| Author: | Yang, Yajing |
| Title: | Orthokeratology for high myopia (OHM) |
| Advisors: | Chan, Henry (SO) Cho, Pauline (SO) |
| Degree: | Ph.D. |
| Year: | 2024 |
| Subject: | Myopia Orthokeratology Hong Kong Polytechnic University -- Dissertations |
| Department: | School of Optometry |
| Pages: | 1 volume (various pagings) : color illustrations |
| Language: | English |
| Abstract: | Introduction and objectives The escalating prevalence of myopia and high myopia has been observed globally, particularly in Asian countries. Orthokeratology (ortho-k) has demonstrated its effectiveness in controlling myopia progression in children. Highly myopic children were found to benefit more from ortho-k treatment because a higher refractive target theoretically led to more peripheral myopic defocus, a greater change in higher-order aberrations (HOAs), and a greater thickening of the choroid. In practice, a conservative approach using a lower target was more commonly adopted for highly myopic children. Recently, a dual reverse curve (RC) ortho-k design aimed at correcting myopia from -5.00 dioptre (D) to -10.00 D has become commercially available. However, to date, there have been no prospective studies to confirm its effectiveness in high myopes. The current two-year prospective study was conducted to investigate the clinical performance, myopia control efficacy and the correlation between axial elongation (AE) and changes in choroidal thickness (ChT) and HOAs in high myopes using this dual RC ortho-k lens design with greater refractive target in comparison to a conventional lens design with a -4.00 D target. During the study, an unexpected corneal microcystic response was observed in many participants during the novel coronavirus pandemic. The details of this corneal response and the managements are described. Methods Seventy-four Chinese children aged 7 to 13 years (inclusive), with high myopia of ≤ -5.00 D and ≥ -2.00 D of astigmatism in both eyes, were recruited. Fifty-three children passed lens handling skills training and were allocated to wear a conventional design targeted for -4.00 D correction or a dual RC design targeted for full correction (control: 30 vs study: 23). Due to the dual RC toric design being out of production, seven participants (six control and one study) were non-randomized and fitted with lenses based on if requiring a toric design. Data were collected prior to the commencement of ortho-k treatment and at six-month intervals over the two-year study period. Axial length (AL) was monitored and measured by a masked examiner. Other measurements, including refraction, ocular health, ChT and HOAs were measured by the same unmasked investigator. Vision-related quality of life was assessed by questionnaire at baseline and after one-year of lens wear. Data from both eyes, including changes in refraction, AE, ChT, HOAs and ocular health were retrieved and analysed. Results A total of 37 and 30 participants completed the one-and two-year study, respectively, with 23 in the control group and 14 in the study group for the first year, and 20 in the control and 10 in the study group for the second year. The first-fit success rate was approximately 80% for both groups at the one-month visit. After one month of lens wear, there was a mean ± standard error reduction of 4.38 ± 0.18 D and 5.27 ± 0.18 D in spherical refraction in the control and study group, respectively. Overall, participants in the study group were more satisfied with their lens wear and experienced greater benefits from full correction. After one year of lens wear, the incidence of central corneal staining and lens binding was 43% and 50% in the study group, respectively, which were approximately twice those of the control group. After one year, “moderate to severe” microcysts (Efron Grading Scales) were observed in around 30% of eyes in both groups. To eliminate the “moderate and severe” microcysts before the higher oxygen permeability lens material was available, 13 participants discontinued treatment for over one month, resulting in the underestimated efficacy in terms of AE compared to that of historical single-vision spectacles data. At the end of the two-year study period, the myopia control efficacy of ortho-k was comparable in both groups. Despite the discontinuation effect due to microcysts, the myopia control efficacy of both the study and control lenses used in this study was greater than that observed in previously reported studies involving highly myopic children. Moreover, ChT significantly increased at the six-month visit and remained stable at least at 18-month visit for both groups. A significant increase in total HOAs root-mean-square (RMS), comatic aberrations RMS, spherical aberration RMS, primary and secondary spherical aberration, and a negative shift in primary vertical coma (Z3−1) were observed over two years of ortho-k treatment. However, no significant differences in ChT or any HOAs term were found between the two groups. In addition to a greater choroidal thickening, a greater change in spherical refraction, and a positive shift in Z3−1,a negative shift in secondary spherical aberration and without discontinuing ortho-k treatment for more than one month were associated with less changes in AL in highly myopic children over two years of ortho-k treatment. Conclusion The dual RC ortho-k lens design targeted for a greater refractive correction exhibited a reduced residual spherical refraction, similar residual astigmatism, and improved unaided visual acuity (VA) after two years. The greater reduction in spherical refraction observed in the study group was associated with an increased prevalence of central corneal staining and lens binding. Corneal microcysts were observed in highly myopic children without a history of contact lens wear. A higher degree of myopia, along with the use of lower oxygen permeability lens materials, may contribute to a greater prevalence and severity of microcystic response. A comparable level of myopia control was observed between the two ortho-k lens designs in highly myopic children, which was greater than that reported in previous studies of children with high myopia. In highly myopic children undergoing long-term ortho-k treatment, changes in AL were negatively significantly associated with a greater thickening of the subfoveal choroid, greater changes in spherical refraction, a positive shift in Z3−1 , a negative shift in Z60 and the discontinuation effect. |
| Rights: | All rights reserved |
| Access: | open access |
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