1
|
Rovira-Gay C, Mestre C, Argiles M, Vinuela-Navarro V, Pujol J. Feasibility of measuring fusional vergence amplitudes objectively. PLoS One 2023; 18:e0284552. [PMID: 37141181 PMCID: PMC10159156 DOI: 10.1371/journal.pone.0284552] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/24/2023] [Accepted: 04/04/2023] [Indexed: 05/05/2023] Open
Abstract
Two tests to measure fusional vergence amplitudes objectively were developed and validated against the two conventional clinical tests. Forty-nine adults participated in the study. Participants' negative (BI, base in) and positive (BO, base out) fusional vergence amplitudes at near were measured objectively in an haploscopic set-up by recording eye movements with an EyeLink 1000 Plus (SR Research). Stimulus disparity changed in steps or smoothly mimicking a prim bar and a Risley prism, respectively. Break and recovery points were determined offline using a custom Matlab algorithm for the analysis of eye movements. Fusional vergence amplitudes were also measured with two clinical tests using a Risley prism and a prism bar. A better agreement between tests was found for the measurement of BI than for BO fusional vergence amplitudes. The means ± SD of the differences between the BI break and recovery points measured with the two objective tests were -1.74 ± 3.35 PD and -1.97 ± 2.60 PD, respectively, which were comparable to those obtained for the subjective tests. For the BO break and recovery points, although the means of the differences between the two objective tests were small, high variability between subjects was found (0.31 ± 6.44 PD and -2.84 ± 7.01 PD, respectively). This study showed the feasibility to measure fusional vergence amplitudes objectively and overcome limitations of the conventional subjective tests. However, these tests cannot be used interchangeably due to their poor agreement.
Collapse
Affiliation(s)
- Cristina Rovira-Gay
- Centre for Sensors, Instruments, and Systems Development (CD6), Universitat Politècnica de Catalunya (UPC), Terrassa, Spain
| | - Clara Mestre
- Centre for Sensors, Instruments, and Systems Development (CD6), Universitat Politècnica de Catalunya (UPC), Terrassa, Spain
- School of Optometry, Indiana University, Bloomington, IN, United States of America
| | - Marc Argiles
- Centre for Sensors, Instruments, and Systems Development (CD6), Universitat Politècnica de Catalunya (UPC), Terrassa, Spain
| | - Valldeflors Vinuela-Navarro
- Centre for Sensors, Instruments, and Systems Development (CD6), Universitat Politècnica de Catalunya (UPC), Terrassa, Spain
| | - Jaume Pujol
- Centre for Sensors, Instruments, and Systems Development (CD6), Universitat Politècnica de Catalunya (UPC), Terrassa, Spain
| |
Collapse
|
2
|
Fogt N, Toole AJ, Rogers DL. A review of proximal inputs to the near response. Clin Exp Optom 2021; 99:30-8. [DOI: 10.1111/cxo.12301] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/10/2014] [Revised: 03/19/2015] [Accepted: 04/08/2015] [Indexed: 11/28/2022] Open
Affiliation(s)
- Nick Fogt
- The Ohio State University College of Optometry, Columbus, Ohio, USA,
| | - Andrew J Toole
- The Ohio State University College of Optometry, Columbus, Ohio, USA,
| | - David L Rogers
- Department of Ophthalmology, Nationwide Children's Hospital, Columbus, Ohio, USA,
- Department of Ophthalmology, The Ohio State University College of Medicine, Columbus, Ohio, USA,
| |
Collapse
|
3
|
Accommodative response in children with attention deficit hyperactivity disorder (ADHD): the influence of accommodation stimulus and medication. Graefes Arch Clin Exp Ophthalmol 2020; 258:1299-1307. [DOI: 10.1007/s00417-020-04645-4] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/27/2019] [Revised: 02/05/2020] [Accepted: 03/04/2020] [Indexed: 12/14/2022] Open
|
4
|
Vera J, Redondo B, Molina R, Koulieris GA, Jiménez R. Validation of an Objective Method for the Qualitative and Quantitative Assessment of Binocular Accommodative Facility. Curr Eye Res 2019; 45:636-644. [DOI: 10.1080/02713683.2019.1688837] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/25/2022]
Affiliation(s)
- Jesús Vera
- Department of Optics, Faculty of Sciences, University of Granada, Granada, Spain
| | - Beatríz Redondo
- Department of Optics, Faculty of Sciences, University of Granada, Granada, Spain
| | - Rubén Molina
- Department of Optics, Faculty of Sciences, University of Granada, Granada, Spain
| | | | - Raimundo Jiménez
- Department of Optics, Faculty of Sciences, University of Granada, Granada, Spain
| |
Collapse
|
5
|
Abstract
Aim: To compare the effect of induced vertical diplopia (small and large separation) on reading speed and accuracy. Methods: The Radner Reading Chart (RRC) was used to measure reading speed (correct words per minute (wpm)) and accuracy (percentage). Accuracy was measured using two different methods: ‘accuracy-omission’ where only the omission of a word reduced the score, and ‘accuracy-addition and omission’ where any error reduced the score. Three viewing conditions were created using Fresnel prisms on plano glasses: a control condition without diplopia (6 prism dioptres (Δ) base up (BU) over each eye), small separation vertical diplopia (3Δ BU right eye and 3Δ base down (BD) left eye) and large separation vertical diplopia (6Δ BU right eye and 6Δ BD left eye). Viewing conditions were counterbalanced to minimise order effects. Results: Twenty-four participants were included with a mean age of 20.1 years. The mean reading speed in the control condition was 156.90 wpm. Both diplopic conditions significantly reduced the reading speed compared to the control condition, small separation diplopia to 62.75 wpm (p < 0.001) and large separation diplopia to 105.71 wpm (p < 0.001). The mean reading speed with small separation diplopia was significantly slower than the mean reading speed with large separation diplopia (p < 0.01). Median accuracy scores in the control and the large separation diplopia conditions were 100% using both methods of measuring accuracy. The small separation diplopia condition significantly reduced accuracy to 92.86% (accuracy-omission method) and to 57.50% (accuracy-addition and omission method) compared to the control condition (p < 0.01) and the large separation diplopia condition (p < 0.05). Conclusion: When vertical diplopia was induced using Fresnel prisms, diplopia of smaller separation resulted in the greatest reduction in reading speed and accuracy, compared to without diplopia and large separation diplopia.
Collapse
Affiliation(s)
- Beckie Lijka
- Academic Unit of Ophthalmology and Orthoptics, University of Sheffield, GB.,Sheffield Teaching Hospitals NHS Foundation Trust, GB
| | - Sonia Toor
- Academic Unit of Ophthalmology and Orthoptics, University of Sheffield, GB.,Sheffield Teaching Hospitals NHS Foundation Trust, GB
| | | |
Collapse
|
6
|
Murray C, Newsham D. The Normal Accommodative Convergence/Accommodation (AC/A) Ratio. J Binocul Vis Ocul Motil 2018; 68:140-147. [PMID: 30358493 DOI: 10.1080/2576117x.2018.1529450] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/20/2018] [Revised: 09/14/2018] [Accepted: 09/22/2018] [Indexed: 06/08/2023]
Abstract
BACKGROUND AND PURPOSE To measure the Accommodative Convergence (PD)/Accommodation ratio (D) (AC/A) in a cohort of visually normal participants using common clinical methods. PATIENTS AND METHODS AC/A ratios of 50 visually normal subjects were measured using the distance gradient (DG), near gradient (NG), gradient using synoptophore, (SG) and heterophoria (H) methods in line with current clinical practice. RESULTS Median AC/A ratios for NG, DG, SG, and H were 2.0 (IQR 2.0), 1.0 (IQR 0.6), 1.0 (IQR 0.6), and 5.0 (IQR 1.7), respectively. There was a statistically significant difference in ratios calculated between all methods in the same subjects (p < 0.05). There were differences in DG vs NG, DG vs H, SG vs H, and NG vs H (p < 0.05); only DG vs SG did not differ significantly (p > 0.05). Lens power toleration was found to affect AC/A ratio in DG (p < 0.05) and latent deviation was significantly associated with (p < 0.05) AC/A ratio in NG. CONCLUSION Calculated AC/A ratios in this cohort were lower than historically cited normal (3-5:1) in all gradient methods. There were differences in AC/A values in the same subjects calculated with different gradient methods, indicating that these methods are not interchangeable and a universal normal range should not be applied for all methods.
Collapse
Affiliation(s)
- Craig Murray
- a Orthoptics and Vision Science , University of Liverpool , Brownlow Hill , United Kingdom
| | - David Newsham
- a Orthoptics and Vision Science , University of Liverpool , Brownlow Hill , United Kingdom
| |
Collapse
|
7
|
Satou T, Ito M, Shinomiya Y, Takahashi Y, Hara N, Niida T. Differences in the Stimulus Accommodative Convergence/Accommodation Ratio using Various Techniques and Accommodative Stimuli. Strabismus 2018; 26:53-61. [DOI: 10.1080/09273972.2018.1459746] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 10/17/2022]
Affiliation(s)
- Tsukasa Satou
- Department of Orthoptics and Visual Sciences, School of Health Sciences, International University of Health and Welfare, Ohtawara, Tochigi, Japan
| | - Misae Ito
- Department of Orthoptics and Visual Sciences, School of Health Sciences, International University of Health and Welfare, Ohtawara, Tochigi, Japan
| | - Yuma Shinomiya
- Department of Orthoptics and Visual Sciences, School of Health Sciences, International University of Health and Welfare, Ohtawara, Tochigi, Japan
| | - Yoshiaki Takahashi
- Department of Orthoptics and Visual Sciences, School of Health Sciences, International University of Health and Welfare, Ohtawara, Tochigi, Japan
| | - Naoto Hara
- Department of Orthoptics and Visual Sciences, School of Health Sciences, International University of Health and Welfare, Ohtawara, Tochigi, Japan
| | - Takahiro Niida
- Department of Orthoptics and Visual Sciences, School of Health Sciences, International University of Health and Welfare, Ohtawara, Tochigi, Japan
| |
Collapse
|
8
|
Horwood AM. 2016 International Orthoptic Congress Burian Lecture: Folklore or Evidence? Strabismus 2017; 25:120-127. [PMID: 28426269 PMCID: PMC5571894 DOI: 10.1080/09273972.2017.1305425] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 10/19/2022]
Abstract
The theme of the 2016 Burian Lecture is how our understanding of strabismus has been changed by the research carried out in our laboratory in Reading over the years. Accommodation and convergence are fundamental to orthoptics, but actual responses have often been very different compared to what we had expected. This paper outlines how our laboratory's understanding of common issues such as normal development of accommodation and convergence, their linkage, intermittent strabismus, anisometropia, orthoptic exercises, and risk factors for strabismus have changed. A new model of thinking about convergence and accommodation may help us to better understand and predict responses in our patients.
Collapse
Affiliation(s)
- Anna M Horwood
- a Infant Vision Laboratory, School of Psychology & Clinical Language Sciences, University of Reading , Reading , United Kingdom
- b Orthoptic Department , Royal Berkshire Hospital , Reading , United Kingdom
| |
Collapse
|
9
|
Armstrong RA. Recommendations for analysis of repeated-measures designs: testing and correcting for sphericity and use of manova and mixed model analysis. Ophthalmic Physiol Opt 2017; 37:585-593. [PMID: 28726257 DOI: 10.1111/opo.12399] [Citation(s) in RCA: 37] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/14/2016] [Accepted: 06/12/2017] [Indexed: 12/26/2022]
Abstract
PURPOSE A common experimental design in ophthalmic research is the repeated-measures design in which at least one variable is a within-subject factor. This design is vulnerable to lack of 'sphericity' which assumes that the variances of the differences among all possible pairs of within-subject means are equal. Traditionally, this design has been analysed using a repeated-measures analysis of variance (RM-anova) but increasingly more complex methods such as multivariate anova (manova) and mixed model analysis (MMA) are being used. This article surveys current practice in the analysis of designs incorporating different factors in research articles published in three optometric journals, namely Ophthalmic and Physiological Optics (OPO), Optometry and Vision Science (OVS), and Clinical and Experimental Optometry (CXO), and provides advice to authors regarding the analysis of repeated-measures designs. RECENT FINDINGS Of the total sample of articles, 66% used a repeated-measures design. Of those articles using a repeated-measures design, 59% and 8% analysed the data using RM-anova or manova respectively and 33% used MMA. The use of MMA relative to RM-anova has increased significantly since 2009/10. A further search using terms to select those papers testing and correcting for sphericity ('Mauchly's test', 'Greenhouse-Geisser', 'Huynh and Feld') identified 66 articles, 62% of which were published from 2012 to the present. SUMMARY If the design is balanced without missing data then manova should be used rather than RM-anova as it gives better protection against lack of sphericity. If the design is unbalanced or with missing data then MMA is the method of choice. However, MMA is a more complex analysis and can be difficult to set up and run, and care should be taken first, to define appropriate models to be tested and second, to ensure that sample sizes are adequate.
Collapse
Affiliation(s)
- Richard A Armstrong
- School of Life and Health Sciences: Ophthalmic Research Group, School of Optometry, Aston University, Birmingham, UK
| |
Collapse
|
10
|
Sreenivasan V, Babinsky EE, Wu Y, Candy TR. Objective Measurement of Fusional Vergence Ranges and Heterophoria in Infants and Preschool Children. Invest Ophthalmol Vis Sci 2017; 57:2678-88. [PMID: 27183054 PMCID: PMC4874477 DOI: 10.1167/iovs.15-17877] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022] Open
Abstract
Purpose Binocular alignment typically includes motor fusion compensating for heterophoria. This study evaluated heterophoria and then accommodation and vergence responses during measurement of fusional ranges in infants and preschoolers. Methods Purkinje image eye tracking and eccentric photorefraction (MCS PowerRefractor) were used to record the eye alignment and accommodation of uncorrected infants (n = 17; 3–5 months old), preschoolers (n = 19; 2.5–5 years), and naïve functionally emmetropic adults (n = 14; 20–32 years; spherical equivalent [SE], +1 to −1 diopters [D]). Heterophoria was derived from the difference between monocular and binocular alignments while participants viewed naturalistic images at 80 cm. The presence or absence of fusion was then assessed after base-in (BI) and base-out (BO) prisms (2–40 prism diopters [pd]) were introduced. Results Mean (±SD) SE refractions were hyperopic in infants (+2.4 ± 1.2 D) and preschoolers (+1.1 ± 0.6 D). The average exophoria was similar (P = 0.11) across groups (Infants, −0.79 ± 2.5 pd; Preschool, −2.43 ± 2.0 pd; Adults, −1.0 ± 2.7 pd). Mean fusional vergence range also was similar (P = 0.1) for BI (Infants, 11.2 ± 2.5 pd; Preschool, 8.8 ± 2.8 pd; Adults, 11.8 ± 5.2 pd) and BO (Infants, 14 ± 6.6 pd; Preschool, 15.3 ± 8.3 pd; Adults, 20 ± 9.2 pd). Maximum change in accommodation to the highest fusible prism was positive (increased accommodation) for BO (Infants, 1.69 ± 1.4 D; Preschool, 1.35 ± 1.6 D; Adults, 1.22 ± 1.0 D) and negative for BI (Infants, −0.96 ± 1.0 D; Preschool, −0.78 ± 0.6 D; Adults, −0.62 ± 0.3 D), with a similar magnitude across groups (BO, P = 0.6; BI, P = 0.4). Conclusions Despite typical uncorrected hyperopia, infants and preschoolers exhibited small exophorias at 80 cm, similar to adults. All participants demonstrated substantial fusional ranges, providing evidence that even 3- to 5-month-old infants can respond to a large range of image disparities.
Collapse
|
11
|
Determining the relative contribution of retinal disparity and blur cues to ocular accommodation in Down syndrome. Sci Rep 2017; 7:39860. [PMID: 28071728 PMCID: PMC5223174 DOI: 10.1038/srep39860] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/04/2016] [Accepted: 11/29/2016] [Indexed: 11/08/2022] Open
Abstract
Individuals with Down syndrome (DS) often exhibit hypoaccommodation alongside accurate vergence. This study investigates the sensitivity of the two systems to retinal disparity and blur cues, establishing the relationship between the two in terms of accommodative-convergence to accommodation (AC/A) and convergence-accommodation to convergence (CA/C) ratios. An objective photorefraction system measured accommodation and vergence under binocular conditions and when retinal disparity and blur cues were removed. Participants were aged 6–16 years (DS n = 41, controls n = 76). Measures were obtained from 65.9% of participants with DS and 100% of controls. Accommodative and vergence responses were reduced with the removal of one or both cues in controls (p < 0.007). For participants with DS, removal of blur was less detrimental to accommodative responses than removal of disparity; accommodative responses being significantly better when all cues were available or when blur was removed in comparison to when proximity was the only available cue. AC/A ratios were larger and CA/C ratios smaller in participants with DS (p < 0.00001). This study demonstrates that retinal disparity is the main driver to both systems in DS and illustrates the diminished influence of retinal blur. High AC/A and low CA/C ratios in combination with disparity-driven responses suggest prioritisation of vergence over accurate accommodation.
Collapse
|
12
|
Horwood AM, Riddell PM. Disparity-driven vs blur-driven models of accommodation and convergence in binocular vision and intermittent strabismus. J AAPOS 2014; 18:576-83. [PMID: 25498466 PMCID: PMC4270963 DOI: 10.1016/j.jaapos.2014.08.009] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/21/2014] [Revised: 07/09/2014] [Accepted: 08/18/2014] [Indexed: 11/30/2022]
Abstract
PURPOSE To propose an alternative and practical model to conceptualize clinical patterns of concomitant intermittent strabismus, heterophoria, and convergence and accommodation anomalies. METHODS Despite identical ratios, there can be a disparity- or blur-biased "style" in three hypothetical scenarios: normal; high ratio of accommodative convergence to accommodation (AC/A) and low ratio of convergence accommodation to convergence (CA/C); low AC/A and high CA/C. We calculated disparity bias indices (DBI) to reflect these biases and provide early objective data from small illustrative clinical groups that fit these styles. RESULTS Normal adults (n = 56) and children (n = 24) showed disparity bias (adult DBI 0.43 [95% CI, 0.50-0.36], child DBI 0.20 [95% CI, 0.31-0.07]; P = 0.001). Accommodative esotropia (n = 3) showed less disparity-bias (DBI 0.03). In the high AC/A-low CA/C scenario, early presbyopia (n = 22) showed mean DBI of 0.17 (95% CI, 0.28-0.06), compared to DBI of -0.31 in convergence excess esotropia (n=8). In the low AC/A-high CA/C scenario near exotropia (n = 17) showed mean DBI of 0.27. DBI ranged between 1.25 and -1.67. CONCLUSIONS Establishing disparity or blur bias adds to AC/A and CA/C ratios to explain clinical patterns. Excessive bias or inflexibility in near-cue use increases risk of clinical problems.
Collapse
Affiliation(s)
- Anna M Horwood
- Infant Vision Laboratory, School of Psychology & Clinical Language Sciences, University of Reading, United Kingdom; Orthoptic Department, Royal Berkshire Hospital, Reading, United Kingdom.
| | - Patricia M Riddell
- Infant Vision Laboratory, School of Psychology & Clinical Language Sciences, University of Reading, United Kingdom
| |
Collapse
|
13
|
Screening and sampling in studies of binocular vision. Vision Res 2012; 62:228-34. [PMID: 22560956 DOI: 10.1016/j.visres.2012.04.012] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/10/2010] [Revised: 03/19/2012] [Accepted: 04/19/2012] [Indexed: 11/20/2022]
Abstract
Binocular deficits are relatively common within a typical sample of observers. This has implications for research on binocular vision, as a variety of stereo deficits can affect performance. Despite this, there is no agreed standard for testing stereo capabilities in observers and many studies do not report visual abilities at all. Within the stereo literature, failure to report screening and sampling has the potential to undermine the results of otherwise strictly controlled research. We reviewed research articles on binocular vision published in three journals between 2000 and 2008 to illustrate how screening for binocular deficits and sampling of participants is approached. Our results reveal that 44% of the studies do not mention screening for stereo deficits and 91% do not report selection of participants. The percentage of participants excluded from studies that report stereo screening amounts to 3.9% and 0.7% for studies that do not report stereo screening. These low numbers contrast with the exclusion of 17.6% of participants in studies that report screening for binocular deficits as well as selection of participants. We discuss various options for stereo testing and the need for stereo-motion testing with reference to recent research on binocular perception.
Collapse
|
14
|
Horwood AM, Riddell PM. Evidence that convergence rather than accommodation controls intermittent distance exotropia. Acta Ophthalmol 2012; 90:e109-17. [PMID: 22280437 DOI: 10.1111/j.1755-3768.2011.02313.x] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
PURPOSE This study considered whether vergence drives accommodation or accommodation drives vergence during the control of distance exotropia for near fixation. High accommodative convergence to accommodation (AC/A) ratios are often used to explain this control, but the role of convergence to drive accommodation (the CA/C relationship) is rarely considered. Atypical CA/C characteristics could equally, or better, explain common clinical findings. METHODS Nineteen distance exotropes, aged 4-11 years, were compared while controlling their deviation with 27 non-exotropic controls aged 5-9 years. Simultaneous vergence and accommodation responses were measured to a range of targets incorporating different combinations of blur, disparity and looming cues at four fixation distances between 2 m and 33 cm. Stimulus and response AC/A and CA/C ratios were calculated. RESULTS Accommodation responses for near targets (p = 0.017) and response gains (p = 0.026) were greater in the exotropes than in the controls. Despite higher clinical stimulus AC/A ratios, the distance exotropes showed lower laboratory response AC/A ratios (p = 0.02), but significantly higher CA/C ratios (p = 0.02). All the exotropes, whether the angle changed most with lenses ('controlled by accommodation') or on occlusion ('controlled by fusion'), used binocular disparity not blur as their main cue to target distance. CONCLUSIONS Increased vergence demand to control intermittent distance exotropia for near also drives significantly more accommodation. Minus lens therapy is more likely to act by correcting overaccommodation driven by controlling convergence, rather than by inducing blur-driven vergence. The use of convergence as a major drive to accommodation explains many clinical characteristics of distance exotropia, including apparently high near stimulus AC/A ratios.
Collapse
Affiliation(s)
- Anna M Horwood
- Infant Vision Laboratory, School of Psychology & Clinical Language Sciences, University of Reading, Reading RG6 6AL, UK.
| | | |
Collapse
|
15
|
Pankhania SR, Firth AY. The response AC/A ratio: differences between inducing and relaxing accommodation at different distances of fixation. Strabismus 2011; 19:52-6. [PMID: 21635166 DOI: 10.3109/09273972.2011.578192] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
PURPOSE To determine if there is a difference between the response AC/A ratios when measured using the gradient method at near and distance fixation with plus and minus lenses respectively in young adults with normal binocular single vision. METHODS A repeated measures design was used. The accommodative response of the right eye was measured objectively using the Shin-Nippon SRW-5000 autorefractor (Grand Seiko Company, Fukuyama, Japan) (open view) at 33 cm with and without plus lenses (2DS or 3DS) and at 3.8 m with and without minus lenses (2DS or 3DS) dependent on the participants' ability to obtain subjectively "clear" vision. The angle of deviation was measured using the alternate prism cover test at 33 cm and 3.8m fixing with the right eye with the participant sat at the autorefractor. LogMAR 0.0 (6/6) was used for fixation. Response AC/A ratios were calculated. RESULTS Twenty-five participants were examined; mean and standard deviation of their ages were 21.2 ± 4.04 years. The mean and standard deviation of the near response AC/A ratios was 4.73 ± 2.34/1 and at distance was 3.05 ± 1.71/1. Pearson's Product Moment Correlation Coefficient showed no correlation between the 2 sets of data. Paired t-test showed that there was a statistically significant difference between the near and distance response AC/A ratios (t = 3.30, p = 0.003). The difference was found to be greater in participants who were non-orthoptic students. CONCLUSION The response AC/A ratio was found to be slightly higher at 33 cm with plus lenses than at 3.8 m with minus lenses. No reason was identified for this difference but adaptation and perceptual effects could be further explored.
Collapse
Affiliation(s)
- Supna R Pankhania
- Academic Unit of Ophthalmology and Orthoptics, University of Sheffield, K Floor, School of Medicine and Biomedical Sciences, Beech Hill Road, Sheffield S10 2RX, UK
| | | |
Collapse
|