Article

Myopia: attempts to arrest progression

Tan Tock Seng Hospital, Tumasik, 00, Singapore
British Journal of Ophthalmology (Impact Factor: 2.81). 12/2002; 86(11):1306-11. DOI: 10.1136/bjo.86.11.1306
Source: PubMed

ABSTRACT Previous studies have evaluated the efficacy of several interventions to decrease the progression of myopia. These include devices that alter the perception of the visual environment and pharmacological treatments. There is no conclusive evidence thus far that alteration of the pattern of spectacle wear, bifocals, ocular hypotensives, or contact lenses retards the progression of myopia. Several randomised clinical trials have demonstrated that the rate of progression of myopia is lower in children given atropine eye drops than those given placebo. However, atropine is associated with short term side effects such as photophobia and possible long term adverse events including light induced retinal damage and cataract formation. Other more selective antimuscarinic agents such as pirenzipine are presently being evaluated. Further well conducted randomised clinical trials with large sample sizes and adequate follow up designed to evaluate treatments to retard the progression of myopia should be conducted, since the identification of an effective intervention may have a greater public health impact on the burden and morbidity from myopia than the few treatments currently available.

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    • "Despite the alarming nature of myopia , the current standard of care for these patients is very limited and the practician can hardly recommend any particular measure to prevent or retard the progression of myopia. Therapeutic attempts to arrest myopic progression comprise administration of cycloplegic or hypotensive drugs like atropine, tropicamide, pirenzipine or timolol, the use of optical corrections such as bifocal and multifocal glasses or rigid contact lenses to assist in near work and accommodation (Wildsoet & Norton 1999; Saw et al. 2002; Rada et al. 2006), and microsurgical scleroplasty (Avetisov et al. 1997). However , the efficiency and success of these methods remain questionable. "
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    ABSTRACT: Chemical crosslinking by glyceraldehyde has been shown to increase significantly the biomechanical rigidity of sclera. It might therefore become an option for a sclera-based treatment of progressive myopia. The present pilot study was designed to test the long-term biomechanical efficiency of the new crosslinking method. Six Chinchilla rabbits were treated with sequential sub-Tenon's injections of 0.15 ml 0.5 m glyceraldehyde, which were given in the supero-nasal quadrant of the right eye (OD) five times over 14 days. The rabbits were killed 4 months and 8 months after crosslinking treatment, respectively. Biomechanical stress-strain measurements of scleral strips from the treatment area were performed and compared to non-treated contralateral control sclera using a microcomputer-controlled biomaterial testing device. In addition, the eyes were examined histologically by light microscopy to evaluate possible side-effects. Following the crosslinking treatment, the ultimate stress was 10.2 +/- 2.3 MPa after 4 months and 8.5 +/- 2.2 MPa after 8 months versus 2.4 +/- 0.3 MPa in the controls (increases of 325% and 254.17%, respectively); Young's modulus was 104.6 +/- 13.7 MPa after 4 months and 53.2 +/- 5.2 MPa after 8 months versus 9.6 +/- 1.3 MPa in the controls (increases of 989.6% and 554.17%, respectively); and ultimate strain was 15.8 +/- 1.5% after 4 months and 24.1 +/- 0.7% after 8 months versus 38.4 +/- 4.6% in the controls (decreases of 58.84% and 37.24%, respectively). Histologically, no side-effects were found. Our new method of scleral collagen crosslinking proved very efficient in increasing scleral biomechanical strength over a period of up to 8 months. Glyceraldehyde can be applied easily by sequential parabulbar injections. Before clinical application in myopic patients, a study in an animal myopia model is recommended.
    Acta ophthalmologica 07/2008; 86(8):887-93. DOI:10.1111/j.1755-3768.2007.01156.x · 2.51 Impact Factor
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    ABSTRACT: While prolonged nearwork is considered to be an environmental risk factor associated with myopia development, an underlying genetic susceptibility to nearwork-induced accommodative adaptation may be one possible mechanism for human myopia development. As the control of accommodation by the autonomic system may be one such genetically predetermined system, this research sought to investigate whether an anomaly of the autonomic control of accommodation may be responsible for myopia development and progression. The emphasis of this work was determining the effect of altering the sympathetic input to the ciliary muscle on accommodation responses such as tonic accommodation and nearwork-induced accommodative adaptation in myopes and non-myopes. The first study of the thesis was based on observations of Gilmartin and Winfield (1995) which suggested that a deficit in the sympathetic inputs to the ciliary muscle may be associated with a propensity for myopia development. The effect of ß-antagonism with timolol application on accommodation characteristics was studied in different refractive error groups. Our results support the previous findings that a deficit of sympathetic facility during nearwork was not a feature of late-onset myopia. However it was found that classifying myopes according to stability of their myopia and their ethnic background was important and this allowed differentiation between accommodation responses and characteristics of the ciliary muscle autonomic inputs, with the greatest difference observed between Caucasian stable myopes and Asian progressing myopes. Progressing myopes, particularly those with an Asian background, demonstrated enhanced susceptibility to nearwork-induced accommodative adaptation and this was suggested to result from a possible parasympathetic dominance and a relative sympathetic deficit to the ciliary muscle. In contrast, stable myopes, particularly those with an Asian background, demonstrated minimal accommodation changes following nearwork (counter-adaptation in some cases), and increased accommodative adaptation with ß-antagonism, suggesting sympathetic dominance as the possible autonomic accommodation control profile. As ethnic background was found to be an important factor, a similar study was also conducted in a group of Hong Kong Chinese children to investigate if enhanced susceptibility to nearwork-induced changes in accommodation may explain in part the high prevalence of myopia in Hong Kong. Despite some minor differences in methodology between the two studies, the Hong Kong stable myopic children demonstrated counter-adaptive changes and greater accommodative adaptation with timolol, findings that were consistent with those of the adult Asian stable myopes. Both Asian progressing myopic children and adults also showed greater accommodative adaptation than the stable myopes and similar response profiles following ß-adrenergic antagonism. Thus a combination of genetically predetermined accommodation profiles that confer high susceptibility and extreme environmental pressures is a likely explanation for the increase in myopia over the past decades in Asian countries. The hypothesis that a sympathetic deficit is linked to myopia was also investigated by comparing the effect of â-stimulation with salbutamol, a ß-agonist, on accommodation with that of ß-antagonism using timolol. It was hypothesized that salbutamol would have the opposite effect of timolol, and that it would have a greater effect on subjects who demonstrated greater accommodative adaptation effects, i.e. the progressing myopes, compared to those who showed minimal changes in accommodation following nearwork. Consistent with the hypothesis, the effect of sympathetic stimulation with salbutamol application was only evident in the progressing myopes whom we hypothesized may have a parasympathetic dominance and a relative sympathetic deficit type of autonomic imbalance while it did not further enhance the rapid accommodative regression profile demonstrated by the stable myopes. Characteristics of the convergence system and the interaction between accommodation and convergence were also investigated in the Hong Kong children. No significant differences in response AC/A ratios between the emmetropic, stable and progressing myopic children were found and it was concluded that elevated AC/A ratios were not associated with higher myopic progression rate in this sample of Hong Kong children. However, ß-adrenergic antagonism with timolol application produced a greater effect on accommodative convergence (AC) in stable myopic children who presumably have a more adequate, robust sympathetic input to the ciliary muscle, but had little effect on AC of progressing myopic children. This finding again points to the possibility that the autonomic control of the accommodation and convergence systems may be different between stable and progressing myopia. The primary contribution of this study to the understanding of myopia development is that differences in the autonomic control of the ciliary muscle may be responsible for producing anomalous accommodation responses. This could have significant impact on retinal image quality and thus results in myopia development. This knowledge may be incorporated into computer models of accommodation and myopia development and provides scope for further investigation of the therapeutic benefits of autonomic agents for myopia control.
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    ABSTRACT: Background: Mechanical forces either due to accommodation or myopia may stretch the retina and/or cause shear between the retina and choroid. This can be investigated by making use of the Stiles-Crawford effect (SCE), which is the phenomenon of light changing in apparent brightness as it enters through different positions in the pupil. The SCE can be measured by psychophysical and objective techniques, with the SCE parameters being directionality (rate of change across the pupil), and orientation (the location of peak sensitivity in the pupil). Aims: 1. To study the changes in foveal SCE with accommodation in emmetropes and myopes using a subjective (psychophysical) technique. 2. To develop and evaluate a quick objective technique of measuring the SCE using the multifocal electroretinogram. Methods: The SCE was measured in 6 young emmetropes and 6 young myopes for up to 8 D accommodation stimulus with a psychophysical technique and its variants. An objective technique using the multifocal electroretinogram was developed and evaluated with 5 emmetropes. Results: Using the psychophysical technique, the SCE directionality increased by similar amounts in both emmetropes and myopes as accommodation increased, with an increase of 15-20% with 6 D of accommodation. However, there were no significant orientation changes. Additional measurements showed that most of the change in the directionality was probably an artefact of optical factors such as higher-order aberrations and accommodative lag rather a true effect of accommodation. The multifocal technique demonstrated the presence of the SCE, but results were noisy and too variable to detect any changes in SCE directionality or orientation with accommodation. Conclusion: There is little true change in the SCE with accommodation responses up to 6 D in either emmetropes or myopes, although it is possible that substantial changes might occur at very high accommodation levels. The objective technique using the multifocal electroretinogram was quicker and less demanding for the subjects than the psychophysical technique, but as implemented in this thesis, it is not a reliable method of measuring the SCE.
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