Long-Term study

Helmholtz National Medical Research Center of Eye Diseases, 14/19 Sadovaya-Chernogryazskaya St., Moscow, Russian Federation, 105062

ABSTRACT

Peripheral defocus plays a significant role in the formation of refraction. Perifocal spectacles allow differentiating correction of central and peripheral refraction of the eye along the horizontal meridian and can correct or reduce peripheral hyperopia.

Purpose — to study the long-term results of wearing perifocal spectacles on the refraction in children with progressive myopia.

Material and methods. Perifocal spectacles were assigned to children of 7—14 years old with progressive myopia from –1.0 to –6.0 D in terms of refractive spherical equivalent. The children were examined before the prescription of perifocal spectacles and after 6 months, 12—18 months, 2 years, 3 years and 4—5 years. We measured visual acuity, the character of vision, refractive error before and after cycloplegia, performed biomicroscopy, ophthalmoscopy and biometry. Peripheral refraction was studied at 15° and 30° points in the nasal (N15 and N30) and temporal (T15 and T30) meridians without correction and while wearing perifocal spectacles.

Results. In perifocal spectacles, in the 15° zone, 100% of the eyes formed myopic defocus, which averaged –0.05±0.1 D in T15°, –0.25±0.16 D in N15° and –0.44±0.03 D in Т30°. In the N30° zone, the hypermetropic defocus decreased by 4 times and amounted to 0.38±0.03 D. The rate of progression of myopia decreased from 0.8 D of baseline values to 0.17 D at 4—5 years of follow-up. After 6 months of wearing perifocal spectacles, the refraction gain was –0.2±0.02 D (in the control group it was –0.38±0.04 D), after 12—18 months — (–)0.38±0.04 D (–0.63±0.09 D in the control group), after 2 years — (– )0,78±0,06 D (–1.18±0,15 D in the control group), after 3 years — (–)0.99±0.12 D (–1.65±0.20D in the control group). During the 4—5 years of the follow-up, the refractive error in treatment group was – 1.16±0.2 D, which is 60% less than in the control group (–1.95±0.2 D).

Conclusion. Constant wearing of perifocal spectacles reduces the rate of myopia progression in children by 4.5 times compared with the initial rate, and by 1.6 times (by 60%) in comparison with the control group. Perifocal spectacles are recommended as optical means to slow the progression of myopia.

Keywords: refraction, myopia, progressive myopia, myopia control, peripheral refraction, myopic defocus, myopia correction.

Influence of different ways of correction and it’s completeness to affects the development and progression of myopia continue to occupy the minds of researchers [1-3]. In the light of the hypothesis about the effect of induced peripheral defocus on the refractogenesis [4] we can see more often attempts are made to manage growth eyes with devices inducing myopic peripheral defocus in the eye. In the experiment, it is shown that the induced peripheral hyperopic defocus stimulates eye growth and formation of axial myopia, and myopic, on the contrary, has a retarding effect on the refraktogenesis [5,6]. The results of clinical studies also indicate the role of peripheral hypermetropic defocus in stimulating eye elongation [7, 8]. The formation of peripheral myopic defocus is explained by stabilizing effect of orthokeratological lenses on refraktogenesis [9-13]. Undertake attempts to create spectacles and contact lenses that can form relative peripheral myopia in the eye. In 2002 was provided a description of potential designs of spectacle lenses for the correction of off-center refraction at emmetropia, myopia and hypermetropia, which, however, had significant aberrations [14]. Later, RRG lenses were designed to maintain high Central vision and increase the positive optical power in all radial directions. Enhancement of the refractive index in RRG lenses from the center to the periphery was about 1.0 D for every 10° compared to uncorrected peripheral refraction [15]. In Russia, the lens, capable of correcting peripheral refraction horizontal Meridian, first appeared in 2012. Declared that this lens enhances refraction from the center to the periphery on the nasal side by 2.0 D, temporal by 2.5 D. Results of a study conducted at the Helmholtz's Moscow state research Institute, it was shown that the Perifocal-M lens corrects peripheral hypermetropia in 15°, forms myopia in 15° to the nose and to the temple from fovea and in 30° of the temporal periphery, in 30° of the nasal periphery it reduces peripheral hypermetropia by 5 times [16, 17]. Different designs of soft contact lenses were proposed for forming peripheral myopic defocus - bi- and multifocal [18-20]. The first data on the effect of spectacles and contact lenses that induce peripheral myopic defocus on the progression of myopia and eye growth are ambiguous. Our Chinese colleagues did not receive convincing data on the stabilizing effect of spectacles designed to reduce peripheral hyperopia during their 6-12-month use. The stabilizing effect was observed only in children 6-12 years old with a burdened family history (which seems very significant to us!). Reduction of myopia progression in this group compared to control (monofocal spectacles) was 0.29 D during the specified period observations (less than 1 year) [21]. In studies of the effect of progressive spectacles on the progression of myopia it is noted that such spectacles can reduce hypermetropic defocus at least in the upper half of the field of view that provides them stabilizing effect. The results of a randomized study to evaluate the effect of progressive spectacles showed the ability of such spectacles reduce peripheral hypermetropia and slow the progression of myopia. Shift of the refractive index for 1 year in children who wore spectacles that induce myopic defocus in the upper half of the field of view were (–)0.38 D, while those who wore spectacles that induce a similar hypermetropic defocus had (–) 0.65 D [22]. A more significant reduction in the progression of myopia was obtained in children using special bifocal contact lenses. During 1 year of follow-up, the difference compared to the control was 0.57 D [18]. Our previous studies of the stabilizing effect of Perifocal-M spectacles on the progression of myopia have shown that the proposed design of spectacles that induce myopic defocus gives convincing results for stabilizing myopia in comparison with the indicators of the control group in terms of up to 18 months [17]. Continued monitoring of children using perifocal spectacles to correct progressive myopia will allow us to assess their impact on refractogenesis in terms of up to 5 years. The aim of the study is to study the long-term effects of wearing perifocal spectacles on refractive dynamics in children with progressive myopia.

Material and methods

The study was conducted on the basis of the Federal state budgetary institution "scientific medical research center of eye diseases. Helmholtz" Ministry of health of Russia in the period from 2012 to 2018 under the supervision of 94 children of treatment group. Perifocal spectacles were assigned to children aged 7-14 years with progressive myopia from (–) 1.0 to (–) 6.0 D according to the refractive index, with the best corrected visual acuity of 0.8 and higher, binocular character of vision. The average age of starting wearing spectacles was 10.5±0.14 years. Spectacles with perifocal defocus were always designated for permanent wear.

The correction was performed close to complete, no more than 0.5 D weaker than cycloplegic refraction. Examination of children was performed before the appointment of spectacles, after 6 months, 12-18 months, 2 years, 3 years and 4-5 years from the beginning of wearing spectacles. The maximum period of observation is 5 years. In children who wore perifocal spectacles, the refraction dynamics was evaluated: after 6 months — in 94 children (188 eyes), after 12-18 months-in 72 children (142 eyes), after 2 years-in 58 children (116 eyes), after 3 years-in 42 children (84 eyes), in 4-5 years-in 28 children (56 eyes). The control group consisted of 52 children with progressive myopia aged 8-14 years. All children in the control group were assigned monofocals spectacles for constant wear, with correction, is close to full. The average age at the time of inclusion in the control group was 10.5±0.15 years.

The dynamics of refraction in children of treatment and control groups was evaluated in comparison with the indicators at the beginning of the observation. It was believed that refraction stable if its value increased by no more than 0.5 DPT over the entire period of observation (dynamics from 0 to 0.5 DPT over 5 years).

The survey of children was carried out before the appointment of spectacles and in each of the designated periods. The examination included visometry without correction and with optimal correction, determination of the nature of vision, refractometry before and after cycloplegia (1% cyclopentolate 2 times), biomicroscopy, ophthalmoscopy, determination of relative accommodation reserves, study of muscle balance (phoria), objective study of peripheral refraction at 15° and 30° points in the nasal (N15 and N30) and temporal (T15 and T30) Meridian without correction, and in perifocal spectacles using an automatic "open field" refkeratometer WR-5100K ("Grand Seiko Co. Ltd.", Japan), measured the length of the axial length (AL) of the eye using biometrics using partially coherent interferometry on the IolMaster device ("Carl Zeiss", Germany).

The study in perifocal spectacles was performed by turning the head in the direct direction of the eye, in order to preserve the situation of the peripheral defocus induced by spectacles in natural conditions when looking into the distance.

Results and discussion

Influence of spectacles with perifocal defocus on the peripheral refraction of the eye.

The results of the peripheral refraction study for spectacles with perifocal defocus, obtained using the automatic open field refkeratometer WR-5100K without correction and in Perifocal-M spectacles, showed that without correction, hypermetropic defocus occurs in 61.5% of eyes in T15° and T30°; in 46% of eyes in N15°; in 100% of eyes in N30°. The magnitude of hyperopic defocus without correction, it averaged +0.11±0.11 D in T15°; +0.72±0.28 D in T30°; +0.02±0.1 D in N15°; +1.53±0.2 D in N30°. In Perifocal-M spectacles, a myopic defocus was formed in the 15° zone in 100% of the eyes, which averaged (–) 0.05±0.1 D in T15°, (–) 0.25±0.16 D in N15°, and (–) 0.44±0.03 D in T30°. In the N30° zone, the hypermetropic defocus decreased by 4 times and amounted to 0.38±0.03 D (Fig. 1). Thus, spectacles with special design lenses with horizontal progression - Perifocal-M form a relative peripheral myopic defocus in the eye or significantly reduce the peripheral hypermetropic defocus.

Fig. 1. Amount of peripheral defocus without correction and in perifocal spectacles. Horizontal axis — area of measurement of relative peripheral defocus: T30 and T15 lie in 30o and 15o across from center in the temporal side, N15 and N30 — in 15o and 30o across the nasal side; vertical axis — amount of relative peripheral defocus, Dioptres.