Overnight Orthokeratology Compared With Atropine in Myopia
Overnight Orthokeratology Compared With Atropine in Myopia
Atropine is a well-known drug for treating myopia. In this study, OK lens is effective in slowing progression of myopia and increasing of axial length over a period of 3 years and is compatible with the effect of atropine. In our knowledge, this is the first paper compare the effect of atropine and Ok lens in controlling progression of myopia. In this study, we find that Ok lens is mild better then atropine in controlling axial length elongation and myopia progression. Besides, Ok lens users do not suffer photophobia and risk of inducing crowding of anterior chamber angle and increasing intraocular pressure (IOP) which may be induced by atropine. Moreover, the benefit of OK lens include that ceasing wearing glasses in daily life which bring convenience, better quality of life, no influence or near vision and somewhat good-looking. Nevertheless, there are still some drawbacks of OK lens, such as risk of cornea damage, infection and decreasing of cornea endothelium cell count; glare at night or vision decrease at evening are seen in OK lens users sometimes. There is no absolutely conclusion that OK lens or atropine is better, we just suggest that from the view of controlling myopia, Ok lens is useful methods.
The data presented in this study, the increase in axial length was 0.28 ± 0.08 mm per year in the OK lens group versus 0.37 ± 0.11 mm per year in the atropine group. In 2005, Cho et al. reported that axial length increased by 0.29 ± 0.27 mm in the OK lens group and 0.54 ± 0.27 mm in a control group treated with spectacles during a 2-year follow-up. In 2009, Walline et al. reported similar findings; the mean increase in axial length after 2 years was 0.25 mm in the OK group and 0.57 mm in the control group. In 2011, Kakita et al. obtained similar changes of 0.39 ± 0.27 mm in the OK lens group versus 0.61 ± 0.24 mm in the control spectacles group over 2 years. The study of Walline et al. was performed with American patients, in whom the progression of myopia is reportedly slower than in the Asian population; this may explain the lesser increase in axial length in their study. The results of Kakita et al. were obtained in Japan with an ethnic group similar to ours, and their results are similar to those of our study. The increase in axial length in our OK lens group (0.28 ± 0.08 mm per year) was a little less than that reported by Cho et al. (0.29 ± 0.27 mm per year). The study of Cho et al. was performed in Hong Kong, in an area with high prevalence of myopia. Differences in the results may be because they used an ultrasonic A-mode device to measure axial length. In the present study, laser interferometry (IOLMaster; Carl Zeiss Meditec) was used to obtain noncontact measurements of axial length. This method has high reproducibility, and the non-contact procedure decreases the influences induced by compression of the cornea. The increase in axial length in our atropine group was the smaller then the control groups of all the studies mentioned above. This can be understood by that 0.125% atropine is effective in decreasing myopia progression and axial length increase. Nevertheless, there were significant difference between the OK lens group and the 0.125% atropine group in quantity of axial length and myopic diopters. Moreover, there are data in our study worth pay attention, that is the standard deviation of atropine group in the second and third year is higher then in OK lens group, this might meant that the controlling myopia in this group is not very stable during the period.
The major limitation of our study is that the myopic diopter and axial length were checked every year after discontinuing use of OK lenses for only 3 weeks; this may not disturb the results of checking axial length but 3 weeks may not enough for the refractive error to completely recover to the baseline condition. However, patients in the OK lens group often relied on the OK lenses for their daily vision and could not discontinue use of the OK lens for 4–6 weeks, and 4–6 weeks has been proved to be sufficient for restoration of corneal curvature to the baseline condition so that the exact myopia diopter can be determined. This limitation is offset by the fact that the axial length, which is not influenced to a great extent by use of the OK lens, was also measured in this study, and a significant difference in axial length was found. Moreover, the included patients who completed the 3 years following-up without washout might be with satisfactory myopia control effect and lower or mild incidence of adverse effects; this induced the study biased towards successful cases. Nevertheless, the bias existed in both OK lens and atropine groups and cannot be neither avoided nor neglected.
Another limitation of our study is that age may influence the progression of myopia. A previous study demonstrated that myopia increased most remarkably at the age of 10–13 years; therefore, if we assessed only 10- to 13-year-old patients, the differences in myopic degree and axial length between the 2 groups were still observed, but to a lesser extent (p = 0.003 and p = 0.0035, respectively). However, the sample number was decreased after age stratification. Therefore, a larger study sample is required for future studies based on age stratification.
Allergic conjunctivitis happened in 37 eyes (17.6%) of OK lens. The care solution of Ok lens used were "Boston Conditioning Solution and Boston Cleaner" (Bausch & Lomb Taiwan Ltd, Taiwan) or BIOCLEN Contact Lens Solution (BIOCLEN OPHTECS, Japan). There was no evident difference that which solution will induce allergic conjunctivitis in our patients. The allergic conditions would subside after gave topic anti-histamine for 2 days without change care solutions. The allergic conjunctivitis might due to the warm and moist climate in our country. Patients selected the care solution at their own convenience. None of the patients had complains of the care solution.
Some of OK lens users exhibited UCVA greater than 0.2 logMAR (20/30) or had obvious fluctuations in diurnal UCVA. These patients often had a flatter cornea curvature, irregular cornea surface, or tight eyelids. The limitations of OK lenses are obvious, and the tight eyelids of Asian subjects are a substantial concern. Although the new multiple-zone, reverse-geometry lenses have a better outcome, not all patients are satisfied with the OK lens. No severe corneal infection occurred in this study group; it is important to educate the patients and their families about maintenance of healthy habits and appropriate handling of OK lenses.
Patients with high myopia at baseline showed less severe increase in axial length than those with low myopia in both the OK lens and atropine groups. The linear correlation was more significant in the OK lens group then in the atropine group (r = 0.259 versus r = 0.169). This phenomenon may occur because peripheral refraction changes are more evident in high myopia patients with OK lenses. Myopic eyes usually have relative hyperopic defocus in the periphery, because the eye is elongated along the optic axis. Recent studies suggest that peripheral vision can influence axial length in human eyes, potentially altering the central refractive error and its development because of the emmetropization effect of eye growth. Conversion of relative peripheral hyperopia to relative peripheral myopia is a good method to limit the axial elongation that leads to myopia, and OK lenses appear to be an excellent option for achieving this objective. OK lenses appear to be a good tool to control high myopia. OK lenses create a small central zone and a smaller central visual field in high myopia patients comparing with lower myopia ones. At the same time, high myopia patients were with a greater area of the peripheral field remaining myopic. If changes of peripheral refraction are the primary reason for slowing progression of myopia, this would be expected to decrease axial length elongation especially in high myopia patients. More human and animal studies are required to clearly test this hypothesis. However, clear central vision is essential for preventing defocus-inducing myopia.
The efficacy and safety of atropine is undoubted. Nevertheless, increasing intraocular pressure and photo-stress of the crystalline lens, retina, photophobia and poor near vision are often to be concerned in the patients using atropine. Low concentration atropine has proved useful in recent study that it can control myopia progression and decrease the side effects of high concentration atropine, low concentration atropine might an another good choice. OK lens with well care and hygiene may be one of the good policies to prevent progression of myopia and it does not just bring convenience for myopic patient to remove glasses in daytime. The combined use of OK lenses and atropine is a potential treatment for myopia progression and is being tested at our department. Hope this can give a new concept in delaying progression of myopia and can go a step further to resolve myopic problems.
Discussion and Conclusions
Atropine is a well-known drug for treating myopia. In this study, OK lens is effective in slowing progression of myopia and increasing of axial length over a period of 3 years and is compatible with the effect of atropine. In our knowledge, this is the first paper compare the effect of atropine and Ok lens in controlling progression of myopia. In this study, we find that Ok lens is mild better then atropine in controlling axial length elongation and myopia progression. Besides, Ok lens users do not suffer photophobia and risk of inducing crowding of anterior chamber angle and increasing intraocular pressure (IOP) which may be induced by atropine. Moreover, the benefit of OK lens include that ceasing wearing glasses in daily life which bring convenience, better quality of life, no influence or near vision and somewhat good-looking. Nevertheless, there are still some drawbacks of OK lens, such as risk of cornea damage, infection and decreasing of cornea endothelium cell count; glare at night or vision decrease at evening are seen in OK lens users sometimes. There is no absolutely conclusion that OK lens or atropine is better, we just suggest that from the view of controlling myopia, Ok lens is useful methods.
The data presented in this study, the increase in axial length was 0.28 ± 0.08 mm per year in the OK lens group versus 0.37 ± 0.11 mm per year in the atropine group. In 2005, Cho et al. reported that axial length increased by 0.29 ± 0.27 mm in the OK lens group and 0.54 ± 0.27 mm in a control group treated with spectacles during a 2-year follow-up. In 2009, Walline et al. reported similar findings; the mean increase in axial length after 2 years was 0.25 mm in the OK group and 0.57 mm in the control group. In 2011, Kakita et al. obtained similar changes of 0.39 ± 0.27 mm in the OK lens group versus 0.61 ± 0.24 mm in the control spectacles group over 2 years. The study of Walline et al. was performed with American patients, in whom the progression of myopia is reportedly slower than in the Asian population; this may explain the lesser increase in axial length in their study. The results of Kakita et al. were obtained in Japan with an ethnic group similar to ours, and their results are similar to those of our study. The increase in axial length in our OK lens group (0.28 ± 0.08 mm per year) was a little less than that reported by Cho et al. (0.29 ± 0.27 mm per year). The study of Cho et al. was performed in Hong Kong, in an area with high prevalence of myopia. Differences in the results may be because they used an ultrasonic A-mode device to measure axial length. In the present study, laser interferometry (IOLMaster; Carl Zeiss Meditec) was used to obtain noncontact measurements of axial length. This method has high reproducibility, and the non-contact procedure decreases the influences induced by compression of the cornea. The increase in axial length in our atropine group was the smaller then the control groups of all the studies mentioned above. This can be understood by that 0.125% atropine is effective in decreasing myopia progression and axial length increase. Nevertheless, there were significant difference between the OK lens group and the 0.125% atropine group in quantity of axial length and myopic diopters. Moreover, there are data in our study worth pay attention, that is the standard deviation of atropine group in the second and third year is higher then in OK lens group, this might meant that the controlling myopia in this group is not very stable during the period.
The major limitation of our study is that the myopic diopter and axial length were checked every year after discontinuing use of OK lenses for only 3 weeks; this may not disturb the results of checking axial length but 3 weeks may not enough for the refractive error to completely recover to the baseline condition. However, patients in the OK lens group often relied on the OK lenses for their daily vision and could not discontinue use of the OK lens for 4–6 weeks, and 4–6 weeks has been proved to be sufficient for restoration of corneal curvature to the baseline condition so that the exact myopia diopter can be determined. This limitation is offset by the fact that the axial length, which is not influenced to a great extent by use of the OK lens, was also measured in this study, and a significant difference in axial length was found. Moreover, the included patients who completed the 3 years following-up without washout might be with satisfactory myopia control effect and lower or mild incidence of adverse effects; this induced the study biased towards successful cases. Nevertheless, the bias existed in both OK lens and atropine groups and cannot be neither avoided nor neglected.
Another limitation of our study is that age may influence the progression of myopia. A previous study demonstrated that myopia increased most remarkably at the age of 10–13 years; therefore, if we assessed only 10- to 13-year-old patients, the differences in myopic degree and axial length between the 2 groups were still observed, but to a lesser extent (p = 0.003 and p = 0.0035, respectively). However, the sample number was decreased after age stratification. Therefore, a larger study sample is required for future studies based on age stratification.
Allergic conjunctivitis happened in 37 eyes (17.6%) of OK lens. The care solution of Ok lens used were "Boston Conditioning Solution and Boston Cleaner" (Bausch & Lomb Taiwan Ltd, Taiwan) or BIOCLEN Contact Lens Solution (BIOCLEN OPHTECS, Japan). There was no evident difference that which solution will induce allergic conjunctivitis in our patients. The allergic conditions would subside after gave topic anti-histamine for 2 days without change care solutions. The allergic conjunctivitis might due to the warm and moist climate in our country. Patients selected the care solution at their own convenience. None of the patients had complains of the care solution.
Some of OK lens users exhibited UCVA greater than 0.2 logMAR (20/30) or had obvious fluctuations in diurnal UCVA. These patients often had a flatter cornea curvature, irregular cornea surface, or tight eyelids. The limitations of OK lenses are obvious, and the tight eyelids of Asian subjects are a substantial concern. Although the new multiple-zone, reverse-geometry lenses have a better outcome, not all patients are satisfied with the OK lens. No severe corneal infection occurred in this study group; it is important to educate the patients and their families about maintenance of healthy habits and appropriate handling of OK lenses.
Patients with high myopia at baseline showed less severe increase in axial length than those with low myopia in both the OK lens and atropine groups. The linear correlation was more significant in the OK lens group then in the atropine group (r = 0.259 versus r = 0.169). This phenomenon may occur because peripheral refraction changes are more evident in high myopia patients with OK lenses. Myopic eyes usually have relative hyperopic defocus in the periphery, because the eye is elongated along the optic axis. Recent studies suggest that peripheral vision can influence axial length in human eyes, potentially altering the central refractive error and its development because of the emmetropization effect of eye growth. Conversion of relative peripheral hyperopia to relative peripheral myopia is a good method to limit the axial elongation that leads to myopia, and OK lenses appear to be an excellent option for achieving this objective. OK lenses appear to be a good tool to control high myopia. OK lenses create a small central zone and a smaller central visual field in high myopia patients comparing with lower myopia ones. At the same time, high myopia patients were with a greater area of the peripheral field remaining myopic. If changes of peripheral refraction are the primary reason for slowing progression of myopia, this would be expected to decrease axial length elongation especially in high myopia patients. More human and animal studies are required to clearly test this hypothesis. However, clear central vision is essential for preventing defocus-inducing myopia.
The efficacy and safety of atropine is undoubted. Nevertheless, increasing intraocular pressure and photo-stress of the crystalline lens, retina, photophobia and poor near vision are often to be concerned in the patients using atropine. Low concentration atropine has proved useful in recent study that it can control myopia progression and decrease the side effects of high concentration atropine, low concentration atropine might an another good choice. OK lens with well care and hygiene may be one of the good policies to prevent progression of myopia and it does not just bring convenience for myopic patient to remove glasses in daytime. The combined use of OK lenses and atropine is a potential treatment for myopia progression and is being tested at our department. Hope this can give a new concept in delaying progression of myopia and can go a step further to resolve myopic problems.