Global summation of radial frequency patterns and the effect of sudden onset glare on shape discrimination

ABSTRACT Global summation of radial frequency patterns and the effect of sudden onset glare on shape discrimination The purpose of this study was to provide evidence of global pooling around the circumference of the Radial frequency (RF) pattern, and to study the effect of sudden onset glare on shape discrimination. The RF stimuli were generated by the amplitude modulation of the radius of a circle which deforms them from circularity, while the cross sectional luminance profile was the fourth derivative of Gaussians (D4). The amplitude of the stimuli determines how distinct the pattern is and thus measures the degree of sensitivity while the radial frequency determines the number of lobes the pattern has. In the first part of the study, whole RF patterns (RF3 to RF16) and open component fractions (0.125, 0.25, 0.5, 0.75), which are incomplete sectors of the whole, were tested against their respective reference unmodulated patterns. Subjects were tasked with discriminating minute deviations from their reference patterns. In the second part of the study, high contrast (20 X detection threshold) RF3 and RF4 contours and equivalent low contrast (5 X detection threshold) RF3 and RF4 contours were used as stimuli. Shape discrimination threshold for the high contrast target was determined with and without sudden onset glare. The result of the first part of the study showed that threshold decreased significantly as larger component RF patterns were tested (p \u3c 0.05). The decrease could not be accounted for by the probabilistic sampling of local filters (probability summation). The result of the second part of the study showed that shape discrimination threshold increased with sudden onset glare. The increase was even more pronounced with lower mean luminance and when smaller fractions of the contours were tested. Shape discrimination threshold was significantly higher with high contrast contours in the presence of glare than equivalent low contrast contours, indicating that the veiling luminance model alone could not account for a decrease in visual performance in this shape discrimination task

The Effect of Smokeless Tobacco on Intra-Ocular Pressure in a Nigerian Population

The study was conducted to find out the effect of smokeless tobacco (ST) on the intraocular pressure (IOP) among non-smokers and smokers. Thirty-seven healthy volunteers of between 19–30 years age, classified into two groups, non-smokers (n=22) and- smokers (n=15), were used. The IOPs of the right eyes were measured before (0min) and 1, 3 and 5mins after sniffing 40mg ST with Pulsair 2000 tonometer. Among non-smokers and smokers, the difference in mean IOP at different times (0min, 1min, 3mins and 5mins) was statistically significant by one-way ANOVA (p<0.05). Post hoc analysis using Duncan multiple range (DMR) test showed that the peak IOP was at 1min after sniffing ST. The difference in IOP before sniffing ST between smokers and non-smokers was statistically significant by Mann-Whitney test (p<0.05). Also the difference in the peak time of 1min between smokers and non-smokers was statistically significant (p<0.05). It was concluded that ST stimulates aqueous humour formation thereby tending to raise IOP and this could enhance the chances of developing ocular hypertension in patients that are predisposed to glaucoma

Prevalence and clinical profile of glaucoma patients in rural Nigeria : a hospital based study

Purpose To determine the prevalence and clinical presentation of participants with glaucoma attending a public eye care facility in Nigeria. Method Hospital based retrospective study of glaucoma participants aged 50 years and above seen over a 5-year period. Descriptive statistics summarized the demographic, clinical characteristics and treatment of the participants and determined the association of variables with gender and age. Prevalence of the glaucoma by type, and their 95% confidence intervals (CI) were also calculated. Result Of the 5482 case files that were reviewed, 995 (18.15%, 95% Cl 17.15–19.19%) had glaucoma particularly primary open angle glaucoma (11.55%, 95%CI 10.73–12.42%) and were mostly females (564, 56.7%) aged 69 ± 12 years (range, 50–103 years). In contrast to other glaucoma types, the prevalence of primary angle closure glaucoma (3.68, 95%CI 3.22–4.22) increased by 15% over 5 years. The mean intraocular pressure ranged from 15–50 mmHg but higher in females than males (27.8 ± 6.1mmHg versus 26.6 ± 6.0 mmHg, P [removed]0.05). On presentation, the glaucoma hemi field test (GHFT) was outside the normal limits in 45.5% and 54.5% of males and females, respectively. The type of visual field defect was associated with glaucoma type (P = 0.047). Arcuate scotoma was most common (35.5%) across glaucoma types, paracentral scotoma more common in Secondary glaucoma while Seidel scotoma was highest in NTG (19.3%). Beta-blocker was the mainstay of management (42.2%) but more likely to be prescribed to males while more females received carbonic anhydrase inhibitors. Conclusions The high prevalence of glaucoma in older people remains a public health problem in Nigeria. The fact that about half of the participants presented with visual field defect suggests there is a need for public health messages to emphasize on early glaucoma screening, detection and management

Systematic review and meta-analysis of myopia prevalence in African school children

PURPOSE: Increased prevalence of myopia is a major public health challenge worldwide, including in Africa. While previous studies have shown an increasing prevalence in Africa, there is no collective review of evidence on the magnitude of myopia in African school children. Hence, this study reviews the evidence and provides a meta-analysis of the prevalence of myopia in African school children. METHODS: This review was conducted using the 2020 Preferred Reporting Items for Systematic reviews and Meta-Analyses (PRISMA) guidelines. Five computerized bibliographic databases, PUBMED, Scopus, Web of Science, ProQuest, and Africa Index Medicus were searched for published studies on the prevalence of myopia in Africa from 1 January 2000 to 18 August 2021. Studies were assessed for methodological quality. Data were gathered by gender, age and refraction technique and standardized to the definition of myopia as refractive error ≥ 0.50 diopter. A meta-analysis was conducted to estimate the prevalence. Significant heterogeneity was detected among the various studies (I2 >50%), hence a random effect model was used, and sensitivity analysis was performed to examine the effects of outliers. RESULTS: We included data from 24 quality assessed studies, covering 36,395 African children. The overall crude prevalence of myopia over the last two decades is 4.7% (95% CI, 3.9-5.7) in African children. Although the prevalence of myopia was slightly higher in females (5.3%, 95%CI: 4.1, 6.5) than in males (3.7%, 95% CI, 2.6-4.7; p = 0.297) and higher in older [12-18 years 5.1% (95% CI, 3.8-6.3) than younger children (aged 5-11 years, 3.4%, 95% CI, 2.5-4.4; p = 0.091), the differences were not significant. There was a significantly lower prevalence of myopia with cycloplegic compared with non-cycloplegic refraction [4.2%, 95%CI: 3.3, 5.1 versus 6.4%, 95%CI: 4.4, 8.4; p = 0.046]. CONCLUSIONS: Our results showed that myopia affects about one in twenty African schoolchildren, and it is overestimated in non-cycloplegic refraction. Clinical interventions to reduce the prevalence of myopia in the region should target females, and school children who are aged 12-18 years

The Effect of Smokeless Tobacco on Intra-Ocular Pressure in a Nigerian Population

The study was conducted to find out the effect of smokeless tobacco (ST) on the intraocular pressure (IOP) among non-smokers and smokers. Thirty-seven healthy volunteers of between 19?30 years age, classified into two groups, non-smokers (n=22) and- smokers (n=15), were used. The IOPs of the right eyes were measured before (0min) and 1, 3 and 5mins after sniffing 40mg ST with Pulsair 2000 tonometer. Among non-smokers and smokers, the difference in mean IOP at different times (0min, 1min, 3mins and 5mins) was statistically significant by one-way ANOVA (p<0.05). Post hoc analysis using Duncan multiple range (DMR) test showed that the peak IOP was at 1min after sniffing ST. The difference in IOP before sniffing ST between smokers and non-smokers was statistically significant by Mann-Whitney test (p<0.05). Also the difference in the peak time of 1min between smokers and non-smokers was statistically significant (p<0.05). It was concluded that ST stimulates aqueous humour formation thereby tending to raise IOP and this could enhance the chances of developing ocular hypertension in patients that are predisposed to glaucoma

THE EFFECT OF TRANSIENT GLARE ON OBJECT-RECOGNITION

Objective. To investigate how object-recognition is affected by transient glare. Background. Disability glare happens when a light source causes a diffusive intraocular light scattering, which reduces target visibility and results in functional impairment. Previous studies have mainly focused on how visual acuity and contrast sensitivity is affected by steady glare source. However, in real world, most glare sources are transient in nature with sudden onset, such as the headlight of approaching car. Moreover, it is not clear how complex visual functions are affected by transient glare. In this study, we studied how object-recognition is affected by transient glare and provided evidences that veiling luminance, which is mechanism of visual impairment caused by steady glare, may not fully explain the impaired visual performance with transient glare. Methods. The stimulus used is a circular contour deformed by applying a radial sinusoidal modulation to the radius (RF-contour). The center of the glare source was at the same height of the stimulus and deviated horizontally 10° away from the line of sight. The amount of glare and the equivalently reduced retinal contrast (Cst-low) of the stimulus were also calculated. The ability to detect the smallest amount of deformations on circular contours was measured with two-alternative forced choice paradigm under a) test condition: RF-contour at high contrast with a transient glare; b) control 1: RF-contour at high contrast without glare; c) control 2: RF-contour at Cst-low without glare; d) control 3: RF-contour at Cst-low without glare, but with partial section missing. Results. 1. Transient glare significantly impaired the ability to detect the smallest radial deformation in RF contour with high contrast (results a vs. b). 2. The impairment caused by transient glare was significantly greater than those caused by reducing contrast (results a vs. c). 3. The impairment caused by transient glare was similar to those measured at low contrast and with ¼ section missing (results a vs. d). Conclusion. Glare impairs the ability of object recognition. Depending on the configuration of the stimulus and the glare source, this impairment may not be fully explained by veiling luminance. Grants. PFRDG201

Performance of Spot Photoscreener in Detecting Amblyopia Risk Factors in Chinese Pre-school and School Age Children Attending an Eye Clinic.

PURPOSE:To evaluate the effectiveness of Spot photoscreener in detecting amblyopia risk factors meeting 2013 the American Association of Pediatric Ophthalmology and Strabismus (AAPOS) criteria in Chinese preschool and school-age children. METHODS:One hundred and fifty-five children (310 eyes), aged between 4 to 7 years (5.74 ± 1.2 years) underwent complete ophthalmologic examination, photoscreening, and cycloplegic retinoscopy refraction. The agreement of the results obtained with the photoscreening and retinoscopy was evaluated by linear regression and Bland-Altman plots. The sensitivity and specificity of detecting amblyopia risk factors were calculated based on the AAPOS 2013 guidelines. The overall effectiveness of detecting amblyopia risk factors was analyzed with Receiver Operating Characteristic (ROC) curves. RESULT:The mean refractive errors measured with the Spot were: spherical equivalent (SE) = 0.70 ± 1.99 D, J0 = 0.87 ± 1.01 D, J45 = 0.09 ± 0.60 D. The mean results from retinoscopy were: SE = 1.19 ± 2.22 D, J0 = 0.77 ± 1.00 D, J45 = -0.02 ± 0.45 D. There was a strong linear agreement between results obtained from those two methods (R2 = 0.88, P<0.01). Bland-Altman plot indicated a moderate agreement of cylinder values between the two methods. Based on the criteria specified by the AAPOS 2013 guidelines, the sensitivity and specificity (in respective order) for detecting hyperopia were 98.31% and 97.14%; for detecting myopia were 78.50% and 88.64%; for detecting astigmatism were 90.91% and 80.37%; for detecting anisometropia were 93.10% and 85.25%; and for detection of strabismus was 77.55% and 88.18%. CONCLUSION:The refractive values measured from Spot photoscreener showed a moderate agreement with the results from cycloplegic retinoscopy refraction, however there was an overall myopic shift of -0.49D. The performance in detecting individual amblyopia risk factors was satisfactory, but could be further improved by optimizing criteria based on ROC curves

Association between Ocular Sensory Dominance and Refractive Error Asymmetry

Purpose To investigate the association between ocular sensory dominance and interocular refractive error difference (IRED). Methods A total of 219 subjects were recruited. The refractive errors were determined by objective refraction with a fixation target located 6 meters away. 176 subjects were myopic, with 83 being anisometropic (IRED ≥ 0.75 D). 43 subjects were hyperopic, with 22 being anisometropic. Sensory dominance was measured with a continuous flashing technique with the tested eye viewing a Gabor increasing in contrast and the fellow eye viewing a Mondrian noise decreasing in contrast. The log ratio of Mondrian to Gabor’s contrasts was recorded when a subject just detected the tilting direction of the Gabor during each trial. T-test was used to compare the 50 values collected from each eye, and the t-value was used as a subject’s ocular dominance index (ODI) to quantify the degree of ocular dominance. A subject with ODI ≥ 2 (p \u3c 0.05) had clear dominance and the eye with larger mean ratio was the dominant one. Otherwise, a subject had an unclear dominance. Results The anisometropic subjects had stronger ocular dominance in comparison to non-anisometropic subjects (rank-sum test, p \u3c 0.01 for both myopic and hyperopic subjects). In anisometropic subjects with clear dominance, the amplitude of the anisometropia was correlated with ODI values (R = 0.42, p \u3c 0.01 in myopic anisometropic subjects; R = 0.62, p \u3c 0.01 in hyperopic anisometropic subjects). Moreover, the dominant eyes were more myopic in myopic anisometropic subjects (sign-test, p \u3c 0.05) and less hyperopic in hyperopic anisometropic subjects (sign-test, p \u3c 0.05). Conclusion The degree of ocular sensory dominance is associated with intraocular refractive error difference

The donkey - a livestock or a pet? (Breeding and use of donkeys in Polabí lowland - a case study)

Donkeys have been useful helpers to people especially at transporting burdens and in agriculture for thousands of years. Nowadays they make livelihoods of rural as well as urban inhabitants over all continents easier. The use of donkeys in agriculture and transport is vanishing in developing countries due to the mechanization. We know only little about how and why people keep breeding of donkeys in developing countries. Theoretical part of the thesis tries to summarize previous basic knowledge about breeding and using donkeys. It focuses on domestication of donkeys, their use in history in different parts of the world, current position of donkeys and partly on relations between men and animals from the view of Human-Animal Studies. A research in a part of Polabí lowland is added. The main practical aim of the thesis is to take a look at the phenomenon of breeding donkeys in the Czech Republic in the present and bring any findings about why do people breed donkeys in modern times in this developing country. Research finds how are donkeys bred, what reasons lead breeders to get donkeys and what their real use is. The thesis contributes to popularization of this theme among experts and laymen and suggests methodology for research of breeding donkeys in other areas as well