The increasing prevalence of the use of distance-centered multifocal (MF) contact lenses as a method of myopia control in the pediatric population calls for a better understanding of binocularity and accommodation in children wearing these lenses. This was a prospective, randomized, crossover, single visit study that enrolled myopic children with normal accommodation and binocular vision and no history of myopia control treatment. All subjects were fitted with Coopervision Biofinity single vision (SV) and MF (+2.50D center distance add) contact lenses. Accommodative responses (photorefraction) and phorias (Modified Thorington) were measured at 4 distances (>3m, 100cm, 40cm, 25cm). Secondary measures included high and low contrast logMAR acuity, accommodative amplitude, and accommodative facility. Differences between MF and SV contact lenses were analyzed using repeated measures regression and paired t-tests. A total of 16 subjects, aged 10-15 years, completed the study. There was a small decrease in high (SV: -0.08, MF: +0.01) and low illumination (SV:-0.03, MF: +0.08) (both p<0.01) visual acuity, and contrast sensitivity (SV: 2.0 log units, MF: 1.9, p=0.015) with MFs. Subjects were more exophoric at 40cm (SV: -0.41 Δ, MF: -2.06 Δ) and 25cm (SV: -0.83 Δ, MF: -4.30 Δ) (both p<0.01). With MFs, subjects had decreased accommodative responses at distance (SV: -0.04 D; MF: -0.37 D, p=0.02), 100 cm (SV: +0.37 D; MF: -0.35 D, p<0.01), 40 cm (SV: +1.82 D; MF: +0.62 D, p<0.01), and 25 cm (SV: +3.38 D; MF: +1.75 D, p<0.01). There were no significant differences in accommodative amplitude (p=0.66) or accommodative facility (p=0.54). Children wearing MF contact lenses exhibited reduced accommodative responses and more exophoria at increasingly higher accommodative demands than with SV contact lenses. This suggests that children may be relaxing their accommodation and using the positive addition or increased depth of focus from added spherical aberration of the MF lenses. Further studies are needed to evaluate other lens designs, different amounts of positive addition and aberrations, and long-term adaptation to lenses.

The use of electronic reading devices has become more prevalent. Many individuals of all ages are using personal electronic readers (e.g., Kindle, Nook, E-Reader) in place of hardcopy printed materials. Previous work in our laboratory has demonstrated that symptoms when reading from a computer screen are significantly greater than those experienced when reading printed text. Accordingly, the aim of the present study was to examine both symptoms and task performance when reading from a Kindle e-reading device, and to compare the findings with those from hardcopy, printed materials.

Purpose: It has been speculated that non-decayed NITM (accommodatively-based nearwork-induced transient myopia) may be myopigenic in nature. Thus, the purpose of the present investigation was to determine objectively the initial magnitude and decay of NITM, and its potential additivity, following successive but interrupted periods of marked, sustained accommodation at near in asymptomatic young-adult myopic subjects. Methods: Fifteen visually-normal, asymptomatic young adults (ages 18 – 28 years) were tested with full distance refractive correction. They included 9 early-onset (EOM) and 6 late-onset (LOM) myopic subjects. Accommodation was assessed objectively with a Canon R-1, open-field, infrared auto-refractor under monocular viewing conditions (RE). The distance refractive state was measured immediately before and after a ten minute period of focusing upon a moderate contrast (50%), very near target (12 cm; 8D) subtending a visual angle of 1 degree. The task was repeated twice with a 5-minute inter-task rest period of imposed far viewing. NITM was defined as the post-task minus pre-task change in distance refractive state immediately following each task. Results: Significant amounts of NITM were generated following nearly each trial in each subject. These ranged from 0.11 to 0.71D, with a mean of 0.31D. The group mean NITM was 0.32, 0.29, and 0.31D for trials 1, 2, and 3, respectively. For the EOMs subgroup, NITM was 0.28, 0.30, and 0.34D, while for the LOMs subgroup, it was 0.38, 0.29, and 0.26D, for for trials 1, 2, and 3, respectively. Decay of NITM was prolonged in many of the subjects (67%). However, additivity of NITM was not found following the sequences of interrupted near tasks. Conclusions: There was no evidence of NITM additivity following a marked and sustained, but interrupted, near task. Although NITM has been reported to be additive following long periods of uninterrupted and sustained reading at lower dioptric levels, providing rest periods between each near task trial appears to prevent a cumulative effect (i.e., additivity effect). These findings support the idea of far viewing being protective in nature from myopia development.

Purpose: To assess static and dynamic parameters of accommodation in a group of patients with mild traumatic brain injury (mTBI) that reported symptoms associated with near work. Methods: A range of laboratory and clinical measurements of accommodative function were assessed in 12 patients with mTBI, as well as in 10 visually-normal control subjects. Static parameters included push-up and minus-lens accommodative amplitude, positive and negative relative accommodation (PRA/NRA), horizontal and vertical near heterophoria, accommodative convergence-to-accommodation (AC/A) ratio, accommodative stimulus/response function (AS/R), and tonic accommodation. Dynamic parameters included time constant, peak velocity, gain, steady-state response level, steady-state response variability, and accommodative flipper facility rate, including changes in flipper rate after a three-minute fatigue session. Results: All individuals with mTBI manifested a multitude of abnormal accommodative response characteristics. With respect to dynamic parameters, abnormal responses in those with mTBI were found for time constant, peak velocity, accommodative flipper facility fatigue, and steady-state response variability. With respect to static parameters, abnormal values in those with mTBI were found for accommodative amplitude, AC/A ratio, PRA/NRA, and horizontal near heterophoria. Conclusions: The results of the present study provide further evidence that there is a substantial impact of mTBI on accommodative function. With the global nature of the brain insult, it may be presumed that accommodation would be affected by disturbances in various cortical, cerebellar, and/or brainstem areas and along related axonal pathways. Specifically, the reduced peak velocity and related increased time constant found in the mTBI group could be due to damage of neurons carrying accommodative velocity information (i.e., burst cells). This could result in a decrease in either their firing rate or the number of activated cells. The resultant symptoms at near, such as transient blur, can have a negative impact on the overall quality of life and functional capabilities.

Purpose: Accommodation responds to wavefront vergence, but the mechanisms for vergence detection are unknown. One possibility is that accommodation responds to the angle of incidence of light at edges blurred by defocus. ‘Averse channels’ that sample light from opposite sides of the pupil were hypothesized by Makous (1968, 1977). Makous named the phenomenon a “transient” Stiles-Crawford effect because he found that there was a reduction in sensitivity to light entering one side of the pupil that lasts for a short period of time. Such ‘averse channels’ that sample modulation across the pupil are a possible mechanism for detecting the sign of defocus. The purpose of the present experiment is to determine whether such ‘averse channels’ can operate separately of each other to specify the sign of defocus for accommodation. Method: Accommodation was monitored continuously while subjects viewed a vertical monochromatic (548nm) luminance edge (1.0 contrast) that stepped either to a far or near direction in a Badal optometer. Various levels of adapting field were used to reduce the contrast of the edge (0.48, 0.36, 0.26, or 0.17 contrast) to determine the contrast threshold for accommodation. In a final experiment, an adapting field entered the eye through the nasal or temporal side of the pupil, to selectively adapt nasally or temporally tuned ‘channels’, while the target stepped randomly toward or away from the eye. The orientation of the vertical edge was either bright on the right side or bright on the left. Results: In a preliminary experiment, only five out of twenty-six subjects showed reliable and consistent responses, with gains >0.5 for both positive and negative step change in vergence. The contrast threshold for accommodation to step changes in target vergence was approximately 26%. Data from three subjects who accommodated reliably to both directions of step changes in vergence do not support the claim that ‘channels’ sample light separately from opposite sides of the pupil to determine the sign of defocus. Conclusion: Potential factors that account for the poor accommodative responses in the present study include: 1) the target was illuminated with monochromatic light, 2) the target was a simplified stimulus in which the blur was in only one direction (one spatial phase), 3) the target was viewed monocularly, 4) the 3mm artificial pupil increased depth-of-focus and removed the normal dynamic behavior of the pupil, 5) our subjects were untrained. The negative results suggest alternate hypotheses: 1)‘averse channels’ work in conjunction with each other, not separately, to detect vergence, 2) ‘averse channels’ can function separately to detect vergence, but the signal was undetectable using the current method, and 3) ‘averse channels’ do not mediate vergence detection.

Purpose: To examine the potential clinical utility of equiluminant chromatic stimuli for assessing glaucomatous damage. Pan et al. (2006) found that equiluminant red-green chromatic stimuli could have good ability to detect defects as well as low test-retest variability, but clinical utility was limited due to the small dynamic ranges for their stimuli. The current study increased the dynamic range by using larger stimuli and including tritan stimuli. Methods: Luminance, red-green (R-G), and tritan stimuli were created by modulating a large square (3 degrees per side) from an equal energy white (20 cd/m2) along three cardinal directions in color space. Contrast sensitivity was measured at four locations with an eccentricity of 12 deg. along the 45, 135, 225, and 315 degree meridia. Twenty-five patients with glaucoma and twenty-six control subjects free of eye disease were tested monocularly at two separate sessions within a two-week time period. Sensitivities were reported in decibel (dB) units, where 1 dB=-1 (log contrast threshold) x 10. Results: The dynamic ranges were 11 and 13 dB for the tritan and red-green stimuli. Test-retest variability was dependent on depth of defect for the two chromatic stimuli (r>0.2, p<0.25) but not for the achromatic stimuli (r=0.01, p=0.46). Matched t-tests found that, on average, defect depths were similar for the red-green and luminance stimuli (t=0.5, p=0.30), and were slightly deeper for the luminance stimulus than for the tritan stimulus (t=4.2, p<0.0001). The relationship between defect depths for the luminance and tritan stimuli was dependent on mean defect (r=-0.42, p<0.0001). Discussion: The effort to increase the dynamic range for the chromatic stimuli by increasing the size of the stimulus and using tritan modulation were successful. However, this came at the cost of increased test-retest variability and decreased ability to detect glaucomatous defects. Conclusion: Equiluminant chromatic stimuli in CRT-based tests may not be clinically useful as perimetric stimuli, since increased dynamic range comes at the expense of increased test-retest variability and decreased ability to detect visual loss. Those findings further support the works of Hart (1988) and Sample et al. (2006).