Abstract
Purpose and background: This study has particular significance in ophthalmic dispensing as well as for optometry when considering the use of readymade readers (RMRs) both in private practice and in the public health sector. This study investigated firstly whether the optical centre (OC) distance for a sample of RMRs correlates with the near–inter-pupillary distance (near-IPD) for presbyopic patients, whether induced prism occurs with convergence when reading and whether RMR lenses are free of optical strain. Methods: Near-IPDs (measured by a single individual) were obtained from record cards of 1080 patients (540 male patients and 540 female patients). The OC distances were determined for 60 RMRs using a Nikon PL-2 screen vertometer, and induced prismatic effects were calculated for vertical and horizontal meridians. The presence of optical strain was analysed and graded using crossed polarised filters (within a polariscope). Results: The measured average near-IPD was 59.04 mm (s.d. ±2.87) for the 540 female patients and 61.59 mm (s.d. ±3.08) for the 540 male patients. The measured average RMR OC distance was 64.49 mm (s.d. ±3.74) for female patients and 62.77 mm (s.d. ±1.57) for male patients. Based on the mean near-IPD and the corresponding RMR OC distance, the average horizontal prismatic effect found in RMRs designed for female patients with induced prism was 0.11 pd base-out (5.06 mm outwards) and 0.04 pd base-in (1.26 mm inwards). For male RMRs, this was 0.03 pd base-out (1.32 mm outwards) and 0.02 pd base-in (1.28 mm inwards). When comparing RMR distances with near-IPDs, t = -7.87, p < 0.001 for female patients and t = -3.69, p < 0.001 for male patients. The average vertical differential prismatic effect for female patients was 0.67 pd and it was 0.68 pd for male patients. Optical strain was observed in 66.67% and 56.67% of RMR lenses for female and male patients, respectively. The strain pattern was found to be most severe in the inferior temporal periphery for 34 RMRs for female patients and for 20 RMRs for male patients, followed by the inferior nasal periphery for 27 and 18 lenses (RMRs) for male and female patients, respectively. Conclusion: Most RMRs were found to be within international standard tolerances for horizontally induced prismatic effects, but 10% of female and 36.67% of male RMRs had vertical prismatic effects, which exceeded international standards. Significant optical strain was found in the inferior nasal reading portion of the RMRs. Keywords: Readymade readers (RMR’s); prismatic effect; strain; interpupillary distance; presbyopia; reading
Highlights
Functional presbyopia is estimated to be uncorrected in 517 million people globally, half of whom suffer from this visual impairment (1.04 billion).[1]
An independent-samples t-test was conducted to investigate whether the means of the near-inter-pupillary distances (IPD) and Readymade readers (RMRs) optical centre (OC) distances were statistically different
In order to produce appropriate RMRs, this study recommends that RMR manufacturers should attempt to align manufacturing specifications of the RMR OC distance with the average near-IPDs found in this study
Summary
Functional presbyopia is estimated to be uncorrected in 517 million people globally, half of whom suffer from this visual impairment (1.04 billion).[1] Underdeveloped countries bear the burden of uncorrected presbyopia with 410 million (94%) of those uncorrected presbyopes unable to perform basic near-work tasks.[1] Functional presbyopia creates significant socio-economic burdens and has a high impact on occupational productivity and vision-related quality of life.[2] To reduce the number of uncorrected presbyopic people, inexpensive, mass-produced and readily available corrections are required. Readymade readers (RMRs), mass-produced spectacles for near-vision with both eyes having equal spherical power and a fixed centration distance, have been shown to be an effective treatment in the absence of custom-made spectacles.[3,4] RMRs are accessible and affordable without the need of a prescription, which makes them ideal as a spare pair of glasses for middle- to high-income patients and as the primary presbyopic correction in low-income areas. The optical quality of these spectacles has been found to be below standard.[5,6,7] It is important to note that the dispensing of RMRs should always be preceded by
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