Diagnosing meridional amblyopia in astigmats on the basis of assessment of asymmetries in visual acuity and refraction as vector quantities
V. A. Kolomiyets, O. V. Kachan, N. V. Kolomiyets
SI "The Filatov Institute of Eye Diseases and Tissue Therapy of the NAMS of Ukraine;
TO CITE THIS ARTICLE: Kolomiyets VA, Kachan OV, Kolomiyets NV. Diagnosing meridional amblyopia in astigmats on the basis of assessment of asymmetries in visual acuity and refraction as vector quantities. J.ophthalmol.(Ukraine).2021;1:17-23. http://doi.org/10.31288/oftalmolzh202111723
Background: Asymmetry in refraction may cause meridional amblyopia and impairments in the mechanisms underlying binocular vision in patients with astigmatism. There have been contradictory reports on the features and incidence of meridional amblyopia in patients with astigmatism. These contradictions have been attributed to the fact that the studies vary in methodologies and criteria used for visual acuity assessment.
Purpose: To improve the algorithm for diagnosing meridional amblyopia in patients with hyperopic astigmatism on the basis of assessment of asymmetries in meridional separable visual acuity and refraction as vector quantities.
Material and Methods: Ninety three patients aged 6 to 12 years, with both refractive amblyopia and compound with-the-rule hyperopic astigmatism were included in the study, and underwent examination. The sphercal component of refraction ranged from 0.5D to 1.75D, and the astigmatic component of refraction, from 0.75D to 2.0D. Best-corrected visual acuity was assessed using letters and Landolt rings of Shevalev Chart and digits generated by a Hoya chart projector. Visual acuity characteristics were determined for the amblyopic eye, fellow eye and binocularly. Meridional separable visual acuity was measured with Landolt rings with the help of specially developed software. Optotypes were presented on the computer screen at a 5-m distance. Threshold meridional separable visual acuity was measured in the meridians corresponding to principal astigmatism axes under gradual change (with an increment of ±7.0 arc second) in the angular size of the optotype. Tests were presented monocularly and binocularly on a 15-inch 1600×1200-resolution display.
Results: Graphic comparison of the results of visual acuity measurements using optotypes of different shapes in amblyopes with similar type of astigmatism demonstrated that, in the groups of patients with the same letter visual acuity, Landolt visual acuities can be higher, lower or equal to letter visual acuities. Of the study patients, 42.5% were found to have no meridional amblyopia, and 57.5%, to have meridional amblyopia, as assessed using Landolt rings. Particularly, 35% and 22.5% of the study patients had visual acuity in the horizontal meridian better and worse, respectively, than in the vertical meridian.
Conclusion: Meridional separable visual acuities in patients with both amblyopia and similar type of hyperopic astigmatism are vector quantities and may vary in orthogonal retinal meridians not only in the magnitude, but also in the sign. Meridional visual acuity studies will allow a diagnosis of meridional amblyopia to be clarified not only based on the presence of asymmetry in visual acuity in orthogonal retinal meridians, but also based on the direction of asymmetry in visual acuity with respect to the principal astigmatic refraction meridians.
Keywords: astigmatism, visual acuity, individual variations, meridional visual acuity, meridional amblyopia
1.Sсhiffman HR. [Sensation and perception: An integrated Approach]. 5th ed. St Petersburg: Piтеr; 2003. Russian.
2.Gwiazda J, Bauer J, Thorn F, Held R. Meridional amblyopia does result from astigmatism in early childhood. Clinical Vision Science. 1986;1:145–52.
3.Harvey EM, McGrath ER, Miller JM, et al. A preliminary study of astigmatism and early childhood development. J AAPOS. 2018 Aug;22(4):294-298. doi: 10.1016/j.jaapos.2018.03.004.
4.Hubel DH. Eye, brain, and vision New York: Scientific American Library;1988.
5.Harvey EM, Miller JM, Apple HP, et al. Accommodation in astigmatic children during visual task performance. Invest Ophthalmol Vis Sci. 2014 Aug 7;55(8):5420-30. doi: 10.1167/iovs.14-14400.
6.Harvey EM. Development and Treatment of Astigmatism-Related Amblyopia. Optom Vis Sci. 2009 Jun;86(6):634-9. doi: 10.1097/OPX.0b013e3181a6165f.
7.Harvey EM, Dobson V, Miller JM, Clifford-Donaldson CE. Amblyopia in astigmatic children: Patterns of deficits. Vision Res. 2007 Feb;47(3):315-26. doi: 10.1016/j.visres.2006.11.008.
8.Hess RF, Thompson B, Baker DH. Binocular vision in amblyopia: structure, suppression and plasticity. Ophthalmic Physiol Opt. 34 146–162 10.1111/opo.12123.
9.Vit VV. [The structure of the human visual system] Odessa: Astroprint; 2003.
10.Polat U, Bonneh Y, Ma-Naim T, et al. Spatial interactions in amblyopia: Effects of stimulus parameters and amblyopia type. Vision Res. 2005 May;45(11):1471-9. doi: 10.1016/j.visres.2004.12.014.
11.Freeman RD, Mitchell DE, Millodot M. A Neural Effect of Partial Visual Deprivation in Humans. Science. 1972 Mar 24;175(4028):1384-6. doi: 10.1126/science.175.4028.1384.
12.Mitchell DE, Freeman M, Millodot M, Haegerstrom G. Meridional amblyopia: evidence for modification of the human visual system by early visual experience. Vision Res. 1973 Mar;13(3):535-8. doi: 10.1016/0042-6989(73)90023-0.
13.Dobson V, Miller JM, Harvey EM, Mohan KM, et al. Amblyopia in astigmatic preschool children. Vis Res. 2003 Apr;43(9):1081–90. doi: 10.1016/s0042-6989(03)00014-2.
14.Rozhkova GI, Belozerov AE, Lebedev DS. [Visual acuity measurement: uncertain effect of the low-frequency components of the optotype fourier spectra]. Sensornyie sistemy. 2012;26(2):160-71. Russian.
15.Rozhkova GI. [LogMAR for visual acuity is worse than horsepower for electric lamp]. Sensornyie sistemy. 2017;31(1):29-41. Russian.
16.Colenbrander A. The historical evolution of visual acuity measurement. Vis Impair Res. 2008;10:57–66.
17.Shamshinova AM, Volkov VV. [Functional methods of research in ophthalmology]. Moscow: Meditsina; 1999. Russian.
18.ISO 8596. International Standard. Ophthalmic optics. Visual acuity testing. Standard optotype and its presentation. 2nd edition. Geneve;2009.
19.ISO 8597. International Standard. Optics and optical instruments. Visual acuity testing. Method of correlating optotypes. Geneve; 1994.
20.Bondarko VM, Danilova MV. What spatial frequency do we use to detect the orientation of a Landolt C? Vision Res. 37(15):2153–76.
21.Bondarko VM, Semenov LA. [Acuity and Hyperacuity for Pupils of 11–17 Years Old]. Fiziol Cheloveka. 2012 May-Jun;38(3):56-61. Russian.
22.Graf M, Becker R. Determining visual acuity with LH symbols and Landolt rings. Klin Monbl Augenheilkd. 1999 Aug;215(2):86-90. doi: 10.1055/s-2008-1034677.
23.McGraw P, Winn B, Whitaker D. Reliability of the Snellen chart. BMJ. 1995 Jun 10;310(6993):1481-2. doi: 10.1136/bmj.310.6993.1481.
24.Onufreichuk ON, Rozenblium Yu.Z. [Using vector analysis to study refractive errors in school children]. In: [Ocular biomechanics. Collection of science works]. Moscow; 2005. p.138-43. Russian.
25.Kolomiyets V, Bandura M, Kolomiyets N. [Meridional vernier visual acuity in children and adults with hypermetropic astigmatism]. Oftalmologiia. Vostochania Evropa. 2015; 3(26):27-34. Russian.
26.Kolomiyets V, Bandura M, Kolomiyets N. [Peculiarities of vernier monocular and binocular visual acuity in the retinal orthogonal meridians in patients with hypermetropic astigmatism]. ScienceRise. 2015; 6/4(11):38-44. Russian. DOI: 10.15587/2313-8416.2015.45310
The authors declare no conflict of interest which could influence their opinions on the subject or the materials presented in the manuscript.