Abstract
Purpose
To evaluate the clinical effect of orthokeratology in controlling myopia and treating anisometropia among children with myopic anisometropia.
Methods
A total of 108 myopic anisometropic children aged 8–16 years old who wore orthokeratology lenses in both eyes were enrolled in this study and followed up for over 1 year. The more severely myopic eye of each patient was assigned to the more myopic group (108 eyes), with a mean spherical equivalent refraction of −4.25 (−5.00, −3.38) D; the opposite eye of each patient was assigned to the less myopic group (108 eyes), with a refraction of −2.75 (−3.63, −1.88) D. This study observed and analyzed changes in ocular parameters after orthokeratology (Wilcoxon signed-rank test).
Results
In children who wore orthokeratology lenses for approximately 1 year, the level of anisometropia significantly dropped from 1.38 (1.13, 1.75) D to 1.25 (1.13, 1.75) D ( P = .005). The difference between the axial lengths of the two eyes significantly dropped from 0.54 (0.37, 0.74) mm to 0.46 (0.28, 0.67) mm ( P < .0001).
Conclusions
Orthokeratology seemed to be more effective at delaying the progression of myopia in the more myopic eyes than in the less myopic eyes of myopic anisometropic children. Orthokeratology lenses are suitable for anisometropic children, although the effectiveness of orthokeratology against anisometropia requires additional follow-up time for further observation and study.
1
Introduction
Anisometropia is an interocular difference in refractive status that can be caused by various refractive properties of the eyes and can lead to a variety of symptoms. This difference is mainly caused by an imbalance in axial growth (especially the depth of the vitreous body) [ , ]. Typical myopic anisometropia is a type of compound anisometropia in which both eyes are myopic and the difference in the spherical equivalent refraction is at least 1.00 D. If the refractive difference between the two eyes is great enough or lasts long enough, it will influence and impair binocular visual function [ , ], and affected patients may suffer from a series of problems with visual functions, such as diplopia, visual fatigue, difficulty in adapting to spectacles, or an inability to carry out fine work. Recently, many studies [ , , ] have found that the incidence and degree of anisometropia increased with age and the degree of myopia. Anisometropia has important consequences in the establishment and development of binocular vision function during childhood. Therefore, additional attention should be paid to anisometropic children.
To date, few clinical methods have been used to correct anisometropia. Most clinical evidence has demonstrated that orthokeratology is an effective and safe means of controlling myopia and delaying axial length growth [ , ]. Orthokeratology is currently widely used in children and adolescents in clinical practice. When myopic anisometropic children wear orthokeratology lenses, are there any differences in the effect when the degree of myopia is unequal between the two eyes? Does orthokeratology accelerate or slow down the progression of myopic anisometropia? This study analyzed retrospective clinical data to answer these clinical questions.
2
Materials and methods
2.1
Subjects and information
This retrospective study included a total of 108 patients (46 male, 62 female) who attended the Eye Hospital of Wenzhou Medical University from January 2014 to December 2016 and were willing to wear orthokeratology lenses or had been wearing orthokeratology lenses for approximately 1 year. The mean age of the patients was 11.53 ± 1.96 years (range, 8–16 years). The mean follow-up time was 15.68 ± 8.41 months. The more severely myopic eye of each patient was assigned to the more myopic group, and the opposite eye of each patient was assigned to the less myopic group. The mean spherical equivalent refraction of the more myopic eyes (108 eyes) was −4.25 (−5.00, −3.38) D (range −1.88 D to −7.88 D), and the 108 opposite eyes (the less myopic eyes) had a mean spherical equivalent refraction of −2.75 (−3.63, −1.88) D (range, −0.50 D to −5.75 D). The average level of anisometropia was 1.38 (1.13, 1.75) D (range, 1.00 D to 3.75 D). Table 1 shows the baseline characteristics of all included eyes in detail.
| Parameters | More myopic eyes | Less myopic eyes | Z | P |
|---|---|---|---|---|
| Number of eyes | 108 | 108 | ||
| UA | 0.80 (0.70, 1.30) | 0.52 (0.40, 0.80) | 11.236 | <.0001 |
| Spherical refraction, D | −4.25 (−5.00, −3.38) | −2.75 (−3.63, −1.88) | −8.960 | <.0001 |
| Cylindrical refraction, D | −0.38 (−0.50, 0.00) | −0.50 (−0.94, −0.25) | −3.946 | <.0001 |
| SER, D | −3.50 (−4.50, −2.50) | −2.75 (−4.00, −2.00) | −3.556 | <.0001 |
| Axial length, mm | 25.13 (24.75, 25.65) | 25.32 (24.91, 25.76) | 8.980 | <.0001 |
| Anterior chamber depth, mm | 3.68 (3.56, 3.85) | 3.69 (3.56, 3.82) | 1.783 | .318 |
| Intraocular pressure, mmHg | 14.10 (10.65, 16.10) | 14.00 (11.00, 16.30) | −2.102 | .169 |
2.2
Methods
The inclusion criteria were as follows: 1) the unaided acuity (logMAR) was equal to or less than 0.1 after the subject had worn orthokeratology lenses for one month; and 2) the initial examinations of the anterior segment, fundus and other structures were all normal. Orthokeratology lenses have an inverse geometric design and have four segmental arcs. Orthokeratology lens fittings were performed by a professional physician in all cases. Every patient had a satisfactory fluorescence profile, appropriate activity and center location with the lenses. The essential follow-up and ocular examinations were completed every three months.
Clinically, when the lens needed to be replaced, the physician asked the patient to wear a trial lens that was identical to the final best-fitted trial lens identified during the initial lens fitting, and the researchers then over-refracted the lenses. The amount of refraction growth that occurred over this period was equal to the difference between the initial and second (after more than 1 year) over-refraction values. When the lenses were removed, the intraocular pressure was measured three times by a Non-Contact Intraocular Pressure Measurement System (Japanese Canon Company) according to the usual procedure. The axial length and anterior chamber depth were measured with an Intraocular Lens Master (IOL-Master, Zeiss, Germany). Corneal topography (Medmont E300, Medmont International Pty, Australia) was used to measure the shape of the cornea. Slit-lamp biomicroscopy was conducted to check the ocular anterior segment. Data were collected from 108 anisometropic patients to analyze the changes in the ocular parameters of both eyes of each person after he or she wore the orthokeratology lenses. This study observed and compared the spherical equivalent refraction, axial length, anterior chamber depth, intraocular pressure, steep K and flat K values (simulated keratometry readings at the flattest and steepest meridians, respectively), and Es and Ef values (eccentricity of the corneal shape at the steepest and flattest meridians, respectively) of the corneal topography before and after the patients wore the lenses for more than 1 year.
2.3
Analysis and statistics
All analyses were performed with SPSS version 19.0 software. All measured d/ce:inf>, P 75 ). The changes from baseline to after 1 year of treatment were analyzed in each eye or compared between eyes using the Wilcoxon signed-rank test (suitable for two related samples). The threshold for statistical significance was set at P < 0.05.
3
Results
3.1
Refraction and axial length
After orthokeratology lenses were worn for over 1 year, the spherical equivalent refraction of the more myopic eyes changed from −4.25 (−5.00, −3.38) D to −4.50 (−5.00, −3.50) D ( Z = −5.149, P < .0001), calculated from the change in over-refraction. In contrast, the refraction of the opposite eyes changed from −2.75 (−3.63, −1.88) D to −3.00 (−3.75, −2.00) D ( Z = −5.754, P < .0001). Importantly, the level of anisometropia was 1.38 (1.13, 1.75) D at baseline and was significantly reduced to 1.25 (1.13, 1.75) D after the orthokeratology lenses were used ( Z = −2.826, P = .005). Fig. 1 shows the change that occurred in the spherical equivalent refraction of each eye and the level of anisometropia after the orthokeratology lenses had been worn for over 1 year.
