Introduction:Myopia has emerged as a major ocular health issuerecently because of its increasing prevalence worldwide1and its progressive nature in children. Myopia or near-sightedness is caused due to increase inaxial length or corneal curvature. The increase in axial length is governed bydifferent etiological factors2, among all near work3and peripheral retinal image formation4 have been formulated to beleading factors. Animal studies5, 6have shown that elimination of signals from the fovea did not interfere withemmetropization, but inducing hyperopicdefocus on the peripheral retina promoted development of axial myopia in infantmonkeys. This experiment led to the proposal, peripheral retina defocus leadsto alternation of retinal shape causing axial elongation and myopia progression7-9.Donder10 and Helmholtz11 considered myopia to be anacquired anomaly associated with over-exertion in near work.
It was observed that during near work myopicchildren shows lag of accommodation 12which results in a reduced power of the eye thus causing relative hyperopicdefocus at near, Since it is known from animal studies5, 6that a hyperopic defocus leads to the development of myopia, the Lag ofaccommodation might be a risk factor for the development and/ or progression ofmyopia.12, 13 As peripheral hyperopicdefocus triggers myopia progression, the treatment modality for Myopia shouldbe potentially focused on modifying peripheral refraction to counterbalance theknown stimulus that triggers eye elongation and subsequent progression of myopia.The conventional myopic spectacle lens increases hyperopic defocus in peripheryso to change RPR profile studies have tried adding tints(radiant refractinglens) or pantascopic tilt which resulted in myopic defocus at peripheralretinal plane14, 15although study has shown that thesechanges are only for distance , hyperopic defocus still persists near work.16 Conventional soft andrigid gas permeable (RGP) contact lenses reduces relative peripheral hyperopia,and can even results in relative peripheral myopia, particularly in high myopia17, 18.Commercially available multifocalcontact lenses (MFSCL) intended for presbyopic correction served as myopiacontrol lenses in some studies 19, 20. The peripheral add power area has shown to induce significant changes in theperipheral refractive error profile in myopic eyes as compared to distancepower in the periphery19. Walline JJ et al., 21in their study found 50% reduction in myopia progression and 29% reduction inaxial elongation during the 2-year treatment period with MSCL.
Reverse geometry contact lenses for corneal reshaping tendto have promising result in retarding eye elongation 22-24. Ortho k lenses alter oculargrowth pattern by inducing relative peripheral myopic refractive error (RPRE)whereas the central refraction is fully corrected. Studies comparingconventional RGP and ortho k lenses have found ortho k lenses have significantlyreduced myopia in the central 20° VF in myopic children25.Majority of studies have measured RPRonly in horizontal meridian using different modalities of myopia correction,Atichson et al.,26 found that in vertical meridian myopeshad peripheral myopic defocus. Study onsize and shape of myopic eye by Verkicherla et al.
,9reported difference in peripheral refraction along horizontal and verticalmeridian. On measurement for near peripheral refraction in myopia by Calver etal.,27showed peripheral hyperopia in low myopes and peripheral myopia in high myopes.However there is a lacunae in all the previous study as none of them havemeasured horizontal and vertical meridian PRP for distant and near with all themodalities such as single vision glasses, Anti-myopia lenses, spherical softcontact lens, multifocal contact lens and ortho-K. So, the aim of our study isto measure horizontal and vertical meridian PRP for distant and near withdifferent corrective modalities. Methodology:Subjects: All participants will be drawn from L V Prasad EyeInstitute, Hyderabad.
Their informed consent will be obtained prior to theexperiment and experiment protocol will be approved by institute’s ethiccommittee.Inclusion criteria:· Age -18 to 25 years· Myopia of at least -1.00D , astigmatism of nomore than -1.00D· Best corrected logMAR visual acuity of 0.
0logMARfor distance and 0.4logMAR for near. Exclusion criteria:· No ocular pathology· Contraindications/ intolerance to contact lenswear Experimental Procedure:One eye from eachsubject will be investigated (eye with the more myopic refraction will be used).Comprehensive eye examination will be performed, which includes subjective noncyclopelgic refraction, slit lamp examination, axial length measurement withlens star and undilated fundus examination.
Peripheral refractionwill be measured in both horizontal and vertical meridians using —- openfield binocular auto refractometer at a distance of 3mtrs and 40cms. Thesubject will be seated with the head stabilized in a chin-rest so that the eyewill be aligned with the central target. Subjects will be asked only to and rotate their eyes to view a series offixation targets. Refractive error will be measured 3 times on-axis, and 3 timesat each eccentricity in 5° increments out to 35° both nasally and temporallyhorizontally and out to 15° vertically.
Readings will be averaged for eachsubject in all positions. The axis of the auto refractor will be aligned withthe centre of the entrance pupil during all measurements. For near Maltasecross will be given as a target placed 40cms away from corneal apex. Each subject will haveto participate for 2 days, Day 1 will consist of measurements with glasses,anti –myopia lenses, Single vision soft contact lens and multifocal contactlenses.Subjects will be fittedwith Ortho K lenses and advised to sleep with lenses on at least for 8 hours,the next day lenses will be removed and measurement will be performed. All thetests will be performed in randomised order. Material / Instrument required:· Open field autorefractometer· Lenstar biometry· Anti- myopia lenses (Essilor)· Single vision SCL (B& L , J & J)· Multifocal SCL (central distance design – lowadd à B& L)· Ortho K lenses (Paragon CRT) References:1. Holden, B.
A., et al., Global Prevalence of Myopia and High Myopiaand Temporal Trends from 2000 through 2050. Ophthalmology, 2016. 123(5): p. 1036-42.2.
Ramamurthy, and S.M. Saw, Worldwideprevalence and risk factors for myopia. Ophthalmic Physiol Opt, 2012. 32(1): p.
3-16.3. Lu,B., et al., Associations between nearwork, outdoor activity, and myopia among adolescent students in rural China:the Xichang Pediatric Refractive Error Study report no. 2. Arch Ophthalmol,2009. 127(6): p.
769-75.4. Hoogerheide,J., F. Rempt, and W.P. Hoogenboom, Acquiredmyopia in young pilots. Ophthalmologica, 1971.
163(4): p. 209-15.5. Smith,E.L., 3rd, et al., Peripheral vision caninfluence eye growth and refractive development in infant monkeys. InvestOphthalmol Vis Sci, 2005.
46(11): p.3965-72.6. Huang,J.
, L.F. Hung, and E.L.
Smith, 3rd, Recoveryof peripheral refractive errors and ocular shape in rhesus monkeys (Macacamulatta) with experimentally induced myopia. Vision Res, 2012. 73: p. 30-9.7. Seidemann,A.
, et al., Peripheral refractive errorsin myopic, emmetropic, and hyperopic young subjects. J Opt Soc Am A OptImage Sci Vis, 2002. 19(12): p.
2363-73.8. Calver,R., Peripheral refraction for distanceand nearvision in emmetropes and myopes.
Ophthal. Physiol. Opt., 2007.
9. Verkicharla,P.K., et al., Eye shape and retinalshape, and their relation to peripheral refraction.
Ophthalmic Physiol Opt,2012. 32(3): p. 184-99.10. Donders,F.C.
and W.D. Moore, On the anomalies ofaccommodation and refraction of the eye: With a preliminary essay onphysiological dioptrics.
Vol. 22. 1864: New Sydenham Society.11.
vonHelmholtz, H., Treatise on PhysiologicalOptics. Hamburg, Germany: Verlag von Leopold Voss; 1909. Translated bySouthhall JPC. 1962, New York: Dover Publications.12. Gwiazda,J.E.
, et al., Accommodation and relatedrisk factors associated with myopia progression and their interaction withtreatment in COMET children. Invest Ophthalmol Vis Sci, 2004. 45(7): p. 2143-51.13. Gwiazda,J., et al.
, A dynamic relationshipbetween myopia and blur-driven accommodation in school-aged children.Vision Res, 1995. 35(9): p.1299-304.14. Bakaraju,R.
C., et al., Pantoscopic tilt inspectacle-corrected myopia and its effect on peripheral refraction.Ophthalmic Physiol Opt, 2008. 28(6):p. 538-49.15.
Tabernero,J., et al., Effects of myopic spectaclecorrection and radial refractive gradient spectacles on peripheral refraction.Vision Res, 2009.
Berntsen,D.A. and C.E. Kramer, Peripheral defocuswith spherical and multifocal soft contact lenses. Optom Vis Sci, 2013. 90(11): p. 1215-24.
17. Shen,J., et al., Peripheral refraction withand without contact lens correction.
Optom Vis Sci, 2010. 87(9): p. 642-55.18. Kwok,E., et al.
, Peripheral refraction in highmyopia with spherical soft contact lenses. Optom Vis Sci, 2012. 89(3): p. 263-70.
19. Allinjawi,K., et al., Peripheral refraction withdifferent designs of progressive soft contact lenses in myopes. F1000Res,2016. 5: p.
2742.20. Rosen,R., et al., Evaluating the peripheraloptical effect of multifocal contact lenses. Ophthalmic Physiol Opt, 2012.
32(6): p. 527-34.21. Walline,J.J., et al., Multifocal contact lensmyopia control. Optom Vis Sci, 2013.
90(11):p. 1207-14.22. Walline,J.J., L.
A. Jones, and L.T. Sinnott, Cornealreshaping and myopia progression. Br J Ophthalmol, 2009. 93(9): p. 1181-5.23.
Downie,L.E. and R. Lowe, Corneal reshapinginfluences myopic prescription stability (CRIMPS): an analysis of the effect oforthokeratology on childhood myopic refractive stability. Eye Contact Lens,2013.
39(4): p. 303-10.24. Li,X., et al.
, Update on Orthokeratology inManaging Progressive Myopia in Children: Efficacy, Mechanisms, and Concerns.J Pediatr Ophthalmol Strabismus, 2017. 54(3):p. 142-148.25. Kang,P.
and H. Swarbrick, Peripheralrefraction in myopic children wearing orthokeratology and gas-permeable lenses.Optom Vis Sci, 2011. 88(4): p.
A., N. Pritchard, and K.L. Schmid, Peripheralrefraction along the horizontal and vertical visual fields in myopia.Vision Res, 2006.
Calver,R., et al., Peripheral refraction fordistance and near vision in emmetropes and myopes.
Ophthalmic Physiol Opt,2007. 27(6): p. 584-93.