Hidetaka Maeda

Diabetes has an additive effect on neural apoptosis in rat retina with chronically elevated intraocular pressure

Purpose. Diabetes mellitus (DM) is a risk factor for open-angle glaucoma, although the mechanistic interrelationship of the two is debatable. The purpose of this study is to test whether DM augments neural apoptosis in rat retina with chronically elevated intraocular pressure (IOP). Methods. Sprague-Dawley rats were made diabetic by intraperitoneal injection of streptozotocin (STZ). At one month after STZ injection, three episcleral veins in one eye were cauterized to elevate IOP. Rats without STZ injection were treated likewise as diabetic controls. At 2 weeks, 1 month, and 2 months after cauterization, the retina was dissected, flat-mounted, and subjected to terminal dUTP nick end labeling (TUNEL) staining. TUNEL positive cells per unit area of the whole retina were measured. Results. DM did not affect base line IOP or augment IOP elevation due to episcleral vein cauterization. TUNEL positive cells, which primarily consisted of the neurons and glial cells in the inner retina including retinal ganglion cell (RGC), were counted consistently eight times more in the diabetic retina without IOP elevation than diabetic controls (n = 9, p < 0.001). The cauterization significantly elevated IOP up to 28.9mmHg (p < 0.001), which was reduced over time, and substantially induced apoptosis in a IOP-dependent fashion (p < 0.001). Ocular hypertensive retinas with DM had significantly more TUNEL positive cells than those without DM despite of the similar time course of IOP changes (p < 0.001). Conclusions. DM has an additive effect on apoptosis induction by chronic elevation of IOP. Diabetes may act as a risk factor of open-angle glaucoma by increasing susceptibility of retinal cells including retinal ganglion cells to apoptosis triggered by additional stresses such as elevated IOP.

Evaluation of the effect of aging on retinal nerve fiber layer thickness measured by optical coherence tomography.

Purpose: To evaluate the relationship between age and retinal nerve fiber layer (RNFL) thickness in normal subjects, as measured by optical coherence tomography (OCT). Methods: One hundred and forty-four normal subjects (144 eyes), ranging from 16 to 84 years of age, were enrolled in this cross-sectional study. The RNFL thickness was determined using OCT with three circle scans 3.4 mm in diameter. Results: The average RNFL thickness was inversely correlated with age (r = –0.348, p < 0.001). Analyzing the quadrants as a parameter, RNFL thickness in the superior, temporal and inferior quadrants also decreased with age. Using 30-degree segments, there were significant correlations between age and the RNFL thickness of temporal segments (7–11 o’clock). The average RNFL thickness had the highest correlation among all parameters (r = –0.348, p < 0.001). Regarding nasal quadrant thickness, RNFL ratios (average, superior, temporal and inferior RNFL thickness relative to the nasal quadrant thickness) were not significantly correlated with age. The refractive error did not affect RNFL thickness (r = 0.091, p = 0.276). Conclusion: Our study revealed that RNFL thickness, in particular in the temporal quadrant, measured by OCT significantly decreased with age. Age has to be taken into consideration when we compare RNFL thickness between normal and glaucomatous eyes.

Regulation of Retinal Cone Bipolar Cell Differentiation and Photopic Vision by the CVC Homeobox Gene Vsx1

Cone bipolar cells of the vertebrate retina connect photoreceptors with ganglion cells to mediate photopic vision. Despite this important role, the mechanisms that regulate cone bipolar cell differentiation are poorly understood. VSX1 is a CVC domain homeoprotein specifically expressed in cone bipolar cells. To determine the function of VSX1, we generated Vsx1 mutant mice and found that Vsx1 mutant retinal cells form but do not differentiate a mature cone bipolar cell phenotype. Electrophysiological studies demonstrated that Vsx1 mutant mice have defects in their cone visual pathway, whereas the rod visual pathway was unaffected. Thus, Vsx1 is required for cone bipolar cell differentiation and regulates photopic vision perception.

In vivo studies of signaling in rod pathways of the mouse using the electroretinogram.

PURPOSE (a) To examine the possibility that there is a threshold in the synaptic mechanism linking rods to rod bipolar cells that can reduce the transmission of continuous noise from the rods without blocking the transmission of any significant proportion of single-photon responses. (b) To estimate the level of this threshold and the amplitude of the continuous noise which it can serve to reduce. (c) To identify the location of the threshold mechanism in the rod to rod bipolar cell pathway. METHODS Corneal electroretinogram recordings were made from dark-adapted mice anesthetized with ketamine/xylazine after inner-retinal components had been suppressed to isolate PII, the response of depolarizing bipolar cells. Suppression was achieved by intravitreal injections of GABA, TTX, or in Cx36 KO animals by crushing the optic nerve and waiting for ganglion cells to degenerate. RESULTS All energy-scaled records of isolated PII obtained with ganzfeld stimuli that gave rise to much less than one photoisomerization (R*) per rod (0.01-0.2 R*/rod), had an essentially identical waveform. Stronger stimuli caused a reduction in the peak amplitude of energy-scaled records (saturation) and stimuli strong enough to produce multiple isomerizations in individual rods resulted in a shortening of the response latency and an increase of the energy-scaled amplitude at early times (supralinearity). The shape of the rising edge of isolated PII changed with flash energy in a way that was consistent with the existence of a synaptic threshold whose level was less than one tenth of the amplitude of single-photon signals and a continuous noise whose rms amplitude was even less than this. However, when measured at the time of the peak, the amplitude of PII increased linearly in proportion to stimulus energy from the very lowest levels up to the point where there was, on average, 0.2 R*/rod. CONCLUSIONS There is a threshold nonlinearity operating at the output of the rod to rod bipolar cell synapse that can usefully reduce the transmission of continuous rod noise without significantly affecting the transmission of single-photon signals. This nonlinearity does not affect the overall linear function of the rod pathway at levels at which it is effectively operating in a photon-counting mode.

Ganglion Cells Are Required for Normal Progenitor- Cell Proliferation but Not Cell-Fate Determination or Patterning in the Developing Mouse Retina

The vertebrate retina develops from an amorphous sheet of dividing retinal progenitor cells (RPCs) through a sequential process that culminates in an exquisitely patterned neural tissue. A current model for retinal development posits that sequential cell-type differentiation is the result of changes in the intrinsic competence state of multipotent RPCs as they advance in time and that the intrinsic changes are influenced by continuous changes in the extracellular environment. Although several studies support the proposition that newly differentiated cells alter the extrinsic state of the developing retina, it is still far from clear what role they play in modifying the extracellular environment and in influencing the properties of RPCs. Here, we specifically ablate retinal ganglion cells (RGCs) as they differentiate, and we determine the impact of RGC absence on retinal development. We find that RGCs are not essential for changing the competence of RPCs, but they are necessary for maintaining sufficient numbers of RPCs by regulating cell proliferation via growth factors. Intrinsic rather than extrinsic factors are likely to play the critical roles in determining retinal cell fate.

Near complete loss of retinal ganglion cells in the math5/brn3b double knockout elicits severe reductions of other cell types during retinal development

Retinal ganglion cells (RGCs) are the first cell type to differentiate during retinal histogenesis. It has been postulated that specified RGCs subsequently influence the number and fate of the remaining progenitors to produce the rest of the retinal cell types. However, several genetic knockout models have argued against this developmental role for RGCs. Although it is known that RGCs secrete cellular factors implicated in cell proliferation, survival, and differentiation, until now, limited publications have shown that reductions in the RGC number cause significant changes in these processes. In this study, we observed that Math5 and Brn3b double null mice exhibited over a 99% reduction in the number of RGCs during development. This severe reduction of RGCs is accompanied by a drastic loss in the number of all other retinal cell types that was never seen before. Unlike Brn3b null or Math5 null animals, mice null for both alleles lack an optic nerve and have severe retinal dysfunction. Results of this study support the hypothesis that RGCs play a pivotal role in the late phase of mammalian retina development.

Comparison of Pentacam Scheimpflug Camera with Ultrasound Pachymetry and Noncontact Specular Microscopy in Measuring Central Corneal Thickness

Purpose: Although central corneal thickness (CCT) can be measured by several methods, interchangeability of different modalities has not been fully investigated. CCT is known to correlate with intraocular pressure (IOP). The aim of this study was to evaluate the agreement of Pentacam Scheimpflug system with noncontact specular microscopy (NCSM) and ultrasound (US) pachymetry in measuring CCT and the relation between IOP taken with Goldmann applanation tonometer (GAT) and the CCT measured with these three methods. Methods: The right eyes of 135 enrolled persons without antiglaucoma drug use (100 females and 35 males), who comprised 32 patients with primary open-angle glaucoma, 14 with ocular hypertension, 45 with primary angle-closure glaucoma, and 44 controls, were studied. Intermethod comparison of CCT was made by the 95% limits of agreement analysis according to Bland and Altman. Linear regression analysis was used to assess the relationship between IOP and CCT taken with each modality. Results: The mean CCT (±SD) taken with Scheimpflug, US, and NCSM was 559.49 ± 38.44 μ m, 553.01 ± 39.33 μ m, and 552.04 ± 42.95 μ m, respectively. The average values of CCT taken with the three instruments were not significantly different (one-factor ANOVA; p = 0.26), although the marginal mean difference between Scheimpflug and US or NCSM was statistically significant (paired t test; p = 0.0009 and 0.005, respectively). The 95% limits of agreement were 6.47 ± 43.21 μm between Scheimpflug and US, 7.45 ± 58.86 μ m between Scheimpflug and NCSM, and 0.98 ± 51.69 μ m between US and NCSM. There was a positive association between IOP and CCT measured with US or NCSM, whereas there was no correlation between IOP and CCT measured with Scheimpflug. Conclusions: Although CCT values measured with Scheimpflug, US, and NCSM are closely similar, clinicians should keep in mind that these methods are not simply interchangeable.

New perimetric threshold test algorithm with dynamic strategy and tendency oriented perimetry (TOP) in glaucomatous eyes.

Purpose To investigate the time-wise reliability and efficiency of two new perimetric test algorithms, two computerised static threshold perimetry strategies, namely dynamic strategy (OS) and tendency oriented perimetry (TOP), were compared with the standard full-threshold strategy (normal strategy, NS).Methods We examined 41 eyes of 41 normal individuals without any ocular disease and 36 eyes of 36 glaucomatous patients, with the NS (4-to-2 dB), OS and TOP using an Octopus 1-2-3 perimeter. We analysed test time, stimulus time and the two global indices, mean sensitivity (MS) and loss variance (LV). Program 32X was used as test grid pattern.Results The mean test time for the NS was reduced by 52% with the OS and by 78% with the TOP strategy. Concerning the global indices, the MS value did not differ among the three strategies in the control or glaucoma group. However, the LV value was lower in the TOP strategy compared with the other two strategies in the glaucoma group. This suggested that the TOP strategy underestimated local glaucomatous visual field defects. The ability to detect early-stage glaucoma with the DS and TOP was inferior to that with the NS.Conclusions The OS was more efficient than the TOP strategy for the detection of early glaucomatous defects, whereas the TOP strategy required less testing time. The TOP strategy may be an appropriate approach for patients in whom time-consuming perimetry is not possible, or in whom the visual field defect is already advanced.

Quantification of retinal nerve fiber layer thickness reduction associated with a relative afferent pupillary defect in asymmetric glaucoma

Aim: The relative afferent pupillary defect (RAPD) is an important clinical sign of asymmetrical retinal ganglion cell and axonal damage. Although glaucoma essentially affects bilateral eyes, a subset of patients manifests asymmetrical glaucomatous optic neuropathy (GON), which exhibits an RPAD in the more advanced eyes. However, the degree to which axonal loss occurs before an RAPD is clinically detectable has not been substantiated. The purpose of this study is to assess the relationship between the depth of a clinically detectable RAPD and the reduction ratio of retinal nerve fiber layer (RNFL) thickness in the more advanced eyes relative to that in the contralateral less advanced eyes of patients with asymmetrical GON. Methods: Enrolled were 29 consecutive glaucoma patients with the clinically detectable RAPD. An RAPD was quantified by placing log-scaled neutral density filters over the less advanced eyes while performing the swinging flashlight test. Average RNFL thickness was determined using the Fast RNFL thickness programme of optical coherence tomography 3000. Correlation coefficient and Linear regression analyses were used in assessing the relationship between the RAPD and the ratio of RNFL thickness in the more advanced eyes relative to that in the less advanced. Results: RAPD ranged from 0.6 to 2.4 log units. The log-scaled RAPD had a statistically significantly inversed correlation with the average RNFL thickness ratio (rs = −0.729, p<0.0001). Linear regression analysis found an equation that the average RNFL thickness ratio in the more affected eyes relative to that in the less advanced (%)  = (0.827−0.169×RAPD (log units))×100 (R2 = 0.557, p<0.0001). Conclusions: When an RAPD is clinically detected, the RNFL thickness in the more advanced eyes was in average reduced to about 73% of that in the less advanced.

Goniosynechialysis with lens aspiration and posterior chamber intraocular lens implantation for glaucoma in spherophakia

A 17-year-old girl presented with bilateral angle-closure glaucoma associated with spherophakia. A previous bilateral laser iridotomy failed to control intraocular pressure (IOP). Goniosynechialysis with lens aspiration and posterior chamber intraocular lens implantation were performed in both eyes. Peripheral iridoplasty was performed 3 days later. The postoperative IOP was controlled without medication for 12 months in the right eye and 24 months in the left eye. By restructuring the physiologic aqueous outflow route, goniosynechialysis safely and effectively treated secondary glaucoma from spherophakia.