Orthokeratology has undergone drastic changes since first described in the early 1960s. The original orthokeratology procedure involved a series of lenses to flatten the central cornea and was plagued by variable results. The introduction of highly oxygen‐permeable lens materials that can be worn overnight, corneal topography, and reverse‐geometry lens designs revolutionised this procedure. Modern overnight orthokeratology causes rapid, reliable, and reversible reductions in refractive error. With modern designs, patients can wear lenses overnight, remove them in the morning, and see clearly throughout the day without the need for daytime refractive correction. Modern reverse‐geometry lens designs cause central corneal flattening and mid‐peripheral corneal steepening that provides clear foveal vision while simultaneously causing a myopic shift in peripheral retinal defocus. The peripheral myopic retinal defocus caused by orthokeratology is hypothesised to be responsible for reductions in myopia progression in children fitted with these lenses. This paper reviews the changes in orthokeratology lens design that led to the reverse‐geometry orthokeratology lenses that are used today and the optical changes these lenses produce. The optical changes reviewed include changes in refractive error and their time course, high‐ and low‐contrast visual acuity changes, changes in higher‐order aberrations and visual quality metrics, changes in accommodation, and changes in peripheral defocus caused by orthokeratology. The use of orthokeratology for myopia control in children is also reviewed, as are hypothesised connections between orthokeratology‐induced myopic peripheral defocus and slowed myopia progression in children, and safety and complications associated with lens wear. A better understanding of the ocular and optical changes that occur with orthokeratology will be beneficial to both clinicians and patients in making informed decisions regarding the utilisation of orthokeratology. Future research directions with this lens modality are also discussed.

Purpose Centre‐distance multifocal contact lenses (MFCLs) for myopia control are thought to slow myopia progression by providing both clear foveal vision and myopic defocus. Characterising the power profile of lenses is important to understanding their possible effects on retinal defocus when worn. The power profiles of three commercially available MFCLs were determined. Methods Three centre‐distance MFCL designs were studied: Biofinity Multifocal D +2.50 add (comfilcon A), Proclear Multifocal D +2.50 add (omafilcon A), and NaturalVue Multifocal (etafilcon A). Two lenses each in power from −1.00D to −6.00D in 1D steps were stored in ISO 18369‐3:2017 standard phosphate buffered saline for 24 h. Optical power profiles were measured in a wet cell with the SHSOphthalmic profiler accounting for centre thickness and manufacturer‐reported material refractive index. Sagittal power maps from the SHSOphthalmic were exported, and custom MATLAB code was used to generate power profiles by averaging along the vertical and horizontal meridians. One‐way anova with Tukey’s HSD post‐hoc t‐tests were used to analyse maximum add power by lens design. Results Plus power increased out from the lens centre for all three MFCLs. Power profiles of Biofinity D and Proclear D MFCLs show three distinct areas within the optic zone; the distance zone (from lens centre to about 1.6 mm radius), intermediate zone (about 1.6 mm radius to 2.1 mm) and near zone (about 2 mm radius to 4 mm). For NaturalVue MFCLs, plus power starts increasing almost immediately from the lens centre, reaching maximum measured mean plus power at a radius of 2.7 mm. From 2.7 mm to 3.0 mm, there was a decrease in plus power, which was then generally maintained out to the optic zone edge. Across all lens powers, maximum add power was highest with the NaturalVue MFCL (+3.32 ± 0.44D), then Proclear D (+1.84 ± 0.28D) and Biofinity D (+1.47 ± 0.34D) MFCLs (all p < 0.04). Add power peaked at different locations for different lens powers and designs. Conclusions Power profiles of MFCLs vary based on lens design and power. These power profiles are consistent with reported myopic and hyperopic changes in peripheral refraction with MFCLs and provide some explanation for reported differences in peripheral refraction with these MFCLs. Further work is needed to determine whether these power profile differences influence myopia progression.

SIGNIFICANCE With multifocal contact lenses (MFCLs) used for myopia control, questions remain regarding visual performance. Information from nonpresbyopic patients provides insight into how MFCLs affect visual acuity and reading performance. PURPOSE The purpose of this study was to examine the visual performance of center-distance MFCLs in nonpresbyopic adults under different illumination and contrast conditions compared with a single-vision contact lens (SVCL). METHODS Twenty-five adult subjects were fit with three different lenses (CooperVision Biofinity D MFCL +2.50 add, Visioneering Technologies NaturalVue MFCL, CooperVision Biofinity sphere). Acuity and reading performance were evaluated. RESULTS A statistically significant difference in high-contrast distance acuity was observed (Biofinity, −0.18 ± 0.06; Biofinity MFCL, −0.14 ± 0.08; NaturalVue MFCL, −0.15 ± 0.03; repeated-measures [RM] ANOVA, P = .02). Under mesopic, high-contrast conditions, MFCLs performed worse than SVCLs (Biofinity, −0.05 ± 0.091; Biofinity MFCL, +0.03 ± 0.09; NaturalVue MFCL, +0.05 ± 0.091; RM-ANOVA, P < .0001). Under low-contrast conditions, MFCLs performed one line worse in photopic lighting and two lines worse under mesopic conditions (RM-ANOVA, P < .0001). Glare reduced acuity by 0.5 logMAR for all lenses (RM-ANOVA, P < .001). A statistically significant difference in near acuity was observed (RM-ANOVA, P = .02), but all lenses achieved acuity better than −0.1 logMAR (Biofinity, −0.16 ± 0.06; Biofinity MFCL, −0.17 ± 0.04; NaturalVue MFCL, −0.13 ± 0.08). Reading performance in words per minute (wpm) was worse with MFCLs (Biofinity MFCL, 144 ± 22 wpm; NaturalVue MFCL, 150 ± 28 wpm) than with SVCLs (156 ± 23 wpm; RM-ANOVA, P = .02) regardless of letter size (RM-ANOVA, P = .13). No difference in acuity between the MFCLs was detected (RM-ANOVA: all, P > .05). CONCLUSIONS Multifocal contact lenses perform similarly to SVCLs for high-contrast targets and display reduced low-contrast acuity and reading speed. Practitioners should recognize that high-contrast acuity alone does not describe MFCL visual performance.

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Background. The purpose of the study was to determine the prevalence of computer vision syndrome (CVS) and poor sleep quality among university students and assess the relationship between digital device usage, CVS, and sleep quality. Methods. A cross-sectional study including undergraduate students was conducted in Ghana between January–March 2020. Information on digital device use and CVS symptoms was collected using a structured questionnaire. Sleep quality was assessed using the Pittsburgh Sleep Quality Index (PSQI). Logistic regression was used to determine the relationship between CVS and digital device use behavior, and linear regression analysis was used to explore the association between sleep quality and digital device use behavior. Statistical significance was set at p  < 0.05. Results. Mean (SD) age of participants was 20.95 (1.68) years and most (54.97%) of them were females. The prevalence of CVS was 64.36%. Factors associated with CVS included hours of digital device use per day (OR = 4.1, p  < 0.001), years of digital device use (OR = 3.0, p  < 0.001), adjustment of digital device screen contrast to the surrounding brightness (OR = 1.95, p  = 0.014), and presence of glare (OR = 1.79, p  = 0.048). Prevalence of poor sleep quality was 62.43%. There was a significant association between poor sleep quality and number of years participants had used a digital device ( p  = 0.015) and the number of hours they used a digital device per day ( p  = 0.005). Conclusion. There is a high prevalence of both CVS and poor sleep quality among undergraduate students in Ghana. This represents a significant public health issue that needs attention.