초독회 Influence of Overnight Orthokeratology on Axial Elongation in Childhood Myopia 2011.4.27 R4 김보윤/AP.신선영

Introduction It is generally thought that progression of youth-onset myopia is attributable to axial elongation Myopia can be corrected by spectacles or contact lenses. However, these treatments do not solve the problem of ocular axial elongation. . Myopia is one of the most common ocular abnormalities in humans. The prevalence of myopia is reported to be between 25% and 30% in the developed countries,1,2 with the incidence being higher among certain Asian populations (Lin LLK, et al. IOVS 1996;37:ARVO Abstract 4600). It is well known that myopia is often associated with sight-threatening complications, such as retinal detachment, macular degeneration, and glaucoma.7–10

What is Orthokeratology : OK, ortho-K, corneal reshaping, corneal refractive therapy(CRT), vision shaping treatment(VST) Specially designed and fitted rigid contact lens Reshaping the corneal contour Temporarily modify or eliminate refractive error , mostly used for reduction of myopia

Purpose This prospective study was conducted to assess the influence of overnight orthokeratology (OK) on axial elongation in children, with those wearing spectacles as controls Myopia is one of the most common ocular abnormalities in humans. The prevalence of myopia is reported to be between 25% and 30% in the developed countries,1,2 with the incidence being higher among certain Asian populations (Lin LLK, et al. IOVS 1996;37:ARVO Abstract 4600). It is well known that myopia is often associated with sight-threatening complications, such as retinal detachment, macular degeneration, and glaucoma.7–10

Method OK group(45명)/ spectacle group(50명) (single-vision glasses) November 2002 and June 2007. OK group(45명)/ spectacle group(50명) (single-vision glasses)

Reverse Geometry RGP Lenses The nominal central thickness of the lenses was 0.22 mm and the diameter was 10.6 mm. wear their OK lenses every night for at least 7 consecutive hours. 4 curved OK lens Emerald Lenses; Euclid Systems Corp., Herndon, VA, manufactured from Boston XO material; Polymer Technology Corp., Wilmington, MA) with a nominal Dk of 100 1011 cm2/s)(mL O2/mL mm Hg).

Method-Baseline data Refraction, visual acuity, axial length Before starting OK, spectacle After 2 yrs Axial length: laser interferometry (IOLMaster; Carl Zeiss Meditec) axial length was measured 3 months after the start of OK axial length was measured when the subject started wearing spectacles. It has been reported that corneal thinning stabilizes by the end of the week after OK,27 or that thinning continues for 1 or 2 months.28,29 . This device is very suitable for axial length measurements in children, thanks to its high reproducibility, precision, lack of direct contact, The OK group returned for examination every 3 months and underwent slit lamp examinations for any adverse events. The OK lens fit was evaluated at these visits. The control group returned for examination every 6 months. OK lenses and spectacles were replaced if visual acuity was found to change by more than 0.30 logMAR units during the follow-up. central corneal thinning caused by OK ranges from -12 to -19um over a span of 3 months

Result(1) At baseline, the two groups were comparable in terms of spherical equivalent refractive error, uncorrected visual acuity, axial length, age (unpaired t-test), and distribution of the sexes (Mann-Whitney U test; Table 2). There were also no significant differences in age distribution (8 –10, 11–13, and 14–16 years) between the groups

Result(2)-after 2yrs f/u baseline 2yrs after tx. P Spherical equivalent refractive error OK group -2.55 ± 1.82 D - 0.68 ± 1.02 D <0.0001 Spectacle group - 2.59 ± 1.66 D -3.83 ± 1.76 D Axial length 24.66 ± 1.11mm 25.05 ± 1.06mm 24.79 ± 0.80mm 25.40 ± 0.84mm 0.39 ± 0.27mm In both groups, significant axial elongation was recognized during 2years (P 0.0001). 0.61 ± 0.24mm

Result(3) OK group Spectacle group Increases in axial length were analyzed in relation to the spherical equivalent refractive error at baseline. A significant correlation was found between these parameters in the OK group (Pearson’s correlation coefficient; r 0.290, P 0.0076), but not in the control group (r 0.038, P 0.7090 Generally, the cornea becomes more oblate (with a flat central area and increasing power toward the periphery) when more severe myopia is corrected by OK lenses with a very flat base curve. This probably leads to a greater decrease of hyperopic defocus at the periphery, thus exerting a greater suppressive effect on axial growth. when the baseline myopia is more severe, the axial elongation after OK is less marked.

Hyperopic defocus Peripheral rays form shell of images behind peripheral retina Axial rays Focus on Retina a visual feedback response to the defocus produced by the eye’s refractive state. the peripheral retina is able to influence ocular growth and refractive Mutti et al.42,43 reported that myopic children have greater relative hyperopia in the periphery with respect to axial refraction, indicating a prolate ocular shape (an axial length exceeding the equatorial diameter), compared with relative peripheral myopia and an oblate shape (an equatorial diameter exceeding the axial length) for emmetropes and hyperopes, suggesting that hyperopic defocus in the periphery promotes axial myopia in humans. Stimulate eye elongation to match the image shell to the oblate retina Hyperopic peri -pheral defocus  MYOPIA 11

Modified Corneal Shape from Ortho-K Shell of images coincide with retinal contour Axial ray focus on retina Reduced hyperopic peripheral defocus Reduced stimulation for eye elongation

Conclusion Although OK cannot completely arrest axial elongation in myopic children, it can retard it to a certain extent, suggesting the potential of this treatment for slowing the progression of myopia.

근시는 왜 진행할까? 많은 가설 Excessive accommodation & uncoordinated eye growth mediated by retinal signals as resposnse to prolonged near work

어떻게 하면 근시 진행을 막을 수 있을까? 눈체조 핀홀안경 침 안경 약물 CL

안경 안경을 끼면 눈이 더 나빠지나요? 저교정 Bifocal or progressive addition lens

안약 안압하강제 Atropine : 0.5% Pirenzepine Unacceptable for longterm therapy Like atropine, muscarinic (M1) antagonist, less likely to produce mydriasis & cycloplegia (M3)

원래 1년으로 계획된 연구로 처음에 참여한 174명 중 84명 (48%) 만이 동의한 것을 주목해야 함 부작용 : 논문에는 약간의 충혈(2명), follicle (1명) 만 보고

Possible Future Treatments Correction of pph ametropia/aberrations Visual signal from fovea may not be essential for normal eye growth Pph retina appear to be able to regulate emmetropinization & induce myopia in response to abnormal visual input Provision of extensive outdoor activity