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

Control of myopia using diffusion optics spectacle lenses: 12-month results of a randomised controlled, efficacy and safety study (CYPRESS)

BACKGROUND

Mutations in the L/M cone opsin gene array cause abnormally high perceived retinal contrast and the development of myopia. Environmental factors may also lead to high visual contrast and cause myopia. Diffusion optics technology (DOT) lenses are designed to reduce contrast signalling in the retina and slow myopia progression.

METHODS

The Control of Myopia Using Peripheral Diffusion Lenses Efficacy and Safety Study (CYPRESS, NCT03623074) is a 36-month, multicentre, randomised, controlled, double-masked trial evaluating two investigational spectacle lenses versus control lenses in myopic children aged 6-10, with a planned interim analysis at 12 months. The primary endpoints are change from baseline in axial length (AL) and spherical equivalent refraction (SER).

RESULTS

256 children (58% female; mean age at screening, 8.1 years) were dispensed spectacles. Across all groups, baseline averages were AL 24.02 mm (SD±0.77 mm), SER -2.01 D (SD±0.9 D) using manifest refraction, and SER -1.94 D (SD±1.0 D) using cycloplegic autorefraction. At 12 months, mean difference in SER progression for test 1 versus control was -0.40 D (p<0.0001), representing a 74% reduction and -0.32 D for Test 2 (p<0.0001), representing a 59% reduction. The difference in AL progression for test 1 versus control was 0.15 mm (p<0.0001) and test 2 versus control was 0.10 mm (p=0.0018).

CONCLUSION

12-month results from this ongoing trial demonstrate the safety and effectiveness of DOT spectacles for reducing myopic progression.

The effect of concentric and aspheric multifocal soft contact lenses on binocular vision in young adult myopes

PURPOSE

Multifocal soft contact lenses (MFCLs) are prescribed to inhibit myopia progression; these include aspheric and concentric designs. The effects of MFCLs on visual quality, accommodation and vergence in young-adult myopes were evaluated.

METHODS

Participants were twenty-six myopes (19-25 years, spherical equivalent -0.50 to -5.75D), with normal binocular vision and no past myopia control. Pupil sizes were 4.4 ± 0.9 mm during distance viewing and 3.7 ± 0.8 mm at near. In random order, participants wore four MFCLs: Proclear single vision distance, MiSight concentric dual focus (+2.00D), distance center aspheric (Biofinity, +2.50D) (CooperVision lenses), and NaturalVue aspheric (Visioneering Technologies). Testing included visual acuity, contrast sensitivity (Pelli-Robson), stereoacuity, accommodation response, negative and positive relative accommodation, horizontal phorias, horizontal fusional vergence and AC/A ratio, and a visual quality questionnaire.

RESULTS

The four lenses differed in distance (p = 0.001) and near visual acuity (p = 0.011), and contrast sensitivity (p = 0.001). Compared with the single vision lens, the Biofinity aspheric had the greatest visual impact: 0.19 ± 0.14 logMAR distance acuity reduction, 0.22 ± 0.15 log contrast sensitivity reduction. Near acuity was affected less than distance acuity; the reduction was greatest with the NaturalVue (0.05 ± 0.07 logMAR reduction). The MFCLs altered the autorefraction measure at distance and near (p = 0.001); the accommodation response was less with aspheric lenses. Negative relative accommodation reduced with the aspheric lenses (p = 0.001): by 0.9 ± 0.5D with Biofinity and 0.5 ± 0.7D with NaturalVue. Exophoric shifts were greater with aspheric lenses (1.8 ± 2.4Δ Biofinity, 1.7 ± 1.7Δ NaturalVue) than with the concentric MiSight (0.5 ± 1.3Δ).

CONCLUSIONS

MFCLs alter visual performance, refraction and vergence; two aspheric lenses had greater effect than a concentric lens.

Visual acuity, near phoria and accommodation in myopic children using spectacle lenses with aspherical lenslets: results from a randomized clinical trial

Objectives

To investigate the short- and long-term effects of myopia control spectacle lenses with highly aspherical lenslets (HAL) and slightly aspherical lenslets (SAL) on visual function and visual quality using data obtained from a randomized controlled clinical trial.

Methods

This was a prospective, randomized, controlled, and double-blinded study; 170 myopic children aged 8–13 years were randomly assigned to the HAL, SAL, or single-vision spectacle lenses (SVL) groups. Distance and near visual acuity (VA) at high (100%) and low (10%) contrast in photopic and scotopic conditions, near phoria, stereoacuity, and accommodative lag, microfluctuations (AMFs), amplitude (AA) were measured after wearing lenses for 10 min, 6 months, and 12 months.

Results

In total, 161 subjects completed all follow-up in 12 months and were included in the analysis. After 10 min of wearing, the HAL and SAL groups had lower scotopic and low-contrast VA than the SVL group (decreased 0.03–0.08 logMAR and 0.01–0.04 logMAR in different VAs in the HAL and SAL groups, respectively, all P < 0.05). The reduction in VA was recovered at 12 months as the HAL and SAL groups exhibited significant VA improvements, and the VA was not different among the three groups (all P > 0.05). The HAL and SAL groups had significantly larger AMFs than the SVL group (HAL vs. SAL vs. SVL: 0.21 ± 0.08 D vs. 0.16 ± 0.05 D vs. 0.15 ± 0.06 D at baseline, 0.19 ± 0.07 D vs. 0.17 ± 0.05 D vs. 0.13 ± 0.07 D at 12 months, all P < 0.05). There were no significant differences in accommodative lag, AA, or phoria between the groups (all P > 0.05). The HAL and SAL groups had reduced stereoacuity compared to the SVL group at baseline (70’ vs. 60’ vs. 50’, P = 0.005), but no difference was observed at 12 months (70’ vs. 70’ vs. 70’, P = 0.11).

Conclusions

HAL and SAL have no significant influence on accommodation and phoria except had larger AMF than SVL. Scotopic VA and low-contrast VA are reduced with short-term HAL and SAL use but recovered to be at same level with the SVL after 1 year of use.

Trial registration Chinese Clinical Trial Registry: ChiCTR1800017683. Registered on 9 August 2018. http://www.chictr.org.cn/showproj.aspx?proj=29789

Convergence Insufficiency Neuro-Mechanism Adult Population Study: Phoria Adaptation Results

Purpose

The purpose of this study was to compare changes in phoria adaptation between young adult binocularly normal controls (BNCs) and participants with symptomatic convergence insufficiency (CI), who were randomized to either office-based vergence accommodative therapy (OBVAT) or office-based placebo therapy (OBPT).

Methods

In the double-masked randomized clinical trial, 50 BNC and 50 CI participants were randomized to the following therapeutic interventions: OBVAT or OBPT with home reinforcement for 12 one-hour office sessions. A 6∆ base-out and 6∆ base-in phoria adaptation experiment at near (40 cm) was conducted using the flashed Maddox rod technique at baseline and at outcome. Measurements included the rate and the magnitude of phoria adaptation.

Results

At baseline, BNC and CI participants had significantly different rates and magnitudes of base-in and base-out phoria adaptation (P < 0.001). When comparing the outcome to baseline measurements, significant main effect differences in longitudinal measurements were observed for the magnitude and the rate of phoria adaptation for both base-out and base-in experiments (P < 0.05). For the magnitude and rate of phoria adaptation, post hoc analyses using paired t-tests revealed that the CI group administered the OBVAT intervention exhibited a significant increase in the magnitude and rate of phoria adaptation compared to baseline for both base-in and base-out phoria adaptation (P < 0.01) but not for those administered OBPT.

Conclusions

Phoria adaptation is significantly different at baseline between those with normal binocular vision and symptomatic CI participants. OBVAT significantly improves the rate and magnitude of both base-out and base-in phoria adaptation at near compared to OBPT. Results have clinical implications for new therapeutic interventions.

Accommodative Response in Patients with Central Field Loss: A Matched Case-Control Study

Purpose: This study was conducted to evaluate the accommodative response in young participants with visual impairment in comparison with visually normal participants. Methods: Fifteen participants with confirmed visual impairment and 30 visually normal participants aged 12–15 years were recruited. Accommodative response was measured using autorefractor (Grand Seiko WV500) at distances of accommodative demand of 33, 25, and 20 cm. The targets were one-line-above participant threshold acuity. The participants’ accommodative responses were compared between both groups after calibration for refractive errors and the vertex distance of the glasses. Visual acuity and refractive status were also assessed. Results: The age was not significantly different between both participant groups. The visual acuity of visually impaired patients was 6/30 to 6/240, and that of visually normal participants was 6/7.5 or better. Ten of the visually impaired patients and 29 of visually normal participants were myopic. In total, 61–73% of visually impaired patients showed an accommodative lead. Five subtypes of accommodative response were observed. In general, the accommodative inaccuracy increased with increasing accommodative demand. However, the visually normal participants largely exhibited an accommodative lag. A mild-to-moderate relationship was observed between visual acuity and accommodative response (r = 0.3–0.5, p < 0.05). Conclusion: Accommodative response in young visually impaired patients can be variable and on an individual basis. Low vision specialists should anticipate accommodative response outside the normal range. Therefore, we shall consider evaluating each patient’s accommodative response before prescribing any near addition lenses. Accommodation inaccuracy is often more complex than predicted due to increased depth of focus caused by reduced visual acuity.

Effect of Defocus Incorporated Multiple Segments Spectacle Lens Wear on Visual Function in Myopic Chinese Children

Purpose

To compare visual function of myopic children who had worn either defocus incorporated multiple segment (DIMS) spectacle lenses or single vision (SV) spectacle lenses over two years.

Methods

We included 160 Chinese myopic (−1 diopter [D] to −5 D) children aged 8 to 13 years in a randomized clinical trial; they wore either DIMS lenses (DIMS; n = 79) or regular SV spectacles lenses (n = 81) full time for 2 years. Visual function, including high-contrast visual acuity (VA) and low-contrast VA at distance and near, binocular functions, and accommodation, before, during, and after 2 years of spectacle wear were assessed when both groups wore SV corrections. Changes of visual function between the two groups and within groups were compared.

Results

There were no statistically significant differences in the 2-year visual function changes between DIMS and SV groups (repeated measures analysis of variance with group as factor; P > 0.05). Statistically significant improvement in the best-corrected distance high-contrast VA (P < 0.001) and stereoacuity score (P < 0.001) were found after DIMS lens wear over 2 years. Similar findings were observed after SV spectacle lens wear. For both the DIMS and SV groups, there were statistically significant decreases in accommodative lag, monocular and binocular amplitude of accommodation after two years (P < 0.01), but not in the changes in distance low-contrast VA, near high-contrast VA, near low-contrast VA, or phoria.

Conclusions

Although changes in some visual function were shown during 2 years of DIMS lens wear, similar changes were found with SV lens wear. Wear of DIMS spectacle lenses for 2 years does not adversely affect major visual function when children return to SV corrections.

Translational Relevance

DIMS spectacle lenses did not cause any adverse effects on visual function.

Effect of Vision Therapy on Accommodative Lag in Myopic Children: A Randomized Clinical Trial

SIGNIFICANCE

Accommodative dysfunction has been suggested to be related to the development and progression of myopia. Office-based accommodative/vergence therapy (OBAVT) improved accommodative facility in Chinese myopic children, but it is unclear if such improvement has a role in decreasing myopic progression.

PURPOSE

The purpose of this study was to compare the effects of OBAVT with home reinforcement and office-based placebo therapy (OBPT) as a treatment to improve accommodative functions (i.e., lag, amplitude, and facility) in myopic children with poor accommodative accuracy.

METHODS

This was a prospective, single-masked, randomized clinical trial. Thirty-four Chinese children 8 to 12 years old with myopia and at least 1 diopter of lag of accommodation measured by autorefraction were enrolled. The participants were randomly assigned to the OBAVT or OBPT group. The primary outcome measure was the change in the monocular lag of accommodation from the baseline visit to the 13-week visit measured by a Shin-Nippon open-field autorefractor. Secondary outcome measures were changes in accommodative amplitude and monocular accommodative facility.

RESULTS

A total of 33 participants completed the study. After 12 weeks of treatment, there were significant improvements in the lag of accommodation in both the OBAVT and OBPT groups (OBAVT: -0.30 ± 0.29 diopters [P < .001; Cohen's d effect size, 1.29]; OBPT: -0.24 ± 0.30 diopters [P = .005; Cohen's d effect size, 1.24]). There was no statistically significant difference between the improvements in the two groups (P = .50). There was statistically significant improvement in monocular accommodative facility only in the OBAVT group (OBAVT: 7.7 ± 4.7 cycles per minute [P < .001; Cohen's d effect size, 2.20]; OBPT: 1.9 ± 4.4 cycles per minute [P = .072]). The change in the OBAVT group was statistically significantly larger than that in the OBPT group (P < .001).

CONCLUSIONS

Office-based accommodative/vergence therapy was no more effective than OBPT in reducing the lag of accommodation in children 8 to 12 years old with low to moderate myopia. It did improve accommodative facility in Chinese myopic children, but it is unclear if such an improvement has a role in decreasing myopic progression.

Higher order aberrations, refractive error development and myopia control: a review

Evidence from animal and human studies suggests that ocular growth is influenced by visual experience. Reduced retinal image quality and imposed optical defocus result in predictable changes in axial eye growth. Higher order aberrations are optical imperfections of the eye that alter retinal image quality despite optimal correction of spherical defocus and astigmatism. Since higher order aberrations reduce retinal image quality and produce variations in optical vergence across the entrance pupil of the eye, they may provide optical signals that contribute to the regulation and modulation of eye growth and refractive error development. The magnitude and type of higher order aberrations vary with age, refractive error, and during near work and accommodation. Furthermore, distinctive changes in higher order aberrations occur with various myopia control treatments, including atropine, near addition spectacle lenses, orthokeratology and soft multifocal and dual-focus contact lenses. Several plausible mechanisms have been proposed by which higher order aberrations may influence axial eye growth, the development of refractive error, and the treatment effect of myopia control interventions. Future studies of higher order aberrations, particularly during childhood, accommodation, and treatment with myopia control interventions are required to further our understanding of their potential role in refractive error development and eye growth.

Vision Performance and Accommodative/Binocular Function in Children Wearing Prototype Extended Depth-of-Focus Contact Lenses

OBJECTIVE

To assess two prototype contact lenses (CLs) that extend depth of focus through deliberate manipulation of multiple spherical aberration terms (extended depth-of-focus [EDOF]) for visual performance, accommodative and binocular function, and objective static near refraction against a single-vision (SV) CL.

METHOD

This was a prospective, randomized, cross-over, single-masked (participant) clinical trial in which 16 myopic children wore 2 prototype CLs (EDOFL/EDOFH) designed for presbyopes and a SV CL, each for one week. Measurements comprised monocular and binocular high-contrast visual acuity (HCVA: 6 m, 40 cm), binocular low-contrast visual acuity (LCVA: 6 m), contrast sensitivity (CS: 6 m), phorias (3 m, 33 cm), monocular-accommodative facility (33 cm), and objective static refraction (spherical equivalent M) at zero, -3, and -5 D vergences. Measurements were taken 10 min after lens insertion. Subjective response was assessed using take-home questionnaires comprising vision clarity (distance/intermediate/near), vision quality (haloes at night/ghosting), vision stability when moving (playing sport/using stairs), and comfort.

RESULTS

Single vision was significantly better than both EDOF CLs for monocular HCVA, LCVA, and CS (6 m); vision clarity (distance), ghosting (P≤0.040), and EDOFL for binocular HCVA (6 m, P=0.047). M was significantly closer to the ideal objective static refraction at -3 and -5 D vergences (P≤0.004) with both EDOF compared with SV CLs. There were no differences between CLs for any other variable (P≥0.169).

CONCLUSION

Extended depth-of-focus CLs caused minimal disruption to the accommodative and binocular system compared with SV CLs when worn by myopic children. Future EDOF designs for children should reduce the difference between SV for distance vision and vision quality while maintaining the same performance for intermediate and near.

Deficient vergence prism adaptation in subjects with decompensated heterophoria

Vergence prism adaptability was evaluated in subjects with high symptomatic and asymptomatic heterophoria and compared to individuals with a heterophoria within normal range (the control group). A computer haploscope was used to measure phoria values and changes in the eye position after introducing 6 prism diopters base out in front of the right eye. Phoria values were measured with a nonius paradigm every minute for a period of 10 minutes during adaptation. The results showed that subjects with symptomatic heterophoria are characterized by a lower rate of prism adaptation and adapted to a smaller extent with respect to the control group. The group with high but asymptomatic heterophoria showed prolonged adaptation time but after several minutes of binocular viewing the subjects were able to adapt to the prism to a level similar to the control group. These findings suggest that an impairment in the slow vergence control system may be responsible for the inability to fully reduce vergence effort, which results in poor vergence ranges and asthenopic symptoms during prolonged viewing.

Optical and pharmacological strategies of myopia control

Recent increases in global myopia prevalence rates have raised significant concerns as myopia increases the lifelong risk of various sight-threatening ocular conditions. This growing public health burden has generated significant research interests into understanding both its aetiology and developing effective methods to slow down or stop its development, methods collectively termed 'myopia control'. The growing body of research has demonstrated benefits of various optical and pharmacological treatments resulting in myopia control management increasingly becoming a part of main stream clinical practice. This review will discuss the peer-reviewed literature on the efficacy of various myopia control interventions including multifocal spectacles and contact lenses, orthokeratology and pharmaceutical eye drops, as well as potential future research directions.

Effects of Near Addition Lenses and Prisms on Accommodative Microfluctuations in Chinese Children

PURPOSE

To investigate the effects of different near addition lenses and prisms on accommodative microfluctuations (AMFs) in Chinese early-onset myopic (EOM) and emmetropic (EMM) children.

METHODS

Twenty-one EMM and 27 EOM children aged between 9 and 14years participated in the study. At near, 23 children were exophoric (exo, <0 Δ), and 25 were esophoric (eso, ≥0 Δ). The AMFs and phoria through multiple addition lenses (-1.00, 0, +1.00, +2.00, and +3.00D on each eye) and prisms (base-in prism power: 3 Δ, 2 Δ, 1 Δ; and base-out prism power: 1 Δ and 2 Δ on each eye) were measured at 25cm under binocular viewing conditions with a Grand Seiko WAM-5500 auto-refractor and a modified Thorington card.

RESULTS

Higher AMFs were found in EOM than in EMM (EOM, 0.19±0.06D; EMM, 0.16±0.03D; p=0.035). Plus additions from +1.00 to +3.00D reduced the AMFs in both EMM and EOM, except +3.00D for EMM. In both refractive groups, -1.00D additions increased AMFs. Esophores showed greater AMFs compared with exophores (esophores, 0.20±0.01D; exophores, 0.16±0.01D; p=0.012). Prisms increased the AMFs in EMM and did not alter the AMFs in EOM.

CONCLUSIONS

Microfluctuations of accommodation decreased with plus addition lenses and increased with negative addition lenses. Plus addition lenses of +2.00 to +3.00D for EOM and +2.00D for EMM decreased AMFs the least at a 25-cm working distance. Esophores had higher AMFs than exophores, indicating that phoria status influences AMFs.

Design, methodology, and baseline data of the Personalized Addition Lenses Clinical Trial (PACT)

BACKGROUND

The aim of this study was to describe the design, methods, and baseline characteristics of children enrolled in the Personalized Addition lenses Clinical Trial (PACT). PACT aims to test the myopia control efficacy of progressive addition lenses (PALs) with personalized addition values compared with standard (+2.00 D) addition PALs and single vision lenses (SVLs).

METHODS

PACT is a randomized, controlled, double-masked clinical trial. Two hundred eleven myopic Chinese children (7-12 years) were enrolled and randomized into 1 of the 3 following groups: personalized addition PALs; +2.00 addition PALs; and SVLs. Personalized addition values were determined based on the highest addition that satisfied Sheard criterion. Axial length and other biometric data were also recorded.

RESULTS

At baseline, no differences were found between the right and left eyes for any of the main parameters. The enrolled children were 9.7 ± 1.1 years' old with cycloplegic autorefraction (right eye [OD]: -2.36 ± 0.64 D), near phoria (1.0 ± 5.0 prism diopter esophoria), lag of accommodation (1.40 ± 0.50 D) and axial length (OD: 24.58 ± 0.74 mm). The personalized addition values ranged from +0.75 to +3.00 (average ± SD: 2.19 ± 0.73 D).

CONCLUSION

PACT is a clinical trial evaluating whether myopia progression in children can be slowed by wearing personalized addition PALs compared with fixed addition PALs and SVLs as measured by cycloplegic autorefraction and axial length. Baseline data were comparable with those of previous myopia control studies in children. Subjects will be followed up every 6 months for 2 years.

The influence of age on adaptation of disparity vergence and phoria

A paucity of research exists to investigate whether the normal aging process influences the ability to adapt disparity vergence and phoria. Vergence eye movements and dissociated phoria were recorded from 49 healthy subjects (ages 20-70years) using an objective eye movement tracking system. Four-degree vergence responses were modified using a double-step protocol. Dynamics of vergence were quantified via peak velocity. The phoria adaptation experiment measured the magnitude (net change in phoria level) and rate (magnitude divided by the time constant) of phoria adaption during 5min of sustained fixation on a binocular target (40cm/8.44° from midline). The magnitude of phoria adaptation decreased as a function of age (r=-0.33; p=0.04). The ability to adapt vergence peak velocity and the rate of phoria adaptation showed no significant age-related influence (p>0.05). The data suggest that the ability to modify the disparity vergence system and the rate of phoria adaptation are not dependent on age; whereas, the magnitude of phoria adaptation decreases as part of the normal adult aging process. These results have clinical and basic science implications because one should consider age when assessing the changes in the magnitude of phoria adaptation which can be abnormal in those with oculomotor dysfunctions.

Effect of Vision Therapy on Accommodation in Myopic Chinese Children

Introduction. We evaluated the effectiveness of office-based accommodative/vergence therapy (OBAVT) with home reinforcement to improve accommodative function in myopic children with poor accommodative response. Methods. This was a prospective unmasked pilot study. 14 Chinese myopic children aged 8 to 12 years with at least 1 D of lag of accommodation were enrolled. All subjects received 12 weeks of 60-minute office-based accommodative/vergence therapy (OBAVT) with home reinforcement. Primary outcome measure was the change in monocular lag of accommodation from baseline visit to 12-week visit measured by Shinnipon open-field autorefractor. Secondary outcome measures were the changes in accommodative amplitude and monocular accommodative facility. Results. All participants completed the study. The lag of accommodation at baseline visit was 1.29 ± 0.21 D and it was reduced to 0.84 ± 0.19 D at 12-week visit. This difference (−0.46 ± 0.22 D; 95% confidence interval: −0.33 to −0.58 D) is statistically significant (p < 0.0001). OBAVT also increased the amplitude and facility by 3.66 ± 3.36 D (p = 0.0013; 95% confidence interval: 1.72 to 5.60 D) and 10.9 ± 4.8 cpm (p < 0.0001; 95% confidence interval: 8.1 to 13.6 cpm), respectively. Conclusion. Standardized 12 weeks of OBAVT with home reinforcement is able to significantly reduce monocular lag of accommodation and increase monocular accommodative amplitude and facility. A randomized clinical trial designed to investigate the effect of vision therapy on myopia progression is warranted.

Differences in the accommodation stimulus response curves of adult myopes and emmetropes: a summary and update

PURPOSE

To provide a summary of the classic paper "Differences in the accommodation stimulus response curves of adult myopes and emmetropes" published in Ophthalmic and Physiological Optics in 1998 and to provide an update on the topic of accommodation errors in myopia.

SUMMARY

The accommodation responses of 33 participants (10 emmetropes, 11 early onset myopes and 12 late onset myopes) aged 18-31 years were measured using the Canon Autoref R-1 free space autorefractor using three methods to vary the accommodation demand: decreasing distance (4 m to 0.25 cm), negative lenses (0 to -4 D at 4 m) and positive lenses (+4 to 0 D at 0.25 m). We observed that the greatest accommodation errors occurred for the negative lens method whereas minimal errors were observed using positive lenses. Adult progressing myopes had greater lags of accommodation than stable myopes at higher demands induced by negative lenses. Progressing myopes had shallower response gradients than the emmetropes and stable myopes; however the reduced gradient was much less than that observed in children using similar methods.

RECENT FINDINGS

This paper has been often cited as evidence that accommodation responses at near may be primarily reduced in adults with progressing myopia and not in stable myopes and/or that challenging accommodation stimuli (negative lenses with monocular viewing) are required to generate larger accommodation errors. As an analogy, animals reared with hyperopic errors develop axial elongation and myopia. Retinal defocus signals are presumably passed to the retinal pigment epithelium and choroid and then ultimately the sclera to modify eye length. A number of lens treatments that act to slow myopia progression may partially work through reducing accommodation errors.

Influence of progressive addition lenses on reading posture in myopic children

Aims

To determine the influence of single-vision lenses (SVLs) and progressive addition lenses (PALs) on the near vision posture of myopic children based on their near phoria.

Methods

Sixty-two myopic children were assigned to wear SVLs followed by PALs. Eighteen children were esophoric (greater than +1), 18 were orthophoric (−1 to 1) and 26 were exophoric (less than −1) at near. Reading distance, head tilt and ocular gaze angles were measured using an electromagnetic system after adaptation to each lens type.

Results

The lens type did not influence reading distance or head tilt angle (p>0.05 for both), but ocular gaze angle decreased significantly with the PALs (F=9.25, p=0.004). With the PALs, exophoric children exhibited significantly increased head tilt angle (p=0.003) and reduced ocular gaze angle (p=0.004) compared with esophoric children. Near non-exophoric children exhibited similar eye and head postures when wearing SVLs and PALs, whereas exophoric children exhibited reduced ocular gaze angle (t=−3.18, p=0.04) with PALs compared with SVLs. Using PALs for reading, the mean addition power employed by esophoric children was significantly greater than exophoric children (p=0.04).

Conclusions

The lens type and the near phoria state affected near vision posture. During reading, myopic esophoric children used a lower portion of their PALs compared with exophoric children, resulting in greater addition power. These results may partially explain why myopic children with near esophoria exhibited superior treatment effects in myopia control trials using PALs.

Comparison of Near Addition Value Prescription Methods for Myopic Children

PURPOSE

To compare personalized near addition values for myopic children that induce a reasonable phoria (Ph) (meeting Sheard's criterion) and induce a null lag of accommodation at near and to evaluate changes in these metrics after lens adaptation.

METHODS

Fifty-three myopic children participated in this study. Accommodative response, Ph, and fusional amplitudes (FAs) were measured at 33 cm through multiple addition lenses (0D, +1.00D, +1.50D, +2.00D, +2.50D, +3.00D). The adaptation effect on measured parameters was evaluated after 6 min of near work with each addition. The FA/Ph ratios were calculated for each addition and fitted using a rational function to obtain the optimal addition value satisfying Sheard's criterion (FA/Ph ≥ 2). Lag of accommodation change in association with addition value was assessed using linear regressions to obtain the addition values inducing a null lag.

RESULTS

Lag of accommodation (r = -0.987, p < 0.001) and Ph (r = -0.999, p < 0.001) decreased linearly with addition value. The 6-min adaptation induced a small but significant increase in accommodative lag and an exophoric shift (p < 0.05). Three FA/Ph patterns with respect to addition lenses were observed based on the near Ph: orthophoria/exophoria, low esophoria, and large esophoria. Addition values based on Sheard's criterion (mean ± SD, +2.16 ± 0.79D) were significantly lower than those based on null lag (+2.83 ± 0.44D, t = 19.86, p < 0.001). The FA/Ph ratio was less than 2.0 in 75.5% of subjects with additions determined through null accommodative lag. Additions determined through FA/Ph ≥ 2 induced a lag of accommodation of 0.38 ± 0.42D.

CONCLUSIONS

Personalized near addition values using Sheard's criterion were lower than those obtained through null lag of accommodation. These values should allow a better binocular balance especially for exophoric children.

Acute and short-term changes in visual function with multifocal soft contact lens wear in young adults

PURPOSE

To characterise the effects on accommodation and binocular vision in young adults of 2 distance centre multifocal soft contact lenses (MFSCLs), differing in add power.

METHODS

Twenty-four young adult myopes (18-28 years; 20 females, 4 males) had baseline visual acuity, accommodation, near phoria, fixation disparity and stereopsis data collected with single vision (SV) SCLs. The same set of measurements was repeated immediately after subjects were fitted with each of two MFSCLs (with either +1.50 or +3.00 D add), and after 2 weeks of daily wear in each case. The order of testing was randomised and a one-week washout period was allowed between the first and second MFSCL trials.

RESULTS

Differences in distance and near acuities with MFSCLs compared to SVSCLs were small and clinically insignificant. Compared to responses with SVSCLs, MFSCLs increased accommodative lags with this change reaching statistical significance for the +1.50 D add lens. Furthermore, both MFSCLs induced significant shifts in near phorias in the exo direction. Finally, there were no significant differences in stereopsis and fixation disparity with MFSCLs compared to SVSCLs.

CONCLUSION

Differences in acuities, accommodation accuracy and binocular posture with MFSCLs compared to SVSCLs were clinically small and mostly not significant. These results predict good tolerance of MFSCLs in young patients fitted with them for myopia control.

Myopia onset and progression: can it be prevented?

Myopia is the commonest ocular abnormality and the high and growing prevalence of myopia, especially but not only in Asian populations, as well as its progressive nature in children, has contributed to a recent surge in interest. Such worldwide growing prevalence seems to be associated with increasing educational pressures, combined with life-style changes, which have reduced the time that children spend outdoors. Highly nearsighted people are at greater risk for several vision-threatening problems such as retinal detachments, choroidal neovascularization, cataracts and glaucoma, thus the potential benefits of interventions that can limit or prevent myopia progression would be of remarkable social impact. Our understanding of the regulatory processes that lead an eye to refractive errors is undoubtedly incomplete but has grown enormously in the last decades thanks to the animal studies, observational clinical studies, and randomized clinical trials recently published. In this review we assess the effects of several types of life-style and interventions, including outdoor activities, eye drops, undercorrection of myopia, multifocal spectacles, contact lenses, and refractive surgery on the onset and progression of nearsightedness.

Accommodative response under monocular and binocular conditions as a function of phoria in symptomatic and asymptomatic subjects

BACKGROUND

The neurological linkage of vergence and accommodation is a factor which can affect accuracy of accommodation, is in turn associated with symptoms of near-related visual discomfort. The purpose of this study was to compare the accommodative response under monocular and binocular conditions in symptomatic and asymptomatic participants with different near phorias.

METHODS

Seventy students at Zahedan University of Medical Sciences, Iran (mean age: 21.2 ± 1.7 years; age range: 18 to 25 years) participated. The participants were divided into symptomatic and asymptomatic groups according to the convergence insufficiency symptom survey questionnaire score. The type and magnitude of the near dissociated phoria were determined using the prism neutralised cover test. The accommodative lag was measured by the 'monocular estimate method' (MEM) retinoscopy, at first under binocular and then monocular conditions. Testing distance was 40 cm.

RESULTS

The accommodative lag in exophoric participants was lower under binocular conditions compared to monocular and in esophoric participants greater under binocular than under monocular conditions. The binocular accommodative response (AR) was greatest in participants with high exophoria at near vision and least in participants with esophoria at near vision (p < 0.001; one-way analysis of variance). The difference between binocular lag and monocular lag was significantly greater in symptomatic participants than in asymptomatic participants in both exophoria (p < 0.001) and esophoria (p = 0.009) (independent samples t-test).

CONCLUSION

The near binocular accommodative response was related to near heterophoria. Higher levels of vergence accommodation, resulting in differences in lag under monocular and binocular conditions, may be a factor in near point asthenopia.

Changes in accommodative responses with multifocal contact lenses: a pilot study

PURPOSE

To evaluate induced changes in pupil and accommodative response for different accommodative stimuli with three different multifocal contact lenses (CLs).

METHODS

Accommodative and pupil responses with three aspheric multifocal CLs of simultaneous focus center near (PureVision Low Add, PureVision High Add and Focus Progressives) for two accommodative stimuli of -2.5 and -4.00 D were recorded in 10 young subjects. Accommodative response, peak velocity, and time constant of accommodation and pupil constriction were assessed. The measurements were evaluated in all the participants with distance-single vision CLs and with the three multifocal CLs. The monocular measurements were performed in a random sequence for each participant. All parameters were measured with a Hartmann-Shack aberrometer (IRX-3; Imagine Eyes, Orsay, France).

RESULTS

Differences were not found in accommodation response for both accommodative stimuli studied between the single vision lens and the three different multifocal CLs (p > 0.05 for both stimuli). For the 2.5 D stimulus, significant differences were not found in peak velocity and time constant between the single vision lens and the three different multifocal CLs (p > 0.05 for all situations); in amplitude of pupil constriction, differences were only found for the situation with PureVision High Add, where the value was lower than the single vision lens (p = 0.015). For the 4.00 D stimulus, differences with single vision lens in peak of velocity and time constant were only found with PureVision Low Add, where the peak velocity value was higher and the time constant was lower (p = 0.024 and p = 0.032 for peak of velocity and time constant, respectively); for amplitude of pupil constriction differences were not found (p > 0.05).

CONCLUSIONS

Data obtained in this pilot study suggest that in young observers, the multifocal CLs studied do not induce large changes in accommodative system compared with the single vision lens.

A randomized trial using progressive addition lenses to evaluate theories of myopia progression in children with a high lag of accommodation

PURPOSE

To compare the effect of wearing, then ceasing to wear, progressive addition lenses (PALs) versus single vision lenses (SVLs) on myopia progression in children with high accommodative lag to evaluate accommodative lag and mechanical tension as theories of myopia progression.

METHODS

Eighty-five children (age range, 6-11 years) with spherical equivalent (SE) cycloplegic autorefraction between -0.75 D and -4.50 D were randomly assigned to wear SVLs or PALs for 1 year; all children wore SVLs a second year. Children had high accommodative lag and also had near esophoria if their myopia was greater than -2.25 D SE. The primary outcome after each year was the previous year's change in SE.

RESULTS

When the children were randomly assigned to SVLs or PALs, the adjusted 1-year changes in SE were -0.52 D (SVL group) and -0.35 D (PAL group; treatment effect = 0.18 D; P = 0.01). When all children wore SVLs the second year, there was no difference in myopia progression between SVL and former PAL wearers (0.06 D; P = 0.50). Accommodative lag was not associated with myopia progression.

CONCLUSIONS

The statistically significant, but clinically small, PAL effect suggests that treatments aimed at reducing foveal defocus may not be as effective as previously thought in myopic children with high accommodative lag. Finding no evidence of treatment loss after discontinuing PAL wear supports hyperopic defocus-based theories such as accommodative lag; however, not finding an association between accommodative lag and myopia progression is inconsistent with the PAL effect being due to decreased foveal blur during near work. (Clinical Trials.gov number, NCT00335049.).

Multifocal versus single vision lenses intervention to slow progression of myopia in school-age children: a meta-analysis

Myopia in school-aged children is a major public health problem in Asians that has been extensively studied. Multifocal lenses (MLs) are advocated as a substitute for single vision lenses (SVLs) to slow myopia progression in children, but results vary greatly across studies. We systematically searched currently available randomized controlled trials that compared the effects of MLs and SVLs in children. A meta-analysis of nine of these trials showed that MLs with powers ranging from +1.50 to +2.00D were associated with a statistically significantly decrease in myopia progression in school-aged children compared with SVLs. The benefit was greater in children with a higher level of myopia at baseline and sustained for a minimum of 24 months. Asian children appeared to have greater benefit from intervention with MLs than white children.

Short-term adaptations of the dynamic disparity vergence and phoria systems

The ability to adapt is critical to survival and varies between individuals. Adaptation of one motor system may be related to the ability to adapt another. This study sought to determine whether phoria adaptation was correlated with the ability to modify the dynamics of disparity vergence. Eye movements from ten subjects were recorded during dynamic disparity vergence modification and phoria adaptation experiments. Two different convergent stimuli were presented during the dynamic vergence modification experiment: a test stimulus (4° step) and a conditioning stimulus (4° double step). Dynamic disparity vergence responses were quantified by measuring the peak velocity (°/s). Phoria adaptation experiments measured the changes in phoria over a 5-min period of sustained fixation. The maximum velocity of phoria adaptation was determined from an exponential fit of the phoria data points. Phoria and dynamic disparity vergence peak velocity were both significantly modified (P < 0.001). The maximum velocity of phoria adaptation was significantly correlated with the changes in convergence peak velocity (r > 0.89; P < 0.001). There was a strong correlation between the ability to adaptively adjust two different oculomotor parameters: a tonic and dynamic component. Future studies should investigate additional interactions between these parameters, and the ability to adaptively change other oculomotor systems such as the saccadic or smooth pursuit system. Understanding the ability to modify phoria, dynamic disparity vergence, and other oculomotor parameters can yield insights into the plasticity of short-term adaptation mechanisms.

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 bifocal add on accommodative lag in myopic children with high accommodative lag

PURPOSE

To determine the effect of a bifocal add and manifest correction on accommodative lag in myopic children with high accommodative lag, who have been reported to have the greatest reduction in myopia progression with progressive addition lenses (PALs).

METHODS

Monocular accommodative lag to a 4-D Badal stimulus was measured on two occasions 6 months apart in 83 children (mean ± SD age, 9.9 ± 1.3 years) with high lag randomized to wearing single-vision lenses (SVLs) or PALs. Accommodative lag was measured with the following corrections: habitual, manifest, manifest with +2.00-D add, and habitual with +2.00-D add (6-month visit only).

RESULTS

At baseline, accommodative lag was higher (1.72 ± 0.37 D; mean ± SD) when measured with manifest correction than with habitual correction (1.51 ± 0.50; P < 0.05). This higher lag with manifest correction correlated with a larger amount of habitual undercorrection at baseline (r = -0.29, P = 0.009). A +2.00-D add over the manifest correction reduced lag by 0.45 ± 0.34 D at baseline and 0.33 ± 0.38 D at the 6-month visit. Lag results at 6 months were not different between PAL and SVL wearers (P = 0.92).

CONCLUSIONS

A +2.00-D bifocal add did not eliminate accommodative lag and reduced lag by less than 25% of the bifocal power, indicating that children mainly responded to a bifocal by decreasing accommodation. If myopic progression is substantial, measuring lag with full correction can overestimate the hyperopic retinal blur that a child most recently experienced. (ClinicalTrials.gov number, NCT00335049.).

Binocular adaptation to +2 D lenses in myopic and emmetropic children

PURPOSE

To compare vergence adaptation to +2 D addition lenses in myopic and emmetropic children and to evaluate the influence of the accommodative-vergence crosslink (AC/A ratio) on this adaptation.

METHODS

Nine myopic and 11 emmetropic children fixated a near target at a distance of 33 cm. Measures of binocular and monocular accommodation and phoria were obtained during a 20-min near task with and without +2 D lenses. Response AC/A ratios were determined from the experimental results. Vergence adaptation was quantified by the magnitude of reduction in phoria and the percentage of completeness (PC, return of adapted phoria to habitual level) after the near task.

RESULTS

Myopic children showed significantly higher AC/A ratios, which led to greater lens-induced exophoria and a greater demand for vergence adaptation. Both refractive groups showed significant vergence adaptation; however, myopes exhibited significantly reduced (p < 0.01) magnitudes compared with emmetropes (myopes = 3.95 +/- 0.15 Delta; emmetropes = 4.41 +/- 0.08 Delta). The mean PC was also significantly (p < 0.001) reduced in myopes (61.02 +/- 1.57) compared with emmetropes (76.6 +/- 2.10). There was a significant correlation between magnitude of adaptation and AC/A in both the refractive groups; however, myopes consistently showed reduced magnitudes compared to emmetropes. AC/A ratio influenced PC in emmetropic but not myopic children. In the accommodation system, +2 D lenses eliminated the accommodative lags observed in myopic children during natural viewing conditions. These lenses resulted in a small over-focus (-0.24 +/- 0.27 D) at the onset of near work, which decreased during sustained viewing through the near add.

CONCLUSIONS

Myopic children demonstrate reduced magnitude and completeness of vergence adaptation to +2 D lenses. The magnitude of vergence adaptation varied with AC/A in both refractive groups; however, the presence of myopia differentiated the amount of adaptation for all AC/A ratios. Conversely, the degree of completeness appears to be primarily associated with the type of refractive error.