Flicker adaptation improves acuity for briefly presented stimuli by reducing crowding.

Adaptation to flickering/dynamic noise improves visual acuity for briefly presented stimuli (Arnold et al., 2016). Here, we investigate whether such adaptation operates directly on our ability to see detail or by changing fixational eye movements and pupil size or by reducing visual crowding. Following earlier work, visual acuity was measured in observers who were either unadapted or who had adapted to a 60-Hz flickering noise pattern. Participants reported the orientation of a white tumbling-T target (four-alternative forced choice [4AFC], ⊤⊣⊥⊢). The target was presented for 110 ms either in isolation or flanked by randomly oriented T's (e.g., ⊣⊤⊢) followed by an isolated (+) or flanked (+++) mask, respectively. We measured fixation stability (using an infrared eye tracker) while observers performed the task (with and without adaptation). Visual acuity improved modestly (around 8.4%) for flanked optotypes following adaptation to flicker (mean, -0.038 ± 0.063 logMAR; p = 0.015; BF10 = 3.66) but did not when measured with isolated letters (mean, -0.008 ± 0.055 logMAR; p = 0.5; BF10 = 0.29). The magnitude of acuity improvement was associated with individuals' (unadapted) susceptibility to crowding (the ratio of crowded to uncrowded acuity; r = -0.58, p = 0.008, BF10 = 7.70) but to neither fixation stability nor pupil size. Confirming previous reports, flicker improved acuity for briefly presented stimuli, but we show that this was only the case for crowded letters. These improvements likely arise from attenuation of sensitivity to a transient low spatial frequency (SF) image structure (Arnold et al., 2016; Tagoh et al., 2022), which may, for example, reduce masking of high SFs by low SFs. We also suggest that this attenuation could reduce backward masking and so reduce foveal crowding.

Clinical Profile of Primary Open-angle Glaucoma Patients at an Eye Center in Nigeria.

Aim: Globally, one of the leading causes of preventable blindness is primary open-angle glaucoma (POAG). The study assessed the clinical presentations of POAG patients attending an eye center in Abuja, Nigeria. Materials and methods: Records of 188 eyes, collected from 94 patients diagnosed with POAG for a period of 1 year at the eye center, were reviewed. Clinical records, including age, gender, visual acuity (VA), central cornea thickness (CCT), intraocular pressure (IOP), cup-to-disk ratios, and retinal nerve fiber layer (RNFL) thickness of the participants, were extracted and analyzed. Results: The majority of the participants were males (56.4%) and adults (57.4%), most of whom had normal VA (>70% in each eye). Our analysis revealed normal average estimates of RNFL thickness, IOP, and CCT among the participants. Females had thicker RNFL compared to males (p = 0.02). Although CCT decreased with age (r = -0.28, p = 0.005), there was no such link between IOP and CCT (r = 0.09, p = 0.38). Conclusion: Central cornea thickness (CCT), RNFL thickness, and IOP in isolation should not be used as early indicators for POAG; rather, a combination of these and other indices is recommended. Early detection through active screening and treatment in the community for at-risk groups is highly advised. How to cite this article: Ezinne NE, Kwarteng MA, Ekemiri KK, et al. Clinical Profile of Primary Open-angle Glaucoma Patients at an Eye Center in Nigeria. J Curr Glaucoma Pract 2023;17(3):113-117.

Scope of optometry practice in Trinidad and Tobago: A cross-sectional study.

Background and Aim: To report the scope of optometry practice in Trinidad and Tobago to identify areas that need improvement. Methods: A cross-sectional study of optometrists in Trinidad and Tobago was conducted using a validated self-structured questionnaire. Data obtained was exported to the Statistical Package for Social Sciences. Descriptive analysis and Pearson χ 2 were used to summarize the demographic data and determine associations, respectively. Result: A total of 63 optometrists participated in the study. Majority of them were females (69.8%, n = 44), Christians (65.1%), East Indians (47.6%), and 30 years and below (66.7%). Most (87%) of them utilized routine optometric equipment in their clinical practice including autorefractors, retinoscopes, direct ophthalmoscopes, lensometers, phoropters, slit lamp biomicroscopes, trial lens boxes, and visual acuity chart projectors. A few of them have noncontact tonometer (4.8%), Volk lenses (1.6%), and perform color vision tests (1.6%). Fewer (12.7%, n = 8) practitioners provided low-vision services. The use of pharmaceutical agents was prevalent among the participants (55.6%). Additionally, the provision of contact lenses was the most frequently practiced service among the participants (85.7%, n = 54). A significant association was observed between the provision of low-vision services and sex (p = 0.03). Conclusion: The scope of optometry practice in Trinidad and Tobago is in accordance with the basic guidelines set out by the World Council of Optometry but there is need to get more involved in the provision of low vision and other specialty services.

Visual Impairment and Blindness among Patients at Nigeria Army Eye Centre, Bonny Cantonment Lagos, Nigeria.

Background: Visual impairment (VI) is a public health problem that can affect an individual's social wellbeing. The study aims to determine the distribution and causes of vision impairment (VI) and blindness among patients at Nigerian Army Eye Centre Lagos, Nigeria. Method: An institutional cross-sectional study was conducted, and a systematic random sampling technique was used to enrol study participants from their medical records. Information about their demography, presenting visual acuity (VA), best corrected visual acuity and cause of VI and blindness, were retrieved. Result: A total of five hundred (500) medical records of patients aged from 4 to 96 years, with a mean age of 54.07 ± 21.43 years, were considered for the study. Among the participants, more than half were males (51.2%) and ≥60 years (53.0%). A large (47.2%) proportion of the patients had moderate VI at the time of presentation, followed by blindness (22.0%). The major cause of blindness was cataract, while glaucoma and refractive error were the major causes of VI. Blindness and VI were significantly associated with the type of VI before and after the provision of intervention (p < 0.05) across different age groups (children, youths, adults, elderly) with an adjusted p < 0.003 after an intervention. Conclusions: Cataracts, glaucoma and uncorrected refractive error (URE) were the major causes of VI and blindness in Lagos State. VI was more prevalent in males than females; however, there was no significant difference between the two proportions. The prevalence of VI among age groups was more significant for those 60 years and above. Early screening for the detection and management of cataract, URE and glaucoma is highly advised to reduce the burden of VI.

Motion adaptation improves acuity (but perceived size doesn't matter).

Recognition acuity-the minimum size of a high-contrast object that allows us to recognize it-is limited by optical and neural elements of the eye and by processing within the visual cortex. The perceived size of objects can be changed by motion-adaptation. Viewing receding or looming motion makes subsequently viewed stimuli appear to grow or shrink, respectively. It has been reported that resulting changes in perceived size impact recognition acuity. We set out to determine if such acuity changes are reliable and what drives this phenomenon. We measured the effect of adaptation to receding and looming motion on acuity for crowded tumbling-T stimuli (). We quantified the role of crowding, individuals' susceptibility to motion-adaptation, and potentially confounding effects of pupil size and eye movements. Adaptation to receding motion made targets appear larger and improved acuity (-0.037 logMAR). Although adaptation to looming motion made targets appear smaller, it induced not the expected decrease in acuity but a modest acuity improvement (-0.018 logMAR). Further, each observer's magnitude of acuity change was not correlated with their individual perceived-size change following adaptation. Finally, we found no evidence that adaptation-induced acuity gains were related to crowding, fixation stability, or pupil size. Adaptation to motion modestly enhances visual acuity, but unintuitively, this is dissociated from perceived size. Ruling out fixation and pupillary behavior, we suggest that motion adaptation may improve acuity via incidental effects on sensitivity-akin to those arising from blur adaptation-which shift sensitivity to higher spatial frequency-tuned channels.

Clinical and sociodemographic characteristics of glaucoma patients at a tertiary referral facility in Zimbabwe.

Purpose: To evaluate the clinical and socio-demographic profile of patients living with glaucoma and receiving care in a tertiary eye center in Zimbabwe. Method: A hospital-based retrospective study of clinical records of glaucoma patients from January 2014 to December 2018. The study involved collating demographic information of patients, visual acuities, (VA) intraocular pressure, (IOP), cup-to-disc ratios, (CDRs), average retinal nerve fibers thickness, (RNFL), cup volume, cup-to-disc area, vertical cup-to-disc ratio, (VCDR), rim area, disc area, glaucoma hemifield test, visual field indices and the management of glaucoma. Results: Nine thousand one hundred and eighty-five (9,185) folders were retrieved. Out of these, 432 (4.7%) qualified for the study and were analyzed. There were 267 (61.8%) males and 165 (38.2%) females. The mean age (± Standard deviation, SD) of the patients was 62.66 ± 15.94 years, (range 10 - 110 years). The means visual acuity (VA): OD =1.30 ± 1.06 Logarithm of the Minimum Angle of Resolution, (logMAR), OS = 1.33 ± 1.06 logMAR; IOP: OD = 29.51 ± 12.89 mmHg, OS: 29.17 ± 12.59 mmHg; CDRs: OD = 0.91 ± 0.14 D, OS = 0.92 ± 0.14 D; and the average RNFL thickness was 72.76 ± 18.26 µm and 71.24 ± 23.17 µm in the right and left eye respectively. The mainstay of treatment was medication only. Conclusion: There were more males than females receiving glaucoma care at the tertiary level. Glaucoma cases included juveniles but the mean age was mostly the elderly. It was characterized by high IOPs, large CDRs, and thin RNFL suggestive of late presentation.

Prevalence of Refractive Error and Visual Impairment among Rural Dwellers in Mashonaland Central Province, Zimbabwe.

PURPOSE: To determine the prevalence of refractive error and visual impairment in a rural population of Zimbabwe. METHODS: This community-based, cross-sectional study used a multi-stage sampling to select the participants from households in four communities within three rural districts in Mashonaland Central Province. Participants' demographic data were collated, and their presenting visual acuity (VA) was measured using the logMAR E chart. Clinical refraction was preceded by an anterior segment and posterior segment eye examinations. Visual impairment was defined as presenting VA worse than 6/12 (0.3 logMAR) in the better eye. Descriptive statistics were presented as frequencies. RESULTS: A total of 519 participants were involved in this study. Their ages ranged from 5 to 100 years (mean age = 50.94; standard deviation ± 21.12 years). Out of the 519 participants, 233 (44.9%) were male, and 286 (55.1%) were female. The prevalence of visual impairment was 56.8% (95% confidence interval [CI]: 55.7-67.2), and blindness was 13.1% (95% CI: 11.2-17.6). The prevalence of near visual impairment based on presenting near VA (N = 408) was 78.6% (95% CI: 78.1-85.4). The two most common causes of visual impairment were uncorrected refractive errors (UREs) (54.2%) and cataract (24.8%). The most common cause of blindness was cataract (41.2%). Hypermetropia (56.9%) was the most common refractive error. CONCLUSIONS: A high burden of visual impairment due to UREs and cataracts was observed among the rural dwellers of Zimbabwe. Public health education, access to refractive error services, and cataract surgery are necessary to mitigate this high burden of visual impairment.

Unorthodox ophthalmic preparations on the Ghanaian market: a potential risk for ocular and enteric infections.

PURPOSE: Microbial contamination of orthodox ophthalmic preparations poses a serious threat to the user by causing ocular infections. There is no such information about unorthodox ophthalmic preparations in a medical pluralistic system such as Ghana. The aim of this study was to assess unorthodox ophthalmic medications on the Ghanaian market for possible microbial contaminations. METHODS: Unorthodox ophthalmic preparations were collected across different herbal and homeopathic outlets in Ghana. A total of 27 samples were collected from the ten (10) regions in Ghana. The samples were inoculated in different culture media (Plate count Agar, Blood Agar, MacConkey Agar, Saboraud Dextrose Agar). The microorganisms isolated were identified using standard microbiological procedures and antimicrobial susceptibility was done to determine whether they were resistant or susceptible strains. RESULTS: All the samples were contaminated with bacteria and the majority were contaminated with fungus. A total of forty-eight bacteria spp. was isolated thus seven different types namely: Staphylococcus aureus, Bacilli spp., Serrati spp., Escherichia coli, Pseudomonas spp., Klebsiella spp. and Shigella spp. with Staphylococcus aureus being the predominant bacteria. For fungi, a total of eleven fungi species thus four different types namely: Cephalosporium spp., Penicillium spp., Cercosporium spp. and Clasdosporium spp. with the predominant fungi being Penicillium spp. Per the class of preparations, 15 contaminants were isolated from ten (10) anti-inflammatory preparations. The fungi were all susceptible to both Ketoconazole and Fluconazole but the bacteria were resistant to all the conventional antibiotics except Ciprofloxacin and Gentamycin. CONCLUSION: Unorthodox ophthalmic preparations found on the Ghanaian market are contaminated with bacteria and fungi of clinical importance.

Prevalence of Trachoma and Access to Water and Sanitation in Benue State, Nigeria: Results of 23 Population-Based Prevalence Surveys.

PURPOSE: We sought to determine the prevalence of trachoma in each local government area (LGA) of Benue State, Nigeria. METHODS: Two-stage cluster sampling was used to conduct a series of 23 population-based prevalence surveys. LGAs were the evaluation units surveyed. In each LGA, 25 households were selected in each of 25 clusters, and individuals aged 1 year and above resident in those households were invited to be examined for trachoma. Data on access to water and sanitation were also collected at household level. RESULTS: A total of 91,888 people were examined from among 93,636 registered residents across the 23 LGAs. The LGA-level prevalence of trachomatous inflammation-follicular (TF) in 1-9 year olds ranged from 0.3% to 5.3%. Two LGAs had TF prevalences of 5.0-9.9%. The LGA-level prevalence of trichiasis in ≥15-year-olds ranged from 0.0% to 0.35%. Access to improved drinking water sources ranged from 0% in Gwer West to 99% in Tarka, while access to improved sanitation ranged from 1% in Gwer West to 92% in Oturkpo. CONCLUSION: There is a need for public health-level interventions against trachoma in three LGAs of Benue State.