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Does Wearing a Contact Lens Overnight Improve Your Vision And Prevent Future Progression?

by | Apr 1, 2022 | Manuscripts | 0 comments

Ms. Tsering lamu shongmu, M.Optometry

Assistant Professor, Sushant University, Gurugram Haryana, India

 

Introduction:

The prevalence of myopia is increasing worldwide, and younger generations are affected more than others.(1-3) Early initiation of ortho-k treatment may be possible to reduce the prevalence of high myopia in younger myopic children. Orthokeratology or Corneal refractive therapy (CRT)  or Corneal reshaping or Vision Shaping Treatment (VST) is a non-invasive and non-surgical method that involves overnight wear of specially designed rigid contact lenses that can temporarily correct myopia and slow its progression by gently flattening the central cornea.(4-9)

Cornea before and after Ortho-k

Hyperopic defocus, which leads to hyperopic retinal blur at the peripheral retina, can occur in children with a significant lag of accommodation during excessive close activity. This is more frequent in myopic children. The beam of light that focuses posterior to the peripheral retina might be a signal for total axial length elongation, which leads to myopia development. Peripheral refraction, which is not affected by central vision, may have an impact on eye growth.(10,11) Myopic eyes display relative hyperopia in the periphery that hyperopic and emmetropic eyes do not, and children with myopia have higher relative hyperopic peripheral defocus two years before the onset of myopia than emmetropic children. The central cornea is flattened using ortho-k lenses, resulting in an oblate shape. The image is focused centrally on the fovea at the juncture where the oblate portion of the cornea returns to its original curvature, whereas peripheral light focuses anterior to the peripheral retina, resulting in a peripheral refractive state that shifts from relative hyperopic defocus to relative myopic defocus, thus optically correcting myopia and controlling its progression. Ortho-K also helped children with their accommodation and convergence.(5) When compared to single vision gas permeable contact lenses, soft contact lenses, (12) and single-vision spectacles, Ortho-k lenses slow axial length growth.(15-19) As a result, Ortho-k has a corrective as well as a preventive/control impact in childhood myopia.(13-16).

Morphological changes in corneal epithelial cell after Orthokeratology

Orthokeratology causes reversible structural changes in the corneal epithelial cells while the depth of the anterior chamber or the shape of the posterior corneal surface is unaffected.(17,18) Corneal changes induced by orthokeratology could be explained by redistribution or remodelling of anterior corneal tissue, rather than an overall bending of the cornea.(19) The central thinning was found to be primarily epithelial in origin, whereas the mid-peripheral thickening included a significant stromal component.(19) The epithelium cells of the central cornea are compressed and flattened by a positive force (push), whereas the reverse zone is subjected to a negative force (pull), resulting in larger and more oval mid-peripheral epithelial cells. This caused fluid to move from the centre to the mid-periphery regions of the cornea. The central corneal thickness reduced due to epithelial thinning, while the mid-peripheral cornea thickened due to epithelial and stromal alterations. Hydraulic forces in the post-lens tear film induce tangential stresses across the corneal epithelial surface, resulting in anterior corneal shape and thickness alterations.(1)

 

References:

  1. Mountford J. A model of forces acting in orthokeratology. In: Mountford J, Ruston D, Dave T, editors. Orthokeratology: principles and practice. Edinburgh: Butterworth-Heinemann; 2004. P. 269–301.
  2. Dolgin, E. Te myopia boom. Nature 519, 2015; 276–278.
  3. Williams, K. M. Et al. Increasing prevalence of myopia in Europe and the impact of education. Ophthalmology 122, 2015; 1489–1497.
  4. Kerns RL. Research in orthokeratology. Part I: introduction and background. J Am OptomAssoc 1976;47:1047–51.
  5. Mountford J, Ruston D, Dave T. Orthokeratology: principles and practice. Edinburgh: Butterworth-Heinemann; 2004.
  6. Chen CC, Cheung SW, Cho P. Myopia control using toric orthokeratology (TO-SEE study). Invest Ophthalmol Vis Sci 2013;54:6510–7.
  7. Cho P, Cheung SW. Retardation of myopia in orthokeratology (ROMIO) study: a 2-year randomized clinical trial. Invest Ophthalmol Vis Sci 2012;53:7077–85.
  8. Huang J, Wen D, Wang Q, mcalinden C, Flitcroft I, Chen HH, et al. Efficacy comparison of 16 interventions for myopia control in children: a network metaanalysis. Ophthalmology 2016;123:697–708.
  9. Robboy MW, Hilmantel G, Tarver ME, Eydelman MB. Assessment of clinical trials for devices intended to control myopia progression in children. Eye Contact Lens 2018;44:212–9.
  10. Troilo D, Wallman J. The regulation of eye growth and refractive state: an experimental study of emmetropization. Vis Res. 1991;31:1237–50.
  11. Schaeffel F, Troilo D, Wallman J, Howland HC. Developing eyes that lack accommodation grow to compensate for imposed defocus. Vis Neurosci. 1990;4:177–83.
  12. Walline JJ, Jones LA, Sinnott LT. Corneal reshaping, and myopia progression. Br J Ophthalmol. 2009;93(9):1181–1185.
  13. Charman WN, Mountford J, Atchison DA, et  al. Peripheral refraction in orthokeratology patients. Optom Vis Sci. 2006;83:641–8.
  14. Queirós A, González-Méijome JM, Jorge J, et al. Peripheral refraction in myopic patients after orthokeratology. Optom Vis Sci. 2010;87(5):323–9.
  15. Kakita T, Hiraoka T, Oshika T. Influence of overnight orthokeratology on axial elongation in childhood myopia. Invest Ophthalmol Vis Sci. 2011;52(5):2170–2174.
  16. Smith EL, Hung LF, Harwerth RS. Effects of optically induced blur on the refractive status of young monkeys. Vision Res. 1994;34(3): 293–301
  17. Seidemann A, Schaeffel F. An evaluation of the lag of accommodation using photorefraction. Vis Res. 2003;43:419–30.
  18. Gwiazda J, Bauer J, Thorn F, et al. A dynamic relationship between myopia and blur-driven accommodation in school-aged children. Vis Res. 1995;35:1299–304.
  19. Swarbrick, HA, Wong, G, O’Leary, DJ. Corneal response to orthokeratology Optom Vis Sci 75,1998; 791-79

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