Evolution of a Glaucoma Fellow's Surgical Training: Improvements in Tube Shunt Case Times during the Academic Year.

Purpose The aim of the study is to report changes in tube shunt placement surgical case times for glaucoma fellows during the course of the academic year. Patients and Methods Electronic health records were retrospectively reviewed to determine patient demographics, surgical case times (defined as procedure start time to procedure end time), and glaucoma fellow involvement. Only cases with a glaucoma fellow as the primary surgeon were included. Operative case times were compared by first and second halves of the academic year (beginning in July and ending in June) using a two-tailed t -test. Results Five hundred and seventy-three individual tube shunt surgeries (385 Ahmed, 188 Baerveldt) performed by 28 glaucoma fellows (17 females, 11 males) at Duke University Eye Center and University of North Carolina Medical Center were included. Overall, case times were significantly shorter in the second half of the academic year as compared with the first (55.3 ± 17.1 minutes vs. 61.0 ± 17.4 minutes, p <0.001). Both male (57.3 ± 16.8 minutes vs. 63.2 ± 18.6 minutes, p = 0.008) and female (53.5 ± 17.3 minutes vs. 59.3 ± 16.4 minutes, p = 0.003) fellows demonstrated shorter case times over the academic year; additionally, female fellows trended toward shorter case times than male fellows in both the first half ( p = 0.072) and second half ( p = 0.053) of the academic year. Fellows also exhibited shorter case times with both Ahmed implants (54.1 ± 16.2 minutes vs. 59.3 ± 15.8 minutes, p = 0.002) and Baerveldt implants (57.8 ± 18.9 minutes vs. 64.2 ± 20.0 minutes, p = 0.025) cases over the academic year. Baerveldt case times were significantly longer than Ahmed cases in the first half ( p = 0.028) and trended toward being longer than Ahmed cases in the second half ( p = 0.070). Conclusion Across 5 years at two academic institutions, glaucoma fellows had shorter primary tube shunt surgical case times in the second half of the academic year. These findings reflect improvement in surgical efficiency throughout glaucoma fellowship. These findings should be taken into consideration when scheduling trainee surgeries at academic medical centers at different points in the academic year.

Contribution of autophagy to ocular hypertension and neurodegeneration in the DBA/2J spontaneous glaucoma mouse model.

Glaucoma is a progressive optic neuropathy characterized by axonal degeneration and retinal ganglion cells loss. Several factors have been postulated to play a role in glaucoma, elevated intraocular pressure (IOP) being the best well-known causative factor. The mechanisms leading to ocular hypertension and glaucoma are still not fully understood. An increasing number of evidence indicates a role of autophagy in the pathophysiological process of ocular hypertension and glaucoma. However, while all of the studies agree that autophagy is induced in RGCs in response to injury, autophagy was found to either protect or promote cell death depending on the experimental model used. In order to gain more insight into both, the role of autophagy in the pathogenesis of glaucoma and the effect of chronic IOP elevation in the autophagy pathway, we have investigated here for the first time autophagy in the iridocorneal angle region, retinal ganglion cell bodies, and ON axons in the spontaneous ocular hypertensive DBA/2J mouse glaucoma model and in the transgenic DBA/2J::GFP-LC3 mice, generated in our laboratory. Our results indicate decreased autophagic flux in the outflow pathway cells in the DBA/2J mice, characterized by increased levels of LC3-II and p62 together with a decrease in the lysosomal marker LAMP1, evaluated by western blot and immunofluorescence. Elevated presence of autophagic vacuoles in the DBA/2J and, in particular, in the DBA/2J::GFP-LC3 mice was also observed. Expression of the GFP-LC3 transgene was associated to higher cumulative IOP in the DBA/2J background. In addition to higher elevation in IOP, DBA/2J::GFP-LC3 were characterized by further RGCs and exacerbated axonal degeneration compared to DBA/2J. This was accompanied by the notable high presence of autophagic figures within degenerating axons. These results strongly suggest overactivation of autophagy as a potential cellular mechanism leading to ON degeneration in the chronic hypertensive DBA/2J mice.

Retinal nerve fiber layer reflectance for early glaucoma diagnosis.

PURPOSE: Compare performance of normalized reflectance index (NRI) and retinal nerve fiber layer thickness (RNFLT) parameters determined from optical coherence tomography (OCT) images for glaucoma and glaucoma suspect diagnosis. METHODS: Seventy-five eyes from 71 human subjects were studied: 33 controls, 24 glaucomatous, and 18 glaucoma-suspects. RNFLT and NRI maps were measured using 2 custom-built OCT systems and the commercial instrument RTVue. Using area under the receiver operating characteristic curve, RNFLT and NRI measured in 7 RNFL locations were analyzed to distinguish between control, glaucomatous, and glaucoma-suspect eyes. RESULTS: The mean NRI of the control group was significantly larger than the means of glaucomatous and glaucoma-suspect groups in most RNFL locations for all 3 OCT systems (P<0.05 for all comparisons). NRI performs significantly better than RNFLT at distinguishing between glaucoma-suspect and control eyes using RTVue OCT (P=0.008). The performances of NRI and RNFLT for classifying glaucoma-suspect versus control eyes were statistically indistinguishable for PS-OCT-EIA (P=0.101) and PS-OCT-DEC (P=0.227). The performances of NRI and RNFLT for classifying glaucomatous versus control eyes were statistically indistinguishable (PS-OCT-EIA: P=0.379; PS-OCT-DEC: P=0.338; RTVue OCT: P=0.877). CONCLUSIONS: NRI is a promising measure for distinguishing between glaucoma-suspect and control eyes and may indicate disease in the preperimetric stage. Results of this pilot clinical study warrant a larger study to confirm the diagnostic power of NRI for diagnosing preperimetric glaucoma.

Disease progression in iridocorneal angle tissues of BMP2-induced ocular hypertensive mice with optical coherence tomography.

PURPOSE: The goal of the present study was to test for the first time whether glaucomatous-like disease progression in a mouse can be assessed morphologically and functionally with spectral domain optical coherence tomography (SD-OCT). METHODS: We monitored progressive changes in conventional outflow tissues of living mice overexpressing human bone morphogenetic protein 2 (BMP2), a model for glaucoma. Intraocular pressure (IOP) and outflow tissue morphology/Young's modulus were followed in mice for 36 days with rebound tonometry and SD-OCT, respectively. Results were compared to standard histological methods. Outflow facility was calculated from flow measurements with direct cannulation of anterior chambers subjected to three sequential pressure steps. RESULTS: Overexpression of BMP2 significantly elevated IOP in a biphasic manner over time compared to mice that overexpressed green fluorescent protein in outflow cells and naïve controls. SD-OCT revealed changes in outflow tissues overexpressing BMP2 that corresponded with the timing of the IOP phases and decreased outflow facility. In the first phase, the angle was open, but the trabecular meshwork and the cornea were thickened. OCT detected increased trabecular meshwork stiffness after provocative IOP challenges of the BMP2 eyes, which corresponded to increased collagen deposition with transmission electron microscopy. In contrast, the angle was closed in the second phase. IOP elevation over 36 days due to BMP2 overexpression resulted in significant retinal ganglion cell and axon loss. CONCLUSIONS: Although not a feasible open-angle glaucoma model, the BMP2 mice were useful for demonstrating the utility of SD-OCT in following disease progression and differentiating between two forms of ocular pathology over time that resulted in ocular hypertension.

Dorsomedial/Perifornical hypothalamic stimulation increases intraocular pressure, intracranial pressure, and the translaminar pressure gradient.

PURPOSE: Intraocular pressure (IOP) fluctuation has recently been identified as a risk factor for glaucoma progression. Further, decreases in intracranial pressure (ICP), with postulated increases in the translaminar pressure gradient across the lamina cribrosa, has been reported in glaucoma patients. We hypothesized that circadian fluctuations in IOP and the translaminar pressure gradient are influenced, at least in part, by central autonomic regulatory neurons within the dorsomedial and perifornical hypothalamus (DMH/PeF). This study examined whether site-directed chemical stimulation of DMH/PeF neurons evoked changes in IOP, ICP, and the translaminar pressure gradient. METHODS: The GABA(A) receptor antagonist bicuculline methiodide (BMI) was stereotaxically microinjected into the DMH/PeF region of isoflurane-anesthetized male Sprague-Dawley rats (n = 19). The resulting peripheral cardiovascular (heart rate [HR] and mean arterial pressure [MAP]), IOP, and ICP effects were recorded and alterations in the translaminar pressure gradient calculated. RESULTS: Chemical stimulation of DMH/PeF neurons evoked significant increases in HR (+69.3 ± 8.5 beats per minute); MAP (+22.9 ± 1.6 mm Hg); IOP (+7.1 ± 1.9 mm Hg); and ICP (+3.6 ± 0.7 mm Hg) compared with baseline values. However, the peak IOP increase was significantly delayed compared with ICP (28 vs. 4 minutes postinjection), resulting in a dramatic translaminar pressure gradient fluctuation. CONCLUSIONS: Chemical stimulation of DMH/PeF neurons evokes substantial increases in IOP, ICP, and the translaminar pressure gradient in the rat model. Given that the DMH/PeF neurons may be a key effector pathway for circadian regulation of autonomic tone by the suprachiasmatic nucleus, these findings will help elucidate novel mechanisms modulating circadian fluctuations in IOP and the translaminar pressure gradient.

Distribution of amyloid precursor protein and amyloid-beta in ocular hypertensive C57BL/6 mouse eyes.

PURPOSE: Amyloid precursor protein (APP) and amyloid-beta (Abeta) appear to participate in the pathophysiology of retinal ganglion cell (RGC) death in glaucoma. We, therefore, determined the distribution of APP and Abeta in the retinas of C57BL/6 mice after induction of chronic ocular hypertension. METHODS: Ocular hypertension was induced in one eye of three-month-old C57BL/6 mice by injection of hypertonic saline into episcleral veins. After 6 weeks of documented elevated intraocular pressure (IOP), retinas were fixed with 4% paraformaldehyde and processed for immunohistochemistry with antibodies including a polyclonal antibody to the C-terminus of Abeta 40 (Novartis 17-40/23) and a polyclonal antibody to the APP ectodomain (Novartis 474). Distribution and semiquantitative expression of APP and Abeta immunolabeling in ocular hypertensive and control retinas were graded in a masked fashion and compared. RESULTS: APP and Abeta immunoreactivity was found in the pia/dura, optic nerve (ON), and RGC layer of ocular hypertensive retinas, whereas APP and Abeta immunoreactivity in the contralateral control eyes was detected only in the pia/dura. Comparison of ocular hypertensive and control eyes for Abeta immunolabeling was significant in the ON and RGC layer (p < 0.05) whereas no significant difference was found when compared for APP staining. CONCLUSIONS: High Abeta and APP levels were seen in ocular hypertensive retinas, probably due to abnormal APP-splicing in the presence of elevated IOP.

Surgical management of hypotony owing to overfiltration in eyes receiving glaucoma drainage devices.

PURPOSE: To assess rates of surgical revision of glaucoma drainage devices (GDDs) from hypotony owing to overfiltration and its management. DESIGN: Retrospective case series. METHODS: Demographic characteristics, type of GDD implanted, type of surgical revision, and outcomes were obtained from the charts of patients undergoing GDD implantation and > or = 1 subsequent GDD revision in 2002 to 2006. All surgical revisions performed owing to hypotony from overfiltration in the absence of a wound leak were identified. RESULTS: Of 1292 eyes undergoing GDD implantation, 21 (1.6%) developed hypotony owing to overfiltration requiring surgical revision: 15 eyes of 488 (3.1%) with a Baerveldt implant and 6 of 804 (0.7%) with an Ahmed (P=0.002). When including primary and secondary revisions, 6 of 12 eyes (50%) treated by using polyglactin suture ligation were successful (did not require additional surgery) compared with 8 of 10 (80%) undergoing suture ligation using prolene. CONCLUSIONS: Hypotony owing to overfiltration is an uncommon GDD-surgery complication. Understanding how to manage patients who develop this complication can improve patient outcomes.

Outcomes of surgical bleb revision for complications of trabeculectomy.

OBJECTIVE: To describe the results of revision surgery for complications of trabeculectomy in a case series from an academic glaucoma service. DESIGN: Retrospective case series. PARTICIPANTS: A total of 177 eyes of 167 adult patients who underwent revision of trabeculectomy at the Wilmer Eye Institute between 1994 and 2007. METHODS: Three indications for surgery were identified: hypotony without leak, bleb leak, and bleb dysesthesia. Revision was deemed successful when all of the following were true: the primary indication was eliminated, further intraocular pressure (IOP)-lowering surgery was not required, no major complication occurred, and a new bleb-related problem did not develop. Patients with less than 3 months of follow-up were excluded unless failure occurred earlier. Surgical procedures included variations on excision of thin or leaking conjunctiva with advancement. MAIN OUTCOME MEASURES: Change in IOP, change in visual acuity, need for further IOP-lowering surgery, and complications after bleb revision. RESULTS: Subjects' mean age was 67+/-14 years, 54% were female, and mean follow-up was 2.8+/-2.7 years, with a mean interval from trabeculectomy to revision of 3.5+/-3.7 years. Overall success rate was 63% (112/177), which was slightly higher for leak repair (65%; 64/98) and hypotony (63%; 32/51) than for dysesthesia (57%; 16/28) indications. By Kaplan-Meier analysis, overall cumulative success rates at 1, 2, 5, and 10 years after bleb revision were 80%, 75%, 50%, and 41%, respectively. IOP and visual acuity improved significantly in both hypotony and leak groups (P values ranging from 0.004 to <0.0001). Additional IOP-lowering surgery was required in 9%. In multivariate regression analysis adjusting for age, gender, and number of prior surgeries, patients with glaucoma other than primary open-angle glaucoma were twice as likely to have failed bleb revision. CONCLUSIONS: Surgical bleb revision often provides successful resolution of bleb-related complications. Most patients maintain IOP control without need for further IOP-lowering surgery. FINANCIAL DISCLOSURE(S): Proprietary or commercial disclosure may be found after the references.

Gene and protein expression pilot profiling and biomarkers in an experimental mouse model of hypertensive glaucoma.

Glaucoma is a group of genetically heterogeneous neurodegenerative disorders causing the degeneration of the ganglion neurons of the retina. Increased intraocular pressure (IOP) is a hallmark risk factor promoting the death of ganglion neurons of the retina in glaucoma. Yet, the molecular processes underlying the degeneration of these neurons by increased IOP are not understood. To gain insight into the early molecular events and discover biomarkers induced by IOP, we performed gene and protein expression profiling to compare retinas of eyes with and without high IOP in a rodent model of experimental glaucoma. This pilot study found that the IOP-mediated changes in the transcription levels of a restricted set of genes implicated in peroxisomal and mitochondrial function, modulation of neuron survival and inflammatory processes, were also accompanied by changes in the levels of proteins encoded by the same genes. With the exception of the inflammatory markers, serum amyloid-A1 (SAA1) and serum amyloid-A2 (SAA2), the IOP-induced changes in protein expression were restricted to ganglion neurons of the retina and they were detected also in the vitreous, thus suggesting an early IOP-mediated loss of ganglion cell integrity. Interestingly, SAA1 and SAA2 were induced in retinal microglia cells, whereas they were reduced in sera of IOP-responsive mice. Hence, this study defines novel IOP-induced molecular processes, biomarkers and sources thereof, and it further validates the extension of the analyses herein reported to other genes modulated by IOP.

Mouse models of retinal ganglion cell death and glaucoma.

Once considered too difficult to use for glaucoma studies, mice are now becoming a powerful tool in the research of the molecular and pathological events associated with this disease. Often adapting technologies first developed in rats, ganglion cell death in mice can be induced using acute models and chronic models of experimental glaucoma. Similarly, elevated IOP has been reported in transgenic animals carrying defects in targeted genes. Also, one group of mice, from the DBA/2 line of inbred animals, develops a spontaneous optic neuropathy with many features of human glaucoma that is associated with IOP elevation caused by an anterior chamber pigmentary disease. The advent of mice for glaucoma research is already having a significant impact on our understanding of this disease, principally because of the access to genetic manipulation technology and genetics already well established for these animals.

Current management of glaucoma and the need for complete therapy.

Glaucoma is a long-term ocular neuropathy defined by optic disc or retinal nerve fiber structural abnormalities and visual field abnormality. Primary open-angle glaucoma is the most common type of glaucoma. Currently available treatments, initiated in a stepwise process, focus on intraocular pressure (IOP) reduction, and initially include topical drug therapy (single then multidrug combinations), followed by laser then surgical treatment. Topical prostaglandin analogues or beta-adrenergic receptor blockers are first used, followed by alpha-agonists or topical carbonic anhydrase inhibitors, and infrequently, cholinergic agonists and oral therapy. Limitations to existing topical IOP-reducing medications include continued disease progression in glaucoma patients with normal IOP, treatment failure, and low rates of compliance and persistence. Therapeutic agents under investigation include neuroprotectants, which target the disease process manifested by death of retinal ganglion cells, axonal loss, and irreversible loss of vision. Neuroprotectants may be used alone or in combination with IOPreducing therapy (a treatment strategy called complete therapy). Memantine, an N-methyl-D-aspartate receptor blocker currently approved for dementia, is the neuroprotectant farthest along in the process seeking regulatory approval for glaucoma treatment and has a favorable safety profile because of its selective mechanism of action. Several other neuroprotectants are in early stage investigation. Complete therapy provides hope for improved outcomes by reducing the significant morbidity and economic consequences that occur as a result of neurodegeneration and disease progression.

Microarray analysis of gene expression in adult retinal ganglion cells.

Retinal ganglion cells (RGCs) transfer visual information to the brain and are known to be susceptible to selective degeneration in various neuropathies such as glaucoma. This selective vulnerability suggests that these highly specialized neurons possess a distinct gene expression profile that becomes altered by neuropathy-associated stresses, which lead to the RGC death. In this study, to identify genes expressed predominantly in adult RGCs, a global transcriptional profile of purified primary RGCs has been compared to that of the whole retina. To avoid alterations of the original gene expression profile by cell culture conditions, we isolated RNA directly from adult RGCs purified by immunopanning without prior sub-cultivation. Genes expressed predominantly in RGCs included: Nrg1, Rgn, 14-3-3 family (Ywhah, Ywhaz, Ywhab), Nrn1, Gap43, Vsnl1, Rgs4. Some of these genes may serve as novel markers for these neurons. Our analysis revealed enrichment in genes controlling the pro-survival pathways in RGCs as compared to other retinal cells.

Tonopen measurement of intraocular pressure in mice.

PURPOSE: To standardize a method of non-invasive measurement of intraocular pressure (IOP) in mice. METHODS: Cannulated-eye study: IOP was measured simultaneously with a Tonopen and by direct cannulation of the vitreous compartment while pressure was manipulated in steps between 10 and 45 mmHg by a saline reservoir via a second vitreal cannula (five mice, one rat). Non-cannulated-eye study: Tonopen and servo-null measurements were performed in independent groups (48 mice) to verify Tonopen measurements in non-cannulated-eyes. Topical brimonidine (0.15%) was used to decrease IOP. RESULTS: In the rat, there was a similar relationship between Tonopen readings and direct measurements via cannulation of the eye as previously reported. Although readings from mice eyes were higher in variability than those obtained from the rat, the measurements were reproducible and the correlation between the invasive and the non-invasive methods was good (r = 0.97). The IOP lowering effect of brimonidine was detected with Tonopen as well as servo-null measurements (p < 0.001) and the results with both techniques were similar. CONCLUSION: The Tonopen can be used for rapid and reproducible measurements of IOP in mice. The method is easy to apply and can provide a useful means for IOP measurement in mouse models of induced ocular hypertension, in knock-out and transgenic mice, or in pharmacological studies.

Antibody-targeted photodynamic therapy.

PURPOSE: To assess the feasibility of conjugation of verteporfin (Visudyne, Parkedale Pharmaceuticals, Rochester, Minnesota, USA) to antibody against vascular endothelial growth factor. DESIGN: Experimental study. METHODS: Rabbit antimouse vascular endothelial growth factor polyclonal antibody was conjugated to verteporfin. Fluorescence excitation-emission spectra of verteporfin and conjugate were examined. Vascular endothelial growth factor-expressing murine endothelial cells were incubated with saline, verteporfin, or conjugate, followed by laser exposure or no laser exposure. Cell viability at 1 and 24 hours was assessed via trypan blue exclusion. Results were analyzed by two-way analysis of variance with replication and the Bonferroni multiple comparison test. RESULTS: The fluorescence excitation-emission spectrum of the conjugate was similar to that of verteporfin. After laser exposure, cell viability in conjugate-treated cells was reduced to 6% at 1 hour (P <.0001) and to 4% at 24 hours (P <.0001), compared with approximately 40% in nonlaser-exposed, conjugate-treated cells. The cytotoxicity in the conjugate-treated cells was higher than in verteporfin-treated cells exposed to laser, although the difference did not reach statistical significance. CONCLUSIONS: The conjugation of verteporfin to polyclonal antibody is possible without the loss of its photosensitizing properties. Conjugated verteporfin destroys cellular targets at least as effectively as verteporfin alone.

Glaucoma: ocular Alzheimer's disease?

Glaucoma is a chronic neurodegeneration of the optic nerve and one of the leading causes of vision loss in the world among the aging. Retinal ganglion cells (RGCs) have been shown to die by apoptosis, or programmed cell death. Central to apoptosis is the activation of specific proteases, termed caspases. Caspases are activated in chronic neurodegenerations such as Alzheimer's disease (AD) as well as in RGCs after optic nerve transection. In rat glaucoma models we have shown that caspase-3, a major effector of the apoptotic cascade, is activated in RGCs and cleaves amyloid precursor protein (APP) to produce neurotoxic fragments that include amyloid-beta. Caspase-8, which initiates apoptosis after activation of receptors of the tumor necrosis factor (TNF) superfamily, is also activated in RGCs. This suggests a new hypothesis for RGC death in glaucoma involving chronic amyloid-beta neurotoxicity, mimicking AD at the molecular level. With loss of the protective effect of APP and upregulation of toxic APP fragments, RGCs die from chronic caspase activation, loss of synaptic homeostasis, amyloid-beta cytotoxicity and excitotoxicity. The benefits are that treatments for AD could be used to treat glaucoma, and strategies developed to treat glaucoma could treat other neurodegenerations.

Bilateral optic disk edema and blindness as initial presentation of acute lymphocytic leukemia.

PURPOSE: To report bilateral optic disk edema and blindness as the unusual initial presentation of acute lymphocytic leukemia (ALL) in an adult. METHODS: A 19-year-old man presented with a history of headaches, back pain, and 10 days of worsening vision that progressed to blindness. Ocular examination revealed light perception acuity in the right eye and no light perception in the left eye. Fundus examination revealed bilateral profound optic disk edema, tortuous vessels, and retinal hemorrhages. Acute lymphocytic leukemia was diagnosed with complete blood count and bone marrow biopsy. Head computed tomography and magnetic resonance imaging, were normal. Lumbar puncture revealed normal opening pressure. Ocular ultrasonography showed bilateral optic nerve enlargement. DESIGN: Interventional case report and literature review. RESULTS: The presumptive diagnosis of leukemic infiltration of the optic nerves was made, and urgent radiotherapy, intrathecal methotrexate, and intravenous daunorubicin were instituted. Visual acuity improved to hand motions in the right eye. CONCLUSIONS: Acute lymphocytic leukemia can rarely present in adults as visual changes due to leukemic optic nerve infiltration. Radiation treatment should be considered as an urgent treatment modality for this rare condition.

Baculoviral IAP repeat-containing-4 protects optic nerve axons in a rat glaucoma model.

Gene therapy represents an attractive approach for the treatment of eye diseases such as glaucoma. Ocular administration of viral vectors produces localized retinal gene expression with reduced risks of side effects reported with systemic administration of viral vectors. Recombinant adeno-associated viral (AAV) vectors have proven effective in producing long-term retinal gene expression, due to stable integration of DNA into the genome and lack of host immune response to the virus. Recently developed AAV constructs using the chicken beta-actin (CBA) promoter drive highly efficient transgene expression in retinal ganglion cells (RGCs), photoreceptors, and pigment epithelium. Rats were given unilateral intravitreal injections of AAV-CBA vector coding for human baculoviral IAP repeat-containing protein-4 (BIRC4), a potent caspase inhibitor. Ocular hypertension was induced in the same eye by sclerosis of aqueous humor outflow channels. After chronic exposure to elevated intraocular pressure, we performed optic nerve axon counts to determine the neuroprotective effects of retinal BIRC4 expression, and compared axon survival with vector and balanced salt solution control groups. Gene therapy delivering BIRC4 significantly promoted optic nerve axon survival in a chronic ocular hypertensive model of rat glaucoma. Blocking RGC apoptosis with caspase inhibitors represents a promising approach for treatment of human glaucoma.

Caspase activation and amyloid precursor protein cleavage in rat ocular hypertension.

PURPOSE: Retinal ganglion cell (RGC) death in glaucoma involves apoptosis. Activation of caspases and abnormal processing of amyloid precursor protein (APP) are important events in other chronic neurodegenerations, such as Alzheimer's disease (AD). The retinal expression and activation of caspases and the patterns of caspase-3-mediated APP processing in ocular hypertensive models of rat glaucoma were investigated. METHODS: RGC death was produced in one eye by chronic exposure to increased intraocular pressure (IOP) or by optic nerve transection. Elevated IOP was produced by obstruction of aqueous humor outflow with laser coagulation or limbal hypertonic saline injection. Caspase activity and APP processing in the retina were examined by RNase protection assay (RPA), immunocytochemistry, immunoblot assay, and colorimetric assay. RESULTS: RPA revealed elevations of caspase-3 mRNA, as well as other apoptosis-related mRNAs. Immunocytochemistry showed caspase-3 activation in RGCs damaged by ocular hypertension. The generation of the caspase-3-mediated APP cleavage product (DeltaC-APP) was also increased in ocular hypertensive RGCs. Western immunoblot assay and colorimetry revealed significantly more activated caspase-3 in ocular hypertensive retinas than in control retinas. The activated form of caspase-8, an initiator caspase, and amyloid-beta, a product of APP proteolysis and a component of senile plaques in AD, were detected in RGCs by immunohistochemistry significantly more often in ocular hypertensive than in control retinas. The amounts of full-length APP were reduced and amyloid-beta-containing fragments were increased in ocular hypertensive retinas by Western immunoblot assay. CONCLUSIONS: Rat RGCs subjected to chronic ocular hypertension demonstrate caspase activation and abnormal processing of APP, which may contribute to the pathophysiology of glaucoma.