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.

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.

Recognition acuity in children measured using The Auckland Optotypes.

PURPOSE: Sloan letters displayed by the Electronic Visual Acuity (EVA) system are the gold standard for recognition acuity measurement in research settings. However, letters are not always appropriate for children. The Auckland Optotypes (TAO) are a new, open-access set of 10 pictograms available in regular and vanishing formats. We sought to assess feasibility of using both formats of TAO for measuring visual acuity (VA) in children using a Bayesian adaptive staircase, in a community setting. METHODS: We tested 121 children (5-12 years old) with both formats of TAO, a handheld flipchart vision screener (Parr vision test), as well as the gold standard EVA. We measured feasibility of the three comparison tests in three ways. First, using limits of agreement (LoA) with EVA, second, calculating area under the receiver operating characteristic curve (AUC), and finally, investigating trial-by-trial responses. RESULTS: Agreement between tests was within test-retest reliability of EVA measures (LoATAOregular  = ±0.14, LoATAOvanishing  = ±0.15, LoAParr  = ±0.16 logMAR). TAO tests were highly effective at identifying children with vision impairment (AUCTAOregular  = 0.96, AUCTAOvanishing  = 0.95), whereas Parr was less effective (AUCParr  = 0.82). In 5-6 year old children there was an enhanced advantage of TAO (AUCTAOregular  = 0.97, AUCTAOvanishing  = 0.98) over Parr (AUCParr  = 0.75). Although each child completed 16 trials, approximately 10 trials were sufficient to achieve excellent LoA, and six trials sufficient for accurate screening. CONCLUSION: Threshold VA assessment and vision screening are feasible using both vanishing and regular formats of TAO.

The Auckland Optotypes: An open-access pictogram set for measuring recognition acuity.

When measuring recognition acuity in a research setting, the most widely used symbols are the Early Treatment of Diabetic Retinopathy Study (ETDRS) set of 10 Sloan letters. However, the symbols are not appropriate for patients unfamiliar with letters, and acuity for individual letters is variable. Alternative pictogram sets are available, but are generally comprised of fewer items. We set out to develop an open-access set of 10 pictograms that would elicit more consistent estimates of acuity across items than the ETDRS letters from visually normal adults. We measured monocular acuity for individual uncrowded optotypes within a newly designed set (The Auckland Optotype [TAO]), the ETDRS set, and Landolt Cs. Eleven visually normal adults were assessed on regular and vanishing formats of each set. Inter-optotype reliability and ability to detect subtle differences between participants were assessed using intraclass correlations (ICC) and fractional rank precision (FRP). The TAO vanishing set showed the strongest performance (ICC = 0.97, FRP = 0.90), followed by the other vanishing sets (Sloan ICC = 0.88, FRP = 0.74; Landolt ICC = 0.86, FRP = 0.80). Within the regular format, TAO again outperformed the existing sets (TAO ICC = 0.77, FRP = 0.75; Sloan ICC = 0.65, FRP = 0.64; Landolt ICC = 0.48, FRP = 0.63). For adults with normal visual acuity, the new optotypes (in both regular and vanishing formats) are more equally legible and sensitive to subtle individual differences than their Sloan counterparts. As this set does not require observers to be able to name Roman letters, and is freely available to use and modify, it may have wide application for measurement of acuity.

Use of the CONSIDER statement by eye health researchers when conducting and reporting research involving Indigenous peoples: an online survey.

BACKGROUND: Indigenous peoples experience worse eye health compared to non-Indigenous peoples. Service providers and researchers must avoid perpetuating this inequity. To help achieve this, researchers can use the CONSolIDated critERia for strengthening the reporting of health research involving Indigenous peoples (CONSIDER) statement. This study aimed to identify the degree to which the CONSIDER statement has been used by eye health researchers when conducting and reporting research with an Indigenous component, and how they perceive its relevance in their future research. METHODS: We used purposive sampling to recruit eye health researchers from any country who have undertaken research with an Indigenous component. The online survey collected quantitative and qualitative data and was analysed using descriptive statistics and reflexive thematic analysis. Responses were gathered on a four-point Likert scale (1 to 4), with four being the most positive statement. RESULTS: Thirty-nine eye health researchers from nine countries completed the survey (Aotearoa New Zealand, Argentina, Australia, Brazil, Canada, Colombia, Guatemala, Panama, Peru); almost two-thirds (n = 24) undertake epidemiological research. On average, participants disclosed only 'sometimes' previously reporting CONSIDER items (2.26 ± 1.14), but they thought the items were relevant to eye health research and were motivated to use these guidelines in their future research. Some participants requested clarity about how CONSIDER aligned with existing guidelines, and when and how to apply the statement. Others shared rich experiences of the benefits to their research of Indigenous leadership and collaboration. CONCLUSIONS: The CONSIDER statement is perceived as a valuable tool by these eye health researchers, and there are opportunities to maximise uptake and use, including increasing awareness of the statement, clarity about when it applies, and availability of institutional-level support.

Research about eye health and eye health services in Pacific Island Countries and Territories: a scoping review.

Background: We aimed to summarise the extent and nature of published research about eye health and eye health services in Pacific Island Countries and Territories since 1980. Methods: We searched Medline, EMBASE, Global Health and Cochrane Library to identify publications about eye health and eye health services in 22 Pacific Island Countries and Territories from 1 January 1980 to 26 January 2024. Study selection and data extraction were conducted by two reviewers independently. Findings: Of the 1610 publications identified, 180 were included. This research was most commonly conducted in Papua New Guinea (n = 52) or Fiji (n = 33) and focused on diabetic retinopathy (n = 29) or trachoma (n = 18), with few focused on cataract or refractive error. While eye health services research was common in the past, recent research focused on trachoma. The included research was largely undertaken and funded by people and organisations from Australia, Aotearoa New Zealand and the USA, though authors with Pacific affiliations is increasing. Interpretation: Few countries have up-to-date estimates of the prevalence of vision impairment or service coverage to enable evidence-informed planning. Increased effort is required to strengthen research capability to ensure research priorities in eye health are set by Pacific Peoples. Funding: The Fred Hollows Foundation New Zealand.

Learning to see after early and extended blindness: A scoping review.

Purpose: If an individual has been blind since birth due to a treatable eye condition, ocular treatment is urgent. Even a brief period of visual deprivation can alter the development of the visual system. The goal of our structured scoping review was to understand how we might better support children with delayed access to ocular treatment for blinding conditions. Method: We searched MEDLINE, Embase and Global Health for peer-reviewed publications that described the impact of early (within the first year) and extended (lasting at least 2 years) bilateral visual deprivation. Results: Of 551 reports independently screened by two authors, 42 studies met our inclusion criteria. Synthesizing extracted data revealed several trends. The data suggests persistent deficits in visual acuity, contrast sensitivity, global motion, and visual-motor integration, and suspected concerns for understanding complex objects and faces. There is evidence for resilience in color perception, understanding of simple shapes, discriminating between a face and non-face, and the perception of biological motion. There is currently insufficient data about specific (re)habilitation strategies to update low vision services, but there are several insights to guide future research in this domain. Conclusion: This summary will help guide the research and services provision to help children learn to see after early and extended blindness.

Visual impairment and its correction among Pacific youth in Aotearoa: findings from the Pacific Islands Families Study.

AIM: Childhood visual impairment has a life-long impact that, with early access to eyecare, is largely avoidable. We aimed to understand visual impairment and its correction among Pacific youth in Aotearoa New Zealand. METHOD: The Pacific Islands Families Study is a birth cohort study that tracks an original sample of 1,398 Pacific children born at Middlemore Hospital (Auckland). This analysis focuses on assessed visual acuity (at 9- and 18-years, using 0.3logMAR or 6/12 as the cut-off for visual impairment) and participants' self-reports about accessing eyecare services. RESULTS: Less than a fifth of children (111/729, 15.2%) and teens (86/457, 18.8%) reported having sought eyecare. The percentage of participants with refractive correction was 3.6% (32/887) at 9-years and 14.3% (66/463) at 18-years. At 9-years, 1.9% of children (16/853) had visual impairment in one eye only, and 0.9% (8/853) had visual impairment impacting both eyes. By 18-years these values increased to 7.9% (36/456) and 4.2% (19/456), respectively. Among those with visual impairment, most children (15/24, 62.5%) and teens (32/55, 58.2%) reported they did not have refractive correction. CONCLUSION: Although prevalence of visual impairment is relatively low compared to non-Pacific youth, much of the reported impairment appears to be avoidable with improved eyecare.

Interventions to promote access to eyecare for non-dominant ethnic groups in high-income countries: a scoping review.

PURPOSE: People who are distinct from the dominant ethnic group within a country can experience a variety of barriers to accessing eyecare services. We conducted a scoping review to map published interventions aimed at improving access to eyecare for non-Indigenous, non-dominant ethnic groups residing in high-income countries. METHODS: We searched MEDLINE, Embase and Global Health for studies that described an intervention to promote access to eyecare for the target population. Two authors independently screened titles and abstracts followed by review of the full text of potentially relevant sources. For included studies, data extraction was carried out independently by two authors. Findings were summarised using a combination of descriptive statistics and thematic analysis. RESULTS: We screened 5220 titles/abstracts, of which 82 reports describing 67 studies met the inclusion criteria. Most studies were conducted in the USA (90%), attempted to improve access for Black (48%) or Latinx (28%) communities at-risk for diabetic retinopathy (42%) and glaucoma (18%). Only 30% included the target population in the design of the intervention; those that did tended to be larger, collaborative initiatives, which addressed both patient and provider components of access. Forty-eight studies (72%) evaluated whether an intervention changed an outcome measure. Among these, attendance at a follow-up eye examination after screening was the most common (n=20/48, 42%), and directly supporting patients to overcome barriers to attendance was reported as the most effective approach. Building relationships between patients and providers, running coordinated, longitudinal initiatives and supporting reduction of root causes for inequity (education and economic) were key themes highlighted for success. CONCLUSION: Although research evaluating interventions for non-dominant, non-Indigenous ethnic groups exist, key gaps remain. In particular, the paucity of relevant studies outside the USA needs to be addressed, and target communities need to be involved in the design and implementation of interventions more frequently.

Evaluation of vision screening of 5-15-year-old children in three Tongan schools: comparison of The Auckland Optotypes and Lea symbols.

BACKGROUND: Comprehensive vision screening programmes for children are an important part of public health strategy, but do not exist in many countries, including Tonga. This project set out to assess: (1) the functional vision of children attending primary schools in Tonga and (2) how a new recognition acuity test (The Auckland Optotypes displayed on a tablet computer) compares to use of a standardised eye chart in this setting. METHODS: Children from three Tongan primary schools were invited to participate. Acuity testing was conducted using a standardised recognition acuity chart (Lea symbols) and the tablet test displaying two formats of The Auckland Optotypes. Measures of ocular alignment, stereo acuity and non-cycloplegic photorefraction were also taken. RESULTS: Parents of 249 children consented to participate. One child was untestable. Only 2.8 per cent of testable children achieved visual acuity worse than 0.3 logMAR in the weaker eye. Results from the Spot Photoscreener suggested that no children had myopia or hyperopia, but that some children had astigmatism. The tablet test was practical in a community setting, and showed ±0.2 logMAR limits of agreement with the Lea symbols chart. CONCLUSION: The sample of children in Tongan primary schools had good functional vision. A modified version of the tablet acuity test is a promising option for vision screening in this context.

Phenomenological approach to childhood cataract treatment in New Zealand using semi-structured interviews: how might we improve provision of care.

PURPOSE: To understand how we might improve the provision of medical care for children with cataracts. DESIGN: A phenomenological design was employed. Semi-structured interviews were conducted to capture rich descriptions of the phenomena. Our goal in the interview and the analysis was to understand the sources of distress associated with treatment for cataract and deprivation amblyopia which (1) could be addressed by the medical community and (2) related to treatment adherence. SETTING: Interviews were conducted by a non-clinician researcher in New Zealand (NZ) in a location chosen by informants. In NZ, the red reflex screening test is performed shortly after birth, and surgery to remove paediatric cataracts is publicly funded. PARTICIPANTS: Families of children who had a history of cataract in Auckland, NZ were posted an invitation to participate. Twenty families were interviewed. RESULTS: Our analysis illustrated that informants described a wide range of experiences, from declined cataract surgery to full adherence to medical advice including years of patching for more than 4 hours a day. Across these experiences, we identified three relevant themes; timing of diagnosis, communication between the parent and clinician, and parental social support networks. CONCLUSION: The medical community may be better placed to support families dealing with childhood cataract by improving detection of childhood cataract, building appropriate communication pathways and promoting social support, with an emphasis on empathetic, individualised care.

Impact of Children's Postural Variation on Viewing Distance and Estimated Visual Acuity.

PURPOSE: Reliable estimation of visual acuity requires that observers maintain a constant distance from the target, but use of chin rests is not always feasible. Our aim was to quantify children's movement during community testing and its impact on near (40 cm) and intermediate (150 cm) acuity measures. METHODS: Thirty-three 7-year-old children performed several acuity tests run on a tablet computer, administered in the child's home by a trained lay screener. The tablet webcam was used to derive a continuous estimate of the child's position during testing. We estimated acuity using both the recommended viewing distance and using trial-by-trial estimates of the child's physical distance from the screen. RESULTS: Although initial positioning in the 40-cm viewing distance condition was accurate, on 18% of trials children moved sufficiently to support a 0.1 logMAR improvement in acuity, leading 16% of staircases to overestimate acuity by more than one line. Initial positioning for the 150-cm condition was less accurate, but the longer viewing distance minimized the impact of children's movement on the visual angle of the target. Overall, at 150 cm 8% of staircases were overestimated by more than 0.1 logMAR. CONCLUSIONS: Children move substantially during intermediate and near acuity tests despite assessors encouraging maintenance of the correct viewing distance. TRANSLATIONAL RELEVANCE: Real-time estimates of the child's physical distance from the target are possible when assessments are conducted on camera-enabled devices. Correction for movement will likely lead to more accurate measures of near and intermediate visual acuity.

A comparison of tests for quantifying sensory eye dominance.

Clinicians rely heavily on stereoacuity to measure binocular visual function, but stereo-vision represents only one aspect of binocularity. Lab-based tests of sensory eye dominance (SED) are commonplace, but have not been translated to wider clinical practice. Here we compare several methods of quantifying SED in a format suitable for clinical use. We tested 30 participants with ostensibly normal vision on eight tests. Seven tests (#1-7) were designed to quantify SED in the form of an interocular balance-point (BP). In tests #1-6, we estimated a contrast-BP, the interocular difference in contrast required for observers to be equally likely to base their judgement on either eye, whereas in test #7 we measured binocular rivalry (interocular ratio of sensory dominance duration). We compare test-retest reliability (intra-observer consistency) and test-validity (inter-observer discriminatory power) and compare BP to stereoacuity (test #8). The test that best preserved inter-observer differences in contrast balance while maintaining good test-retest reliability was a polarity judgement using superimposed opposite-contrast polarity same-identity optotypes. A reliable and valid measure of SED can be obtained rapidly (20 trials) using a simple contrast-polarity judgement. Tests that use polarity-rivalrous stimuli elicit more reliable judgments than those that do not. SIGNIFICANCE STATEMENT: Although sensory eye dominance is central to understanding normal and disordered binocular vision, there is currently no consensus as to the best way to measure it. Here we compare several candidate measures of sensory eye dominance and conclude that a reliable measure of SED can be achieved rapidly using a judgement of stimulus contrast-polarity.

Contrast-balanced binocular treatment in children with deprivation amblyopia.

BACKGROUND: Children with deprivation amblyopia due to childhood cataract have been excluded from much of the emerging research into amblyopia treatment. An investigation was conducted to determine whether contrast-balanced binocular treatment - a strategy currently being explored for children with anisometropic and strabismic amblyopia - may be effective in children with deprivation amblyopia. METHODS: An unmasked, case-series design intended to assess proof of principle was employed. Eighteen children with deprivation amblyopia due to childhood cataracts (early bilateral n = 7, early unilateral n = 7, developmental n = 4), as well as 10 children with anisometropic (n = 8) or mixed anisometropic and strabismic amblyopia (n = 2) were prescribed one hour a day of treatment over a six-week period. Supervised treatment was available. Visual acuity, contrast sensitivity, global motion perception and interocular suppression were measured pre- and post-treatment. RESULTS: Visual acuity improvements occurred in the anisometropic/strabismic group (0.15 ± 0.05 logMAR, p = 0.014), but contrast sensitivity did not change. As a group, children with deprivation amblyopia had a smaller but statistically significant improvement in weaker eye visual acuity (0.09 ± 0.03 logMAR, p = 0.004), as well a significant improvement in weaker eye contrast sensitivity (p = 0.004). Subgroup analysis suggested that the children with early bilateral deprivation had the largest improvements, while children with early unilateral cataract did not improve. Interestingly, binocular contrast sensitivity also improved in children with early bilateral deprivation. Global motion perception improved for both subgroups with early visual deprivation, as well as children with anisometropic or mixed anisometropic/strabismic amblyopia. Interocular suppression improved for all subgroups except children with early unilateral deprivation. CONCLUSION: These data suggest that supervised contrast-balanced binocular treatment should be further investigated as a treatment option for children with deprivation amblyopia. However, for children with more severe deprivation amblyopia due to early unilateral cataracts, supplementary or alternative options should also be explored.

Global processing in amblyopia: a review.

Amblyopia is a neurodevelopmental disorder of the visual system that is associated with disrupted binocular vision during early childhood. There is evidence that the effects of amblyopia extend beyond the primary visual cortex to regions of the dorsal and ventral extra-striate visual cortex involved in visual integration. Here, we review the current literature on global processing deficits in observers with either strabismic, anisometropic, or deprivation amblyopia. A range of global processing tasks have been used to investigate the extent of the cortical deficit in amblyopia including: global motion perception, global form perception, face perception, and biological motion. These tasks appear to be differentially affected by amblyopia. In general, observers with unilateral amblyopia appear to show deficits for local spatial processing and global tasks that require the segregation of signal from noise. In bilateral cases, the global processing deficits are exaggerated, and appear to extend to specialized perceptual systems such as those involved in face processing.

Xenopus laevis tadpoles can regenerate neural retina lost after physical excision but cannot regenerate photoreceptors lost through targeted ablation.

PURPOSE: To determine whether the Xenopus laevis retina is capable of regenerating photoreceptor cells lost through apoptotic cell death in an inducible transgenic X. laevis model of retinitis pigmentosa (RP). METHODS: Acute rod photoreceptor apoptosis was induced in transgenic X. laevis expressing drug-inducible caspase 9. We subsequently monitored the ability of the retina to regenerate lost photoreceptors in the absence of drug, and in combination with physical injury or ectopic supplementation of basic fibroblast growth factor (FGF2). RESULTS: Direct activation of caspase 9 in rod photoreceptors resulted in the initiation of apoptosis and complete removal of rod photoreceptors within 4 days. Photoreceptors lost by apoptosis were not replaced over a 4-week recovery time frame. In contrast, physical disruption of rod-ablated retina was repaired by the end of a 3-week time frame, but did not result in rod photoreceptor regeneration other than at the site of injury. Furthermore, ectopic supplementation of FGF2 did not stimulate regeneration of photoreceptors lost by apoptosis. However, FGF2 supplementation increased the rate of regeneration of retina (including rod photoreceptors) in eyes from which retinal tissue was surgically removed. CONCLUSIONS: In the X. laevis retina, rod photoreceptors that undergo drug-induced caspase-9-mediated apoptosis are permanently lost and do not regenerate. In contrast, the neural retina (including rod photoreceptors) can regenerate in injured or retinectomized eyes, and this regeneration is promoted by supplementation with FGF2. However, FGF2 does not promote regeneration of rod photoreceptors that are selectively lost by apoptosis.

Controlled rod cell ablation in transgenic Xenopus laevis.

PURPOSE: Because of their high cone/rod ratio, Xenopus laevis may be a useful system for examining rod-cone interactions during retinal degeneration and mechanisms that underlie secondary cone degeneration. The authors developed an inducible model of retinitis pigmentosa (RP) in X. laevis to investigate these issues. METHODS: The authors generated transgenic X. laevis that express a modified caspase-9 (iCasp9) under the control of the X. laevis rod opsin promoter. iCasp9 is activated by the compound AP20187, resulting in an apoptotic cascade. Confocal microscopy, Western blot analysis, and electroretinography (ERG) were used to determine the effects of AP20187 on transgenic retinas. RESULTS: AP20187 induced rod cell apoptosis in transgenic tadpoles and postmetamorphic frogs. Longitudinal results indicate rod cell death led to cone cell dysfunction within 3 months; however, cone function was reinstated after 6 months. Returning cone function may be associated with increased numbers of morphologically normal cone cells and thickening of the inner nuclear layer. CONCLUSIONS: These studies indicate that X. laevis may be a useful system for examining cone dysfunction associated with rod death in RP and longer term regeneration of cone responses. This inducible model of RP is unique in that rod death proceeds through a well-understood mechanism, rod death can be carefully controlled to occur at any stage of development, and the stimulus for rod death can be removed at any time.