About

J. Daniel Twelker, OD, PhD, is a professor in the Department of Ophthalmology and a faculty member in the College of Medicine at The University of Arizona. He holds degrees in optometry and a doctorate from the University of California, Berkeley, obtained in 1992 and 2001 respectively. His research focuses on various aspects of visual development, refractive errors, and childhood eye health, with particular attention to astigmatism, myopia, and visual motor performance in children. Dr. Twelker has contributed to understanding the longitudinal changes in refractive and keratometric parameters in childhood, the predictors of juvenile-onset myopia, and the impact of visual conditions on academic performance. His work also explores the influence of environmental factors such as outdoor activity and near work on myopia progression. Throughout his career, he has been involved in numerous studies examining the relationship between ocular components, ethnicity, and visual function, advancing knowledge in pediatric eye care and refractive development.

Research topics

• Ophthalmology
• Medicine
• Internal medicine
• Optometry
• Physics
• Demography
• Optics
• Psychiatry
• Surgery
• Physical therapy

Selected publications

• Agreement between the Spot Vision Screener and cycloplegic retinoscopy for toddlers with astigmatism

  Journal of American Association for Pediatric Ophthalmology and Strabismus · 2025-10-01

  article1st authorCorresponding
  PublisherDOI

• Vision and developmental delay in toddlers

  Journal of American Association for Pediatric Ophthalmology and Strabismus · 2025-09-23

  articleOpen access
  PublisherOA PDFDOI

• Axial length as a function of age, sex, and ethnicity: Results from the CLEERE study

  Optometry and Vision Science · 2025-10-23 · 3 citations

  articleOpen access

  SIGNIFICANCE: Axial length is emerging as the primary outcome variable used for assessing myopia control efficacy, in both clinic and clinical trials. This report provides a model of axial length as a function of age, sex, and race/ethnicity, in addition to percentiles of axial length across age in childhood. PURPOSE: To model axial length in juvenile-onset myopia and children in general as a function of age, sex, race/ethnicity, parental history of myopia, diopter-hours of near work, and hours of outdoor/sports activities. METHODS: Axial length from the time of myopia onset was modeled using quadratic fits as a function of age, sex, race/ethnicity, and other covariates. Myopic participants were 590 children in the Collaborative Longitudinal Evaluation of Ethnicity and Refractive Error (CLEERE) study with at least three annual visits: one without myopia, an onset visit 1 year later (spherical equivalent at least -0.75 D), and another visit after myopia onset. Percentiles for axial length from the entire CLEERE sample were determined using 23,154 observations from 4877 children. RESULTS: Axial elongation in myopic children was greatest at younger ages, slowing with age in a quadratic trajectory between 6 and 14 years. The average rate of elongation at a given age, however, was independent of the age of myopia onset. In the general sample of children, axial length percentiles at age 6 years were similar across racial/ethnic groups, but Asian American children had the steepest increases in axial length with age, followed by Native American and Hispanic children. The shallowest increases occurred in Black and White children. Females had shorter axial lengths than males by 0.4 to 0.5 mm, but a higher probability of being myopic for a given age and axial length percentile. Parental history of myopia, time spent reading, and time spent in outdoor/sports activity were not significant factors for axial length in multivariate models. CONCLUSIONS: The models of axial length as a function of age, sex, and race/ethnicity, along with their percentiles, may prove useful in sample size planning for clinical trials, for judging efficacy of myopia control in individual children, and for comparison to more recent datasets.

  PublisherOA PDFDOI

• Predicting the onset of myopia in children by age, sex, and ethnicity: Results from the CLEERE Study

  Optometry and Vision Science · 2024-04-01 · 15 citations

  articleOpen access

  SIGNIFICANCE: Clinicians and researchers would benefit from being able to predict the onset of myopia for an individual child. This report provides a model for calculating the probability of myopia onset, year-by-year and cumulatively, based on results from the largest, most ethnically diverse study of myopia onset in the United States. PURPOSE: This study aimed to model the probability of the onset of myopia in previously nonmyopic school-aged children. METHODS: Children aged 6 years to less than 14 years of age at baseline participating in the Collaborative Longitudinal Evaluation of Ethnicity and Refractive Error (CLEERE) Study who were nonmyopic and less hyperopic than +3.00 D (spherical equivalent) were followed up for 1 to 7 years through eighth grade. Annual measurements included cycloplegic autorefraction, keratometry, ultrasound axial dimensions, and parental report of children's near work and time spent in outdoor and/or sports activities. The onset of myopia was defined as the first visit with at least -0.75 D of myopia in each principal meridian. The predictive model was built using discrete time survival analysis and evaluated with C statistics. RESULTS: The model of the probability of the onset of myopia included cycloplegic spherical equivalent refractive error, the horizontal/vertical component of astigmatism (J0), age, sex, and race/ethnicity. Onset of myopia was more likely with lower amounts of hyperopia and less positive/more negative values of J0. Younger Asian American females had the highest eventual probability of onset, whereas older White males had the lowest. Model performance increased with older baseline age, with C statistics ranging from 0.83 at 6 years of age to 0.92 at 13 years. CONCLUSIONS: The probability of the onset of myopia can be estimated for children in the major racial/ethnic groups within the United States on a year-by-year and cumulative basis up to age 14 years based on a simple set of refractive error and demographic variables.

  PublisherOA PDFDOI

• Myopia Progression as a Function of Sex, Age, and Ethnicity

  Investigative Ophthalmology & Visual Science · 2021 · 135 citations

  • Demography
  • Medicine
  • Ophthalmology

  Purpose: To model juvenile-onset myopia progression as a function of race/ethnicity, age, sex, parental history of myopia, and time spent reading or in outdoor/sports activity. Methods: Subjects were 594 children in the Collaborative Longitudinal Evaluation of Ethnicity and Refractive Error (CLEERE) Study with at least three study visits: one visit with a spherical equivalent (SPHEQ) less myopic/more hyperopic than -0.75 diopter (D), the first visit with a SPHEQ of -0.75 D or more myopia (onset visit), and another after myopia onset. Myopia progression from the time of onset was modeled using cubic models as a function of age, race/ethnicity, and other covariates. Results: Younger children had faster progression of myopia; for example, the model-estimated 3-year progression in an Asian American child was -1.93 D when onset was at age 7 years compared with -1.43 D when onset was at age 10 years. Annual progression for girls was 0.093 D faster than for boys. Asian American children experienced statistically significantly faster myopia progression compared with Hispanic (estimated 3-year difference of -0.46 D), Black children (-0.88 D), and Native American children (-0.48 D), but with similar progression compared with White children (-0.19 D). Parental history of myopia, time spent reading, and time spent in outdoor/sports activity were not statistically significant factors in multivariate models. Conclusions: Younger age, female sex, and racial/ethnic group were the factors associated with faster myopic progression. This multivariate model can facilitate the planning of clinical trials for myopia control interventions by informing the prediction of myopia progression rates.

  PublisherDOI

• Interventions to slow progression of myopia in children

  Cochrane library · 2020 · 195 citations

  Senior authorCorresponding
  • Medicine
  • Ophthalmology
  • Optometry

  Background Nearsightedness (myopia) causes blurry vision when one is looking at distant objects. Interventions to slow the progression of myopia in children include multifocal spectacles, contact lenses, and pharmaceutical agents. Objectives To assess the effects of interventions, including spectacles, contact lenses, and pharmaceutical agents in slowing myopia progression in children. Search methods We searched CENTRAL; Ovid MEDLINE; Embase.com; PubMed; the LILACS Database; and two trial registrations up to February 2018. A top up search was done in February 2019. Selection criteria We included randomized controlled trials (RCTs). We excluded studies when most participants were older than 18 years at baseline. We also excluded studies when participants had less than ‐0.25 diopters (D) spherical equivalent myopia. Data collection and analysis We followed standard Cochrane methods. Main results We included 41 studies (6772 participants). Twenty‐one studies contributed data to at least one meta‐analysis. Interventions included spectacles, contact lenses, pharmaceutical agents, and combination treatments. Most studies were conducted in Asia or in the United States. Except one, all studies included children 18 years or younger. Many studies were at high risk of performance and attrition bias. Spectacle lenses: undercorrection of myopia increased myopia progression slightly in two studies; children whose vision was undercorrected progressed on average ‐0.15 D (95% confidence interval [CI] ‐0.29 to 0.00; n = 142; low‐certainty evidence) more than those wearing fully corrected single vision lenses (SVLs). In one study, axial length increased 0.05 mm (95% CI ‐0.01 to 0.11) more in the undercorrected group than in the fully corrected group (n = 94; low‐certainty evidence). Multifocal lenses (bifocal spectacles or progressive addition lenses) yielded small effect in slowing myopia progression; children wearing multifocal lenses progressed on average 0.14 D (95% CI 0.08 to 0.21; n = 1463; moderate‐certainty evidence) less than children wearing SVLs. In four studies, axial elongation was less for multifocal lens wearers than for SVL wearers (‐0.06 mm, 95% CI ‐0.09 to ‐0.04; n = 896; moderate‐certainty evidence). Three studies evaluating different peripheral plus spectacle lenses versus SVLs reported inconsistent results for refractive error and axial length outcomes (n = 597; low‐certainty evidence). Contact lenses: there may be little or no difference between vision of children wearing bifocal soft contact lenses (SCLs) and children wearing single vision SCLs (mean difference (MD) 0.20D, 95% CI ‐0.06 to 0.47; n = 300; low‐certainty evidence). Axial elongation was less for bifocal SCL wearers than for single vision SCL wearers (MD ‐0.11 mm, 95% CI ‐0.14 to ‐0.08; n = 300; low‐certainty evidence). Two studies investigating rigid gas permeable contact lenses (RGPCLs) showed inconsistent results in myopia progression; these two studies also found no evidence of difference in axial elongation (MD 0.02mm, 95% CI ‐0.05 to 0.10; n = 415; very low‐certainty evidence). Orthokeratology contact lenses were more effective than SVLs in slowing axial elongation (MD ‐0.28 mm, 95% CI ‐0.38 to ‐0.19; n = 106; moderate‐certainty evidence). Two studies comparing spherical aberration SCLs with single vision SCLs reported no difference in myopia progression nor in axial length (n = 209; low‐certainty evidence). Pharmaceutical agents: at one year, children receiving atropine eye drops (3 studies; n = 629), pirenzepine gel (2 studies; n = 326), or cyclopentolate eye drops (1 study; n = 64) showed significantly less myopic progression compared with children receiving placebo: MD 1.00 D (95% CI 0.93 to 1.07), 0.31 D (95% CI 0.17 to 0.44), and 0.34 (95% CI 0.08 to 0.60), respectively (moderate‐certainty evidence). Axial elongation was less for children treated with atropine (MD ‐0.35 mm, 95% CI ‐0.38 to ‐0.31; n = 502) and pirenzepine (MD ‐0.13 mm, 95% CI ‐0.14 to ‐0.12; n = 326) than for those treated with placebo (moderate‐certainty evidence) in two studies. Another study showed favorable results for three different doses of atropine eye drops compared with tropicamide eye drops (MD 0.78 D, 95% CI 0.49 to 1.07 for 0.1% atropine; MD 0.81 D, 95% CI 0.57 to 1.05 for 0.25% atropine; and MD 1.01 D, 95% CI 0.74 to 1.28 for 0.5% atropine; n = 196; low‐certainty evidence) but did not report axial length. Systemic 7‐methylxanthine had little to no effect on myopic progression (MD 0.07 D, 95% CI ‐0.09 to 0.24) nor on axial elongation (MD ‐0.03 mm, 95% CI ‐0.10 to 0.03) compared with placebo in one study (n = 77; moderate‐certainty evidence). One study did not find slowed myopia progression when comparing timolol eye drops with no drops (MD ‐0.05 D, 95% CI ‐0.21 to 0.11; n = 95; low‐certainty evidence). Combinations of interventions: two studies found that children treated with atropine plus multifocal spectacles progressed 0.78 D (95% CI 0.54 to 1.02) less than children treated with placebo plus SVLs (n = 191; moderate‐certainty evidence). One study reported ‐0.37 mm (95% CI ‐0.47 to ‐0.27) axial elongation for atropine and multifocal spectacles when compared with placebo plus SVLs (n = 127; moderate‐certainty evidence). Compared with children treated with cyclopentolate plus SVLs, those treated with atropine plus multifocal spectacles progressed 0.36 D less (95% CI 0.11 to 0.61; n = 64; moderate‐certainty evidence). Bifocal spectacles showed small or negligible effect compared with SVLs plus timolol drops in one study (MD 0.19 D, 95% CI 0.06 to 0.32; n = 97; moderate‐certainty evidence). One study comparing tropicamide plus bifocal spectacles versus SVLs reported no statistically significant differences between groups without quantitative results. No serious adverse events were reported across all interventions. Participants receiving antimuscarinic topical medications were more likely to experience accommodation difficulties (Risk Ratio [RR] 9.05, 95% CI 4.09 to 20.01) and papillae and follicles (RR 3.22, 95% CI 2.11 to 4.90) than participants receiving placebo (n=387; moderate‐certainty evidence). Authors' conclusions Antimuscarinic topical medication is effective in slowing myopia progression in children. Multifocal lenses, either spectacles or contact lenses, may also confer a small benefit. Orthokeratology contact lenses, although not intended to modify refractive error, were more effective than SVLs in slowing axial elongation. We found only low or very low‐certainty evidence to support RGPCLs and sperical aberration SCLs.

  PublisherOA PDFDOI

• Uncorrected Refractive Error and Distance Visual Acuity in Children Aged 6 to 14 Years

  Optometry and Vision Science · 2020 · 22 citations

  • Optometry
  • Medicine
  • Ophthalmology

  SIGNIFICANCE: This study presents the relationship between distance visual acuity and a range of uncorrected refractive errors, a complex association that is fundamental to clinical eye care and the identification of children needing refractive correction. PURPOSE: This study aimed to analyze data from the Collaborative Longitudinal Evaluation of Ethnicity and Refractive Error Study to describe the relationship between distance uncorrected refractive error and visual acuity in children. METHODS: Subjects were 2212 children (51.2% female) 6 to 14 years of age (mean ± standard deviation, 10.2 ± 2.1 years) participating in the Collaborative Longitudinal Evaluation of Ethnicity and Refractive Error Study between 2000 and 2010. Uncorrected distance visual acuity was measured using a high-contrast projected logMAR chart. Cycloplegic refractive error was measured using the Grand Seiko WR-5100K autorefractor. The ability of logMAR acuity to detect various categories of refractive error was examined using receiver operating characteristic curves. RESULTS: Isoacuity curves show that increasing myopic spherical refractive errors, increasing astigmatic refractive errors, or a combination of both reduces distance visual acuity. Visual acuity was reduced by approximately 0.5 minutes of MAR per 0.30 to 0.40 D of spherical refractive error and by approximately 0.5 minutes of MAR per 0.60 to 0.90 D of astigmatism. Higher uncorrected hyperopic refractive error had little effect on distance visual acuity. Receiver operating characteristic curve analysis suggests that a logMAR distance acuity of 0.20 to 0.32 provides the best balance between sensitivity and specificity for detecting refractive errors other than hyperopia. Distance acuity alone was ineffective for detecting hyperopic refractive errors. CONCLUSIONS: Higher myopic and/or astigmatic refractive errors were associated with predictable reductions in uncorrected distance visual acuity. The reduction in acuity per diopter of cylindrical error was about half that for spherical myopic error. Although distance acuity may be a useful adjunct to the detection of myopic spherocylindrical refractive errors, accommodation presumably prevents acuity from assisting in the detection of hyperopia. Alternate procedures need to be used to detect hyperopia.

  PublisherOA PDFDOI

• A preliminary study of astigmatism and early childhood development

  Journal of American Association for Pediatric Ophthalmology and Strabismus · 2018-06-19 · 22 citations

  article
  PublisherDOI

• Spectacle Wear in Toddlers: Frequency of Wear and Impact of Treatment on the Child and Family

  Translational Vision Science & Technology · 2018-12-28 · 4 citations

  articleOpen access

  Purpose: We assessed the frequency of spectacle wear and impact of spectacle treatment in toddlers. Methods: Children 12 to <36 months old with significant refractive error were provided spectacles. After 12 (±6) weeks, parents reported the frequency of spectacle wear and completed the Amblyopia Treatment Index (ATI, modified for spectacle treatment). Factor analysis assessed usefulness of ATI for spectacle treatment. Spectacle wear and ATI results were compared across age (1- vs. 2-year-olds) and sex. Results: Participants were 91 children (60% male; mean age, 22.98 [SD 6.24] months, 41 1- and 50 2-year-olds) prescribed spectacles for astigmatism (92%), hyperopia (9%), or myopia (1%). Reported frequency of wear was low (<2 hours/day) in 41%, moderate in 23% (2 to <6 hours/day), and high (≥6 hours/day) in 36% and did not differ across age or sex. ATI factor analysis identified three subscales: adverse effects, treatment compliance, and perceived benefit. One-year-olds had poorer scores on adverse effects (P = 0.026) and treatment compliance scales (P = 0.049). Low frequency of spectacle wear was associated with poorer scores on treatment compliance (P < 0.001) and perceived benefit scales (P = 0.004). Conclusions: Frequency of spectacle wear was not related to age or sex. Younger children may have more difficulty adjusting to treatment. Parents of children with low spectacle wear reported less perceived benefit of treatment. Translational Relevance: Data on factors associated with frequency of spectacle wear in toddlers is valuable for parents and clinicians and may lead to methods to improve compliance and reduce the negative impact of treatment.

  PublisherOA PDFDOI

• Childhood age, time outdoors, and the risk of juvenile-onset myopia

  Investigative Ophthalmology & Visual Science · 2018-07-13

  articleOpen access
  Publisher

Recent grants

• NIH Grant K23EY000372

  NIH · $263k · 2002

Frequent coauthors

• Donald O. Mutti

  59 shared

• Erin M. Harvey

  Medical College of Wisconsin

  36 shared

• Joseph M. Miller

  Henry Ford Hospital

  35 shared

• Karla Zadnik

  33 shared

• Susan A. Cotter

  Marshall B. Ketchum University

  24 shared

• Robert N. Kleinstein

  University of Alabama at Birmingham

  22 shared

• Ruth E. Manny

  22 shared

• Lisa Jones

  21 shared

Labs

• McKay LabPI