The pathophysiology and treatment of glaucoma: a review

IMPORTANCE

Glaucoma is a worldwide leading cause of irreversible vision loss. Because it may be asymptomatic until a relatively late stage, diagnosis is frequently delayed. A general understanding of the disease pathophysiology, diagnosis, and treatment may assist primary care physicians in referring high-risk patients for comprehensive ophthalmologic examination and in more actively participating in the care of patients affected by this condition.

OBJECTIVE

To describe current evidence regarding the pathophysiology and treatment of open-angle glaucoma and angle-closure glaucoma.

EVIDENCE REVIEW

A literature search was conducted using MEDLINE, the Cochrane Library, and manuscript references for studies published in English between January 2000 and September 2013 on the topics open-angle glaucoma and angle-closure glaucoma. From the 4334 abstracts screened, 210 articles were selected that contained information on pathophysiology and treatment with relevance to primary care physicians.

FINDINGS

The glaucomas are a group of progressive optic neuropathies characterized by degeneration of retinal ganglion cells and resulting changes in the optic nerve head. Loss of ganglion cells is related to the level of intraocular pressure, but other factors may also play a role. Reduction of intraocular pressure is the only proven method to treat the disease. Although treatment is usually initiated with ocular hypotensive drops, laser trabeculoplasty and surgery may also be used to slow disease progression.

CONCLUSIONS AND RELEVANCE

Primary care physicians can play an important role in the diagnosis of glaucoma by referring patients with positive family history or with suspicious optic nerve head findings for complete ophthalmologic examination. They can improve treatment outcomes by reinforcing the importance of medication adherence and persistence and by recognizing adverse reactions from glaucoma medications and surgeries.

Primary open-angle glaucoma

Primary open-angle glaucoma is a progressive optic neuropathy and, perhaps, the most common form of glaucoma. Because the disease is treatable, and because the visual impairment caused by glaucoma is irreversible, early detection is essential. Early diagnosis depends on examination of the optic disc, retinal nerve fibre layer, and visual field. New imaging and psychophysical tests can improve both detection and monitoring of the progression of the disease. Recently completed long-term clinical trials provide convincing evidence that lowering intraocular pressure prevents progression at both the early and late stages of the disease. The degree of protection is related to the degree to which intraocular pressure is lowered. Improvements in therapy consist of more effective and better-tolerated drugs to lower intraocular pressure, and more effective surgical procedures. New treatments to directly treat and protect the retinal ganglion cells that are damaged in glaucoma are also in development.

Retinal ganglion cell atrophy correlated with automated perimetry in human eyes with glaucoma

We measured the number and size of retinal ganglion cells from six human eyes with glaucoma. In each, the histologic findings were correlated with visual field results. Five age-matched normal eyes were studied for comparison. In general, there were fewer remaining large ganglion cells in retinal areas with atrophy. In the perifoveal area, however, no consistent pattern of cell loss by size was found. Our estimates suggest that visual field sensitivity in automated testing begins to decline soon after the initial loss of ganglion cells. Throughout the central 30 degrees of the retina, 20% of the normal number of cells were gone in locations with a 5-dB sensitivity loss, and 40% cell loss corresponded to a 10-dB decrease. There were some remaining ganglion cells in areas that had 0-dB sensitivity in the field test.

Morphologic changes in the lamina cribrosa correlated with neural loss in open-angle glaucoma

We divided 25 glaucomatous human eyes into three groups representing mild (Group 1, seven eyes), moderate (Group 2, 11 eyes), and severe (Group 3, six eyes) optic nerve damage, based on visual field testing or remaining number of optic nerve fibers. The optic nerve head of each eye was examined by scanning electron microscopy. Compression of the successive lamina cribrosa sheets was the earliest detected abnormality, occurring in some eyes before the detection of visual field loss. Backward bowing of the entire lamina cribrosa was a later change and involved its upper and lower poles more than the mid-nerve head. The diameter of the scleral opening at the level of Bruch's membrane did not enlarge in these adult glaucomatous eyes. Mechanical compression of the nerve head occurred early enough to be considered a primary pathogenetic event in glaucomatous damage.

Trabecular meshwork cellularity in primary open-angle glaucoma and nonglaucomatous normals

The trabecular meshwork cellularity (cells/unit tissue area) was compared in patients with primary open-angle glaucoma (POAG) with that of nonglaucomatous (NG) individuals. The NG specimens (n = 69) include specimens from the prenatal period (n = 14) as well as the postnatal period to age 98 years (n = 55). The glaucoma specimens (n = 49) covered a wide-range of ages (23-80 years) and were obtained at trabeculectomy (n = 31) or at autopsy (n = 18). Our results show that the trabecular cellularity in NG specimens decreases most rapidly and in a nonlinear manner in the late fetal period and for the first few years of postnatal life. This rapid decline in cellularity then slows down to proceed in a nearly linear manner for the remainder of the 98 years of life studied. The meshworks from patients with POAG have a lower cellularity than normals over the wide range of ages examined, but both types of specimens undergo similar declines in cellularity with age. Thus, the age-cellularity curves for both the NG and POAG specimens are parallel to each other. The loss of cells occurs in a gradient-like manner with the inner tissues being most affected and the outermost tissues least affected. A variety of statistical tests show that these changes in cellularity are highly significant and specific. These findings are compared to the loss of endothelial cells in the cornea and they are discussed in relation to the important clinical characteristics of POAG.

Pseudoexfoliation syndrome for the comprehensive ophthalmologist. Intraocular and systemic manifestations

BACKGROUND

Renewed interest in pseudoexfoliation syndrome (PEX) may be attributed to an increased awareness of many clinical risks not only for open-angle glaucoma and its recent recognition as a generalized disorder. This review summarizes the range of intraocular and extraocular manifestations. Involvement of all tissues of the anterior segment of the eye results in a spectrum of intraocular complications that have management implication for all practicing ophthalmologists.

DESIGN

The study design was a review.

METHODS

Clinical diagnosis depends on biomicroscopy, biocytology, and laser-tyndallometry. Laboratory research methods range from light and electron microscopy, to immunohistochemical and molecular biologic approaches.

OBSERVATIONS

Clinical-histopathologic correlations focus on the involvement of lens (PEX-phacopathy), zonular apparatus (zonulopathy), ciliary body (cyclopathy), iris (iridopathy), trabecular meshwork (trabeculopathy), and cornea (corneal endotheliopathy) leading to the following complications: (1) open-angle glaucoma as well as angle-closure glaucoma due to pupillary and ciliary block; (2) phacodonesis, lens dislocation, and increased incidence of vitreous loss in extracapsular cataract surgery caused by alterations of the zonular apparatus and its insertion into the ciliary body and lens; (3) blood-aqueous barrier breakdown (pseudouveitis), anterior chamber hypoxia, iris stromal hemorrhage, pigment epithelial melanin dispersion, poor or asymmetric pupillary dilatation, and formation of posterior synechiae due to involvement of all cell populations of the iris; and (4) early diffuse corneal endothelial decompensation explained by a damaged and numerically reduced endothelium.

CONCLUSIONS

In view of the multitude of clinical complications, PEX is of relevance to comprehensive ophthalmologists, including specialists in glaucoma, cataract, cornea, neuro-ophthalmology, and retina. Special attention to the risks associated with PEX is advised before, during, and after surgery.

The effect of age on the nerve fiber population of the human optic nerve

Nerve fiber counts of 16 normal human optic nerves from subjects aged 3.5 to 82 years showed a significant effect of age (P = .0207). The delay between death or enucleation and fixation also significantly affected the result (P = .0078). The mean (+/- S.E.M.) count for the 16 nerves was 1,244,005 +/- 20,033 fibers, giving a 99% confidence level between 1,192,400 and 1,295,610 fibers.

Human glaucoma and neural degeneration in intracranial optic nerve, lateral geniculate nucleus, and visual cortex

The pathology of glaucoma has been extensively studied at the level of the retina and optic nerve head. Here the first clinicopathological case of human glaucoma is reported demonstrating degenerative changes in the brain involving the intracranial optic nerve, lateral geniculate nucleus, and visual cortex. Pathological evidence of neural degeneration in this patient is correlated with clinical, optic nerve head, visual field, and neuroradiology findings. Neuropathology in the glaucoma brain is compared to age matched controls. In the presence of advanced human glaucoma with 50% visual field loss, neural damage is evident in multiple vision stations within the brain.

Common variants near CAV1 and CAV2 are associated with primary open-angle glaucoma

We conducted a genome-wide association study for primary open-angle glaucoma (POAG) in 1,263 affected individuals (cases) and 34,877 controls from Iceland. We identified a common sequence variant at 7q31 (rs4236601[A], odds ratio (OR) = 1.36, P = 5.0 × 10⁻¹⁰). We then replicated the association in sample sets of 2,175 POAG cases and 2,064 controls from Sweden, the UK and Australia (combined OR = 1.18, P = 0.0015) and in 299 POAG cases and 580 unaffected controls from Hong Kong and Shantou, China (combined OR = 5.42, P = 0.0021). The risk variant identified here is located close to CAV1 and CAV2, both of which are expressed in the trabecular meshwork and retinal ganglion cells that are involved in the pathogenesis of POAG.

TUNEL-positive ganglion cells in human primary open-angle glaucoma

OBJECTIVE

To determine whether retinal ganglion cell death in primary open-angle glaucoma occurs by apoptosis.

METHODS

Eighteen eyes of 17 subjects with documented primary open-angle glaucoma were compared with 21 control eyes that were group matched for age, race, and sex. Staging of glaucoma severity was performed by histologic optic nerve evaluation. Fixed, paraffin-embedded retinal sections were assayed by the TUNEL (terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate (UTP)-biotin nick end-labeling) method to detect the internucleosomal DNA fragmentation that is characteristic of apoptosis.

RESULTS

A positive TUNEL reaction was observed among ganglion layer cells in 10 of 18 cases with glaucoma, compared with 1 of 11 control cases without confounding systemic disease (5 control eyes were excluded owing to artifactual staining and 4 eyes had confounding systemic disease). Sections containing more than 250,000 cells in the ganglion cell layer were examined in cases and controls. The frequency of TUNEL-positive cells in the ganglion cell layer in cases with glaucoma was 1.76 per 10,000, or 15.2 times greater than the control frequency from individuals without confounding disease (P < .001; 95% CI, 2.46-623). Eyes without glaucoma from subjects with diabetes and amyotrophic lateral sclerosis showed more positive cells than other controls.

CONCLUSION

Apoptosis seems to be a mechanism of cell death in human eyes with primary open-angle glaucoma.

Mechanisms of optic nerve damage in primary open angle glaucoma

Several mechanisms have been postulated to explain the optic nerve damage that occurs in primary open angle glaucoma (POAG). No single mechanism can adequately explain the great variations in susceptibility to damage and the patterns of damage seen in this syndrome. The etiology of POAG is likely to be multifactorial. Mechanical, vascular and other factors may influence individual susceptibility to optic nerve damage. An enhanced understanding of the nature of the optic nerve damage in POAG and improved methods of study may result in earlier diagnosis or may allow us to distinguish among different pathological processes all currently grouped under the diagnosis of POAG. As we gain a better understanding of the neuropharmacology and cellular biology of injury and repair of the visual system we will undoubtedly refine the concepts of glaucomatous optic neuropathy.

Scanning laser polarimetry to measure the nerve fiber layer of normal and glaucomatous eyes

PURPOSE

To determine whether retardation (change in polarization) measurements of healthy subjects and glaucoma patients obtained by using a confocal scanning laser polarimeter correspond to known properties of the nerve fiber layer.

METHODS

A polarimeter, an optical device used to measure the change in linear polarization of light (retardation), was interfaced with a scanning laser ophthalmoscope to obtain retardation data at 65,536 locations (256 x 256 pixels) in a study of normal subjects and patients with primary open-angle glaucoma. To validate the instrument, we compared our measurements with known properties of the human retinal nerve fiber layer in 105 normal subjects. Additionally, we compared retardation measurements in eyes of 64 normal subjects and 64 age-matched glaucoma patients treated in a referral practice.

RESULTS

In normal eyes, mean (+/- S.D.) peripapillary retardation was highest in the superior and inferior arcuate regions and lowest in the temporal and nasal regions, 12.0 +/- 1.9, 13.1 +/- 2.0, 7.0 +/- 1.8, and 7.0 +/- 1.6 degrees, respectively. Retardation decreased toward the periphery and was lower over blood vessels. In normal eyes, retardation decreased with increasing age in the superior and inferior regions. Mean retardation was statistically significantly higher among normal eyes than glaucoma eyes in the inferior and superior regions but not in the temporal or nasal areas.

CONCLUSIONS

Scanning laser polarimetry provides quantitative measurements that correspond to known properties of the retinal nerve fiber layer in normal and glaucomatous eyes.

Distribution of central corneal thickness and its association with intraocular pressure: The Rotterdam Study

PURPOSE

To perform a cross-sectional study on the distribution of central corneal thickness and its association with intraocular pressure in an elderly population.

METHODS

We measured central corneal thickness and intraocular pressure in 395 subjects (352 control subjects, 13 patients with ocular hypertension, and 30 patients with primary open-angle glaucoma) aged 55 years or more.

RESULTS

Mean central corneal thickness in the 352 control subjects was 537.4 microm (95% confidence interval [CI], 533.8 to 540.9 microm; range, 427 to 620 microm), with a maximal difference between eyes of 42 microm. There were no differences between sexes and no significant association with age. Linear regression analysis showed an increase of 0.19 mm Hg in intraocular pressure with each 10-microm increase in central corneal thickness (95% CI, 0.09 to 0.28 mm Hg). This association was similar in both eyes and in both sexes. The 13 patients with ocular hypertension had corneas a mean of 16.0 microm thicker (95% CI, -2.6 to +34.6 microm) compared with control subjects (P = .093); the 30 patients with primary open-angle glaucoma had corneas a mean of 21.5 microm thinner (95% CI, 8.8 to 34.1 microm) compared with control subjects (P = .001).

CONCLUSION

Mean central corneal thickness was similar to that found in clinical studies, was slightly higher in patients with ocular hypertension, and was significantly lower in patients with primary open-angle glaucoma. Intraocular pressure was positively related with central corneal thickness. Central corneal thickness may influence the division between normal and increased intraocular pressure at a simple cutoff point of 21 mm Hg.

Genetic risk of primary open-angle glaucoma. Population-based familial aggregation study

OBJECTIVES

To study familial aggregation of primary open-angle glaucoma in a general population and to determine the absolute and relative risks for first-degree relatives.

METHODS

First-degree relatives of patients with glaucoma (n = 48) and control subjects (n = 155) from the population-based Rotterdam Study underwent a standardized examination, including perimetry.

MAIN OUTCOME MEASURES

Intraocular pressure, vertical cup-disc ratio; and the presence of glaucoma, defined as a visual field defect with a cup-disc ratio of 0.7 or higher or asymmetry of 0.3 or higher between both eyes.

RESULTS

The prevalence of glaucoma was 10.4% in siblings of patients, 1.1% in offspring of patients, 0.7% in siblings of controls, and 0% in offspring of controls. Life-time risk of elevated intraocular pressure in relatives of patients vs relatives of controls was 42.5% vs 6.7%, of enlarged cup-disc ratio was 62.2% vs 16.6%, and of glaucoma was 22.0% vs 2.3%, yielding a risk ratio for glaucoma of 9.2 (95% confidence interval = 1.2-73.9). The population-attributable risk of glaucoma was 16.4%.

CONCLUSIONS

In a general population, relatives of patients with glaucoma have a strongly increased risk of glaucoma. Enlarged cup-disc ratio, not intraocular pressure, was the earliest and most prominent feature of familial aggregation. Further studies are needed to disentangle the genetic components of the increased familial risk.

Expert agreement in evaluating the optic disc for glaucoma

The authors studied intraobserver and interobserver agreement, under monoscopic and stereoscopic conditions, in estimating vertical cup-to-disc ratios and in assessing whether a disc had glaucomatous damage. Six glaucoma experts evaluated 75 optic disc photographs under both viewing conditions. The experts also re-evaluated 25 photographs. Intraobserver agreement in estimating vertical cup-to disc ratios was high (median weighted kappa, 0.79). Interobserver agreement in estimating vertical cup-to-disc ratios was moderate (stereoscopic median weighted kappa, 0.67); individual experts differed by as much as 0.2 disc diameters (DD) monoscopically and 0.16 DD stereoscopically. The observers estimated larger vertical cup-to-disc ratios when evaluating the same discs under stereoscopic conditions than under monoscopic conditions. Intraobserver agreement in assessing glaucomatous disc damage was substantial (median kappa, 0.76). Interobserver agreement in assessing glaucomatous damage was moderate (stereoscopic median kappa, 0.50). This study confirms the ability of experts to reliably evaluate the optic disc within themselves and emphasizes the need for developing standardized methods for interobserver evaluation of the optic disc in glaucoma.

Changes in anterior chamber angle width and depth after intraocular lens implantation in eyes with glaucoma

OBJECTIVE

To examine the changes in anterior chamber angle width and depth induced by intraocular lens (IOL) implantation in eyes with angle-closure glaucoma (ACG), in eyes with open-angle glaucoma (OAG), and in eyes with no evidence of glaucoma or ocular hypertension.

DESIGN

A comparative, nonrandomized, interventional study.

PARTICIPANTS

Seventy-seven eyes with ACG, 73 eyes with OAG, and 74 control eyes undergoing cataract extraction and IOL implantation.

INTERVENTION

All eyes underwent phacoemulsification and soft acrylic IOL implantation.

MAIN OUTCOME MEASURES

The angle width and depth of the anterior chamber were measured using a Scheimpflug videophotography system before surgery, and at 1 week and at 1, 3, 6, 9, and 12 months after surgery.

RESULTS

Before surgery, the mean anterior chamber angle width and depth in the ACG group was less than that in either the OAG or control groups by approximately 10 degrees in angle width and 1.0 mm in depth (P < 0.0001). After cataract extraction and IOL implantation, the angle width and depth increased significantly in all three groups (P < 0.0001). Although the width and depth in the ACG group were still smaller than that in the other groups, the differences decreased to 2 degrees for angle width and 0.3 mm for depth. In addition, no significant differences were found in these values between the OAG and control groups before or after surgery. Furthermore, no significant changes were observed in the angle width or depth in any of the three groups throughout the postoperative observation period. As expected, the mean preoperative intraocular pressure (IOP) in the ACG and OAG groups was higher than that in the control group. After cataract surgery, however, the mean IOP decreased significantly and was almost the same in all three groups at 1, 6, and 12 months after surgery.

CONCLUSIONS

The width and depth of the anterior chamber angle in eyes with ACG increased significantly after cataract extraction and IOL implantation and became similar to that in eyes with OAG and that in normal eyes, which may lead to the decrease in IOP seen in the postoperative period. No significant changes were observed in angle width and depth in any of the three groups after surgery.

The National Survey of Trabeculectomy. III. Early and late complications

PURPOSE

There is a considerable body of literature relating to trabeculectomy, however there are no data representative of the national experience of trabeculectomy in the United Kingdom (UK). The Department of Health funded a national survey of trabeculectomy to establish current practice patterns and the outcome of trabeculectomy in the National Health Service (NHS). In this paper we present the reported complications of first-time trabeculectomy from a nationally representative cohort of patients with chronic open angle glaucoma.

METHODS

Cross-sectional study of consultant ophthalmologists performing trabeculectomy in the NHS. Participants recruited their four most recent consecutive first-time trabeculectomy cases with chronic open angle glaucoma according to study eligibility criteria and data were collected by self-administered questionnaire.

FOLLOW-UP

one year post-trabeculectomy.

MAIN OUTCOME MEASURES

occurrence of early and late complications.

RESULTS

Clinical outcome data were available for 1240 (85.3%) of cases. Early complications were reported in 578 (46.6%) cases and late complications in 512 (42.3%) cases. Some cases had more than one complication. The most frequent early complications were hyphaema (n = 304, 24.6%), shallow anterior chamber (n = 296, 23.9%), hypotony (n = 296, 24.3%), wound leak (n = 216, 17.8%) and choroidal detachment (n = 175, 14.1%). The most frequent late complications were cataract (n = 251, 20.2%), visual loss (n = 230, 18.8%) and encapsulated bleb (n = 42, 3.4%). The occurrence of most complications was not associated with a consultant's specialist interest, level of activity, type of hospital or region. Encapsulated bleb was reported more frequently in a university hospital setting.

CONCLUSIONS

The complication rates reported in this paper represent the national experience of first-time trabeculectomy for open angle glaucoma in the UK. These are similar to previous published studies and highlight in particular, the impact of trabeculectomy on visual acuity in the first year following surgery. This survey provides valid and clinically relevant data on the complications of trabeculectomy for the production of guidelines and standards for audit at regional, local and individual level.

Conjunctival Proinflammatory and Proapoptotic Effects of Latanoprost and Preserved and Unpreserved Timolol: An Ex Vivo and In Vitro Study

PURPOSE

To compare the toxicity of latanoprost and preserved and unpreserved timolol on conjunctival cells. Expression of inflammatory markers and MUC5AC-related mucin production were evaluated by impression cytology in a case-control ex vivo study. The proapoptotic effect of the same drugs was also evaluated in vitro in a conjunctival cell line and compared with that of benzalkonium chloride (BAC).

METHODS

Impression cytology (IC) specimens were obtained from a series of normal subjects and from patients with glaucoma treated for at least 1 year with latanoprost eye drops or preserved or unpreserved timolol. All groups were comparable in age and duration of treatment. Expression of HLA-DR, intercellular adhesion molecule (ICAM)-1, and mucin was evaluated in a masked manner by flow cytometry. For the in vitro study, a human conjunctiva-derived cell line was treated with 0.02% BAC-containing latanoprost or timolol, unpreserved timolol, or 0.02% BAC alone for 15 minutes, followed or not by 4 or 24 hours of cell recovery in normal medium. Cell viability and chromatin condensation were evaluated using microplate cold light cytofluorometry with the neutral red and the Hoechst 33342 tests, respectively. The Hoechst-neutral red ratio was defined for the apoptosis assay, and cytoskeleton changes were assessed by confocal microscopy.

RESULTS

No difference was found between normal eyes and those receiving unpreserved timolol. Preserved latanoprost and timolol significantly increased the inflammatory marker expression and decreased MUC5AC expression, but to a significantly higher extent in the preserved timolol group compared with latanoprost. In vitro, 0.02% BAC-containing timolol and latanoprost triggered conjunctival cell apoptosis-however, to a significantly lesser extent than did 0.02% BAC alone. Unpreserved timolol did not cause any cell toxicity.

CONCLUSIONS

These ex vivo and in vitro studies demonstrate that BAC-containing latanoprost and timolol exhibit higher proinflammatory and proapoptotic effects on conjunctival cells than does unpreserved timolol. Latanoprost caused less toxicity, however, than preserved timolol, and both drugs were less toxic than BAC alone. These results suggest a potential protective effect of the prostaglandin analogue and to a lesser extent of timolol against the toxicity of BAC in conjunctival cells.

The retinal nerve fiber layer thickness in ocular hypertensive, normal, and glaucomatous eyes with optical coherence tomography

OBJECTIVE

To quantitatively assess and compare the thickness of the retinal nerve fiber layer (RNFL) in ocular hypertensive eyes with normal and glaucomatous eyes using the Optical Coherence Tomograph (OCT 2000, software version A4X1; Humphrey Instruments, San Leandro, Calif).

METHODS

The mean RNFL thickness of ocular hypertensive (n = 28) eyes was compared with age-matched normal (n = 30) and glaucomatous (n = 29) eyes. Subject eyes were classified into diagnostic groups based on intraocular pressure, stereoscopic disc photographs, and standard automated perimetry. Three circular scans were obtained for each eye at a diameter of 3.4 mm around the optic disc. In each eye, average RNFL thickness measurements were obtained in temporal, superior, nasal, and inferior quadrants. A single index of average RNFL thickness throughout 360 degrees also was obtained.

RESULTS

Mean (95% confidence interval) RNFL was significantly thinner in ocular hypertensive eyes than in normal eyes, 72.8 microm (66.4-78.1 microm) and 85.8 microm (80.2-91.7 microm), respectively. More specifically, RNFL was significantly thinner in ocular hypertensive eyes than in normal eyes in the inferior quadrant, 84.8 microm (75.6-94.0 microm) vs 107.6 microm (99.3-115.9 microm); and in the nasal quadrant, 44.1 microm (37.5-51.7 microm) vs 61.8 microm (53.0-65.6 microm). Retinal nerve fiber layer was significantly thinner in glaucomatous eyes than in ocular hypertensive and normal eyes throughout 360 degrees and in all quadrants.

CONCLUSION

These findings suggest that quantitative differences in RNFL thickness exist between age-matched ocular hypertensive, normal, and glaucomatous eyes.

Microglia in the optic nerve head and the region of parapapillary chorioretinal atrophy in glaucoma

BACKGROUND

Microglia, the macrophages and immune surveillance cells of the central nervous system, are quiescent normally but become activated in injured neural tissue. We have determined the distribution and potential participation of microglia in glaucomatous optic nerve degeneration.

METHODS

Microglia were localized by immunohistochemistry on paraffin sections of age-matched normal and glaucomatous human eyes obtained within 24 hours after death. Monoclonal and polyclonal antibodies that recognize specific epitopes on microglia and other cell types were localized by immunoperoxidase and immunofluorescence.

RESULTS

Stellate cells with thin, ramified processes, positive for HLA-DR and CD45 but negative for glial fibrillary acid protein, were identified as quiescent microglia. These cells were found throughout the normal optic nerve head in the walls of large blood vessels and surrounding capillaries in glial columns and cribriform plates. In glaucomatous eyes with moderate and severe optic nerve head damage, microglia were present as clusters of large ameboid, activated cells in the compressed lamina cribrosa and as formations of concentric circles surrounding blood vessels. In the parapapillary chorioretinal region of glaucomatous optic nerve heads, large, activated microglia were present as single cells or clusters on the termination of the Bruch's membrane. In addition, along the optic nerve/choriocapillaris-scleral interface, activated microglia appeared to form linear arrays near the choriocapillaris vessels. These cells were parenchymal and not in close association with the vasculature.

CONCLUSIONS

In glaucoma, microglia in the optic nerve head become activated and redistributed. Enlarged, activated microglia appear in the parapapillary chorioretinal region, perhaps due to migration from the disorganized prelaminar and laminar tissue. Strategically positioned microglia may also serve a neuroprotective function in relation to a damaged blood-retinal barrier. The activity of microglia in the parapapillary chorioretinal region in glaucoma may be responsible for some of the biomicroscopic and histological changes that are associated with parapapillary chorioretinal atrophy.

Matrix metalloproteinases and tumor necrosis factor alpha in glaucomatous optic nerve head

OBJECTIVE

To study expression and location of matrix metalloproteinases (MMPs) and tumor necrosis factor alpha (TNF-alpha) in glaucomatous optic nerve heads, which are known to be secreted in response to a variety of neuronal injury.

METHODS

Four postmortem eyes from patients with primary open-angle glaucoma, 7 eyes from patients with normal-pressure glaucoma, and 4 eyes from age-matched normal donors were studied by immunohistochemistry. The sections of the optic nerve heads were examined after immunostaining with antibodies to MMPs (MMP-1, MMP-2, and MMP-3), TNF-alpha, or TNF-alpha receptor 1.

RESULTS

The intensity of the immunostaining and the number of stained cells for MMPs, TNF-alpha, or TNF-alpha receptor 1 were greater in the glaucomatous optic nerve heads, particularly in eyes with normal-pressure glaucoma compared with age-matched controls. Positive immunostaining was observed in all regions of the glaucomatous optic nerve heads, but most prominently in the postlaminar region. Immunostaining was observed mainly in glial cells and their processes around the axons and blood vessels and in pial septae.

CONCLUSION

There is increased immunostaining for MMPs, TNF-alpha and TNF-alpha receptor 1 in the glaucomatous optic nerve head, which suggests increased expression of these proteins in glaucoma and thereby implies a role in the tissue remodeling and degenerative changes seen in glaucomatous optic nerve heads.

CLINICAL RELEVANCE

The MMPs and TNF-alpha may be components of astroglial activation that occurs in glaucomatous optic nerve heads. The biological alterations in the expression of these proteins may play a role in the progression of glaucomatous optic neuropathy.

Targeted Disruption of the Myocilin Gene (Myoc) Suggests that Human Glaucoma-Causing Mutations Are Gain of Function

Glaucoma is a heterogeneous eye disease and a major cause of blindness worldwide. Recently, primary open angle glaucoma (POAG)-associated mutations have been found in the trabecular meshwork inducible glucocorticoid response gene (TIGR), also known as the myocilin gene (MYOC), at the GLC1A locus on chromosome 1q21-q31. These mutations occurred in a subset of patients with juvenile- and adult-onset POAG and exhibited autosomal dominant inheritance. Ocular expression and its involvement in POAG suggest that TIGR/MYOC may have a role(s) in regulating intraocular pressure (IOP). Here, we report the generation and analysis of mice heterozygous and homozygous for a targeted null mutation in Myoc. Our study shows that Myoc mutant mice are both viable and fertile. Our in vivo findings further demonstrate that Myoc is not required for normal IOP or normal ocular morphology. The lack of a discernable phenotype in both Myoc-heterozygous and Myoc-null mice suggests that haploinsufficiency is not a critical mechanism for POAG in individuals with mutations in MYOC. Instead, disease-causing mutations in humans likely act by gain of function.

Glaucomatous outflow pathway and oxidative stress

Oxidative free radicals and reactive oxygen species (ROS) are able to affect the cellularity of the human trabecular meshwork (HTM). These findings suggest that intraocular pressure increase, which characterises most glaucomas, is related to oxidative degenerative processes affecting the HTM and specifically its endothelial cells. Much evidence indicates that in this region ROS play a fundamental pathogenic role by reducing local antioxidant activities, inducing outflow resistance and exacerbating the activities of superoxide dismutase and glutathione peroxidase in glaucomatous eyes. Furthermore, hydrogen peroxide induces rearrangement of HTM cells and compromises their integrity. Glaucomatous subjects might have a genetic predisposition rendering them more susceptible to ROS-induced damage. A fairly significant correlation between oxidative DNA damage in the HTM and intraocular pressure increase and visual field defects in glaucomatous patients has been demonstrated. Thus, oxidative stress may play a significant role during glaucoma course initially damaging HTM cells, then contributing to the alteration of the homeostasis between NO and endothelins, and finally through its possible involvement in ganglional cell death. On the whole, these findings support the hypothesis that oxidative damage is an important step in the pathogenesis of primary open-angle glaucoma, and might be a relevant target for both prevention and therapy.

Progression of disc and field damage in early glaucoma

To assess the temporal relationship between visual field progression and optic disc deterioration in early glaucoma, we studied 15 patients with unilateral visual field loss from primary open angle glaucoma. Planimetric optic disc measurements were compared with automated static threshold perimetry during a mean follow-up of 6.1 years. Eight (53%) of 15 eyes with an initially normal visual field showed progression of the disc; six of these eyes did not develop field abnormalities. The mean rates of rim-area loss were 1.7%/y in eyes with initially normal fields and 2.1%/y in eyes with initial field loss. The mean rate of visual field deterioration (change in corrected loss variance) was lower in the eyes with an initially normal field (0.3 dB2/y) than in eyes with initial field loss (3.6 dB2/y; P = .016). This longitudinal study documents progressive disc damage prior to field loss in early glaucoma.

Ocular surface alteration after long-term treatment with an antiglaucomatous drug

BACKGROUND

This study was undertaken to see whether long-term locally applied ocular medications produced any alterations in the ocular surface, and, in particular, whether it caused damage to the mucus layer of the tear film.

METHODS

The authors studied the ocular surface of 40 control subjects (group 1), 21 patients (group 2) chronically treated with a commercial preparation of 0.5% timolol maleate, and 20 previously untreated glaucomatous patients (group 3) in need of treatment with the same drug. Parameters studied were Schirmer's test, lacrimal meniscus height, break-up time, fluorescein and rose Bengal stains, conjunctival impression cytology, mucus staining, and the ferning test.

RESULTS

Patients in groups 2 and 3 showed a significant decrease (P less than 0.001) in the number of normal Schirmer's and break-up time tests. All had positive vital stains. Results showed a significant decrease (P less than 0.001) in goblet-cell density, mucus granules, and reticular sheets, and an increase (P less than 0.001) in pathologic crystallization patterns.

CONCLUSION

These results demonstrate that chronic application of a commercial preparation of timolol maleate damaged the ocular surface, especially the mucus layer of the tear film.