The origins of spatial and color vision in the human retina.

Higher-order aberration correction in abnormal eyes can result in significant vision improvement, especially in eyes with abnormal corneas. Customized optics such as phase plates and customized contact lenses are one of the most practical, nonsurgical ways to correct these ocular higher-order aberrations. We demonstrate the feasibility of correcting higher-order aberrations and improving visual performance with customized soft contact lenses in keratoconic eyes while compensating for the static decentration and rotation of the lens. A reduction of higher-order aberrations by a factor of 3 on average was obtained in these eyes. The higher-order aberration correction resulted in an average improvement of 2.1 lines in visual acuity over the conventional correction of defocus and astigmatism alone.

Purpose To investigate the feasibility of correcting ocular higher order aberrations (HOA) in keratoconus (KC) using wavefront-guided optics in a scleral lens prosthetic device (SLPD). Methods Six advanced keratoconus patients (11 eyes) were fitted with a SLPD with conventional spherical optics. A custom-made Shack-Hartmann wavefront sensor was used to measure aberrations through a dilated pupil wearing the SLPD. The position of SLPD, i.e. horizontal and vertical decentration relative to the pupil and rotation were measured and incorporated into the design of the wavefront-guided optics for the customized SLPD. A submicron-precision lathe created the designed irregular profile on the front surface of the device. The residual aberrations of the same eyes wearing the SLPD with wavefront-guided optics were subsequently measured. Visual performance with natural mesopic pupil was compared between SLPDs having conventional spherical and wavefront-guided optics by measuring best-corrected high-contrast visual acuity and contrast sensitivity. Results Root-mean-square of HOA(RMS) in the 11 eyes wearing conventional SLPD with spherical optics was 1.17±0.57μm for a 6 mm pupil. HOA were effectively corrected by the customized SLPD with wavefront-guided optics and RMS was reduced 3.1 times on average to 0.37±0.19μm for the same pupil. This correction resulted in significant improvement of 1.9 lines in mean visual acuity (p<0.05). Contrast sensitivity was also significantly improved by a factor of 2.4, 1.8 and 1.4 on average for 4, 8 and 12 cycles/degree, respectively (p<0.05 for all frequencies). Although the residual aberration was comparable to that of normal eyes, the average visual acuity in logMAR with the customized SLPD was 0.21, substantially worse than normal acuity. Conclusions The customized SLPD with wavefront-guided optics corrected the HOA of advanced KC patients to normal levels and improved their vision significantly.

Keratoconic eyes are affected by an irregular optical blur induced by significant magnitude of higher order aberrations (HOAs). Although it is expected that correction of ocular aberrations leads to an improvement in visual performance, keratoconic eyes might not achieve the visual benefit predicted by optical theory because of long-term adaptation to poor retinal image quality. To investigate this, an adaptive optics (AO) system equipped with a large-stroke deformable mirror and a Shack–Hartmann wavefront sensor was used to correct the aberrations and measure high contrast tumbling E visual acuity (HCVA) in 8 keratoconic eyes. Eight normal eyes were employed as control. Aberrations were dynamically corrected with closed-loop AO during visual acuity testing, with residual root-mean-square error of around 0.1 μm in both groups over 6-mm pupil (p = 0.11). With AO correction, the HCVA in logMAR was −0.26 ± 0.063 in normal eyes, and in keratoconic eyes, it was −0.07 ± 0.051 (p = 0.0001) for the same pupil size. There was no correlation in the AO-corrected HCVA for normals with the magnitudes of their native HOA. However, within keratoconic eyes, poorer AO-corrected HCVA was observed with an increase of the native magnitudes of HOA (R2 = 0.67). This may indicate that long-term visual experience with poor retinal image quality, induced by HOA, may restrict the visual benefit achievable immediately after correction in keratoconic eyes.

Photoreceptors initiate vision by converting photons to electrical activity. The onset of the phototransduction cascade is marked by the isomerization of photopigments upon light capture. We revealed that the onset of phototransduction is accompanied by a rapid (<5 ms), nanometer-scale electromechanical deformation in individual human cone photoreceptors. Characterizing this biophysical phenomenon associated with phototransduction in vivo was enabled by high-speed phase-resolved optical coherence tomography in a line-field configuration that allowed sufficient spatiotemporal resolution to visualize the nanometer/millisecond-scale light-induced shape change in photoreceptors. The deformation was explained as the optical manifestation of electrical activity, caused due to rapid charge displacement following isomerization, resulting in changes of electrical potential and surface tension within the photoreceptor disc membranes. These all-optical recordings of light-induced activity in the human retina constitute an optoretinogram and hold remarkable potential to reveal the biophysical correlates of neural activity in health and disease.