High myopia induced by form deprivation is associated with altered corneal biomechanical properties in chicks

The cornea is a soft, transparent, composite organic tissue, which forms the anterior outer coat of the eyeball. Although high myopia is increasing in prevalence worldwide and is known to alter the structure and biomechanical properties of the sclera, remarkably little is known about its impact on the biomechanics of the cornea. We developed and validated a novel optical-coherence-tomography-indentation probe–to measure corneal biomechanical properties in situ, in chicks having experimentally-induced high myopia, while maintaining intraocular pressure at levels covering the physiological range. We found that the cornea of highly myopic chicks was more steeply curved and softer, at all tested intraocular pressures, than that in contralateral, non-myopic eyes, or in age-matched normal, untreated eyes. These results indicate that the biomechanical properties of the cornea are altered in chicks developing experimentally-induced myopia

Cell-Type Specific Roles for PTEN in Establishing a Functional Retinal Architecture

BACKGROUND: The retina has a unique three-dimensional architecture, the precise organization of which allows for complete sampling of the visual field. Along the radial or apicobasal axis, retinal neurons and their dendritic and axonal arbors are segregated into layers, while perpendicular to this axis, in the tangential plane, four of the six neuronal types form patterned cellular arrays, or mosaics. Currently, the molecular cues that control retinal cell positioning are not well-understood, especially those that operate in the tangential plane. Here we investigated the role of the PTEN phosphatase in establishing a functional retinal architecture. METHODOLOGY/PRINCIPAL FINDINGS: In the developing retina, PTEN was localized preferentially to ganglion, amacrine and horizontal cells, whose somata are distributed in mosaic patterns in the tangential plane. Generation of a retina-specific Pten knock-out resulted in retinal ganglion, amacrine and horizontal cell hypertrophy, and expansion of the inner plexiform layer. The spacing of Pten mutant mosaic populations was also aberrant, as were the arborization and fasciculation patterns of their processes, displaying cell type-specific defects in the radial and tangential dimensions. Irregular oscillatory potentials were also observed in Pten mutant electroretinograms, indicative of asynchronous amacrine cell firing. Furthermore, while Pten mutant RGC axons targeted appropriate brain regions, optokinetic spatial acuity was reduced in Pten mutant animals. Finally, while some features of the Pten mutant retina appeared similar to those reported in Dscam-mutant mice, PTEN expression and activity were normal in the absence of Dscam. CONCLUSIONS/SIGNIFICANCE: We conclude that Pten regulates somal positioning and neurite arborization patterns of a subset of retinal cells that form mosaics, likely functioning independently of Dscam, at least during the embryonic period. Our findings thus reveal an unexpected level of cellular specificity for the multi-purpose phosphatase, and identify Pten as an integral component of a novel cell positioning pathway in the retina

Modified Cav1.4 Expression in the Cacna1fnob2 Mouse Due to Alternative Splicing of an ETn Inserted in Exon 2

The Cacna1fnob2 mouse is reported to be a naturally occurring null mutation for the Cav1.4 calcium channel gene and the phenotype of this mouse is not identical to that of the targeted gene knockout model. We found two mRNA species in the Cacna1fnob2 mouse: approximately 90% of the mRNA represents a transcript with an in-frame stop codon within exon 2 of CACNA1F, while approximately 10% of the mRNA represents a transcript in which alternative splicing within the ETn element has removed the stop codon. This latter mRNA codes for full length Cav1.4 protein, detectable by Western blot analysis that is predicted to differ from wild type Cav1.4 protein in a region of approximately 22 amino acids in the N-terminal portion of the protein. Electrophysiological analysis with either mouse Cav1.4wt or Cav1.4nob2 cDNA revealed that the alternatively spliced protein does not differ from wild type with respect to activation and inactivation characteristics; however, while the wild type N-terminus interacted with filamin proteins in a biochemical pull-down experiment, the alternatively spliced N-terminus did not. The Cacna1fnob2 mouse electroretinogram displayed reduced b-wave and oscillatory potential amplitudes, and the retina was morphologically disorganized, with substantial reduction in thickness of the outer plexiform layer and sprouting of bipolar cell dendrites ectopically into the outer nuclear layer. Nevertheless, the spatial contrast sensitivity (optokinetic response) of Cacna1fnob2 mice was generally similar to that of wild type mice. These results suggest the Cacna1fnob2 mouse is not a CACNA1F knockout model. Rather, alternative splicing within the ETn element can lead to full-length Cav1.4 protein, albeit at reduced levels, and the functional Cav1.4 mutant may be incapable of interacting with cytoskeletal filamin proteins. These changes, do not alter the ability of the Cacna1fnob2 mouse to detect and follow moving sine-wave gratings compared to their wild type counterparts

Die Fledermaus: regarding optokinetic contrast sensitivity and light-adaptation, chicks are mice with wings.

Through adaptation, animals can function visually under an extremely broad range of light intensities. Light adaptation starts in the retina, through shifts in photoreceptor sensitivity and kinetics plus modulation of visual processing in retinal circuits. Although considerable research has been conducted on retinal adaptation in nocturnal species with rod-dominated retinas, such as the mouse, little is known about how cone-dominated avian retinas adapt to changes in mean light intensity.We used the optokinetic response to characterize contrast sensitivity (CS) in the chick retina as a function of spatial frequency and temporal frequency at different mean light intensities. We found that: 1) daytime, cone-driven CS was tuned to spatial frequency; 2) nighttime, presumably rod-driven CS was tuned to temporal frequency and spatial frequency; 3) daytime, presumably cone-driven CS at threshold intensity was invariant with temporal and spatial frequency; and 4) daytime photopic CS was invariant with clock time.Light- and dark-adaptational changes in CS were investigated comprehensively for the first time in the cone-dominated retina of an avian, diurnal species. The chick retina, like the mouse retina, adapts by using a "day/night" or "cone/rod" switch in tuning preference during changes in lighting conditions. The chick optokinetic response is an attractive model for noninvasive, behavioral studies of adaptation in retinal circuitry in health and disease

Preventing Myopia Progression by Novel Blue-SAD light therapy and the Potential Role of Nitric Oxide

Background: An alarming increase in prevalence has made myopia (near-sightedness) a worldwide health concern. Presently, there is no effective and widely accepted treatments for myopia. However, recent research shows outdoor light may prevent myopia, even with long periods of near-work. Outdoor light contains a large portion of short-wavelength (‘blue’) light. Therefore, I tested whether only blue-light prevents form-deprivation myopia in chicks. I also tested whether nitric oxide (NO), a known modulator of eye growth, was implicated in the underlying mechanisms. Understanding retinal mechanisms involved can assist in developing more specific therapies. Hypothesis: Blue light inhibits myopia in chicks better than red or white light. NO may be involved in the signaling cascade that prevents myopia. Methods: Goggled chicks were treated with 0h (control), 0.5h, 1.5h, or 3.0h by 10,000-lux SAD-lights, either unfiltered (white) or filtered to pass only short or long wavelengths. For NO experiments, chicks were injected with 300uM L-NMMA, a NO synthase inhibitor, prior to light treatment. Refractive error, axial length, equatorial diameter, and wet weight were measured and one-way ANOVA (p<0.05) was applied. Results: Blue light significantly reduced myopia development, while white light only reduced myopia at 3h. Red light appeared to induce myopia. Injection of L-NMMA abolished the anti-myopic effect. Conclusions: Sunlight may inhibit myopia because of its high content of blue-light. Short-wavelength light inhibits FDM in chicks via a signalling cascade in which NO mediates an obligatory step. For preventing myopia, understanding the blue-light mechanism may help understand how myopia progresses. * Indicates faculty mento

Nighttime, scotopic CS function of Lohmann chicks at minimal mean luminance (I_mean = −1.62 log cd/m²).

<p>(A) At the two spatial frequencies to which chicks were most sensitive, CS was clearly tuned to TF, with maximum CS = 7.32±0.804 at about 1.8 cyc/sec (n = 8–10). (B) In contrast, over a wide range of temporal frequencies, CS was poorly tuned to SF, with no significant dependence upon SF at any TF (n = 7–10). (C) Contrast sensitivity function for quail pERG (purple line; Ref. 24) scaled and fitted by eye to CS function of Lohmann chicks (n = 8–10). Estimated temporal acuity is 10–20 Hz.</p

Daytime, photopic temporal CS functions.

<p>(A) Lohmann chicks (n = 6–8) and (B) Bovan chicks (n = 7–8), at unattenuated luminance (I_mean =1.98 log cd/m²); mean ± SD. The CS functions of Lohmann chicks showed no statistically significant preference for any temporal frequency (A). In Bovan chicks, at SF = 0.2 and 0.32 cyc/deg, CS appeared to be bandpass, whereas at SF = 0.1 and 0.5 cyc/deg, they appeared to be more high-pass (at SF = 0.5 cyc/deg, difference in CS between the three highest TFs was insignificant, one-way ANOVA). SF, spatial frequency.</p

Examples of daytime, photopic spatial CS functions.

<p>(A) Bovan chicks (n = 6–8), (B) Lohmann chicks (n = 8). Contrast sensitivity peaks at about 0.5 cyc/deg. (C) Contrast sensitivity function for quail pERG (purple line; Ref. 24) scaled and fitted by eye to CS function of Bovan chicks (n = 6–8). Unattenuated mean luminance (I_mean =1.98 log cd/m²) in all cases; mean ± SD. Peak CS is 13.2±2.8 in Bovan chicks (A, n = 8) and 19.1±5.2 in Lohmann chicks (B, n = 8), at ∼0.5 cyc/deg, and estimated SF_max (acuity) is ≥2 cyc/deg. TF, temporal frequency.</p

Contrast sensitivity functions under three conditions of adaptation and day-night cycle.

<p>(A) Temporal CS function at a specific SF (SF = 0.5 cyc/deg), under (i) daytime, photopic, (ii) daytime, threshold luminance, and (iii) nighttime, scotopic conditions. (B) Spatial CS functions at a specific TF (TF = 4.5 cyc/s), under the same three conditions as in (A).</p