The human axial length and choroidal thickness responses to continuous and alternating episodes of myopic and hyperopic blur.

PURPOSE: To investigate the change in axial length (AxL) and choroidal thickness (ChT) in response to continuous and alternating episodes of monocular myopic and hyperopic defocus. METHODS: The right eye of sixteen young adults was exposed to 60 minute episodes of either continuous or alternating myopic and hyperopic defocus (+3 DS & -3 DS) over six separate days, with the left eye optimally corrected for distance. During alternating defocus conditions, the eye was exposed to either 30 or 15 minute cycles of myopic and hyperopic defocus, with the order of defocus reversed in separate sessions. The AxL and ChT of the right eye were measured before, during and after each defocus condition. RESULTS: Significant changes in AxL were observed over time, dependent upon the defocus condition (p < 0.0001). In general, AxL exhibited a greater magnitude of change during continuous than alternating defocus conditions. The maximum AxL elongation was +7 ± 7 µm (p = 0.010) in response to continuous hyperopic defocus and the maximum AxL reduction was -8 ± 10 µm of (p = 0.046) in response to continuous myopic defocus. During both 30 and 15 minute cycles of alternating myopic and hyperopic defocus of equal duration, the effect of opposing blur sessions cancelled each other and the AxL was near baseline levels following the final defocus session (mean change from baseline across all alternating defocus conditions was +2 ± 10 µm, p > 0.05). Similar, but smaller magnitude, changes were observed for ChT. CONCLUSIONS: The human eye appears capable of temporal averaging of visual cues from alternating myopic and hyperopic defocus. In the short term, this integration appears to be a cancellation of the effects of the preceding defocus condition of opposite sign.

Recovery of corneal topography and vision following opaque-tinted contact lens wear.

PURPOSE: To investigate corneal changes after wearing cosmetic tinted contact lens and the recovery of corneal topography. METHODS: Seven subjects took part in the study. Three cosmetic tinted lens types and one control soft contact lens were investigated (Crazy Lens, WildEyes, FreshLook, and SofLens Comfort). Lenses were worn for 1 hour. Corneal topography data were measured before lens wear, with the contact lens in situ and at 0, 10, 20, 30, 60, 90, 120, and 150 minutes after lens removal. Height data difference maps were calculated and corneal recovery measured. Visual acuity was taken before lens removal and at 1, 10, 30, 60, 120, and 150 minutes after lens removal. Subjective ratings of haloes and ghosting following lens wear were also recorded. RESULTS: For the Crazy Lens, concentric rings of steepening and flattening with a mean height change of 2.17 +/- 0.98 microm (P < 0.05) were found in the central cornea at a location corresponding to the edge of the clear pupil diameter. Corneal recovery after removal of the Crazy Lens took up to 150 minutes. Visual acuity loss in high luminance during Crazy Lens wear was 0.29 LogMAR (P < 0.01). For the WildEyes and FreshLook lenses, smaller changes in corneal topography and vision were found after 1 hour of lens wear. CONCLUSIONS: Patients who wear cosmetic tinted lenses need to be aware of the potential for reduced visual performance, both during lens wear and for several hours after lens wear.