Metric-Optimized Spectacle Prescriptions for Children With Down Syndrome

The purpose of this study is to test the hypothesis that metric-derived spectacle prescriptions based on wavefront aberration measurements of the eyes of children with Down syndrome can provide an improvement in visual acuity over that obtained with spectacle prescriptions based on standard clinical prescribing techniques. Twenty-four children with Down syndrome will be enrolled to participate in this phase II clinical trial of spectacle prescriptions. The study is a randomized, cross-over design with two treatment arms that will consist of 5 study visits over the course of 12 months for each participant.

Participant eligibility will first be assessed at an enrollment exam by an unmasked examiner. Individuals enrolled in the study will have distance refraction measured with an open-field autorefractor (Grand Seiko), pupil size measured with an infrared camera in both normal and dim room illumination, and wavefront aberration measured with the Complete Ophthalmic Analysis System (COAS) wavefront aberrometer. Following the enrollment exam, the metric-optimized refraction (treatment arm 1) will be determined from the wavefront measurements. A clinical examiner (who will later serve as a masked examiner) will perform a complete eye examination on the participants at the enrollment exam to include presenting distance and near visual acuity, measures of binocular function (depth perception, eye alignment), and collection of data from any clinical techniques indicated to determine what she believes to be the best clinical refraction for each individual participant. This may include the prescription of a bifocal, given evidence that the majority of individuals with Down syndrome do not have adequate accommodation and may benefit from bifocal prescriptions. Participants will then select a single frame for their new spectacle prescriptions from the College of Optometry's Eyewear Gallery. Two identical frames will be ordered to produce the spectacles for the two treatment arms. If a bifocal was prescribed by the clinical examiner, the same bifocal power will be included for both refractions to maintain an equal shift in the image plane for near viewing with each prescription. Throughout the examination, the parent/guardian of each participant will complete the Vineland Behavioral Assessment survey about the participant's adaptive abilities. This survey will be scored by study personnel to assign an adapted age to the patient as an indication of their developmental ability. Data will later be analyzed with this adapted age as a predictor variable to identify associations between acuity and developmental ability.

Participants will return for a dispensing visit when the spectacles are ready. At the initial dispensing visit, an unmasked examiner will verify the power of each pair of spectacles and label them according to the randomization order for dispensing. A masked examiner will then perform both distance and near visual acuity, as well as binocularity testing (cover test and near stereoacuity) for the participant's presenting correction (unaided if they do not currently wear spectacles) and each of the experimental prescriptions. The values for the experimental prescriptions will be compared to the presenting measures to ensure participants are not dispensed spectacles that provide worse visual function than they had when presenting to the study. Any experimental prescription which causes visual acuity to degrade more than 3 lines from presenting acuity at either distance or near, depth perception to decrease more than 2 levels from presenting, or results in the manifestation of an eye-turn that was previously not observed, will not be dispensed to the patient provided findings are confirmed on a re-test the day the prescription is randomized for dispense. Prescriptions passing this safety check will be dispensed to the participant one at a time in random order for two month wearing intervals with a Smart Button data logger placed in a mount on the temple of the spectacles. The data logger will provide an objective assessment of spectacle wear time for each prescription. The decision to select a two month wear interval was based on clinical experience related to patient adaptation time to new spectacle corrections, scientific evidence for perceptual adaptation time to previously uncorrected astigmatic refractive error, the time course expected for the most rapid improvement in vision in children previously uncorrected, and a desire to allow adequate time for assessment of the wearing profile of each individual. Participants will be asked to return at two-month intervals to perform adapted visual acuity measures, download data logger readings, and complete a brief survey regarding their opinion of each spectacle treatment.

After completion of both spectacle prescription dispensing periods, the clinical examiner will determine, through evaluation of all clinical measures and consultation with the patient and their parent/guardian, which pair of spectacles is recommended for continued wear. This decision will occur without un-masking the examiner or the participant. Participants will be asked to return for one additional follow-up after 6 months additional wear of the recommended prescription. At the follow-up visit, visual acuity and binocularity will be measured to determine whether additional improvements occur with continued spectacle wear.

The primary outcome measure for this study is comparison of 2 month adapted visual acuity between prescriptions. The small within subject variability in visual acuity translates into high study power for comparisons in the cross-over study. For our sample size, we have greater than 99% power to detect a difference of 7 letters. However, given that the desired statistical analysis includes not only adapted visual acuity, but also compliance, via temperature sensors, and survey scores, a sample size of 24 provides greater than 80% power to detect effect size values of 0.80 (large effect) or higher for these factors.