Functional characterization of retina and optic nerve after acute and chronic elevation of the intraocular pressure in rats

Purpose. To characterize the pupil light reflex (PLR), electroretinographic (ERG) and tonometric parameters in healthy, acute and chronic hypertensioe rat eyes. Methods. Brown Norway rats were used for experiments. The PLR was evaluated with a computerized pupillometer, ERGs were recorded simultaneously from both eyes and intraocular pressure (IOP) was measured with a Tonopen. Retinal ischemia was induced in rats by acutely increasing the IOP (110 mmHg/60 minutes), while chronic ocular hypertension was induced by cauterizing vortex and episcleral veins. Results. The analysis of the PLR parameters confirmed the consensual PLR was significantly smaller in amplitude (p = 0.03) and increased latency time (p = 0.001) compared to the direct PLR in healthy rats. Acute ocular ischemia caused significant decrease in retinal function. Preoperative values for the PLRratio in rats exposed to the acute ocular ischemia (ratio = consensual/direct PLR) were 76.7 +/- 2.6 (mean +/- SEM; %). 24h postoperatively the PLR ratio was 15.2 +/- 12.8, 10 days postoperatively 11.6 +/- 9.8, 20 days postoperatively 26.5 +/- 8.0 and 28 days postoperatively PLRratio was 33.27 +/- 9.3. However, at day 35 the PLR was significantly recovered when compared to the 24h postoperative values (PLR ratio = 41.1 +/- 7.3%, p \u3c 0.01, Repeated measures ANOVA). 42 days after surgery the PLR started to decrease once again in the operated eyes. Electroretinographic amplitudes followed a similar pattern. Seven days after surgery 5/14 rats, which received cauterization of the vortex and episcleral veins developed significant elevation of the IOP in operated eyes (p = 0.0004; Paired t-test). Elevation of the IOP was sustained at 3 (p = 0.002) and 5 (p = 0.007) weeks postoperatively. However, IOP values did not significantly differ between control and operated eyes 8 weeks postoperatively (p = 0.192, Paired t-test). Rats with elevated IOP had significant pupil defects at 7 (p \u3c 0.05, Repeated measures ANOVA, n = 5) and 28 days postoperatively (p \u3c 0.05), but not at 62 days postoperatively (p \u3e 0.05) comparing to preoperative values. Rats with elevated IOP displayed a significant decrease in ERG amplitudes in operated eyes at 4 but not at 8 weeks postoperatively. Conclusions. Functional monitoring of the ERG and PLR is sensitive technique for the detection of retina and optic nerve deficits after acute and chronic elevation of the IOP

Recovery of canine retina and optic nerve function after acute elevation of intraocular pressure: implications for canine glaucoma treatment

Purpose  To characterize the timing and extent of functional recovery in healthy canine eyes exposed to acute elevation of intraocular pressure (IOP). Methods  Acute elevation of IOP was induced in 14 healthy Beagles by elevating IOP above the levels of systolic blood pressure for 60 min (average elevation was between 100 and 160 mmHg). Menace, dazzle and pupillary light reflexes (PLR) were tested at 1, 7, 14 and 28 days post elevation. Optical coherence tomography was used to evaluate retinal thickness preoperatively and at 15 and 30 days post elevation. Results  One day post elevation all animals were blind in the operated eye (no positive menace), 5/14 had positive PLR and 10/14 had positive dazzle response. Seven days post elevation 4/14 animals had positive menace response and all animals (14/14) had positive dazzle and PLR responses. Fourteen and 28 days post elevation all animals had positive menace, PLR and dazzle responses. Optical coherence tomography analysis revealed significant thinning of the inferior retina (pre elevation: 156.3 ± 4.8 µm; 15 days post elevation: 125 ± 10.4 µm; 30 days post elevation 123 ± 11.9 µm; P \u3c 0.01, anova). The superior retina, however, did not show any detectable decrease in thickness compared to control eyes (pre elevation: 193.8 ± 2.6 µm; 15 days post elevation: 176.9 ± 8.5 µm; 30 days post elevation 176.9 ± 7 µm; P = 0.057, anova). Conclusions  Detailed functional and morphologic analysis revealed precise information about retinal damage after acute elevation of IOP. Canine retina has the capacity to recover at least some visual function even at 14 days after acute elevation of the IOP. More aggressive medical and surgical treatment of canine glaucomatous patients may be indicated despite complete loss of visual function, PLR and dazzle responses in early days after development of an acute glaucomatous attack

Functional Characterization of Retina and Optic Nerve after Acute Ocular Ischemia in Rats

purpose. To functionally characterize the status of the rat retina and optic nerve after acute elevation of intraocular pressure (IOP) and to determine the dynamics of the pathologic changes in the ischemic retina and optic nerve. methods. Retinal ischemia was induced in rats by acutely increasing the IOP (110 mm Hg/60 minutes). Direct and indirect pupil light reflexes (PLRs) were recorded from the noninjured eye, and electroretinograms (flash and flicker ERG) were recorded from the injured and control eyes before and after surgery. Amplitudes and latencies were calculated for each recording session. results. Preoperative PLRratios (indirect/direct PLR) were 76.7 ± 2.6 (mean ± SEM). Twenty-four hours after surgery the PLRratio was 15.2 ± 12.8, 10 days after surgery, 11.6 ± 9.8; 20 days after surgery, 26.5 ± 8.0; and 28 days after surgery, 33.27 ± 9.3. However, at day 35, the PLR had significantly recovered (41.1 ± 7.3) when compared with the 24-hour postoperative ratios (P \u3c 0.01, repeated-measures ANOVA). Forty-two days after surgery, the PLRratio started to decrease once again in the injured eyes (28.7 ± 5.9). Electroretinographic amplitudes (full-field flash ERG) followed a similar pattern. Cone responses (flicker ERG) were measured 42 days after surgery and revealed defects in injured eyes (control eyes: 46.6 ± 2.9 μV, injured eyes: 3.4 ± 1.7 μV). Histologic analysis revealed ischemic damage to all retinal layers, with the primary defects localized to the central retina. conclusions. Acute ocular ischemia causes a significant decrease in retinal function, as measured by PLR and ERG, although over time the rat retina and optic nerve show partial regain of function

Evaluation of retinal status using chromatic pupil light reflex activity in healthy and diseased canine eyes

purpose. To differentiate rod-cone–mediated pupil light reflexes (PLRs) from intrinsic melanopsin-mediated pupil light reflexes by comparing pupil responses with red and blue light stimuli of differing intensities in normal dog eyes and in those with sudden acquired retinal degeneration syndrome (SARDS) exhibiting a nonrecordable electroretinogram. methods. The PLR was evaluated in 14 healthy dogs using a computerized pupillometry system and in five dogs with SARDS. Contraction amplitude, velocity, and implicit time of the PLR were studied as a function of peak wavelength (480 nm vs. 630 nm) and light intensity (−0.29 to 5.3 log units) to determine characteristics of the rod-cone versus predominantly melanopsin-mediated PLR activity. results. The PLR in healthy, mildly sedated dogs could be elicited at low light intensities (−0.29 log units; 0.51 cd/m2). Canine SARDS patients displayed a complete absence of vision, electroretinographic amplitude, and PLR at low light intensity. However, in SARDS dogs, a pupil light reflex could be elicited with wavelengths corresponding to the melanopsin spectral sensitivity (blue light − peak at 480 nm) and at relatively high intensity (4.3 log units or higher), whereas red light (630 nm peak wavelength) was ineffective in eliciting any detectable PLR response even at light intensities of 6 log units (1,000,000 cd/m2). conclusions. The PLR in healthy canine eyes can be elicited at very low light intensities using red and blue wavelengths of light, but in dogs with blindness caused by SARDS, the pupil reacts only to high-intensity blue wavelength light, implying loss of the rod-cone–mediated PLR and most likely the presence of intrinsic, melanopsin-mediated, retinal ganglion cell–mediated PLR.This article is from Investigative Ophthalmology & Visual Science 48 (2007): 5178, doi: 10.1167/iovs.07-0249.</p

Detection and characterization of glaucoma-like canine retinal tissues using Raman spectroscopy

Early detection of pathological changes and progression in glaucoma and other neuroretinal diseases remains a great challenge and is critical to reduce permanent structural and functional retina and optic nerve damage. Raman spectroscopy is a sensitive technique that provides rapid biochemical characterization of tissues in a nondestructive and noninvasive fashion. In this study, spectroscopic analysis was conducted on the retinal tissues of seven beagles with acute elevation of intraocular pressure (AEIOP), six beagles with compressive optic neuropathy (CON), and five healthy beagles. Spectroscopic markers were identified associated with the different neuropathic conditions. Furthermore, the Raman spectra were subjected to multivariate discriminate analysis to classify independent tissue samples into diseased/healthy categories. The multivariate discriminant model yielded an average optimal classification accuracy of 72.6% for AEIOP and 63.4% for CON with 20 principal components being used that accounted for 87% of the total variance in the data set. A strong correlation (R2\u3e0.92) was observed between pattern electroretinography characteristics of AEIOP dogs and Raman separation distance that measures the separation of spectra of diseased tissues from normal tissues; however, the underlining mechanism of this correlation remains to be understood. Since AEIOP mimics the pathological symptoms of acute/early-stage glaucoma, it was demonstrated that Raman spectroscopic screening has the potential to become a powerful tool for the detection and characterization of early-stage disease

Laser-induced mouse model of chronic ocular hypertension

PURPOSE. To develop an inducible mouse model of glaucoma. METHODS. An obstruction of aqueous humor outflow in adult C57BL6/J mice was induced by combined injection of indocyanine green (ICG) dye into the anterior chamber and diode laser treatment. To evaluate intraocular pressure (IOP), tonometry was performed with a modified Goldmann tonometer. The function of the retina was evaluated with electroretinography (ERG). RESULTS. IOP was significantly elevated in surgical eyes compared with control eyes: before surgery, 15.2 Ϯ 0.6 mm Hg; 10 days after surgery, 33.6 Ϯ 1.5 mm Hg (P Ͻ 0.001); and 30 days after surgery, 27.4 Ϯ 1.2 mm Hg (P Ͻ 0.001). However, 60 days after surgery, IOP in the surgical eyes decreased to 19.5 Ϯ 0.9 mm Hg and was not significantly different compared with control eyes (control, 17.3 Ϯ 0.7 mm Hg; P ϭ 0.053). ERG amplitudes, expressed as a ratio (surgical/control), were decreased in surgical eyes. The amplitudes for b-wave were: before surgery, 107.6% Ϯ 4.6%; 28 days after surgery, 61% Ϯ 4% (P Ͻ 0.001); and 56 days after surgery, 62% Ϯ 5.6% (P Ͻ 0.001). Oscillatory potentials were the most dramatically affected: before surgery, 108.6% Ϯ 6.7%; 28 days after surgery, 57.5% Ϯ 5% (P Ͻ 0.01); and 56 days after surgery, 57% Ϯ 8.5% (P Ͻ 0.001). Amplitudes of the a-waves had relatively smaller but still significant deficits: before surgery, 105.8% Ϯ 6.9%; 28 days after surgery, 72.2% Ϯ 5.4% (P Ͻ 0.01); and 56 days after surgery, 79.8% Ϯ 11.0% (P Ͻ 0.01). Histologic analysis of the surgical eyes revealed development of anterior synechia, loss of retinal ganglion cells (RGCs), and thinning of all retinal layers. Electron microscopy of optic nerve cross sections revealed swelling and degeneration of the large diameter axons and gliosis. CONCLUSIONS. Diode laser treatment of ICG saturated episcleral veins causes a chronic elevation of IOP and sustained ERG deficits. (Invest Ophthalmol Vis Sci. 2003;44:4337-4346

Topical ocular sodium 4-phenylbutyrate rescues glaucoma in a myocilin mouse model of primary open-angle glaucoma

PURPOSE. Mutations in the myocilin gene (MYOC) are the most common known genetic cause of primary open-angle glaucoma (POAG). The purpose of this study was to determine whether topical ocular sodium 4-phenylbutyrate (PBA) treatment rescues glaucoma phenotypes in a mouse model of myocilin-associated glaucoma (Tg-MYOC Y437H mice). METHODS. Tg-MYOC Y437H mice were treated with PBA eye drops (n ϭ 10) or sterile PBS (n ϭ 8) twice daily for 5 months. Long-term safety and effectiveness of topical PBA (0.2%) on glaucoma phenotypes were examined by measuring intraocular pressure (IOP) and pattern ERG (PERG), performing slit lamp evaluation of the anterior chamber, analyzing histologic sections of the anterior segment, and comparing myocilin levels in the aqueous humor and trabecular meshwork of Tg-MYOC Y437H mice. Sci. 2012;53: 1557-1565 RESULTS. Tg-MYO