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Perifocal spectacle lenses - safe multi-factorial influence on myopia
Perifocal spectacle lenses - safe multi-factorial influence on myopia
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Peripheral defocus induced by Perifocal spectacles

Scientific papers
Tarutta E.P.¹, Proskurina O.V.¹, Milash S.V.¹, Ibatulin R.A.², Tarasova N.A.¹, Kovychev A.S.², Smirnova T.S.¹, Markosyan G.A.¹, Khodzhabekyan N.V.¹, Maksimova M.V.¹ Penkina A.V.¹
PERIPHERAL DEFOCUS INDUCED BY «PERIFOCAL-M» SPECTACLES AND MYOPIA PROGRESSION IN CHILDREN
¹ The Helmholtz Moscow Research Institute of Eye Diseases, 105062, Moscow, Russia;
² Vision Center "ArtOptika" 117461, Moscow, Russia
Resume.
Peripheral defocus has significant role in developing of refraction. «Perifocal - М» spectacle lens provides different correction in central and peripheral refraction of the eye in horizontal.
Purpose. To examine influence of «Perifocal - М» spectacles on wavefront aberrations, peripheral refraction and myopia development in children.  Materials and methods. Prospective parallel cohort open clinical study was contributed, with 75 children involved, children aged from 9 to 14 with progressive myopia from -1,0 to -6,0 D. Trial period was 6-18 months. Patients was randomly selected to wear «Perifocal - М» or monofocal spectacles. Results and discussion. «Perifocal – M» spectacles create relative peripheral myopic defocus or significantly decreases peripheral hyperopic defocus, and induces positive spherical aberrations, in turn monofocal spectacles creates negative. After 6 months of using «Perifocal - М» spectacles noticed less axial growth by 0,05 mm, less myopic shift: manifest refraction – by 0,19D, cycloplegic refraction by 0,11D comparing to control group. After 12-18 months of using «Perifocal - М» spectacles noticed less axial growth by 0,07mm, less myopic shift: manifest refraction – by 0,3D, cycloplegic by 0,27D. There no cases of heteroforia decompensation during using «Perifocal - М» spectacles. Conclusion. «Perifocal – M» spectacles contribute to slow myopia progression comparing to control group.
Key words: refraction of children, peripheral refraction, relative peripheral defocus, myopia progression, myopia correction.
In recent years, peripheral defocus has played a significant role in the formation of refraction.  The latter refers to the relative weakening or strengthening of ray’s refraction during the transition from the center of the fovea to the peripheral parts of the retina. In the first case, talk about the relative peripheral hypermetropia, or hyperopic defocus, in the second of myopic peripheral defocus. In a number of experimental studies have shown that hyperopic defocus in the periphery of the retina stimulates the growth of the eye and the formation of axial myopia, and myopic on the contrary, inhibits the refractogenesis [1,2]. The results of clinical studies also indicate a stimulating eye lengthening role of hyperopic defocus [3], the connection of myopia with peripheral hypermetropia [4].
A lot of work is devoted to the study of peripheral refraction in various types of correction. It is reported that traditional single vision spectacles increase peripheral hyperopic defocus compared to uncorrected myopic eyes [5]; that traditional spherical contact lenses create myopic defocus on the periphery, unlike spectacles [6]; that these lenses, on the contrary, form hyperopic defocus, and relative myopia on the periphery creates multifocal contact lenses [7].
Interest in the study of peripheral refraction in recent years is supported by the results of clinical observations of children using orthokeratological contact lenses. It is here that the inhibition of myopia progression and axial length growth observed by all can be most associated with a significant permanent induced myopic peripheral defocus [8.9]. This effect is provided by changing the topography of the cornea under the action of OK lenses. The central part of the cornea is flattened, and the paracentral and peripheral becomes "steeper" and more refracted. This leads to the formation of a positive spherical aberration and, due to a stronger peripheral refraction, a relative myopic defocus on the periphery.
By analogy with multifocal contact lens and orthokeratology, there is a development of special spectacle lens design [10] or designed to create a relative myopia at the periphery [11].
Few years ago, such lenses were created and introduced on Russian market. «Perifocal - М» spectacles have special design with progression of refraction (addition) both sides from optical center in horizontal, stable refraction in geometric center, refraction along vertical meridian is similar to central refraction in geometric center. «Perifocal - М» lens allow to correct differently central and peripheral refraction of the eye in horizontal meridian.
Physical and mathematical calculations in the "Perifocal-M" optical surface design modeling carried out by a leading expert in the field of optical surface design - Professor of the University of Madrid Jose Alonso (University Complutense of Madrid, Madrid, Spain). The unique properties of the "Perifocal-M" lens make it possible for the first time in practice to identify the effectiveness of different correction of nasal and temporal relative peripheral hyperopia to control the progression of myopia in children.
Purpose. To study the effect of «Perifocal - М» spectacles on wavefront aberrations, peripheral refraction and myopia development in children.
Materials and methods. A clinical prospective parallel open-label study was conducted in 75 children aged 9-14 years with progressive myopia from -1.0D to -6.0D and astigmatism of not more than 1.0D, requiring no optical correction, with the best corrected visual acuity of 0.8 or more, binocular character of vision. The follow-up period was 6-18 months. Patients of the main group (60 children) were assigned "Perifocal - M" spectacles for permanent using. Patients in the control group wore monofocal spectacles. Correction was weaker by 0.5D than objectively identified cycloplegic refraction.
Examination of all children was carried out before spectacles prescription, 6 months and 12-18 months after the start of using spectacles. The examination included: visometry without correction and with the best subjective correction, determining the nature of vision, autorefractometry before and after cycloplegia (cyclomed 1% - 2 times), biomicroscopy, ophthalmoscopy, accommodation study (determination of relative accommodation reserves, objective accommodation response measured by open field autorefractometer Grand Seiko WR-5100K, absolute accommodation), muscle balance study (Forias) , study of the ratio of accommodation convergence and accommodation (AC/a) gradient method by Von Noorden, an objective study of peripheral refraction at 15° and 30° in the nasal (N15 and N30) and temporal (T15 and T30) meridian without correction and in new spectacles using the open-field autorefkeratometer Grand Seiko WR-5100K (Japan), ultrasonic echobiometry - A/B Scan System Model 837 of the company "Allergan Humphrey" (USA); the aberrometry – ОРDScan (Nidek, Japan).
Results and discussion.
Adaptation.
"Perifocal - M" spectacles was prescribed for constant using. All patients adapted to the lenses easily. Terms and ease of adaptation did not differ from the adaptation to any new spectacles. The maximum period of adaptation was 7 days. There was not any single case of refusal to use "Perifocal-M" spectacles, associated with difficult adaptation.
Influence of «Perifocal-M» spectacles on peripheral refraction of the eye.
"Perifocal – M" spectacles form myopic or reduce hyperopic relative peripheral defocus in myopic eyes. The results of the peripheral refraction study of lenses "Perifocal-M", obtained by Grand Seiko WR – 5100K without correction and using spectacles "Perifocal – M", showed that without correction hyperopic defocus occurs: in 61.5% of eyes in T15° and T30°; in 46% of eyes in N15°; in 100% of eyes in N30°. Without correction hyperopic defocus averaged: + 0.11±0.11D in T15° and + 0.72±0.28D in T30°; +0,02±0,1D in N15° and +1,53±0,2D in N30°.
Myopic defocus was formed in "Perifocal – M" spectacles in the zone of 15°, which averaged -0.03±0.1D in T15° and -0.35±0.16D in N15°. In the area of 30° hyperopic defocus was decreased on average by 0.1±0,35D at T30° and 0.34±0,07D to N30° (Fig. 1).
Thus, spectacles with lenses of special design with horizontal progression "Perifocal-M" form a relative peripheral myopic defocus in the eye or significantly reduce peripheral hyperopic defocus.
Influence of «Perifocal-M» spectacles on aberrations of the eye.
In our study, according to aberrometry without correction in 50% of the examined eyes with myopia, spherical aberration of the highest order had a negative sign. Negative spherical aberration plays an unfavorable role in the progression of myopia, because it creates hyperopic peripheral defocus. The mean value of higher-order spherical aberration in the examined group was positive and amounted to 0.003±0.01 µm.
Aberrometry in monofocal spectacles showed an increase of negative spherical aberration. It was found in 75% of the eyes and its average value was -0.06±0.01 µm (p<0.01). Along with the natural, by reducing defocus, reducing the overall level of aberrations (Total RMS) from 4.19±0.5 µm without correction to 2.9±0.2 µm in monofocal glasses (p<0.05), there was a tendency to increase higher – order aberrations (RMS-HO) from 0.282±0.03 µm to 0.36±0.04 µm in the correction of myopia with monofocal glasses (p>0.05).
In "Perifocal - M" spectacles due to a more complete correction of central refraction, the decrease in the overall level of aberrations was even more pronounced than in monofocal spectacles. Its value in "Perifocal - M" spectacles was 1.66±0.3 microns compared to 4.19± 0.5 before correction (p<0.01). Low-order spherical aberration tended to increase from 0.35±0.05 µm to 0.42±0.1 µm (p>0.05). Coma and trefoil increased significantly: from 0.15±0.02 µm to 0.23±0.09 µm and from 0.17±0.02 µm to 0.27±0.09 µm, respectively (p>0.05).
Spherical aberration of the highest order in the eyes, where it had a negative value without correction, decreased or even turned into a positive one. The mean value of spherical aberration (NO-sph) was 0.022±0.04 µm, that is, there was a tendency to increase the positive spherical aberration by 7 times compared to non-corrected eyes (p>0.05), the difference is unreliable. As already noted, positive spherical aberration forms myopic peripheral defocus, which plays a crucial role in inhibiting the progression of myopia. The main purpose of "Perifocal-M" spectacles is the formation of such a defocus due to the special design of this lens. Studies have confirmed the achievement of this goal: "Perifocal" spectacles induce positive spherical aberration, while monofocal spectacle lenses form a negative (table.1).
Influence of «Perifocal-M» spectacles on refraction and axial growth dynamics
The dynamics of central refraction and AL values were monitored in 60 patients who used "Perifocal - M" spectacles for 6 months, in 51 patients for 12-18 months (table. 2,3). The dynamics of refraction in all patients of the control group was monitored during 12-18 months with intermediate control at 6 months.
Manifest subjective refraction after 6 months of "Perifocal - M" spectacles using increased by an average of 0.09±0.04D (varied from 0 to -1.0D), after 12-18 months increased by 0.28±0.04D (changed from 0 to -1.5D). The myopic shift of the subjective refraction was significantly lower than in the control group. In the control group, manifest subjective refraction increased by an average of 0.23±0.04D after 6 months, and by 0.55± 0.03D after 12-18 months (p<0.01).
Manifest objective refraction measured by autorefractometry, after 6 months increased on average by 0.15±0,04D, 12-18 months 0.28±0,04 diopters. In the control group, manifest objective refraction increased by an average of 0.25±0.04D after 6 months and 0.55±0.03D after 12-18 months. The difference between the main and control groups was significant for each observation period (p<0.01).  
Cycloplegic objective refraction after 6 months of using "Perifocal - M" spectacles changed from +0.25D to -1,25D. The average shift of cycloplegic objective refraction was +0.02±0.01D. Stabilization of cycloplegic refraction was observed in 16.7% of cases (20 eyes), weakening of cycloplegic refraction was observed in 40% of cases (48 eyes), in 41.6% of cases (50 eyes) manifest refraction increased by 0.25-0.75D (average -0.29±0.04D), one child (1.7%) had bilateral enhancement of cycloplegic refraction by -1.25 D.
After 12-18 months of "Perifocal - M" using cycloplegic objective refraction increased by an average of -0.28±0.04D. Stabilization of cycloplegic refraction was observed in 39.2% of cases (40 eyes), the weakening of cycloplegic refraction was observed in 9.8% of cases (10 eyes), in 51% of cases (52 eyes) cycloplegic refraction increased by an average of -0.4±0.03D.
The myopic shift of the objective cycloplegic refraction was significantly lower in children who used "Perifocal M" spectacles, than in the control group.  In the control group, cycloplegic objective refraction after 6 months increased by an average of           -0.13±0.04 D (p<0.01) after 12-18 months at -0.55±0.03D (p<0.01).
The axial length value after 6 months of "Perifocal-M" spectacles using increased by an average of 0.03±0.02mm, after 1 year by 0.08±0.02mm. in the control group, the axial length growth was twice as much: after 6 months, AL increased by 0.08±0.02mm, after 12-18-by 0.15±0.03mm (table. 3). The difference was significant for each observation period (p<0.05).
Influence of «Perifocal-M» spectacles on visual acuity, accommodation, phoria.
"Perifocal – M" spectacles spherical component were prescribed 0.5D less than objectively identified cycloplegic refraction. In the appointment of such a correction binocular visual acuity in "Perifocal-M" spectacles ranged from 0.9 to 1.0 and averaged 0.95±0.04.
Binocular visual acuity in "Perifocal-M" spectacles after 6 months remained consistently high and averaged 0.94±0.04. After 12-18 months binocular visual acuity in "Perifocal – M" spectacles was 0.84±0.04.
In the control group, binocular visual acuity in spectacles at the beginning of the study was 0.88±0.04, after 6 months - 0.78±0.04, after 12-18 months – 0.67±0.04.
Relative Accommodation Reserves after 6 months of "Perifocal-M" spectacles using increased by an average of 0.3 ±0.04D, after 12-18 months RAR increased by 0.4±0.04D from baseline (p>0.05).   
In control group RAR has not changed.
Absolute Accommodation volume after 6 months of "Perifocal-M" spectacles using increased by an average of 2.27±0.16D, after 12-18 months-by 3.0±0.18D compared with the baseline value and 27.5% (33 eyes) reached the age norm.
In the control group, the absolute accommodation volume increased by 1.0±0.12D and 1.4±0.13D compared with the initial values, respectively, and at the end of the observation reached the age norm in 2 cases. The increase in the values of absolute accommodation volume to groups of children who wore glasses "Perifocal – M" in comparison with the control group was reliable for each of observation periods (p<0.01).
Objective accommodation response after 6 months of "Perifocal-M" spectacles using increased slightly, on average by 0.1±0.04D, after 1 year-by 0.3±0.04D (p>0.05).
In the control group, the objective accommodation response has not changed. The difference in the value of the objective accommodation response in the main and control groups was unreliable.
The tone of accommodation after 6 months "Perifocal – M" spectacles using has changed slightly: increased by an average of 0.03±0.02 D, and the tone of accommodation of the open field-0.08±0.03D. After 12-18 months, the tone of accommodation remained within the reference values, the tone of accommodation in the open field has changed - have decreased on 0,1±0,03D from baseline. According to E. P. Tarutta and N. A. Tarasova decrease in accommodation tone is a favorable prognostic sign and is associated with a decrease in the rate of further myopia progression [12].
In the control group, after 6 months, the tone increased by 0.03±0.02D, the open field tone by 0.1±0.02D.
Phorias. In the main and control groups were included only subjects with physiological values of heterophoria for near. After 6 months and 1 year from the beginning of using "Perifocal-M" spectacles in any case, the values of phoria did not go beyond physiological. This distinguishes the "Perifocal – M" spectacles from the usual progressive spectacles, using which it is possible to form a decompensated exophoria for near and far, and in particularly severe cases – exotropy [13].
There were no cases of decompensated phoria during the observation period in the control group.
AC/A. The AC/A ratio is slightly decreased on average by 0.2 prism.D/D, presumably at the expense of some increase in accommodative ability of the eye, however, this change was not reliable.
Conclusion:
1.  «Perifocal - М» spectacles can be used in children for permanent using, adaptation goes easy.
 2. «Perifocal – M» spectacles create myopic or decrease hyperopic peripheral defocus in myopic eyes. «Perifocal-М» spectacles induce positive spherical aberration in the eye, while monofocal spectacles form negative.
3. «Perifocal – M» spectacles contribute to relative refraction stabilization in myopia comparing to control group. The most significant difference with the control group in first 6 months of observation.
Binocular visual acuity when using the same «Perifocal – M» spectacles stay high during 12-18 months.
«Perifocal – M» spectacles have obvious advantages over usual progressive spectacles, because there is no decompensated exophoria during it’s using, which may be noticed with progressive spectacles.
References
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