Myopia, or near-sightedness, is the most common refractive vision disorder and predisposes the eye to many blinding conditions in adulthood. Recent research has suggested that myopia is associated with increased endogenous melatonin production. Researchers investigated the differences in melatonin circadian timing and output in young adult myopes and non-myopes (or emmetropes) as a pathogenesis for myopia. Eighteen myopic (refractive error [mean ± standard deviation] -4.89 ± 2.16D) and 14 emmetropic participants (-0.09 ± 0.13D), ages 22.06 ± 2.35 years were recruited. Circadian timing was assessed using salivary dim light melatonin onset, collected half-hourly for seven hours, beginning five hours before and finishing two hours after individual average sleep onset in a sleep laboratory. Total melatonin production was assessed via aMT6s levels from urine voids collected from 6 pm and until wake-up time the following morning. Objective measures of sleep timing were acquired for a week prior to the sleep laboratory visit using an actigraphy device.

Myopes (22:19 ± 1.8 hours) exhibited a dim light melatonin onset phase-delay of 1 hour 12 minutes compared with emmetropes (21:07 ± 1.4 hours), p=0.026, d = 0.73. Urinary aMT6s melatonin levels were significantly lower among myopes (29.17 ± 18.67) than emmetropes (42.51 ± 23.97, p=0.04, d=0.63). Myopes also had a significant delay in sleep onset, greater sleep onset latency, shorter sleep duration and more evening-type diurnal preference than emmetropes (all p<0.05).

These findings suggested a potential association between circadian rhythms and myopia in humans.

To investigate the incidence and peak elevation of conjunctival prolapse during short-term open eye scleral lens wear and its association with lens fitting characteristics, 10 young, healthy adults (mean age ± SD, 30 ± 4 years) wore a high Dk sealed scleral lens for 90 minutes with an initial central post-lens fluid reservoir thickness defined as low (144 ± 23 μm), medium (487 ± 63 μm) and high (726 ± 55 μm). Optical coherence tomography was used to quantify limbal clearance, lens settling and changes in conjunctival thickness.

The incidence of conjunctival prolapse was 37% across all fluid reservoir thickness conditions, with 80% of participants exhibiting conjunctival prolapse at least once. Prolapse was observed more frequently nasally (73%) than temporally (27%) (p<0.01). The peak prolapse elevation did not vary with fluid reservoir thickness condition or anatomical location (both p>0.05). For the low fluid reservoir thickness condition, eyes with conjunctival prolapse had greater initial limbal clearance (97 ± 38 μm compared with 43 ± 34 μm, p=0.01) and more settling after 90 minutes of lens wear (-85 ± 30 μm compared with -34 ± 29 μm, p < 0.01). Greater limbal settling was associated with a higher peak elevation of the conjunctival prolapse (r=0.48, p=0.02), but not with landing zone tissue compression (r=0.22, p=0.33), or the initial or final limbal fluid reservoir thickness asymmetry (r≤0.07, p>0.05).

Conjunctival prolapse was commonly observed during short-term sealed scleral lens wear in healthy eyes. The peak elevation of the conjunctival prolapse was associated with the extent of limbal settling, but not landing zone tissue compression or fluid reservoir thickness asymmetry.

Investigators conducted a retrospective analysis of five trials using similar protocols with non-presbyopic (NP) myopes or presbyopic participants (Px) wearing various simultaneous-image designs (SM) and single-vision (SV) CL (NP only). Questionnaires (vision satisfaction, vision clarity: distance/intermediate/near, comfort) on one to 10 scale were administered one week after fitting. The vision/comfort relationship was analyzed using linear mixed model and presented as regression coefficient with 95% confidence intervals (CIs).

Vision ratings correlated with comfort ratings, although this varied depending on type of vision rating and Px category. Vision satisfaction influenced comfort for the NP-SV group (slope: 0.8; 95% CI: 0.58 to 1.01, p≤0.001), but was significantly lower in the presbyopic group (slope: 0.38; 95% CI: 0.33 to 0.42; p≤0.001). Controlling for lens material obtained similar results. In the reverse relationship, comfort had a significant impact on vision satisfaction, although again at varying levels for each Px group. NP-SV demonstrated the weakest relationship (slope: 0.47; 95% CI: 0.35 to 0.59, p≤0.001) in comparison with NP-SM and P-SM groups.

Vision and comfort in CL wear were inter-related. Investigators wrote that consideration of Px characteristics, visual stimulus and CL comfort need to be accounted for when assessing overall CL experience.