Desmond Cheng

Randomized Trial of Effect of Bifocal and Prismatic Bifocal Spectacles on Myopic Progression: Two-Year Results

OBJECTIVE To determine whether bifocal and prismatic bifocal spectacles could control myopia in children with high rates of myopic progression. METHODS This was a randomized controlled clinical trial. One hundred thirty-five (73 girls and 62 boys) myopic Chinese Canadian children (myopia of > or =1.00 diopters [D]) with myopic progression of at least 0.50 D in the preceding year were randomly assigned to 1 of 3 treatments: (1) single-vision lenses (n = 41), (2) +1.50-D executive bifocals (n = 48), or (3) +1.50-D executive bifocals with a 3-prism diopters base-in prism in the near segment of each lens (n = 46). MAIN OUTCOME MEASURES Myopic progression measured by an automated refractor under cycloplegia and increase in axial length (secondary) measured by ultrasonography at 6-month intervals for 24 months. Only the data of the right eye were used. RESULTS Of the 135 children (mean age, 10.29 years [SE, 0.15 years]; mean visual acuity, -3.08 D [SE, 0.10 D]), 131 (97%) completed the trial after 24 months. Myopic progression averaged -1.55 D (SE, 0.12 D) for those who wore single-vision lenses, -0.96 D (SE, 0.09 D) for those who wore bifocals, and -0.70 D (SE, 0.10 D) for those who wore prismatic bifocals. Axial length increased an average of 0.62 mm (SE, 0.04 mm), 0.41 mm (SE, 0.04 mm), and 0.41 mm (SE, 0.05 mm), respectively. The treatment effect of bifocals (0.59 D) and prismatic bifocals (0.85 D) was significant (P < .001) and both bifocal groups had less axial elongation (0.21 mm) than the single-vision lens group (P < .001). CONCLUSIONS Bifocal lenses can moderately slow myopic progression in children with high rates of progression after 24 months. APPLICATIONS TO CLINICAL PRACTICE: Bifocal spectacles may be considered for slowing myopic progression in children with an annual progression rate of at least 0.50 D.

Myopia prevalence in Chinese-Canadian children in an optometric practice

Purpose. The high prevalence of myopia in Chinese children living in urban East Asian countries such as Hong Kong, Taiwan, and China has been well documented. However, it is not clear whether the prevalence of myopia would be similarly high for this group of children if they were living in a Western country. This study aims to determine the prevalence and progression of myopia in ethnic Chinese children living in Canada. Methods. Right eye refraction data of Chinese-Canadian children aged 6 to 12 years were collated from the 2003 clinical records of an optometric practice in Mississauga, Ontario, Canada. Myopia was defined as a spherical equivalent refraction (SER) equal or less than −0.50 D. The prevalence of myopia and refractive error distribution in children of different ages and the magnitude of refractive error shifts over the preceding 8 years were determined. Data were adjusted for potential biases in the clinic sample. A questionnaire was administered to 300 Chinese and 300 Caucasian children randomly selected from the clinic records to study lifestyle issues that may impact on myopia development. Results. Optometric records of 1468 children were analyzed (729 boys and 739 girls). The clinic bias adjusted prevalence of myopia increased from 22.4% at age 6 to 64.1% at age 12 and concurrently the portion of the children that were emmetropic (refraction between −0.25 and +0.75 D) decreased (68.6% at 6 years to 27.2% at 12 years). The highest incidence of myopia for both girls (∼35%) and boys (∼25%) occurred at 9 and 10 years of age. The average annual refractive shift for all children was −0.52 ± 0.42 D and −0.90 ± 0.40 D for just myopic children. The questionnaire revealed that these Chinese-Canadian children spent a greater amount of time performing near work and less time outdoors than did Caucasian-Canadian children. Conclusions. Ethnic Chinese children living in Canada develop myopia comparable in prevalence and magnitude to those living in urban East Asian countries. Recent migration of the children and their families to Canada does not appear to lower their myopia risk.

The effect of positive‐lens addition and base‐in prism on accommodation accuracy and near horizontal phoria in Chinese myopic children

The effect of positive‐lens addition (0, +0.75, +1.50, +2.25, +3.00 D each eye) and base‐in prism power (0, 1.5, 3 Δ each eye) on both near focusing errors and latent horizontal deviations was evaluated in 29 Chinese myopic children (age: 10.3 ± 1.9 years, refractive error: −2.73 ± 1.31 D). Accommodation response and phoria were measured by the Shin‐Nippon auto‐refractor (right eye) and Howell–Dwyer near phoria card at 33 cm with each of the 15 lens/prism combinations in random order. The initial accommodative error was −0.96 ± 0.67 D (lag) and near phoria was −0.8 ± 5.0 Δ (exophoria). The positive‐lens addition decreased the accommodative lag but increased the exophoria as the power increased (e.g. up to −9.1 ± 4.1 Δ with +3 D). A 6‐Δ base‐in prism totally controlled the exophoria induced by a +1.50 D addition (−0.3 ± 4.3 Δ), but the accommodative lag was still considerable (−0.69 ± 0.54 D). In the graphical analysis of the data, a lens addition of +2.25 D combined with a 6‐Δ base‐in prism minimized both the lag and lens‐induced exophoria to −0.33 D and −2.4 Δ respectively (regression analysis). This lens and prism combination decreased the lens‐induced exophoria by 4.5 Δ compared with that measured with +2.25 D alone (−2.4 Δ vs −6.9 Δ). The results suggest that incorporating near base‐in prism when prescribing bifocal lenses for young progressing myopes with exophoria could reduce the positive lens‐induced oculomotor imbalance.

Effect of Bifocal and Prismatic Bifocal Spectacles on Myopia Progression in Children: Three-Year Results of a Randomized Clinical Trial

IMPORTANCE Myopia is a significant public health problem, making it important to determine whether a bifocal spectacle treatment involving near prism slows myopia progression in children. OBJECTIVE To determine whether bifocal and prismatic bifocal spectacles control myopia in children with high rates of myopia progression and to assess whether the treatment effect is dependent on the lag of accommodation and/or near phoria status. DESIGN, SETTING, AND PARTICIPANTS This 3-year randomized clinical trial was conducted in a private practice. A total of 135 (73 female and 62 male) Chinese-Canadian children (aged 8-13 years; mean [SE] age, 10.29 [0.15] years; mean [SE] myopia, -3.08 [0.10] D) with myopia progression of at least 0.50 D in the preceding year were randomly assigned to 1 of 3 treatments. A total of 128 (94.8%) completed the trial. INTERVENTIONS Single-vision lenses (control, n = 41), +1.50-D executive bifocals (n = 48), and +1.50-D executive bifocals with 3-Δ base-in prism in the near segment of each lens (n = 46). MAIN OUTCOMES AND MEASURES Myopia progression (primary) measured using an automated refractor following cycloplegia and increase in axial length (secondary) measured using ultrasonography at intervals of 6 months for 36 months. RESULTS Myopia progression over 3 years was an average (SE) of -2.06 (0.13) D for the single-vision lens group, -1.25 (0.10) D for the bifocal group, and -1.01 (0.13) D for the prismatic bifocal group. Axial length increased an average (SE) of 0.82 (0.05) mm, 0.57 (0.07) mm, and 0.54 (0.06) mm, respectively. The treatment effect of bifocals (0.81 D) and prismatic bifocals (1.05 D) was significant (P < .001). Both bifocal groups had less axial elongation (0.25 mm and 0.28 mm, respectively) than the single-vision lens group (P < .001). For children with high lags of accommodation (≥ 1.01 D), the treatment effect of both bifocals and prismatic bifocals was similar (1.1 D) (P < .001). For children with low lags (<1.01 D), the treatment effect of prismatic bifocals (0.99 D) was greater than of bifocals (0.50 D) (P = .03). The treatment effect of both bifocals and prismatic bifocals was independent of the near phoria status. CONCLUSIONS AND RELEVANCE Bifocal spectacles can slow myopia progression in children with an annual progression rate of at least 0.50 D after 3 years. These results suggest that prismatic bifocals are more effective for myopic children with low lags of accommodation. TRIAL REGISTRATION clinicaltrials.gov Identifier: NCT00787579.

Bifocal lens control of myopic progression in children

Bifocal spectacle lenses have been used as a strategy to slow myopic progression in children since the 1950s and perhaps earlier. The reported success of this strategy varies greatly, as does the design of studies reporting the outcomes of their use—from earlier retrospective analysis of records to later prospective clinical trials. Collectively, published data support the suggestion that bifocal lenses inhibit myopic development in children but only by a small amount and only in a subset of children. Possible reasons for the greatly varying outcomes include a lack of individualism of the treatment and failure to take the vergence system into account. This review summarises the results of bifocal and multifocal studies, describes how accommodation, convergence and their interaction are linked to myopic development and details how a bifocal treatment that takes this into account may be devised. Also discussed is whether alterations to peripheral retinal blur contribute to bifocal lens effects.

The effect of positive-lens addition and base-in prism on accommodation accuracy and near horizontal phoria in Chinese myopic children

The effect of positive‐lens addition (0, +0.75, +1.50, +2.25, +3.00 D each eye) and base‐in prism power (0, 1.5, 3 Δ each eye) on both near focusing errors and latent horizontal deviations was evaluated in 29 Chinese myopic children (age: 10.3 ± 1.9 years, refractive error: −2.73 ± 1.31 D). Accommodation response and phoria were measured by the Shin‐Nippon auto‐refractor (right eye) and Howell–Dwyer near phoria card at 33 cm with each of the 15 lens/prism combinations in random order. The initial accommodative error was −0.96 ± 0.67 D (lag) and near phoria was −0.8 ± 5.0 Δ (exophoria). The positive‐lens addition decreased the accommodative lag but increased the exophoria as the power increased (e.g. up to −9.1 ± 4.1 Δ with +3 D). A 6‐Δ base‐in prism totally controlled the exophoria induced by a +1.50 D addition (−0.3 ± 4.3 Δ), but the accommodative lag was still considerable (−0.69 ± 0.54 D). In the graphical analysis of the data, a lens addition of +2.25 D combined with a 6‐Δ base‐in prism minimized both the lag and lens‐induced exophoria to −0.33 D and −2.4 Δ respectively (regression analysis). This lens and prism combination decreased the lens‐induced exophoria by 4.5 Δ compared with that measured with +2.25 D alone (−2.4 Δ vs −6.9 Δ). The results suggest that incorporating near base‐in prism when prescribing bifocal lenses for young progressing myopes with exophoria could reduce the positive lens‐induced oculomotor imbalance.

A study of the central and peripheral refractive power of the cornea with orthokeratology treatment

Abstract The central and peripheral refracting power of the cornea after orthokeratology treatment was studied by a cross-sectional method. Three Asian subject groups were recruited. Group 1 consisted of 31 normal non-contact lens wearers, group 2 consisted of 14 subjects who wore orthoK contact lenses for 10–20 months, and group 3 consisted of 14 subjects who wore orthoK contact lenses for more than 20 months. Our results showed that the corneal refracting power (central 3.3 mm) in both of the groups with orthoK contact lens treatment did not differ significantly from the average cornea. The group that wore orthoK lenses for more than 20 months had a flatter temporal peripheral cornea than did the normal group at approximately 2.95 mm from the corneal apex. Because the temporal cornea is steeper than the nasal cornea in normal eyes, a relatively flatter temporal cornea in the orthoK group produces a more symmetrical peripheral cornea.