Discussion
A number of studies13 17 23 have indicated that a range of good refractive results and VA were achievable with self-refraction in children although variations in the results reported. The discrepancies in the accuracy of self-refraction reported in their results may be attributed to several factors including the background and refraction experience of the subjects. The current investigation was, therefore, carried out to assess the accuracy of two commonly available self-refraction spectacles in urban and rural school children in the Central Region of Ghana.
The distribution of refractive error among the study population showed that myopia was more common in urban children (54.4%), while hyperopia was more common in rural children (58.0%). The differences in the prevalence of refractive error could be attributed to modern lifestyle activities, especially near work with technological devices (eg, computers, laptops, phones and video games) which may cause myopia. On the other hand, less access to activities with demanding near visual activity and nutritional changes in rural children may predispose them to hyperopia.24 25
The results from this study indicate that while the differences in refractive power achieved with the two Alvarez spectacles were not different from each other they were appreciable when compared with the traditional clinical gold standard of refraction in children (ie, CSR). The refractive results from both self-refractions also differed from refraction obtained with autorefraction. The refractive results from both self-refractions also differed from refraction obtained with autorefraction. The results are consistent to a previous study conducted on Chinese children16, which found differences in the methods and reported that SE differed by 1.0 D in either direction from CSR, which was more frequent for self-refraction (11.2%) than non-cycloplegic autorefraction (6.0%). In a study conducted in Ghana among myopes,17 it found that the mean SE refractive error measured by CSR and self-refraction were significantly different by −0.44 D. The study found that more children undercorrected or overcorrected their myopia greater than 0.50 D (15.3%) and greater than or equal to −1.00 D (8.4%) with self-refraction using FocusSpec.
The finding in this study is also consistent with previous studies which indicated that there was a higher propensity for some of the children to either undercorrect or overcorrect their refractive errors by self-refraction, as indicated by relatively high SD. For instance, about 4% and 3% (translating to about six individuals) of the children undercorrected and overcorrected their myopia with FocusSpec, respectively, while about 7% of the children undercorrected or overcorrected the refractive errors over the clinical subjective values using Adlens. Correspondingly, the visual outcomes determined by CSR were better than those by self-refraction, as the former gold standard method included correction for existing astigmatism.17
The results also showed that generally, there were no statistically significant differences in mean SE refractive value correction between the two self-refraction devices in urban and rural children, with negligible mean differences. However, when compared with the clinical standard, the mean differences between FSSR and CSR in urban (−0.27±0.09 D) and rural (−0.20±0.06 D) children were significant. Similarly, there were statistically significant differences in mean SE refractive values between ASR and CSR in urban (−0.19±0.09 D) and in rural (−0.26±0.047D) children. These results revealed that difference in refractive error correction using the two Alvarez self-refraction methods was not different in both urban and rural children. However, when compared with cycloplegia subjective refraction, the refraction differed for all methods in urban and rural children. This finding is similar to previous studies that also reported differences in refractive outcomes between self-refracting methods and clinical standard of CSR due to mechanical and optical limitations of adjustable glasses.18 23 25–27 The results, however, are contrary to suggestions that children from less socioeconomic background are less likely to accurately perform self-refraction compared with their counterparts from more privileged backgrounds.17 It is suggested that children from less resourced environments, who are likely not to habitually wear spectacles were at greater risk for less accurate results with adjustable glasses possibly because such children are more tolerant of imperfectly corrected VA and were thus less inclined to carefully adjust the SRSs until optimal VA had been achieved.17 18
In addition, in this study, the findings revealed that refractive correction using the two self-refraction spectacles were similar and produced similar SE refractive values within acceptable margins of optical error for Alvarez designs,28–30 irrespective of the background of the end user. This was despite the fact that the study found low spectacle wear among the children, with only about a quarter of the study population reporting wearing spectacle, and nearly two-thirds (72.5%) of those wearing spectacles were from urban areas compared with slightly over one-third (27.5%) of rural children. The finding does not support our presumption that refraction and spectacle wear experience could influence self-refraction regarding appreciation of power changes.
On the other hand, the finding observed could be associated with the relative ease of manipulating the two adjustable devices, even though the styles of manipulating the adjustable are different. In performing self-refraction, the instruction for FocusSpec requires scrolling the wheel to adjust the lens power, with about 2.5 turns of the adjustment screw producing a 4D power change. That translates to a setting accuracy of 0.25 D which corresponds to screw scrolling of about 60°. On the other hand, Adlens design requires dialling or twisting the wheel on the sides to adjust the lens power, with about five complete rotations producing a 9.0 D power change. That translates to a setting accuracy of 0.25 D corresponding to screw rotations of about 50°.29 These angular rotations are quite large so that, from the purely mechanical point of view, no great skill is required when adjusting the lens powers. This perhaps explains why there was no significant difference in results among the children in adjusting for the lenses, by dialling or twisting the wheel on the sides to the Adlens adjustable or scrolling the wheel on the sides of the FocusSpec adjustable to recognise changes in refractive power. The results also revealed that refraction among myopes from both urban and rural schools across all refraction methods were statistically not significant, but there were statistically significant differences in mean SE refractive value obtained in hyperopes from both urban (FocusSpec and CSR, −0.28 D; Adlens and CSR, −0.28 D) and rural schools (FocusSpec and CSR, −0.35 D; Adlens and CSR, −0.38 D). This finding perhaps indicated that the children easily appreciated differences in minus correction than spherical blur plus corrections. Indeed, inspection of that data showed that myopes from urban schools tended to over minus with self-refraction compared with rural children, with the over minus more with FocusSpec (more myopic) than with Adlens.
Although a comparison of the distribution of refractive error values obtained is an easier, simple and objective way to compare the refractive modalities, the range of visual acuities achieved is in many ways of greater clinical significance. Inspection of the VA outcomes after refraction showed that the proportion of urban children who achieved VA of ≥6/7.5 for all refraction methods were more than rural children, except CSR. In percentage terms, 11%, 6.2% and 6.0% more urban children obtained better VA with FocusSpec, Adlens and autorefraction, respectively, than in rural children. For urban children, when the self-refraction methods were compared against each other and to the clinical gold standard, there was no difference in the proportions who achieved the expected VA of ≥6/7.5 in urban schools. In contrast, for rural schools, the proportion of children failing to achieve VA of ≥6/7.5 with both self-refractions differed significantly from each other (<5%), and from the proportion failing to achieve the same VA with CSR for FocusSpecs (13.8%) and Adlens (9.2%). Self-refraction outcome was, however, better when autorefraction results are compared with results of CSR in urban (32.6%) and rural children (41.4%) or to FocusSpec (32.6%; 27.6%) and Adlens (32.4%; 32.2%) self-refractions in urban and rural children, respectively. The results further showed that more urban school children achieved VA of ≥6/7.5 with both types of self-refraction devices compared with rural children. Improvement in worse VA was better in urban school children across all methods. Indeed, this study is the first to report on the refractive and visual outcome among rural and urban children in the same study, other studies have reported in urban15 and rural16–18 30 31 children separately.
While greater proportions of children that achieved desired visual acuities have been reported elsewhere,15–17 the proportion that achieved VA of ≥6/7.5 in this study is consistent with findings in urban15 and rural children.16 In reported studies in China using Adspecs self-refraction spectacles (fluid-filled lenses of refractive index 1.579) found the proportion of urban children with VA of 6/7.5 in the better eye with habitual correction, self-refraction, non-cycloplegic autorefraction and CSR were 34.8%, 92.4%, 99.5% and 99.8%, respectively, while another study among rural children found the proportion with similar VA to be 5.2% for uncorrected vision, 30.2% for currently worn spectacles, 96.9% for self-refraction, 98.4% for automated refraction and 99.1% for subjective refraction.15 16 In Ghana, a previous study in Ghana in myopic school children indicated that the proportion of children correctable to greater than or equal to 6/7.5 in the better eye by CSR was 99.0%, followed by cycloplegic retinoscopy (94.1%) and self-refraction was 85.2%.18 It must be noted that while the proportion of rural and urban school pupils in China who achieved the desired VA with self-refraction and clinical standards were similar, the study in Ghana found substantial difference in VA outcomes between the refractive methods, perhaps due to refraction experience of the subjects used. While the findings on the value of SE is consistent with other studies, and relatively similar for both self-refraction devices used, the difference in the visual outcome between rural and urban may be due to differences in refraction experience. In China, both rural and urban children may have relatively better access to refractive services, and therefore, have comparable refraction experience.
The results and the implications of this study must be understood within the context of its limitations. As indicated, self-refraction spectacles are incapable of correcting high astigmatism, which resulted in the exclusion of children with high astigmatic error from the study. Again, the limits of spherical correction for FocusSpecs are +0.50 to +4.50 and −1.00 to −5.00 D, and+3.00 to −6.00D for Adlens meant that the devices could not be used to correct very high amount of refractive errors. This may have resulted in failure to achieve ≥6/7.5 as seen in some cases. A larger sample size could have resulted in greater percentages of agreements with more predictive power. In addition, a reliability study using intraobserver measurement (test, retest) and interobserver measurement was not performed due to the time and scheduling constraint as the study was performed during school hours. Despite the study’s limitations, the results here are able to provide previously unavailable comparative data on the potential use of different self-refraction spectacles to improve vision in young people in urban and rural schools who carry a considerably large burden of inadequately corrected refractive error. The findings also show that self-refraction produces better refractive and visual outcome than that of autorefraction, which seems to indicate that their results may be less prone to accommodative inaccuracy than non-cycloplegic autorefraction,15 another modality advocated for use in areas where access to eye care providers is limited.