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Scleral capsule biophysical properties in the prognosis of the stabilizing effectiveness of orthokeratological myopia correction
- Authors: Tarutta Y.P.1, Iomdina Y.N.1, Toloraya R.R.1, Kruzhkova G.V.1
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Affiliations:
- Moscow Helmholtz Research Institute of Eye Diseases
- Issue: Vol 10, No 3 (2017)
- Pages: 6-11
- Section: Articles
- URL: https://journals.eco-vector.com/ov/article/view/7188
- DOI: https://doi.org/10.17816/OV1036-11
- ID: 7188
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Abstract
Purpose: determine the impact of biophysical properties of the scleral capsule on the stabilizing effect of orthokeratological correction in progressive myopia.
Material and methods. In 57 patients (114 eyes) aged 8-18 (average age 12.5 ± 0.6 years) with myopia from 1.0 to 7.0 D, acoustic scleral density (ASD) was tested. All patients used (during different terms) orthokeratological (OK) lenses Contex – OKE-System during the night time. To measure ASD (in conventional units) we used digital analysis of ultrasound tissue histograms obtained with a multifunctional ultrasound diagnostic device Voluson 730 Pro (Kretztechnik AG) with a linear frequency sensor of 10 to 16 mHz. ASD was measured in the posterior pole and in the superior temporal quadrant of the equatorial zone. The anteroposterior axis (APA) was measured by ultrasound biometry using an ultrasound device A/B Scan System Model 837 (Allergan Humphrey, USA). Myopia progression was found in 18 eyes of 9 patients with APA increase over 0.1 mm in 6 months, i. e. in 15.5% of cases, while the remaining 48 patients (96 eyes) showed no myopia progression over the follow-up period.
Results. APA was less in eyes with progressive myopia as compared to those with stabilized myopia, both in the equatorial and the posterior pole zones. In progressive myopia, mean APA was 213 ± 3.6 units in the posterior pole and 208 ± 2.19 units in the equatorial zone. In cases of stable myopia, APA was 2.1% higher in the posterior pole area (217 ± 1.3 units) and 1.86% higher in the equatorial area (212 ± 1.4 units). On average, APA in stable myopia was 4 ± 2.0 units higher than in progressive myopia (р < 0.05).
Conclusion. The APA parameter could serve as a prognostic criterion for the myopia course by OK-correction, and as an indicator for choosing treatment tactics.
Full Text
Introduction
In the past few years, orthokeratology (OK) vision correction has gained popularity as a treatment method for progressive myopia in children [8–10, 19]. However, the stabilizing effect of this treatment seems to vary among patients. In 20%–30% of myopia cases, wearing OK lenses has not prevented myopia progression [3, 14, 16, 19].
Recently, a longitudinal study [8] assessed the effect of wearing OK lenses on the dynamics of refraction and anteroposterior axis (APA) in eyes of children and adolescents (84 patients, 168 eyes) of mean age 10.15 ± 3.87 years and a myopia of –3.88 ± 0.12 D; they observed that 20% of the patients experienced the myopia progression of >1.0 D (APA elongation by 0.35 mm) during the follow-up period. The reason underlying such variability in the effect of wearing OK lenses on myopia progression remains unclear and difficult to predict [6, 16].
According to the current concepts of myopia, the disturbance of biophysical (primarily biomechanical) characteristics of the sclera is crucial for myopia pathogenesis [1, 4, 5, 15, 18]. Multiple experimental and laboratory studies have demonstrated that progressive myopia was associated with reduced insoluble collagen and glycosaminoglycans levels in the sclera, decreased collagen cross-linking, and impaired metabolism of microelements that are crucial for the maintenance of the connective tissue, which altogether result in decreased supporting function and elasticity of the sclera, reduced range of reversible deformations, and accumulation of plastic deformations. Finally, these conditions lead to irreversible scleral stretching and axial elongation [4].
In 1990s, researchers from the Helmholtz Moscow Research Institute of Eye Diseases developed a method for the clinical assessment of biophysical and biomechanical characteristics of the sclera by evaluating its acoustic density. The scleral acoustic density (SAD) was estimated by measuring the amplitude attenuation of the echo signal reflected from the scleral tissue [2, 13]. Patients with myopia were showed significantly reduced SAD, which correlated with myopia severity and the state of the fundus. The developers of this technique also developed a method for predicting peripheral chorioretinal dystrophies in children and adolescents with myopia as well as a method for predicting myopia progression, including a list of indications for the additional strengthening of the sclera [11].
The aim of the present study was to investigate the role of biomechanical characteristics of the sclera in the stabilizing effect of OK correction for progressive myopia.
Materials and Methods
To estimate SAD, digital analysis of ultrasonic tissue histograms was performed using a multifunctional ultrasonic diagnostic device (Voluson 730 Pro; Kretztechnik, Austria) equipped with a linear frequency sensor (range: 10–16 MHz). SAD was measured in the posterior pole and in the equatorial region of the upper temporal quadrant of the eye. Using the grayscale mode, a horizontal section of the posterior segment of the eyeball passing through the optic nerve was obtained. The sclera was visualized as hyperechogenic lines. All images were analyzed at the same distance from the optic disc using various magnifications, followed by the quantitative assessment of the characteristics and densitometric parameters of a selected area measured in conventional units for the digital analysis of the ultrasonic images (Figures 1 and 2).
Fig. 1. Acoustic scleral density assessment using Voluson 730 Pro (Kretztechnik, Germany) multifunctional diagnostic system with a linear probe and 10 to 16 MHz frequency
Fig. 2. Acoustic scleral density assessment using digital analysis of ultrasound tissue histogram: а – histogram of emmetropic eye sclera; b – histogram of myopic eye sclera
SAD was measured in 57 patients (114 eyes) aged 8–18 (mean age, 12.5 ± 0.6) years, with a myopia of 1.0–7.0 D. All patients were using overnight OK lenses (Contex – OKE-System).
Once a patient starts using OK lenses, the refraction in the cornea and in the entire optical system of the eye changes, which creates obstacles for the refraction control. Moreover, the refraction may vary significantly depending on the duration of overnight lens wear and the time between lens removal and examination. Therefore, the dynamics of myopic process in these patients is primarily evaluated using ultrasound examination, particularly by measuring the axial length of the eye [10, 12].
Ultrasonography was performed to assess the axial length of the eye using the A/B Scan System (Model 837; Allergan Humphrey, USA).
Results and Discussion
Myopia progression (APA elongation >0.1 mm during the last 6 months) was observed in 9 patients (15.5%, 18 eyes), whereas no myopia progression was observed in 48 participants (96 eyes) for at least 6 months predating the examination.
The results of SAD measurement in the equatorial area and at the posterior pole in patients with progressive and non-progressive myopia are summarized in Table 1.
Table 1. ASD (conventional units) value in progressive and stable myopia when using OK-correction
Таблица 1. Величина акустической плотности (усл. ед.) склеры глаз с прогрессирующей и непрогрессирующей на фоне ношения ОК-линз миопией (M ± σ)
Area of the sclera | Progressive myopia | Non-progressive myopia |
Equatorial area | 208 ± 2.19* | 212 ± 1.4 |
Posterior pole | 213 ± 3.6* | 217 ± 1.3 |
Mean | 210 ± 2.7* | 214 ± 1.4 |
* Differences between the patients with progressive and non-progressive myopia are statistically significant, р < 0.05 | ||
SAD in both the equatorial area and at the posterior pole was lower in patients with progressive myopia than in patients with stable myopia. In eyes with progressive myopia, mean SAD was 213 ± 3.6 units at the posterior pole and 208 ± 2.19 units in the equatorial area, whereas in eyes with non-progressive myopia, this was 217 ± 1.3 units and 212 ± 1.4 units, respectively; values of mean SAD were 2.1% (posterior pole) and 1.86% (equatorial area) higher in eyes with non-progressive myopia than in eyes with progressive myopia. Mean SAD in patients with stable myopia was 4 ± 2.0 units higher than that in patients with progressive myopia (р < 0.05).
Therefore, patients with progressive myopia had significantly lower SAD in the equatorial area and at the posterior pole than patients with stable refraction. Thus, it is obvious that the initial impairments of the biophysical characteristics of the sclera contribute to the further progression of myopia, regardless of OK correction.
Thus, SAD can be used as a prognostic factor for myopia progression in patients wearing OK lenses, which should be considered when selecting a treatment strategy. Our results suggest that SAD values of <215 units at the posterior pole and <210 units in the equatorial area are prognostically unfavorable for further myopia progression. In such cases, the patients are recommended to undergo additional stabilization procedures, such as scleroplastic surgery [6].
Conclusions
- Biophysical characteristics of the sclera were investigated in myopic patients who have been wearing overnight OK lenses. Patients with progressive myopia had significantly lower SAD in the equatorial area and at the posterior pole than patients with stable refraction.
- SAD can be used as a prognostic factor for myopia progression in patients wearing OK lenses, and it should be considered when selecting a treatment strategy.
The study was supported in part by a grant from the Russian Foundation for Basic Research No. 15-29-03874.
The authors declare no conflict of interest.
Authors’ contribution:
Development of a research concept and study design: E.P. Tarutta and E.N. Iomdina.
Data collection and processing: R.R. Toloraya and G.V. Kruzhkova.
Data analysis and drafting the manuscript: E.P. Tarutta and E.N. Iomdina.
About the authors
Yelena P. Tarutta
Moscow Helmholtz Research Institute of Eye Diseases
Author for correspondence.
Email: elenatarutta@mail.ru
doctor of medical science, professor
Russian Federation, MoscowYelena N. Iomdina
Moscow Helmholtz Research Institute of Eye Diseases
Email: iomdina@mail.ru
Dr. Sci., Professor, Principal researcher
Russian Federation, MoscowRusadani R. Toloraya
Moscow Helmholtz Research Institute of Eye Diseases
Email: dr.toloraya@gmail.com
MD, PhD, Researcher
Russian Federation, MoscowGalina V. Kruzhkova
Moscow Helmholtz Research Institute of Eye Diseases
Email: info@igb.ru
MD, PhD, Senior Researcher
Russian Federation, MoscowReferences
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