Contrast detection thresholds are elevated with optical quality loss in keratoconus. This study hypothesized that suprathreshold contrast perception is also impaired in keratoconus, with the impairment being predictable from the pattern of loss in threshold-level performance. Contrast detection thresholds were determined across a range of spatial frequencies in 12 cases with mild to severe keratoconus and 12 age-similar controls. These values were used to predict the contrast needed to achieve perceptual matches between reference and test spatial frequency pairs (peak of CSF Vs. 0.3x, 0.5x, 2x or 3x spatial frequency from the peak) for stimuli at 10% and 50% suprathreshold contrast. Contrast thresholds predicted a 1.5 to 6.7-fold increase in the test pattern's contrast to obtain a perceptual match with the reference pattern in keratoconus, relative to controls. Contrary to predictions, the empirical data of contrast matches between test and reference patterns were similar for higher than peak spatial frequencies at both contrast levels. However, as predicted, test patterns required higher contrast than the reference pattern for a perceptual match for lower than peak spatial frequencies. These results were similar to controls and invariant of disease severity, interocular asymmetry and short-term changes in optical quality. Unlike thresholds, suprathreshold contrast perception of resolvable high spatial frequencies appears immune to optical quality losses in keratoconus. These results are discussed in the context of the prevailing models of contrast constancy in healthy humans. Breakdown of contrast constancy at lower than peak spatial frequencies may reflect the properties of the testing paradigm employed here.

AIM:To assess the performance of a bespoke software for automated counting of intraocular lens (IOL) glistenings in slit-lamp images.METHODS:IOL glistenings from slit-lamp-derived digital images were counted manually and automatically by the bespoke software. The images of one randomly selected eye from each of 34 participants were used as a training set to determine the threshold setting that gave the best agreement between manual and automatic grading. A second set of 63 images, selected using randomised stratified sampling from 290 images, were used for software validation. The images were obtained using a previously described protocol. Software-derived automated glistenings counts were compared to manual counts produced by three ophthalmologists.RESULTS:A threshold value of 140 was determined that minimised the total deviation in the number of glistenings for the 34 images in the training set. Using this threshold value, only slight agreement was found between automated software counts and manual expert counts for the validating set of 63 images (κ=0.104, 95%CI, 0.040-0.168). Ten images (15.9%) had glistenings counts that agreed between the software and manual counting. There were 49 images (77.8%) where the software overestimated the number of glistenings.CONCLUSION:The low levels of agreement show between an initial release of software used to automatically count glistenings in in vivo slit-lamp images and manual counting indicates that this is a non-trivial application. Iterative improvement involving a dialogue between software developers and experienced ophthalmologists is required to optimise agreement. The results suggest that validation of software is necessary for studies involving semi-automatic evaluation of glistenings.

BACKGROUND:'Blue-light filtering', or 'blue-light blocking', spectacle lenses filter ultraviolet radiation and varying portions of short-wavelength visible light from reaching the eye. Various blue-light filtering lenses are commercially available. Some claims exist that they can improve visual performance with digital device use, provide retinal protection, and promote sleep quality. We investigated clinical trial evidence for these suggested effects, and considered any potential adverse effects. OBJECTIVES:To assess the effects of blue-light filtering lenses compared with non-blue-light filtering lenses, for improving visual performance, providing macular protection, and improving sleep quality in adults. SEARCH METHODS:We searched the Cochrane Central Register of Controlled Trials (CENTRAL; containing the Cochrane Eyes and Vision Trials Register; 2022, Issue 3); Ovid MEDLINE; Ovid Embase; LILACS; the ISRCTN registry; ClinicalTrials.gov and WHO ICTRP, with no date or language restrictions. We last searched the electronic databases on 22 March 2022. SELECTION CRITERIA:We included randomised controlled trials (RCTs), involving adult participants, where blue-light filtering spectacle lenses were compared with non-blue-light filtering spectacle lenses. DATA COLLECTION AND ANALYSIS:Primary outcomes were the change in visual fatigue score and critical flicker-fusion frequency (CFF), as continuous outcomes, between baseline and one month of follow-up. Secondary outcomes included best-corrected visual acuity (BCVA), contrast sensitivity, discomfort glare, proportion of eyes with a pathological macular finding, colour discrimination, proportion of participants with reduced daytime alertness, serum melatonin levels, subjective sleep quality, and patient satisfaction with their visual performance. We evaluated findings related to ocular and systemic adverse effects. We followed standard Cochrane methods for data extraction and assessed risk of bias using the Cochrane Risk of Bias 1 (RoB 1) tool. We used GRADE to assess the certainty of the evidence for each outcome. MAIN RESULTS:We included 17 RCTs, with sample sizes ranging from five to 156 participants, and intervention follow-up periods from less than one day to five weeks. About half of included trials used a parallel-arm design; the rest adopted a cross-over design. A variety of participant characteristics was represented across the studies, ranging from healthy adults to individuals with mental health and sleep disorders. None of the studies had a low risk of bias in all seven Cochrane RoB 1 domains. We judged 65% of studies to have a high risk of bias due to outcome assessors not being masked (detection bias) and 59% to be at high risk of bias of performance bias as participants and personnel were not masked. Thirty-five per cent of studies were pre-registered on a trial registry. We did not perform meta-analyses for any of the outcome measures, due to lack of available quantitative data, heterogenous study populations, and differences in intervention follow-up periods. There may be no difference in subjective visual fatigue scores with blue-light filtering lenses compared to non-blue-light filtering lenses, at less than one week of follow-up (low-certainty evidence). One RCT reported no difference between intervention arms (mean difference (MD) 9.76 units (indicating worse symptoms), 95% confidence interval (CI) -33.95 to 53.47; 120 participants). Further, two studies (46 participants, combined) that measured visual fatigue scores reported no significant difference between intervention arms. There may be little to no difference in CFF with blue-light filtering lenses compared to non-blue-light filtering lenses, measured at less than one day of follow-up (low-certainty evidence). One study reported no significant difference between intervention arms (MD - 1.13 Hz lower (indicating poorer performance), 95% CI - 3.00 to 0.74; 120 participants). Another study reported a less negative change in CFF (indicating less visual fatigue) with high- compared to low-blue-light filtering and no blue-light filtering lenses. Compared to non-blue-light filtering lenses, there is probably little or no effect with blue-light filtering lenses on visual performance (BCVA) (MD 0.00 logMAR units, 95% CI -0.02 to 0.02; 1 study, 156 participants; moderate-certainty evidence), and unknown effects on daytime alertness (2 RCTs, 42 participants; very low-certainty evidence); uncertainty in these effects was due to lack of available data and the small number of studies reporting these outcomes. We do not know if blue-light filtering spectacle lenses are equivalent or superior to non-blue-light filtering spectacle lenses with respect to sleep quality (very low-certainty evidence). Inconsistent findings were evident across six RCTs (148 participants); three studies reported a significant improvement in sleep scores with blue-light filtering lenses compared to non-blue-light filtering lenses, and the other three studies reported no significant difference between intervention arms. We noted differences in the populations across studies and a lack of quantitative data. Device-related adverse effects were not consistently reported (9 RCTs, 333 participants; low-certainty evidence). Nine studies reported on adverse events related to study interventions; three studies described the occurrence of such events. Reported adverse events related to blue-light filtering lenses were infrequent, but included increased depressive symptoms, headache, discomfort wearing the glasses, and lower mood. Adverse events associated with non-blue-light filtering lenses were occasional hyperthymia, and discomfort wearing the spectacles. We were unable to determine whether blue-light filtering lenses affect contrast sensitivity, colour discrimination, discomfort glare, macular health, serum melatonin levels or overall patient visual satisfaction, compared to non-blue-light filtering lenses, as none of the studies evaluated these outcomes. AUTHORS' CONCLUSIONS:This systematic review found that blue-light filtering spectacle lenses may not attenuate symptoms of eye strain with computer use, over a short-term follow-up period, compared to non-blue-light filtering lenses. Further, this review found no clinically meaningful difference in changes to CFF with blue-light filtering lenses compared to non-blue-light filtering lenses. Based on the current best available evidence, there is probably little or no effect of blue-light filtering lenses on BCVA compared with non-blue-light filtering lenses. Potential effects on sleep quality were also indeterminate, with included trials reporting mixed outcomes among heterogeneous study populations. There was no evidence from RCT publications relating to the outcomes of contrast sensitivity, colour discrimination, discomfort glare, macular health, serum melatonin levels, or overall patient visual satisfaction. Future high-quality randomised trials are required to define more clearly the effects of blue-light filtering lenses on visual performance, macular health and sleep, in adult populations.

Purpose: The purpose of this study was to determine changes in spatial and depth vision with increasing severity of keratoconus and to model the structure-function relationship to identify distinct phases of loss in visual function with disease severity. Methods: Best-spectacle corrected, monocular high-contrast visual acuity, contrast sensitivity function (CSF) and stereoacuity of 155 cases (16-31 years) with mild to advanced bilateral keratoconus was determined using standard psychophysical tests. Disease severity was quantified using the multimetric D-index. The structure-function relationship was modeled using linear, positive exponential, negative exponential, and logistic nonlinear regression equations. Results: The logistic regression model explained the highest proportion of variance for spatial vision, without bias in the residual plots (R-2 >= 66%, P < 0.001). Visual acuity showed a distinct ceiling phase and a steeper loss rate with increasing D-index (1.8 units/D-index) in this model. The area under the CSF lacked this ceiling phase and had a shallower loss rate (0.28 units/D-index). Stereoacuity loss with D-index was poorly explained by all models tested (P <= 0.2). Cases with lower and bilaterally symmetric D-index had better stereoacuity (181.6-376 arc seconds) than those with higher D-index (>400 arc second); both were significantly poorer than controls (approximately 30 arc second). Conclusions: Vision loss in keratoconus varies with the visual function parameter tested. Contrast sensitivity may be an earlier indicator of spatial vision loss than visual acuity. Depth perception is significantly deteriorated from very early stages of the disease.

We thank Drs. Kanclerz and Grzybowski for their interest in our work. In our review,we extensively discussed the published literature pertaining to the effects of lens glistenings on visual function. We agree that forward light scatter from glistenings will cause reduced image contrast However, the key question is whether the forward light scatter is sufficient to cause disability glare. As noted by Drs Kanclerz and Grzybowski, laboratory models have demonstrated correlations between glistenings density and size and light scatter, including our own publication, but clinical studies reporting visual impairment with glistenings occurrence are in the minority and have limitations. Indeed, the retrospective cohort studyofHenriksen et al., referenced in the letter,was a small pilot study, lacking methodology relating to image acquisition and analysis, such as ambient illumination level and digital/analogue camera settings, and with glistenings quantification and analysis undertaken using operatordependent, general purpose, image processing software (‘ImageJ’). In addition, the authors stated themselves, that the study was underpowered to detect the true effect. Wewould like to directDrs.Kanclerz andGrzybowski to our recent paper, undertaken to further address such issues and which is referenced and discussed in the review. In a prospective methodology we evaluated forward light scatter in a cohort of patients with glistenings. Using a newly developed, defined, reproducible, standardized 8-point ordinal scale of glistenings density and an array of computerized visual function tests (Advanced Vision and Optometric Tests, City Occupational, London, UK), performed under strictly controlled ambient conditions and based on the same scientific principle as the C-Quant test (Oculus, Optigeräte, Germany), we found no association between glistening grades and visual function including straylight parameter or integrated straylight parameter. This study we feel further adds to the evidence that glistenings, unless present in extremely large amounts, have a minimal effect on visual performance in vivo. We do, however, recognise the limitations of light scatter testing that is currently available to undertake such in vivo investigations. In their study Colin and Orignac could only obtain valid results in about 50% of cases with the C-quant test This same test was used by Henriksen et al. although no mention was made in their paper of the percentage of successfully completed tests. It is of note that in our own study. approximately 20% of participants were not able to complete our light scatter test It must also be recognized that evaluation of glistenings themselves and their visual perturbations in vivo is much more challenging than in vitro. In our experience, the precise quantification of glistenings in vivo has proven difficult and dependent on multiple factors often not discussed in studies, such as ambient illumination, slit lamp parameters and image acquisition parameters.

Purpose: Superiority in corneal diameter, white-to-white (WTW) distance, measurements using objective imaging devices over subjective face-to-face measurements by eye care practitioners (ECP) have been reported previously. The primary aim of this study was to compare manual and automated corneal diameter measurements using two different objective imaging devices. A secondary aim was to compare results obtained by an experienced ECP and novice user.

Purpose: The aim of this study was to assess the agreement of anterior corneal parameters and pupil diameter and offset measured with the Medmont E300 corneal topographer and the Aladdin optical biometer.

Purpose: To review the published scientific literature concerning clinical and material degradations of intraocular lenses after implantation in cataract surgery. Methods: A search was undertaken using the following databases: CENTRAL (including Cochrane Eyes and Vision Trials Register; The Cochrane Library: Issue 2 of 12 February 2019), Ovid MEDLINE (R) without Revisions (1996 to February week 2, 2019), Ovid MEDLINE (R) (1946 to February week 2, 2019), Ovid MEDLINE (R) Daily Update 19 February 2019, MEDLINE and MEDLINE non-indexed items, Embase (1980–2019, week 7), Embase (1974–2019, 19 February), Ovid MEDLINE (R) and Epub Ahead of Print, in-Process & Other Non-Indexed Citations and Daily (1946 to 19 February 2019), Web of Science (all years), the metaRegister of Controlled Trials ( mRCT) ( www.controlled-trials.com ), ClinicalTrials.gov ( www.clinicaltrial.gov ) and the WHO International Clinical Trials Registry Platform ( www.who.int/ictrp/search/en ). Only published articles in English were selected. Search terms/keywords included ‘IOL’ or ‘intraocular lens’, combined with ‘opacification’, degradation, glistenings, nanoglistenings, whitening, transmittance, light scatter, discolouration/discoloration, performance, quality, material, biocompatibility, calcification, explantation and ultraviolet/UV radiation. Relevant in-article references not returned in our searches were also considered. Results: After review of the available articles, the authors included 122 publications in this review, based on the quality of their methodology and their originality. The studies included in this review were randomized controlled trials, cohort studies, case-controlled studies, case series, case reports, laboratory studies and review papers. Differing material degradations of intraocular lenses have been described and their associated pathophysiology studied. Reported anomalies include photochemical alterations, water vacuoles, internal and surface calcific deposits, surface coatings and discolouration. The nature of such changes has been shown to depend on the type of intraocular lenses material used and/or manufacturing processes and storage conditions employed. Changes in the intraocular lens can also be influenced by surgical technique, coexisting ocular pathologies and topical and systemic medications. The clinical significance of these degradations is variable, with some resulting in significant visual disturbance and the need for intraocular lens explantation and others producing only minimal visual impairments. Failure to recognize the precise nature of the problem may lead to unnecessary laser capsulotomy procedures. Conclusion: Clinical degradations of intraocular lenses are uncommon but have been reported following the implantation of intraocular lenses made of differing biomaterials. Their correct identification and thorough investigation to determine the underlying cause is necessary for optimal patient management and the prevention of such problems. Choosing a lens made of a particular material may be important in patients with certain ocular conditions.

Purpose: To compare the Clareon IOL with the Tecnis PCB00 IOL in terms of visual performance, refractive outcomes, glistenings occurrence, and quality-of-life outcomes. Setting: Guy's and St Thomas' NHS Foundation Trust, London, United Kingdom. Design: Single-center, single-masked, prospective, randomized controlled trial. Methods: One hundred thirty-nine patients with bilateral cataracts were randomized to receive the Clareon (C IOL) or Tecnis (T IOL) IOL. Visual acuity, refraction, central corneal thickness (CCT), endothelial cell loss, contrast sensitivity, mesopic gap acuity, evaluation of glistenings, and rates of perioperative and postoperative complications were recorded. Quality-of-life outcomes were measured with the EuroQOL-5 dimensions questionnaire and the patient-reported outcome measures (PROMs) questionnaire. Optimized A-constants were available for the T IOL but not for the C IOL. Results: Seventy-one patients (140 eyes) received the C IOLs and 68 patients (134 eyes) received the T IOLs. Data were analyzed for the first implanted eye. At 12 months, mean uncorrected distance visual acuity (logarithm of the minimum angle of resolution) was 0.02 +/- 0.10 and 0.01 +/- 0.08 (mean +/- SD; P =.49; 95% CI, -0.02 to 0.04) in the C IOL and T IOL groups, respectively. Corrected distance visual acuity was -0.02 +/- 0.09 and -0.03 +/- 0.06, respectively (P =.45; 95% CI, -0.02 to 0.04). The increase in CCT was 14 +/- 19 and 16 +/- 28 mm, respectively (P =.63; 95% CI, -10.16 to 6.16). Mean absolute refraction spherical equivalent error from target refraction was 0.41 +/- 0.28 for the C IOL and 0.25 +/- 0.2 for the T IOL groups (P =.002; 95% CI, 0.08 to 0.24). Glistenings were minimal (median grade 0), with no difference in grades between groups (P =.2). PROMs improved postoperatively and were similar in both groups. Conclusions: There were no differences in visual outcomes between the Clareon IOL and Tecnis PCB00 IOL. Glistenings were rarely observed in either IOL with no difference in grades. There was no difference in perioperative or postoperative complications. Surgeon optimization of the A-constant for the Clareon IOL is recommended. Copyright (C) 2020 Published by Wolters Kluwer on behalf of ASCRS and ESCRS

Purpose: Variations in corneal curvature and astigmatism influence contact lens fit and acuity. The aim of this study was to investigate the asymmetry in corneal shape between eyes and its association with gender in a healthy student population.

Is bigger better? Glistenings, forward light scatter and visual performance C. Hull, N. Stanojcic, E. Philippaki, D. O'Brart CityUniversity of London, Centre for Applied Vision Research, London, United Kingdom, ST Thomas’ Hospital, GKT Department of Ophthalmology, London, United Kingdom, Kings College London, Department of Physics, London, United Kingdom, ST Thomas’ Hospital, GKT Department of Ophthalmology, London, United Kingdom

Blue‐blocking (BB) spectacle lenses, which attenuate short‐wavelength light, are being marketed to alleviate eyestrain and discomfort when using digital devices, improve sleep quality and potentially confer protection from retinal phototoxicity. The aim of this review was to investigate the relative benefits and potential harms of these lenses.

Refractive changes in diabetic eyes have long been reported but with equivocal results. The lens has been a more recent focus as the source of any change but it is possible that multiple sources of variation have made it difficult to demonstrate a systematic change clinically. The aim of this study was therefore to use a bovine lens model to investigate the optical changes in hyperglycaemia and when lenses are returned to normal glucose levels as would occur following commencement of treatment. Bovine eyes were obtained and their lenses excised under sterile conditions before placing them in culture medium within an incubator using standard tissue culture techniques. In the first experiment, lenses were transferred into culture medium containing 5 mm (n = 12), 15 mm (n = 12) and 30 mm (n = 12) glucose. Measurements were made of the change in back vertex focusing distance with equatorial lens diameter using the ScanTox™ measurement system. From these measurements, the back vertex focal length and primary longitudinal spherical aberration were derived. In a second experiment, lenses maintained at 30 mm glucose (n = 7) were stepped down to 5 mm glucose to simulate starting diabetic therapy and measured in the same way. Changes over time were assessed with a linear regression model. A trend towards myopia was observed with increasing hyperglycaemia, this was not statistically significant. When lenses were stepped-down from hyperglycaemia to normal physiological levels of glucose, a hyperopic shift was observed in line with published clinical studies that again failed to reach statistical significance. High variability in the measurement on longitudinal spherical aberration prevented any significant trends being measured. Our results suggest that there are no consistent crystalline lens-induced refractive changes following exposure to hyperglycaemia for time-periods up to 5 days used in the current study. It is possible that bovine lenses are able to offset the raised osmotic pressure from high glucose levels in the short-term by a process of osmoregulation and that repeated osmotic stress or longer term exposure may be required to induce the changes in refraction that are seen clinically.

Purpose: Cataract enhanced service (direct referral) schemes have been in existence for over 12 years. Such schemes make better use of the primary care practitioner's professional expertise and have the potential to reduce costs and provide an improved patient pathway. Surprisingly little has been published about these schemes, hence there is a lack of evidence to inform local decision making about existing and future services. The aim of this study was to provide more evidence by surveying the Local Optical Committees (LOCs) to obtain their views on their involvement or lack of involvement in cataract enhanced service schemes in the London region. Secondary aims were to compare how schemes operate and determine why schemes do not exist in some areas. Method: A structured survey of London’s 14 LOCs was carried out on two occasions (2007 and 2012). LOCs were contacted via e-mail, telephone or written letter. Some supporting information was obtained from PCTs. All data were analysed qualitatively. Results: In 2007, only two out of the 10 LOCs that had participated in the 2005 Cataract Choose and Book scheme were involved in running a full direct referral scheme. This had risen to six by 2012 with a total of 11 LOCs having participated in a trial/pilot scheme by that date. The remaining three LOCs have never participated in a scheme. Although there are similarities across schemes (e.g. requirement for accreditation, a referral fee etc), marked differences were found in patient booking arrangements, requirements during initial assessment and post-operative assessment. The percentage of LOCs involved in full schemes in the London region (43%) is lower than for the rest of England (69%). Where trial/pilot schemes had run but no full scheme had been implemented the major reasons reported were: lack of central funding; the schemes were only feasibility studies; and the requirement for a Unique Booking Reference Number (UBRN) for the Choose and Book process. Conclusions: Enhanced cataract service schemes do not always develop into full schemes even if the trial/pilot scheme has been deemed successful. Schemes may have a more prominent role in future with requirements on Clinical Commissioning Groups to provide an improved patient experience within tighter financial constraints. The co-ordinating activity across England of the Local Optical Committee Support Unit (LOCSU) and the newly formed Local Professional Networks for Eyecare should help increase uniformity of approach. All established cataract schemes will need to be re-procured during 2013/14 if they are to continue without interruption.

Purpose: The aim of this study was to evaluate optical and visual functional performance of the osteo-odonto-keratoprosthesis (OOKP).Methods: Optical design and analysis was performed with customized optical design software. Nine patients with implanted OOKP devices and 9 age-matched control patients were assessed. Contrast sensitivity was assessed and glare effect was measured with a brightness acuity test. All OOKP patients underwent kinetic Goldmann perimetry and wavefront aberrometry and completed the National Eye Institute Visual Function Questionnaire-25 (NEI VFQ-25).Results: Optical analysis showed that the optical cylinder is near diffraction-limited. A reduction in median visual acuity (VA) with increasing glare settings was observed from 0.04 logMAR (without glare) to 0.20 logMAR (with glare at "high" setting) and significantly reduced statistically when compared with the control group at all levels of glare (P < 0.05). Contrast sensitivity was significantly reduced when compared with age-matched controls at medium and high spatial frequencies (P < 0.05). Median Goldmann perimetry was 65 degrees (interquartile range, 64-74 degrees; V-4e isopters) and 69 degrees excluding 2 glaucomatous subjects. Several vision-related NEI VFQ-25 subscales correlated significantly with VA at various brightness acuity test levels and contrast sensitivity at medium spatial frequencies, including dependency, general vision, near activities and distance activities.Conclusions: The OOKP optical cylinder provides patients with a good level of VA that is significantly reduced by glare. We have shown in vivo that updates to the optical cylinder design have improved the patient's field of view. Reduction of glare and refinement of cylinder alignment methods may further improve visual function and patient satisfaction.