Measurement Accuracy When Using Spot Vision Screener With or Without Cycloplegia in Young Adults.

Purpose: There are many unclear points about the accuracy of measurement of cycloplegic refraction using the Spot Vision Screener (SVS). This study aimed to investigate the accuracy of SVS measurements with cycloplegia for myopia. Materials and Methods: Forty-nine healthy subjects were included, and refraction was measured. Objective refractions were measured by SVS, table-mounted autorefractometer (RT7000), and handheld autorefractometer (Retinomax Screeen) at noncycloplegic and cycloplegic conditions by 1% cyclopentolate. Subjective noncycloplegic refraction was obtained by a visual acuity and refraction test performed by certified orthoptists using a cross-cylinder. One-way repeated-measures analysis of variance was used to examine whether the measured refractions fluctuate due to different reflection tests. Results: In the noncycloplegic condition, the mean (±standard deviation) spherical equivalent (SE) measured by subjective method, SVS, RT7000, and Retinomax Screeen were -2.56 ± 3.00, -2.62 ± 2.38, -3.05 ± 2.84, and -3.26 ± 2.97, respectively. The subjective SE and objective SE measured by SVS had significantly less myopic value than the objective SE measured by two autorefractometers (p < 0.001). In the cycloplegic condition, the mean (± standard deviation) SE measured by SVS, RT7000, and Retinomax Screeen were -2.07 ± 2.66, -2.62 ± 2.98, and -2.66 ± 3.02, respectively. The objective SE measured by SVS had significantly less myopic value than SEs measured using other methods (p < 0.001). In the cycloplegic condition, SVS showed a fixed error wherein the SE was more hyperopic than that with the subjective method and SVS had a proportional error. Conclusion: In the measurement under cycloplegic conditions, use of an autorefractometer rather than a photorefractometer such as SVS was preferable.

Impact of induced pseudomyopia and refractive fluctuations of accommodative spasm on visual acuity.

CLINICAL RELEVANCE: High-contrast visual acuity is disproportionately poor in patients with accommodative spasm subtype of near reflex (SNR-A), relative to uncorrected refractive errors of equivalent magnitude. This exaggerated loss of performance in SNR-A may be explained by the combination of pseudomyopia and its fluctuations, vis-à-vis, each factor considered separately. BACKGROUND: To determine how combinations of pseudomyopic refraction and its temporal variations in SNR-A impact high-contrast visual acuity by inducing these patterns in healthy cyclopleged adults, relative to their baseline acuity. METHODS: Refractive profiles of 15 patients with SNR-A were obtained from a previous study, averaged, and induced before the right eye of 14 cyclopleged adults (mean ±1 SD age: 22.7 ± 2.6 yrs) by feeding the profile into a coaxially placed, motorised, Badal optometer. LogMAR acuity was measured using the method of constant stimuli: (1) before cycloplegia, (2) after cycloplegia and post-cycloplegia with (3) combination of pseudomyopia and its temporal fluctuations, (4) only pseudomyopia, (5) only temporal fluctuations in refraction about emmetropia, (6) condition 5 with double the amplitude of induced fluctuations and (7) condition 5 with half the amplitude of induced fluctuations. RESULTS: The induced refractive fluctuations ranged from -0.80 to -1.75D, around a mean pseudomyopia of -1.20D. Visual acuity deterioration was maximum for the combination of pseudomyopia and temporal fluctuations condition (0.51 ± 0.07logMAR), followed by only pseudomyopia (0.27 ± 0.05logMAR) and only refractive fluctuations conditions (0.17 ± 0.04logMAR), all relative to baseline post-cycloplegia (0.13 ± 0.04logMAR) (p < 0.001). Visual acuity loss increased with doubling of refractive fluctuations (0.20 ± 0.04logMAR), relative to native fluctuations or halving the amplitude (0.15 ± 0.03logMAR) (p < 0.01). Task precision, as adjudged from the slope of psychometric function, followed a similar pattern of loss as visual acuity. CONCLUSION: Combination of induced pseudomyopia and temporal fluctuations in refraction produces an additive loss of visual acuity and task precision, relative to baseline and each factor considered separately.

Deep learning for predicting refractive error from multiple photorefraction images.

BACKGROUND: Refractive error detection is a significant factor in preventing the development of myopia. To improve the efficiency and accuracy of refractive error detection, a refractive error detection network (REDNet) is proposed that combines the advantages of a convolutional neural network (CNN) and a recurrent neural network (RNN). It not only extracts the features of each image, but also fully utilizes the sequential relationship between images. In this article, we develop a system to predict the spherical power, cylindrical power, and spherical equivalent in multiple eccentric photorefraction images. Approach First, images of the pupil area are extracted from multiple eccentric photorefraction images; then, the features of each pupil image are extracted using the REDNet convolution layers. Finally, the features are fused by the recurrent layers in REDNet to predict the spherical power, cylindrical power, and spherical equivalent. RESULTS: The results show that the mean absolute error (MAE) values of the spherical power, cylindrical power, and spherical equivalent can reach 0.1740 D (diopters), 0.0702 D, and 0.1835 D, respectively. SIGNIFICANCE: This method demonstrates a much higher accuracy than those of current state-of-the-art deep-learning methods. Moreover, it is effective and practical.

Photorefraction with Spot Vision Screener versus Visual Acuity Testing as Community-Based Preschool Vision Screening at the Age of 3.5 Years in Japan.

Nationwide in Japan, a community-based vision-screening program in 3.5-year-old children is conducted in three steps: questionnaires and home visual acuity testing as the primary screening; visual acuity testing by nurses and pediatricians' inspection in community health centers as the secondary screening; and examinations by ophthalmologists as the tertiary screening. In this study, we introduced photorefraction with a Spot vision screener in addition to visual acuity testing to answer the clinical question of whether photorefraction could better detect eye diseases and potentially replace visual acuity testing. Photorefraction was performed on 813 consecutive 3.5-year-old children in a center. The children were sent to tertiary examinations, which were based on the Spot vision screener standard, in addition to the visual acuity testing standard: failure in either eye to pass 0.5 visual acuity in a center. A notice to visit ophthalmologists was issued for 95 children (11%), and documents with the diagnosis were sent back to the Heath Office for 76 children (80%). The rate of children with anisometropic or ametropic amblyopia or accommodative esotropia as treatment-requiring diseases was highest in cases of no pass at both standards (10/15 = 66%), and higher in cases of no pass only at the Spot vision screener standard (13/45 = 28%), compared with cases of no pass only at the visual acuity testing standard (6/33 = 18%, p = 0.0031). Photorefraction, in addition to visual acuity testing and inspection led to additional eye diseases detection at 3.5 years. Visual acuity testing at home would not be omitted in the introduction of photorefraction.

Drive-by Photoscreening: Plusoptix, 2WIN and Blinq Amblyopia Detection During the COVID-19 Pandemic.

BACKGROUND: Community photoscreening for amblyopia had successfully been adopted by many communities, however many clinics curtailed screening as a result of the COVID-19 pandemic. We modified three conventional devices and tested them for outdoor, drive-by socially distanced photoscreening and refraction. METHODS: External frames that provide luminance control and focus distance were fashioned for plusoptiX S12 (Nuremberg, Germany), Adaptica 2WIN in Kaleidos case (Padova, Italy) and the Rebion blinq (Boston, USA). Children were screened by each device and then Retinomax (Righton, Japan) before AAPOS guideline validation. RESULTS: Eighty-eight children average age 8±7 years had precise refraction and alignment from which 69% AAPOS 2003 risk factors were determined. The sensitivity/specificity/inconclusive rate for plusoptiX was 85%/96%/16%, for 2WIN 79%/89%/5% and for blinq 43%/74%/8%. Blinq improved to 54%/70% when screening for amblyopia ± strabismus. Bland Altman analysis of spherical equivalent showed plusoptiX and 2WIN with less over-minus than Retinomax and J0 and J45 vectors highly reliable for astigmatism determination. CONCLUSION: The infrared photorefractors in modified cases reliably screened amblyopia risk factors and refraction. The birefringent scanner provided drive-by results but less reliably with wire-frame opaque case than without the case in a dimly lit room. Modified drive-by photoscreeners could help reduce amblyopia and provide socially distanced refraction during an extended pandemic.

Does the Accuracy and Repeatability of Refractive Error Estimates Depend on the Measurement Principle of Autorefractors?

Purpose: The purpose of this study was to determine the accuracy and repeatability of refractive errors obtained using three autorefractors based on different measurement principles, vis-à-vis, gold-standard retinoscopy. Methodology: Accuracy of noncycloplegic, sphero-cylindrical refractive error of 234 eyes was obtained using the rotary prism-based RM-8900 closed-field autorefractor, photorefraction based Spot vision screener, wavefront aberrometry based E-see, and streak retinoscopy by four different examiners, masked to the results of each other. Intersession repeatability of autorefractors was determined by repeat measurements in a subset of 40 subjects. Results: Retinoscopy values of M, J0, and J45 power vectors for the cohort ranged from -10.2 to 8 D, -1.4 to 1.8 D, and -0.9 to 1.2 D, respectively. Across autorefractors, the interequipment bias of M and J0 power vectors were statistically insignificant (< ±0.5 D; P > 0.05) but the corresponding limits of agreement were ±2.5 and ±1 D, respectively, without any trend across instruments or the patient's age (P > 0.5). Repeatability of M and J0 power vectors were ±0.75 D and ±0.40 D, respectively, across autorefractors. The range of J45 power vector was too narrow for any meaningful analysis. Conclusions: Refractive errors measured using autorefractors operating on different principles show minimal bias and good short-term repeatability but relatively large agreement limits, vis-à-vis, retinoscopy. Among them, the wavefront aberrometry based E-see autorefractor performs relatively better in all measurement parameters evaluated here. Translational Relevance: Although autorefractor estimates of noncycloplegic refractive error appears independent of their measurement principle, their relatively poor agreement with gold-standard retinoscopy warrants caution while used for screening and quantification of refractive errors.

A One-Step, Streamlined Children's Vision Screening Solution Based on Smartphone Imaging for Resource-Limited Areas: Design and Preliminary Field Evaluation.

BACKGROUND: Young children's vision screening, as part of a preventative health care service, produces great value for developing regions. Besides yielding a high return on investment from forestalling surgeries using a low-cost intervention at a young age, it improves school performance and thus boosts future labor force quality. Leveraging low-skilled health care workers with smartphones and automated diagnosis to offer such programs can be a scalable model in resource-limited areas. OBJECTIVE: This study aimed to develop and evaluate an effective, efficient, and comprehensive vision screening solution for school children in resource-limited areas. First, such an exam would need to cover the major risk factors of amblyopia and myopia, 2 major sources of vision impairment effectively preventable at a young age. Second, the solution must be integrated with digital patient record-keeping for long-term monitoring and popular statistical analysis. Last, it should utilize low-skilled technicians and only low-cost tools that are available in a typical school in developing regions, without compromising quality or efficiency. METHODS: A workflow for the screening program was designed and a smartphone app was developed to implement it. In the standardized screening procedure, a young child went through the smartphone-based photoscreening in a dark room. The child held a smartphone in front of their forehead, displaying pre-entered personal information as a quick response code that duplexed as a reference of scale. In one 10-second procedure, the child's personal information and interpupillary distance, relative visual axis alignment, and refractive error ranges were measured and analyzed automatically using image processing and artificial intelligence algorithms. The child's risk for strabismus, myopia, and anisometropia was then derived and consultation given. RESULTS: A preliminary evaluation of the solution was conducted alongside yearly physical exams in Luoyang, Henan, People's Republic of China. It covered 20 students with suspected strabismus and 80 randomly selected students, aged evenly between 8 and 10. Each examinee took about 1 minute, and a streamlined workflow allowed 3 exams to run in parallel. The 1-shot and 2-shot measurement success rates were 87% and 100%, respectively. The sensitivity and specificity of strabismus detection were 0.80 and 0.98, respectively. The sensitivity and specificity of myopia detection were 0.83 and 1.00, respectively. The sensitivity and specificity of anisometropia detection were 0.80 and 1.00, respectively. CONCLUSIONS: The proposed vision screening program is effective, efficient, and scalable. Compared with previously published studies on utilizing a smartphone for an automated Hirschberg test and photorefraction screening, this comprehensive solution is optimized for practicality and robustness, and is thus better ready-to-deploy. Our evaluation validated the achievement of the program's design specifications.

Deep Learning-Based Prediction of Refractive Error Using Photorefraction Images Captured by a Smartphone: Model Development and Validation Study.

BACKGROUND: Accurately predicting refractive error in children is crucial for detecting amblyopia, which can lead to permanent visual impairment, but is potentially curable if detected early. Various tools have been adopted to more easily screen a large number of patients for amblyopia risk. OBJECTIVE: For efficient screening, easy access to screening tools and an accurate prediction algorithm are the most important factors. In this study, we developed an automated deep learning-based system to predict the range of refractive error in children (mean age 4.32 years, SD 1.87 years) using 305 eccentric photorefraction images captured with a smartphone. METHODS: Photorefraction images were divided into seven classes according to their spherical values as measured by cycloplegic refraction. RESULTS: The trained deep learning model had an overall accuracy of 81.6%, with the following accuracies for each refractive error class: 80.0% for ≤-5.0 diopters (D), 77.8% for >-5.0 D and ≤-3.0 D, 82.0% for >-3.0 D and ≤-0.5 D, 83.3% for >-0.5 D and <+0.5 D, 82.8% for ≥+0.5 D and <+3.0 D, 79.3% for ≥+3.0 D and <+5.0 D, and 75.0% for ≥+5.0 D. These results indicate that our deep learning-based system performed sufficiently accurately. CONCLUSIONS: This study demonstrated the potential of precise smartphone-based prediction systems for refractive error using deep learning and further yielded a robust collection of pediatric photorefraction images.

Accommodation responses following contrast adaptation.

The current study explored the effects of contrast adaptation on the accommodation response (AR), using low- and high-pass filtered video clips as stimuli. Ten young myopic (mean ± standard deviation: -2.91 ± 1.36D) and 10 near emmetropic subjects (-0.19 ± 0.14D) participated in the study. The AR was monitored under monocular viewing conditions using an eccentric infrared photorefractor. A 2-stage procedure was used: (1) the minimum spatial frequency content necessary to produce a proper individual AR; and (2) the AR was compared before and after adaptation to low-pass (s = -0.5), control (s = 0) and high-pass (s = +0.5) filtered videos. We found that (1) the average threshold Sinc-blur of both myopes and emmetropes necessary to evoke accommodation was (mean ± standard deviation) λ = 7.40 ± 4.05 cpd. Myopes required a higher Sinc blur (average, 10.00 ± 4.05 cpd) compared to emmetropes (average, 4.80 ± 1.60 cpd). (2) Adaptation to low-pass filtered videos increased the AR by 0.41 ± 0.33D in the myopic group and reduced it in the emmetropic group by 0.31 ± 0.25D. Adaptation to high pass-filtered videos induced similar changes in both refractive groups (an increase of 0.41 ± 0.40D and 0.46 ± 0.29D for myopes and emmetropes, respectively). Our measurements show that the human AR can be modified by spatial frequency selective contrast adaptation although these were short-term effects. The perhaps most striking finding was that adaptation to low pass filtered videos had opposite effects on the AR in emmetropes and myopes. It remains to be studied whether these differences were a consequence of myopia or a contributing factor in myopia development.

Estimation Dynamic Distance Direct Ophthalmoscopy (eDDDO): A novel, objective method for the quantitative assessment of accommodation in young children.

Purpose: To describe estimation dynamic distance direct ophthalmoscopy (eDDDO) and compare it with the monocular estimation method of dynamic retinoscopy (eDR) for the assessment of accommodation in children. Methods: In this prospective observational cohort study, an ophthalmologist performed eDDDO followed by eDR in children with normal eyes, and then under the partial effects of cyclopentolate and tropicamide to assess performance of eDDDO with eDR under the condition of pharmacologically induced accommodation failure. Only one eye of each child was recruited in the study. To study the inter-observer variation, two masked pediatric ophthalmology fellows performed eDDDO in the similar manner. Results: For the comparison of eDDDO with eDR, 60 eyes of 60 patients were recruited. The mean age of the patients was 10.4 years. The mean accommodation on eDDDO was 3.0D, 5.1D, 9.8D, and 11.3D at 40 cm, 25 cm, 10 cm, and 8 cm, respectively and 3.0D, 5.0D, 9.5D, and 11.0D on eDR. The eDDDO overestimated accommodation by a mean 0.17D (95% CL 0-0.48D, P = 0.5). The correlation of eDDDO with eDR was excellent (Pearson r 0.98, T value 76.0). The inter-observer difference with eDDDO was not significant (mean 1D, 95% CL 0-2.6D, P = 0.9) and the correlation between two observers was excellent (Pearson r 0.9, T value 12.7). The eDDDO and eDR were also performed on 12 eyes of 6 children with a mean age of 8.5 years (range 8-12 years) under the partial effect of cyclopentolate and tropicamide, where eDDDO overestimated the accommodation by a mean 0.3D (95% CL 0- 1.2D, P = 0.7) and the correlation was excellent (Pearson r 1.0, T value 45). Conclusion: eDDDO is a simple, reliable, quantitative, and objective technique of accommodation assessment for children. Further studies with larger sample are required to assess its performance in disorders of accommodation affecting younger children and in children with ocular comorbidities.

Effect of spatial filtering on accommodation.

The purpose of this study was to develop and test a new method that uses natural images to investigate the influence of their spatial frequency content on the accommodation response (AR). Furthermore, the minimum spatial frequency content was determined that was necessary to induce an AR. Blur of the images was manipulated digitally in the Fourier domain by filtering with a Sinc function. Fourteen young subjects participated in the experiment. A 2-step procedure was used: (1) verifying that a high amount of Sinc-blur does not evoke accommodation, (2) increasing the width of the Sinc-blur filter in logarithmic steps until an AR was evoked. AR was continuously monitored using eccentric infrared photorefraction at 60 Hz sampling rate under monocular viewing conditions. Under condition (1), Sinc-blur of λ = 1 cpd did not evoke accommodation, while under condition (2) an average (mean ±â€¯standard deviation) Sinc-blur of λ = 5.57 ±â€¯4.67 cpd (median: 4 cpd, interquartile range: 2-7 cpd) evoked accommodation. Dividing the subjects into myopes and emmetropes revealed that the myopic group required higher amounts of λ (higher spatial frequencies) to stimulate their accommodation (mean λ = 9.33 ±â€¯4.99 cpd, for myopes; and mean λ = 2.75 ±â€¯0.97 cpd, for emmetropes). Our results support the notion that the AR is most effectively stimulated at mid-spatial frequencies and that myopes may require higher spatial frequencies to elicit a comparable AR.

Calibration of the PlusOptix PowerRef 3 with change in viewing distance, adult age and refractive error.

PURPOSE: The PowerRef 3 is frequently used in studying the near triad of accommodation, vergence and pupil responses in normal and clinical populations. Within a range, the defocus measurement of the PowerRef 3 is linearly related to the eye's defocus. While the default factory-calibrated slope of this relation (calibration factor) is 1, it has been shown that the slope can vary across individuals. Here, we addressed the impact of changes in viewing distance, age and defocus of the eye on the calibration factor. METHODS: We manipulated viewing distance (40 cm, 1 m and 6 m) and recruited participants with a range of accommodative capabilities: participants in their 20s, 40s and over 60 years old. To test whether any effect was larger than the range of measurement reliability of the instrument, we collected data for each condition four times: two in the same session, another on the same day, and one on a different day. RESULTS: The results demonstrated that viewing distance did not affect the calibration factor over the linear range, regardless of age or uncorrected refractive error. The largest proportion of the variance was explained by between-subject differences. CONCLUSIONS: Calibration data for the PowerRef 3 were not sensitive to changes in viewing distance. Nevertheless, our results re-emphasise the relevance of calibration for studies of individual participants.

Role of microfluctuations in accommodation: a novel approach to reduce non-accommodative noise.

Accommodative response and its possible role in myopia development has been explored through the study of the microfluctuations (MFs) of accommodation, which are commonly divided in high (1.0 to 2.3 Hz) and low (0.1 to 0.6 Hz) frequency components. Previous research efforts have evidenced that a certain percentage of the amplitude of MFs seems not to originate in the accommodative response. We aimed to develop and test a new approach to reduce this non-accommodative noise. For this purpose, ten healthy participants were enrolled to determine the difference between the amplitude of MFs at near and distance for each range of frequencies, which was defined as the relative amplitude of MFs. The findings support the exploration of the relative rather than absolute values of the amplitude of MFs to better understand the contribution of both accommodative and non-accommodative factors to MFs.

Comparison of the PlusOptix S09 and Spot Vision photorefractor to cycloretinoscopy.

PURPOSE: The purpose of this study was to compare refraction measurements for children with the PlusOptix S09 and Spot Vision with cycloplegic retinoscopy. METHODS: One hundred thirty-six eyes of 68 children (26 boys and 42 girls) were evaluated prospectively. The subjects were separated into two groups. Group 1 comprised the subjects age between 5 and 9 years. Group 2 comprised the subjects age between 10 and 18 years. Photorefraction with PlusOptix S09, photorefraction with Spot Vision and cycloplegic retinoscopy were performed in each patient. Spherical equivalents, spherical power, cylindrical power and axis values were compared between three methods. RESULTS: The mean age of the patients was 7.12 ± 1.5 years in group 1 and 12.24 ± 1.8 years in group 2. Spherical equivalent and spherical power measured with PlusOptix S09 were statistically smaller than measured with cycloplegic retinoscopy for group 1 (p = 0.001, p = 0.001) and for group 2 (p = 0.000, p = 0.000). The mean cylindrical power measured with PlusOptix S09 was not statistically different compared to cycloplegic retinoscopy for both groups (p = 0.314, p = 0.05). Spherical equivalents measured with Spot Vision were statistically smaller than measured with cycloplegic retinoscopy for both groups (p = 0.000, p = 0.012). Spherical power measured with Spot Vision was statistically smaller than measured with cycloplegic retinoscopy for group 1 (p = 0.000), but the difference was not statistically significant for group 2 (p = 0.084). The mean cylindrical power measured with Spot Vision was statistically higher than cycloplegic retinoscopy for both groups (p = 0.000, p = 0.012). CONCLUSIONS: PlusOptix S09 and Spot Vision devices give acceptable results for screening, but prescription of spectacles should not be made according to PlusOptix S09 or Spot Vision devices alone.

Tribal Odisha Eye Disease Study # 4: Accuracy and utility of photorefraction for refractive error correction in tribal Odisha (India) school screening.

Purpose: To compare the photorefraction system (Welch Allyn Spot™) performance with subjective refraction in school sight program in one Odisha (India) tribal district. Methods: In a cross-sectional study school students, aged 5-15 years, referred after the preliminary screening by trained school teachers received photoscreening and subjective correction. The photoscreener was compared to subjective refraction in the range of +2D to -7.5D. Statistical analysis included Friedman nonparametric test, Wilcoxon signed-rank test, linear regression, and Bland-Altman plotting. Results: The photoscreener was used in 5990 children. This analysis included 443 children (187 males, 256 females, and the mean age was 12.43 ± 2.5 years) who received both photorefraction and subjective correction, and vision improved to 6/6 in either eye. The median spherical equivalent (SE) with spot photorefraction was 0.00 D (minimum -5.0D; maximum +1.6 D), and with subjective correction was 0.00D (minimum -6.00 D; maximum +1.5 D). The difference in the SE between the two methods was statistically significant (P < 0.001) using Friedman nonparametric test; it was not significant for J 45 and J 180 (P = 0.39 and P = 0.17, respectively). There was a good correlation in linear regression analysis (R2 = 0.84) and Bland-Altman showed a good agreement between photorefraction and subjective correction in the tested range. Conclusion: Photorefraction may be recommended for autorefraction in school screening with reasonable accuracy if verified with a satisfactory subjective correction. The added advantages include its speed, need of less expensive eye care personnel, ability to refract both eyes together, and examination possibility in the native surrounding.

Two-dimensional simulation of eccentric photorefraction images for ametropes: factors influencing the measurement.

PURPOSE: Eccentric photorefraction and Purkinje image tracking are used to estimate refractive state and eye position simultaneously. Beyond vision screening, they provide insight into typical and atypical visual development. Systematic analysis of the effect of refractive error and spectacles on photorefraction data is needed to gauge the accuracy and precision of the technique. METHODS: Simulation of two-dimensional, double-pass eccentric photorefraction was performed (Zemax). The inward pass included appropriate light sources, lenses and a single surface pupil plane eye model to create an extended retinal image that served as the source for the outward pass. Refractive state, as computed from the luminance gradient in the image of the pupil captured by the model's camera, was evaluated for a range of refractive errors (-15D to +15D), pupil sizes (3 mm to 7 mm) and two sets of higher-order monochromatic aberrations. Instrument calibration was simulated using -8D to +8D trial lenses at the spectacle plane for: (1) vertex distances from 3 mm to 23 mm, (2) uncorrected and corrected hyperopic refractive errors of +4D and +7D, and (3) uncorrected and corrected astigmatism of 4D at four different axes. Empirical calibration of a commercial photorefractor was also compared with a wavefront aberrometer for human eyes. RESULTS: The pupil luminance gradient varied linearly with refractive state for defocus less than approximately 4D (5 mm pupil). For larger errors, the gradient magnitude saturated and then reduced, leading to under-estimation of refractive state. Additional inaccuracy (up to 1D for 8D of defocus) resulted from spectacle magnification in the pupil image, which would reduce precision in situations where vertex distance is variable. The empirical calibration revealed a constant offset between the two clinical instruments. CONCLUSIONS: Computational modelling demonstrates the principles and limitations of photorefraction to help users avoid potential measurement errors. Factors that could cause clinically significant errors in photorefraction estimates include high refractive error, vertex distance and magnification effects of a spectacle lens, increased higher-order monochromatic aberrations, and changes in primary spherical aberration with accommodation. The impact of these errors increases with increasing defocus.

A Comparison of Refraction Defects in Childhood Measured Using Plusoptix S09, 2WIN Photorefractometer, Benchtop Autorefractometer, and Cycloplegic Retinoscopy.

PURPOSE: To compare Plusoptix (Gmbh, Nuremberg, Germany), 2WIN (Adaptica, Padua, Italy), the benchtop refractometer (Auto-Kerato-Refractometer KR-8900; Topcon Co, Tokyo, Japan), and retinoscopy with regard to the consistencies. MATERIALS AND METHODS: In our prospective study, 200 eyes of 100 patients were included. We analyzed the demographics and characteristics of the patients, the percentage of patients from whom measurements could not be obtained, the measurements from both patients' eyes of pupil diameter, spherical, cylindrical, axis, and spherical equivalence. RESULTS: The mean age ± SD was 7.8±4.5 years (range, 1-18 years). Pupil diameter measurements were found to be consistent (Cronbach's alpha value >0.8). The sphere and spherical equivalence measurements for both eyes were found to be consistent with each other in all apparatus (Cronbach's alpha value >0.8). However, consistency was found to be lower in cylindrical values and the Jackson cross-cylinder measurements at 0° and 45° axis were found to be inconsistent with each other (Cronbach's alpha value <0.8). CONCLUSIONS: While consistency was observed in all methods in terms of sphere and spherical equivalence, consistency dropped in cylindrical values and no consistency was observed in axis values. It is important to take this point into consideration, especially in axis measurements.

Reducing the lag of accommodation by auditory biofeedback: A pilot study.

The purpose of this study was to investigate whether a reduction of the accommodative lag is possible by training the accuracy of accommodation using auditory biofeedback. Accommodation responses were measured in thirty-one young adults with myopia for dioptric target distances of 2.0, 2.5, and 3.0D using an eccentric infrared photorefractor. For the biofeedback training, subjects were randomly assigned to an experimental (n=15) or a control group (n=16). Subjects of the experimental group were provided with two tones while fixating a target, one tone was related to their accommodative response and the second to the target distance. Their task was to match these tones. The control group did not receive any auditory biofeedback. Two different training methods were applied, a continuous training of 200s, and ten consecutive sessions of 20s each. The training effects on the lag of accommodation (change Δ) were highly variable. Regarding the entire study group, the observed change in the accommodative lag was greater at closer distances, while no difference between the two training methods was revealed. Nevertheless, seven experimental subjects reduced their lag by ⩾0.3D (3.0D target distance: Δlong=-0.29±0.20D, Δshort=-0.24±0.21D). This reduction was also seen in two control subjects. Remeasurement revealed that the average training effect cannot be preserved over a period of 5-7days. The current investigation has shown that the accuracy of accommodation can be trained in some subjects using auditory biofeedback for target distances of 2.5D or closer.

Accommodation and pupil responses to random-dot stereograms.

We investigated the dynamics of accommodative and pupillary responses to random-dot stereograms presented in crossed and uncrossed disparity in six visually normal young adult subjects (mean age=25.8±3.1 years). Accommodation and pupil measures were monitored monocularly with a custom built photorefraction system while subjects fixated at the center of a random-dot stereogram. On each trial, the stereogram initially depicted a flat plane and then changed to depict a sinusoidal corrugation in depth while fixation remained constant. Increase in disparity specified depth resulted in pupil constriction during both crossed and uncrossed disparity presentations. The change in pupil size between crossed and uncrossed disparity conditions was not significantly different (p>0.05). The change in pupil size was also accompanied by a small concomitant increase in accommodation. In addition, the dynamic properties of pupil responses varied as a function of their initial (starting) diameter. The finding that accommodation and pupil responses increased with disparity regardless of the sign of retinal disparity suggests that these responses were driven by apparent depth rather than shifts in mean simulated distance of the stimulus. Presumably the need for the increased depth of focus when viewing stimuli extended in depth results in pupil constriction which also results in a concomitant change in accommodation. Starting position effects in pupil response confirm the non-linearity in the operating range of the pupil.

Comparison of non-cycloplegic photorefraction, cycloplegic photorefraction and cycloplegic retinoscopy in children.

AIM: To compare the results of noncycloplegic photorefraction, cycloplegic photorefraction and cycloplegic refraction in preschool and non-verbal children. METHODS: One hundred and ninety-six eyes of 98 children (50 females, 48 males) were included in the study. Firstly, non-cycloplegic photorefraction was achieved with Plusoptix A09; secondly, cycloplegic photorefraction was carried out with Plusoptix A09 after 10 min cyclopentolate. Finally, 30min after instillation of twice cyclopentolate, cycloplegic refraction was obtained with autorefraction and/or standard retinoscopy. Spheric equivalent, spheric power, cylindric power and cylindrical axis measurements were statistically compared. RESULTS: The mean age was 28.8±18.5mo (range 12-72mo). The differences in spherical equivalent, spheric power and cylindrical power measured by the three methods were found statistically significant (P<0.05). The spherical equivalent and spheric power measured by cycloplegic photorefraction were statistically higher than the measurements of the other methods (P<0.05). The cylindrical power measured by cycloplegic refraction was statistically lower than the measurements of the photorefraction methods (P<0.05). There was no significant difference in cylindrical axis measurements between three methods (P>0.05). CONCLUSION: For the determination of refractive errors in children, the Plusoptix A09 measurements give incorrect results after instillation of cyclopentolate. Additionally, the cylindrical power measured by Plusoptix A09 with or without cycloplegia is higher. However, the non-cycloplegic Plusoptix A09 measures spheric equivalent and spheric power similar to cycloplegic refraction measurements in preschool and non-verbal children.