Frequency of sustained glaucomatous-type visual field loss and associated optic nerve cupping in Beaver Dam, Wisconsin

Pattern Electroretinography and Visual Evoked Potentials Provide Clinical Evidence of CNS Modulation of High- and Low-Contrast VEP Latency in Glaucoma

Purpose

Both pattern electroretinography (PERG) and visual evoked potentials (VEP) can be performed using low- (15%; Lc) and high- (85%; Hc) contrast gratings that may preferentially stimulate the magno- and parvocellular pathways. We observed that among glaucomatous patients showing only one VEP latency deficit per eye, there appeared to be a very strong tendency for an Hc delay in one eye and an Lc delay in the other.

Methods

Diopsys NOVA-LX system was used to measure VEP Hc and Lc latency among a clinical glaucoma population to find all individuals with either a single Hc or Lc latency abnormality in each eye (group 1), or with greater than 0 and less than 4 Hc or Lc VEP latency abnormalities in the two eyes (group 2) to determine whether a significant inverse correlation existed for these values in either group. Hc and Lc PERG data were also evaluated to assess associated retinal ganglion cell responses.

Results

A strong inverse correlation (P = 0.0000003) was observed between the Hc and Lc VEP latency values among the 64 eyes in group 1. Group 2 provided a comparable result (n = 143; 286 eyes; P = 0.0005). PERG (n = 81; 162 eyes) also showed strong bilateral symmetry for magnitude values (P < 0.0001 for both Lc and Hc in groups 1 and 2).

Conclusions

Bilateral retention of both low-resolution/high-speed and high-resolution/low-speed function may persist with both eyes open despite symmetrically pathologic retinal ganglion cell PERG waveform asynchrony for Hc and Lc stimuli in the paired eyes.

Translational Relevance

Clinical electrophysiology strongly suggests binocular compensation for dynamic dysfunction operates under central nervous system (CNS) control in glaucoma.

Making Basic Science Studies in Glaucoma More Clinically Relevant: The Need for a Consensus

Glaucoma is a chronic, progressive, and debilitating optic neuropathy that causes retinal damage and visual defects. The pathophysiologic mechanisms of glaucoma remain ill-defined, and there is an indisputable need for contributions from basic science researchers in defining pathways for translational research. However, glaucoma researchers today face significant challenges due to the lack of a map of integrated pathways from bench to bedside and the lack of consensus statements to guide in choosing the right research questions, techniques, and model systems. Here, we present the case for the development of such maps and consensus statements, which are critical for faster development of the most efficacious glaucoma therapy. We underscore that interrogating the preclinical path of both successful and unsuccessful clinical programs is essential to defining future research. One aspect of this is evaluation of available preclinical research tools. To begin this process, we highlight the utility of currently available animal models for glaucoma and emphasize that there is a particular need for models of glaucoma with normal intraocular pressure. In addition, we outline a series of discoveries from cell-based, animal, and translational research that begin to reveal a map of glaucoma from cell biology to physiology to disease pathology. Completion of these maps requires input and consensus from the global glaucoma research community. This article sets the stage by outlining various approaches to such a consensus. Together, these efforts will help accelerate basic science research, leading to discoveries with significant clinical impact for people with glaucoma.

A biomechanical paradigm for axonal insult within the optic nerve head in aging and glaucoma

This article is dedicated to Rosario Hernandez for her warm support of my own work and her genuine enthusiasm for the work of her colleagues throughout her career. I first met Rosario as a research fellow in Harry Quigley's laboratory between 1991 and 1993. Along with Harry, John Morrison, Elaine Johnson, Abe Clark, Colm O'Brien and many others, Rosario's work has provided lamina cribrosa astrocyte cellular mechanisms that are biomechanically plausible and in so doing provided credibility to early notions of the optic nerve head (ONH) as a biomechanical structure. We owe a large intellectual debt to Rosario for her dogged persistence in the characterization of the ONH astrocyte and lamina cribrosacyte in age and disease. Two questions run through her work and remain of central importance today. First, how do astrocytes respond to and alter the biomechanical environment of the ONH and the physiologic stresses created therein? Second, how do these physiologic demands on the astrocyte influence their ability to deliver the support to retinal ganglion cell axon transport and flow against the translaminar pressure gradient? The purpose of this article is to summarize what is known about the biomechanical determinants of retinal ganglion cell axon physiology within the ONH in the optic neuropathy of aging and Glaucoma. My goal is to provide a biomechanical framework for this discussion. This framework assumes that the ONH astrocytes and glia fundamentally support and influence both the lamina cribrosa extracellular matrix and retinal ganglion cell axon physiology. Rosario Hernandez was one of the first investigators to recognize the implications of this unique circumstance. Many of the ideas contained herein have been initially presented within or derived from her work (Hernandez, M.R., 2000. The optic nerve head in glaucoma: role of astrocytes in tissue remodeling. Prog Retin Eye Res. 19, 297-321.; Hernandez, M.R., Pena, J.D., 1997. The optic nerve head in glaucomatous optic neuropathy. Arch Ophthalmol. 115, 389-395.).

Premise and prediction-how optic nerve head biomechanics underlies the susceptibility and clinical behavior of the aged optic nerve head

We propose that age-related alterations in optic nerve head (ONH) biomechanics underlie the clinical behavior and increased susceptibility of the aged ONH to glaucomatous damage. The literature which suggests that the aged ONH is more susceptible to glaucomatous damage at all levels of intraocular pressure is reviewed. The relevant biomechanics of the aged ONH are discussed and a biomechanical explanation for why, on average, the stiffened peripapillary scleral and lamina cribrosa connective tissues of the aged eye should lead to a shallow (senile sclerotic) form of cupping is proposed. A logic for why age-related axon loss and the optic neuropathy of glaucoma in the aged eye may overlap is discussed. Finally, we argue for a need to characterize all forms of clinical cupping into prelaminar and laminar components so as to add precision to the discussion of clinical cupping which does not currently exist. Such characterization may lead to the early detection of ONH axonal and connective tissue pathology in ocular hypertension and eventually aid in the assessment of etiology in all forms of optic neuropathy including those that may be purely age-related.

Detection of undiagnosed glaucoma by eye health professionals

PURPOSE

To examine the clinical features of undiagnosed open-angle glaucoma (OAG) in people who have attended an eye care provider within the previous 12 months and to suggest strategies to assist in the early detection of glaucoma.

DESIGN

Population based cross-sectional study.

PARTICIPANTS

Permanent residents aged 40 years and older at recruitment during 1992 through 1996.

METHODS

A cluster-stratified random sample of 4744 participants from the urban and rural cohorts was studied. Structured standardized interviews and dilated ocular examinations were conducted in all eligible participants. Data on demographic characteristics, prior knowledge of eye disease, use of eye care services, intraocular pressures, cup-to-disc ratios, visual fields, and photography of optic discs were obtained. All suspected glaucoma cases were submitted to a panel of 6 ophthalmologists to determine glaucoma diagnosis.

MAIN OUTCOME MEASURES

Clinical features of participants seen by eye health professionals within the previous 12 months who have previously undiagnosed OAG, previously diagnosed OAG, and no glaucoma.

RESULTS

Thirty-five previously undiagnosed and 43 previously diagnosed participants had visited an optometrist or ophthalmologist or both in the previous 12 months. Age and gender were not significantly different between the undiagnosed and diagnosed glaucoma cases. After logistic regression, the type of eye professional seen (odds ratio [OR], 45.17; 95% confidence interval [95% CI], 5.89-346.17; P = 0.0002) and the presence of visual field defects (OR, 0.06; 95% CI, 0.01-0.69, P = 0.020) were the only statistically significant variables between the diagnosed and undiagnosed glaucoma groups.

CONCLUSIONS

Raised intraocular pressure should not be relied on as the only triggering factor in glaucoma investigations.

Patterns of glaucomatous visual field defects in an older population: the Blue Mountains Eye Study

This report aims to describe the frequency of different patterns of visual field loss in open-angle glaucoma (OAG). The Blue Mountains Eye Study examined 3654 persons (aged 49+) during 1992-1994. Humphrey supra-threshold visual fields were performed in 88.9%. Those classified as glaucoma suspects had 30-2 full-threshold fields (9.2%). Of OAG cases (n = 108) with field tests in both eyes (n = 97), unilateral defects were present in 49 (50.5%) and bilateral in 48 (49.5%). Advanced field loss was found in 16 (15.4%) subjects and in 22 (10.9%) eyes, with bilateral loss present in 6 (6.2%) cases. Of all eyes of OAG cases (n = 201), 49 (24.4%) had no defects, 52 (25.9%) upper, 61 (30.3%) lower, and 17 (8.5%) had combined upper and lower loss. Of the upper and lower cases (n = 113), the types of defects included nasal step (36), arcuate (26), nasal plus arcuate (26), and hemispherical defects (25). Of subjects with fields in at least one eye (n = 104), there was a similar proportion in the worse eye of upper defects (28.8%), lower (31.7%), and combined upper and lower (24.0%). Undiagnosed OAG was more frequent in unilateral (65.3%) than bilateral (34.7%) cases (P = 0.003). This study reports the pattern of typical glaucomatous field loss in an older Australian population.