 2‐week lens‐wearing trial during which subjective responses were recorded daily using visual analogue scales. ChromaGen lenses significantly reduced Ishihara error rates(p<0.001; ANOVA), particularly for deutan subjects. There was also a significant reduction in errors(p<0.005) on the D‐15 test. Conversely, lens wear had no significant effect on Farnsworth Lantern test performance. Subjectively, subjects reported enhanced colour perception, but poor vision in dim light. Judgement of distance and motion were only slightly affected. We conclude that ChromaGen lenses may enhance subjective colour experience and assist in certain colour‐related tasks, but are not indicated as an aid for CVD in occupations with colour vision‐related restrictions.
Optimal reading speed in simulated cataract: development of a potential vision test
Authors: Patel Bhavesh , Elliott David B. , Whitaker David 
Published: March 2003

SummaryPrevious studies suggest that optimal reading speed is unaffected by cataract, yet is significantly reduced in age‐related macular disease. This raises the question of whether a reading speed test could be developed to assess potential vision after cataract surgery. In this study, 20 young subjects, with and without a simulation of dense cataract, read aloud Bailey‐Lovie word charts. From the results, critical print size, optimal reading speed and word acuity were calculated. The simulated cataract reduced word acuity and increased the critical print size, yet optimal reading speed remained unchanged. Measurements were also taken with the charts in reversed contrast polarity. Reversing the contrast polarity of the charts improved the word acuity and optimal reading speed with the cataract simulation. The results suggest that optimal reading speed could be used as a potential vision test. Further investigations using patients with cataract and ARMD are required.
Peripheral astigmatism in emmetropic eyes
Authors: Gustafsson Jörgen , Terenius Erik , Buchheister Jan , Unsbo Peter 
Published: March 2003

SummaryThe long‐term aim of the work introduced here is to investigate the influence of off‐axis aberrations on human vision, especially for subjects with a large central scotoma. The latter use their peripheral vision in spite of its poor off‐axis optical quality, and a correction of the off‐axis aberrations might be of great assistance. The eccentric fixation angles used by these subjects can be up to 20–30°. In this initial study we have measured oblique astigmatism, the major off‐axis aberration, in 20 emmetropic eyes in 10° steps out to 60° nasally and temporally using a ‘double pass’ setup. The results show very large individual differences and the oblique astigmatism also varies from nasal to temporal side. In an off‐axis measurement angle of 30° the astigmatism varied between subjects from 1 to 7‐D, with a mean astigmatism of about 4‐D on the nasal side and about 1.5‐D lower on the temporal side. At 60° temporally, the mean astigmatism was 7‐D. At 60° nasally, all subjects had astigmatism larger than 8‐D and the mean astigmatism was 11‐D. The results indicate that any attempt to correct the off axis astigmatism in an eye with central scotoma cannot be based on central refraction; instead, individual measurements are necessary.
Diagnosis of eccentric fixation using a calibrated ophthalmoscope: defining clinically significant limits
Authors: Cleary M. , Thompson C.M. 
Published: March 2003

SummaryVisuscopy and other ophthalmoscopic methods are widely applied in the assessment of fixation behaviour in amblyopia, although the reliability and inter‐examiner variability of this test has not been established. Typically eccentric fixation is diagnosed solely on the basis of retinal position, but this fails to address the accompanying sensorimotor adaptations. A double‐blind (masked) trial of a paediatric population was undertaken (n=30, age range 3 years 9 months to 11 years, mean 5.6±1.5 years), involving three examiners applying a detailed protocol. The criteria for eccentric fixation were established from the non‐amblyopic eyes. The most reliable criterion for the diagnosis of fixation was established from the results of the study. No single parameter proved 100% reliable, and amplitude showed greatest inconsistencies. It is recommended that a consensus of at least three parameters from position, zero retinomotor point, principal visual direction and percent foveation is required to diagnose the fixation status reliably.
A multiple regression approach to study optical components of myopia in Singapore school children
Authors: Tong Louis , Wong Ee Hwee , Chan Yiong Huak , Balakrishnan Vivian 
Published: March 2003

Purpose: Previous studies on the optical components of childhood myopia adjusted only for age and gender or reported only the change of individual components with time. We perform a study to assess the association of the optical components of the eye contributing to the degree of myopia by building a statistical model which can better assess the individual effects of each optical component.Methods: Children 6–12 years old with myopia of −1 to −6 D were used in this study. Autokeratometry was performed to determine the mean corneal power in two perpendicular meridia. Ultrasonography was used to determine the vitreous chamber depth (VCD). Ultrasonography and Scheimflug biometry were used to determine lens thickness (LT) and anterior chamber depth. A stepwise multiple linear regression was used to determine statistically significant independent variables that explain the variation in the mean spherical equivalent of the left eye. The independent variables investigated were anterior chamber length, LT, VCD, mean corneal power, age and gender. The first regression model used measurements of anterior chamber depth and LT from ultrasonography, while the second model used measurements from Scheimflug photography. Statistical significance was set atp < 0.05.Results: Both statistical models have the same significant independent variables – VCD, LT and gender, with similar estimates. In both models, VCD was found to have the strongest partial association with mean spherical equivalent, followed by gender and LT. A more myopic refractive error was associated with (1) a longer eye, (2) an increased LT, and (3) female gender.Conclusions: Myopia was associated with a longer vitreous chamber. This remained the primary determinant of myopia in Chinese children after consideration of other optical components. The effect of gender and LT on myopia requires further study. These results are in agreement with multiple regression analyses in Singapore adults.
Optimal green (red‐free) digital imaging of conjunctival vasculature
Authors: Owen Christopher G. , Ellis Timothy J. , Rudnicka Alicja R. , Woodward E. Geoffrey 
Published: March 2003

Aims/background: Green illumination is commonly used to image vessels of the retina and conjunctiva. The purpose was to derive the best optical set‐up for imaging vessels of the conjunctiva. Methods: The concept of exposure density was used to predict a digital camera response to imaging vessels on a scleral background. Practical verification was performed to verify vessel contrast because of the difficulties in measuring the spectral components of the imaging system, such as the spectral reflectivity of vessels and sclera. Images of the same conjunctiva were repetitively taken through different coloured filters, using the Nikon FS‐2 photo slit‐lamp and recorded on different coloured channels of the Kodak DCS 100 digital camera. Gaussian blurred tubular models were fitted to densitometric profiles across three vessels from each image, allowing vessel contrast and width to be objectively measured. These measures were compared using different optical set‐ups. Results: Optimal exposure density calculations and vessel contrast was obtained with the xenon light source filtered with Wratten 99 (green) and Wratten 96 (neutral density, 0.2 log units) gelatine absorption filters using the green channel of the digital camera. This image set‐up was associated with a 46% (99% CI 43–51%) to 64% (99% CI 58–72%) increase in contrast compared with vessels imaged without filtration, using the combined colour channel of the digital camera. Although differences in vessel widths resulted, absolute differences were marginal. Conclusion: With the increased use of digital imaging, and the need for image processing of vascular networks, image optimisation is beneficial. This study verified the optimal set‐up for non‐invasively imaging vessels of the bulbar conjunctiva.
Benefit of coloured lenses for age‐related macular degeneration
Authors: Wolffsohn J. S. , Dinardo C. , Vingrys A. J. 
Published: March 2003

Purpose: To evaluate and compare the functional and perceived benefits of wearing coloured lenses by patients with age‐related macular degeneration (ARMD). Method: Ten subjects with early ARMD and five elderly controls wore a selection of NoIR wrap‐around coloured lenses (yellow 29.7% light transmission, orange 22.9%, red 16.8% and grey 10.3%), each for a duration of 7 days. Contrast sensitivity, colour vision, visual acuity, the effect of glare and peripheral sensitivity were measured for each lens and compared with a control (no lens) condition. Subjective ratings of visual performance were also scored. Results: Compared with the no filter condition, red and grey lenses reduced contrast sensitivity whereas yellow and orange lenses increased contrast sensitivity. These objective changes were supported by subjective ratings in subjects with ARMD. Grey lenses reduced the loss of contrast sensitivity usually suffered in the presence of glare, whereas visual acuity and peripheral sensitivity decreased with red lenses. Colour vision became distorted with red lenses in control subjects, but was relatively unaffected by the use of coloured lenses in subjects with ARMD. Conclusions: The subjective benefit of coloured lenses appears to be due to a minor enhancement of contrast sensitivity.
Steady‐state VEP and behavioural measures of visual acuity in infants and children with Down syndrome
Authors: John Ff. M. , Bromham N. R. , Candy T. R. , Woodhouse J. M. 
Published: March 2003

Purpose:  Children with Down syndrome (DS) have reduced behavioural visual acuity (VA). This may reflect sensory deficits, or alternatively, a loss of performance in later mechanisms responsible for behavioural responses. This study compared acuity measured using visual‐evoked potentials (VEP), with behavioural tests, in children with DS. The goal was to determine whether reduced VA could be detected in VEP recordings from the first stages of the response pathway.Methods:  The subject group contained 34 children with DS and 35 controls, aged 3 months to 14 years. VA was measured using steady‐state, swept VEP (Norcia and Tyler, 1985). VA was also measured using behavioural techniques.Results:  Visual acuity was analysed using a subject group (DS vs controls) × test type (behavioural vs VEP) anova with age as a covariate. A significant effect of subject group was observed (F1,59 = 8.632, p < 0.001) and a significant interaction between subject group and test type (F1,59 = 5.169, p = 0.027). The DS group showed reduced VA compared with the controls in both VEP and behavioural tests, but the deficit was more pronounced with behavioural testing. Reduced VA in the DS group was still seen when analysis was restricted to children who accommodate accurately (F1,26 = 8.047, p = 0.009).Conclusions:  Reduced VEP acuity in the DS group supports the idea of an underlying sensory deficit in the DS visual system. Increased reduction with behavioural techniques implies additional losses at later stages of processing. Accommodative inaccuracy does not fully explain reduced VA in DS. Children with DS who do not have significant levels of defocus still exhibit reduced VA when compared with controls.
Distribution of rod bipolar cells in the retina of the albino rat
Authors: Davda P. , Dovey M. , Jeffery G. , Baker G. 
Published: March 2003

Purpose:  In the retina of albino mammals so far examined there is a deficit in the rod photoreceptor population. We reasoned that a consequence of the rod deficit might be a subsequent abnormality in the next level of the rod pathway, the rod bipolar cell. We therefore compared the distribution of rod bipolar cells in pigmented and albino rats.Methods:  Rod bipolar cells were labelled in 15 µm thick sections of fixed retinas with a monoclonal antibody directed against protein kinase C, and visualized using the ABC method. Counts of the cell bodies and processes of rod bipolar cells were undertaken at various locations across the retina.Results:  Qualitatively, the protein kinase C staining suggested differences between the albino and pigmented phenotypes both in the outer and inner plexiform layers and in the inner nuclear layer. Staining was denser in the pigmented retina and the bipolar cell bodies were arranged in multiple rows rather than a single row as found in the albino retina. The actual number of rod bipolar cells was reduced in the albino phenotype. At the neonatal age we examined (post‐natal day 15), there was a 14% reduction in the total number whereas in the adult retina the reduction was around 9%.Conclusions:  Although the reduction in the rod bipolar population is not as great as that previously found for the rod photoreceptors (∼25%), the reduction in both populations suggests a general abnormality in the rod pathway of albinos. Further, our data support the view that melanin is crucially involved in the normal development of retinal structure.
Postural stability changes in elderly subjects due to disruption of the somatosensory and vestibular system inputs, refractive blur and dual tasking
Authors: Anand V. , Elliott D. B. 
Published: March 2003

Purpose:  To determine the effect of disruption of the inputs from the somatosensory and vestibular systems, refractive blur and dual tasking on postural stability in healthy, elderly subjects.Methods:  Fifteen healthy, elderly subjects (mean age 71 ± 5 years, binocular VA −0.07 ± 0.05 logMAR, Snellen 20/17) with no history of falls and normal vision were recruited. Postural stability during standing was assessed using an AMTI force plate, and was determined as the Root Mean Square (RMS) of the Centre of Pressure (COP) signal in the anterior–posterior (AP) and medial–lateral (ML) directions collected over 30 s periods. Data were collected under normal standing conditions and when the inputs from the somatosensory and vestibular systems were disrupted. Measurements were also repeated with the subject being given an additional physical task (holding a tray of cups) and/or mental task (counting backwards). For all measurement conditions, postural sway was measured under conditions of binocular refractive blur of 0,1, 2, 4 and 8 D and with eyes closed. The data were analysed using a population‐averaged linear model.Results:  All factors except the additional physical task significantly decreased postural stability (p < 0.001). The greatest decreases in postural stability were because of disruption of the somatosensory system (95% AP increase) and disruption of both the somatosensory and vestibular systems (152% AP increase). Increasing refractive blur caused decreasing postural stability, with 8 D blur causing a 44% increase in AP RMS COP under normal standing conditions. The effect of refractive blur was greater when the input from the other sensory systems was disrupted (81% increase in AP RMS COP with 8 D blur). Performing an additional mental and physical task increased AP RMS COP by approximately 24%. All these detrimental effects on postural stability were cumulative.Conclusions:  All the factors tested, except the additional physical task, significantly decreased postural stability and were cumulative. This highlights the multifactorial nature of balance control. Findings indicate that the visual system becomes increasingly relied upon when inputs from the other two balance control systems are disrupted.
Mindsight: pathological completion in a case of occipital damage without neglect
Authors: McCarthy R. A. , Galton M. , Plant G T. 
Published: March 2003

Purpose:  Islands of blindness (scotomata) caused by damage to the visual regions of the brain may be accompanied by the subjective experience of completion of forms that ‘should’ be occluded by the visual defect, a symptom termed Pathological Visual Completion. We report our investigations of the basis of this phenomenon and the level of visual processing that is implicated.Methods:  We report a single case with left occipital brain injury who showed pathological visual completion in a clear and reliable form. His disorder could not be explained by residual vision or an attentional disorder.Results:  The likelihood of completion was systematically influenced by changes in the stimulus display. Pattern masking, varying the contrast characteristics of stimuli and changing visible cues to structural symmetry all had precise effects whereas familiarity and structural coherence did not.Conclusion:  We suggest that in this case, pathological completion may be a positive cognitive event implicating processes that underpin the normal experience of occluded forms.
Ability of frequency doubling perimetry and scanning laser polarimetry to detect ocular hypertension and POAG in an Indian population
Authors: Sukumar S. , Balekuduru S. , Mani B. , Vijaya L. 
Published: March 2003

Purpose:  To evaluate the ability of Frequency doubling perimetry (FDP) and scanning laser polarimetry (GDx) in the detection of Ocular hypertension (OHT) and Primary Open Angle Glaucoma (POAG) in an Indian population.Methods:  Subjects were classified as being normal or having OHT or POAG (mild, moderate and severe) based on clinical findings and visual field results. A total of 104 eyes of 86 subjects who satisfied the inclusion criteria and completed the tests successfully were analysed. Sensitivity and specificity of N‐30 Full field FDP tests were analysed for OHT and three POAG groups. GDx parameters were compared between normal subjects and other groups.Results:  When compared with normal subjects, superior‐based GDx parameters were significantly different (p < 0.05) in OHT and mild POAG. Average‐based parameters showed significant difference (p < 0.05) only in moderate and severe POAG. Among all the GDx parameters ‘The number’ (cut off value >19) showed significant results in OHT (sensitivity 66% and specificity 92%) and in POAG groups (sensitivity ≥88% and specificity ≥92%). OHT changes were detected by N 30 Full Threshold FDP test (sensitivity 22% and specificity 83%) and in mild (sensitivity 59% and specificity 87%), moderate (sensitivity 88% and specificity 96%) and severe (sensitivity 100% and specificity 100%) POAG groups when mean deviation (P < 5) was used as the cut off value.Conclusion:  Both FDP and GDx are valid screening tools for detecting OHT and POAG. The ability of GDx in detecting OHT and POAG improved if normal subjects from the Indian population are used for comparison.
Within‐texture alignment improves human texture segmentation
Authors: Harrison S. J. , Keeble D. R. T. 
Published: March 2003

Purpose:  Spatial arrangement has been shown to be a critical factor both in detection facilitation of a threshold target by collinear flankers and in detection of smooth chains within random arrays of suprathreshold elements. Here, we investigate the effect of alignment between texture elements on human texture perception.Methods:  Texture displays, consisting of arrays of elements, were presented to observers for 100 ms. Trials were completed with both line elements and with Gabor patches. A discrimination task consisted of one stimulus presentation, and observers distinguished between two possible orthogonal orientations of a central block, which differed from the surround by the orientation of its elements. A detection task required observers to indicate in which of two presentations the central block was present. For both tasks, the degree of alignment within stimuli was varied either by increasing orthogonal offset between elements or by decreasing the length of chains of aligned elements. Both alterations result in an overall reduction of collinearity within the display. A close‐spaced and a far‐spaced condition were tested. Global element density was kept constant within all line trials and within all Gabor trials.Results:  For nearly all conditions, alignment was found to improve thresholds. The effect was robust to orientational jitter up to a standard deviation of the array‐element population of 8°.Conclusions:  Our results suggest that collinearity between elements results in both short and long‐range interactions, which contribute to the formation of a texture‐defined surface. Interactions between close‐spaced elements might be explicable in terms of a linear‐filter summation paradigm, but results for far‐spaced elements would definitely require additional mechanisms.
Retinal projections to the thalamus in albino frogs
Authors: Grant S. , Waller W. , Bhalla A. , Kennard C. 
Published: March 2003

Melanin in the embryonic retinal pigment epithelium (RPE) is essential for normal development of the mammalian visual system: in albino and other mutant mammals lacking this pigment, many temporal retinal ganglion cells (RGCs) that usually project ipsilaterally misroute their axons across the optic chiasm to the opposite side of the brain. In human albinos, this misrouting results in higher visual centres receiving predominantly monocular input from the opposite eye and in defective binocular stereovision. The RPE–RGC signalling mechanisms that govern the chiasmatic pathway choices of ganglion cell axons are unknown, but may involve gap junctions, which are a conserved feature of the embryonic retina in all vertebrate classes.To determine whether chiasmatic abnormalities also generalize to non‐mammalian pigment mutants, we compared the distribution of crossed and uncrossed retinal projections to the thalamus in normal and albino Xenopus frogs. In both phenotypes, retinal terminations from the opposite eye covered ∼80% of the neuropil of Bellonci and corpus geniculatum thalamicum (analogous to the mammalian lateral geniculate nuclei), with uncrossed inputs occupying ∼75 and 25%, respectively, of the two terminal fields. Ipsilateral projections originated from ∼3000 RGCs in the wild‐type and albino frogs, and in both phenotypes they were restricted to a ventrotemporal crescent comprising ∼40% of the total retinal area.In sum, we found no evidence of chiasmatic misrouting in albino Xenopus, despite the fact that this species normally possesses retinal projections with a substantial ipsilateral component. Our findings support other recent evidence that a lack of RPE melanin leads to defective development of the retina and its central pathways only in mammals.