Glaucomatous Nerve Research Articles

Retinal nerve fiber layer thickness measured with optical coherence tomography is related to visual function in glaucomatous eyes

Purpose To determine the relationship between areas of glaucomatous retinal nerve fiber layer thinning identified by optical coherence tomography and areas of decreased visual field sensitivity identified by standard automated perimetry in glaucomatous eyes. Design Retrospective observational case series. Partcipants Forty-three patients with glaucomatous optic neuropathy identified by optic disc stereo photographs and standard automated perimetry mean deviations >−8 dB were included. Methods Participants were imaged with optical coherence tomography within 6 months of reliable standard automated perimetry testing. Main outcome measures The location and number of optical coherence tomography clock hour retinal nerve fiber layer thickness measures outside normal limits were compared with the location and number of standard automated perimetry visual field zones outside normal limits. Further, the relationship between the deviation from normal optical coherence tomography–measured retinal nerve fiber layer thickness at each clock hour and the average pattern deviation in each visual field zone was examined by using linear regression ( R 2). Results The retinal nerve fiber layer areas most frequently outside normal limits were the inferior and inferior temporal regions. The least sensitive visual field zones were in the superior hemifield. Linear regression results ( R 2) showed that deviation from the normal retinal nerve fiber layer thickness at optical coherence tomography clock hour positions 6 o'clock, 7 o'clock, and 8 o'clock (inferior and inferior temporal) was best correlated with standard automated perimetry pattern deviation in visual field zones corresponding to the superior arcuate and nasal step regions ( R 2 range, 0.34–0.57). These associations were much stronger than those between clock hour position 6 o'clock and the visual field zone corresponding to the inferior nasal step region ( R 2 = 0.01). Conclusions Localized retinal nerve fiber layer thinning, measured by optical coherence tomography, is topographically related to decreased localized standard automated perimetry sensitivity in glaucoma patients.

Glaucomatous optic neuropathy: mechanisms of disease.

The optic neuropathy of glaucoma appears to be multifactorial in etiology. Both mechanical and vasogenic theories remain viable explanations for the observed nerve damage and the destructive effect of trophic withdrawal could be espoused by either theory. Each theory feeds into the final common pathway of cell death; even the immune system may kill cells in glaucoma by apoptosis. This knowledge has led to the hope that glaucomatous nerve damage can be curtailed or even prevented with the use of neuroprotective agents. Indeed, there are many intriguing new therapeutic possibilities on the horizon. Until evidence from clinical trials demonstrates the effectiveness of these agents however, control of IOP will remain the mainstay of treatment for glaucoma.

Medical backgrounders: glaucoma.

Glaucoma is a leading cause of irreversible blindness in the world. Currently, glaucoma is diagnosed as a progressive optic neuropathy with characteristic optic disc and nerve fiber layer damage, usually associated with loss of visual function. The intraocular pressure (IOP) is the most important risk factor for the disease, although a significant proportion of patients do not have elevated IOP. Other risk factors include older age, African descent, myopia and family history of the disease. The ophthalmoscopic examination of the optic disc is essential to identify the signs of glaucomatous optic neuropathy, such as increased cupping, neuroretinal rim thinning or optic disc hemorrhages. Glaucomatous visual field loss usually starts in the periphery, and loss of central vision does not occur until late in the course of the disease. Visual function is most commonly assessed by standard automated perimetry; however, as many as 50% of nerve fibers can be lost before the appearance of visual field defects in this test. Newer technologies have been developed to find more sensitive ways to detect early glaucoma using both functional (short-wavelength automated perimetry and frequency-doubling perimetry) and structural (scanning laser topography, optical coherence tomography and scanning laser polarimetry) measurements. The management of glaucoma is based on lowering the intraocular pressure to prevent further optic nerve damage. Currently, there are five major classes of medications that are used to lower the intraocular pressure: Beta-adrenergic antagonists, adrenergic agonists, parasympathomimetics, prostaglandin-like analogues and carbonic anhydrase inhibitors. The goal of therapy is to maintain adequate vision for patients during their lifetime, keeping in mind the possible adverse effects of the drugs. If additional lowering of IOP is indicated or if medication fails to sufficiently lower the IOP, laser trabeculoplasty is usually the next step. If IOP is still not adequately controlled, incisional glaucoma surgery is indicated. Neuroprotective agents, which directly protect the optic nerve in glaucoma, are being evaluated in clinical trials.

Slope analysis of the optic disc in eyes with ocular hypertension and early normal tension glaucoma by confocal scanning laser ophthalmoscope

AIMSTo determine whether quantitative differences in sector based slope can differentiate between eyes with ocular hypertension with and without glaucomatous disc changes and eyes with normal tension glaucoma with glaucomatous...

Evaluation ausgedehnter Gesichtsfelddefekte mittels computerassistierter kinetischer Perimetrie123

Conventional kinetic perimetry is of especial use in case of advanced scotoma. However, examiner dependency is a major drawback. Purpose of this study was to evaluate the clinical feasibility and intraindividual scatter of computer-assisted kinetic perimetry in monitoring advanced visual field defects of various origins. Examinations were carried out with the Tuebingen Computer Campimeter (background lumincance 10 cd/m2). In an initial session, the localization of the scotoma border is estimated with conventional manual kinetic perimetry. In the subsequent computer assisted kinetic mode, an individually adjusted set of vectors is designed. Each vector crosses the manually assessed visual field defect border almost perpendicularly, starting approximately 3 degrees within the scotoma. Each individual set of vectors can be stored and recalled for follow-up. Stimuli move along these vectors with identical characteristics as in manual kinetic perimetry. Stimulus presentations are repeated six times in a randomized order. Patients' responses are recorded and additionally corrected for mean individual reaction time. A "local kinetic threshold" (mean) and a related parameter for dispersion (standard deviation) are assessed. Four subjects with advanced visual field loss of various origin (retinitis pigmentosa, vigabatrin-associated visual field defect, glaucomatous nerve fibre layer defect, and postgeniculate visual pathway defect) participated in this study. Maximal difference between manual-kinetic and automated kinetic thresholds reaches from 1.7 degrees to 5 degrees. Local scatter (standard deviation) of kinetic threshold, assessed by computer-assisted perimetry, varies between 0.1 degree and 3.0 degrees. Computer assisted kinetic perimetry is a new, useful, examiner-independent, reliable method for effective evaluation and monitoring of advanced visual field loss.

Dopamine and intraocular pressure in critically ill patients.

A recently released dopamine-1 receptor agonist, fenoldopam, increases intraocular pressure (IOP) in both healthy volunteers and patients with chronic ocular hypertension. Dopamine, a potent agonist at both dopamine-1 and -2 receptors, is frequently infused in critically ill patients for its inotropic, renal vasodilatory, and natriuretic effects. The authors hypothesized that low doses of dopamine would significantly increase IOP. Patients in the intensive care unit who were currently receiving dopamine infusions of less than 5 microg x kg(-1) x min(-1) were studied After local ocular anesthesia was obtained, baseline IOP was measured in each eye with a hand-held tonometer. IOP was then determined after dopamine was discontinued. Twenty-three patients received a mean dopamine infusion of 2.6 +/- 0.2 microg x kg(-1) x min(-1). Twelve of the 23 patients were receiving mechanical ventilation during the study. Mean IOPs in nonventilated patients (n = 11) off dopamine were 13.1 +/- 0.9 mmHg (left eye) and 12.6 +/- 0.9 mmHg (right eye). Mean IOPs for the same patients receiving dopamine were significantly higher at 16.1 +/- 0.9 mmHg (left eye) and 15.9 +/- 1.1 mmHg (right eye). Mean IOPs in intubated patients (n = 12) off dopamine were 12.3 +/- 0.7 mmHg (left eye) and 12.5 +/- 1.2 mmHg (right eye). Mean IOPs for the same patients while receiving dopamine were significantly higher in intubated patients at 17.8 +/- 1.3 mmHg (left eye) and 17.3 +/- 1.3 mmHg (right eye). The average mean elevation in IOP in patients while receiving dopamine was significantly higher in intubated patients as compared with nonintubated patients (5.2 +/- 0.9 mmHg vs. 3.1 +/- 0.6 mmHg). Commonly used doses of dopamine are associated with increased IOP in critically ill patients. Although normal patients should be able to tolerate this elevation safely for several weeks, there may be a potential risk in patients with preexisting glaucomatous nerve damage or ocular hypertension, especially if they are sedated and mechanically ventilated.

Scanning laser polarimetry via intravitreal silicone oil.

To investigate whether scanning laser polarimetry, a promising new technique for early detection of glaucomatous nerve fiber loss, is a suitable method to measure retinal nerve fiber layer thickness in eyes with intravitreal silicone oil. Eleven eyes of 11 consecutive patients two days to 16 months after successful vitrectomy and intravitreal silicone oil injection and 12 eyes of 12 consecutive subjects, who never had any vitreoretinal surgery were examined using the GDx Nerve Fiber Analyzer. Three individual images were computed to a mean image using the software in each case. "Variance", a software-provided parameter, which represents the differences between the individual images used to calculate the mean image was higher in the "silicone oil" group (unpaired t test for different variances, p = 0.02). Good-quality mean images with a "Variance" value similar to that of the control eyes were obtained in seven of the 11 cases. Characteristic artifacts caused by intravitreal silicone oil were observed in five of the 11 cases. Successful scanning laser polarimetry is possible after vitrectomy and intravitreal silicone oil injection, and may help to monitor the retinal nerve fiber layer of these eyes in case of silicone oil induced glaucoma.

In memoriam: A. Edward Maumenee, Jr., MD 1913–1998

In memoriam: A. Edward Maumenee, Jr., MD 1913–1998

Acquired pits of the optic nerve in glaucoma: prevalence and associated visual field loss.

This study was performed to determine the prevalence of acquired pits of the optic nerve (APON) in glaucoma and the characteristics of associated visual field loss. Stereoscopic optic disc photos from 235 patients with a low-tension variety of primary open-angle glaucoma (LTG) and 251 primary open-angle glaucoma patients with intraocular pressures higher than 21 mmHg (HTG) were examined for the presence of typical APON as defined by a standard photograph (Fig 1). Associated visual field loss was evaluated with automated perimetry and patterns of field loss were identified. Out of a total of 486 patients, 63 APON were found in 51 eyes of 44 glaucoma patients. APONs were more prevalent in women. Acquired pits were more frequently (p<0.001) located inferiorly (70%) than superiorly (30%). There was a significantly higher prevalence (p<0.001) of APON in LTG patients (12.7%) than in HTG patients (5.6%). Dense visual field defects within five degrees of fixation occurred in 96% of patients with APON. Acquired pits of the optic nerve are more often located at the inferior optic disc than at the superior disc and are nearly always associated with visual field loss close to fixation. In a glaucoma referral center setting, APON are more prevalent in lower pressure glaucoma than in higher pressure glaucoma.

Retinal Nerve Fiber Layer Height in High-Tension Glaucoma and Healthy Eyes

To determine the correlations between the retinal nerve fiber layer height measured by Heidelberg Retina Tomograph, version 1.11, and visual field indices in healthy individuals and patients with glaucoma. One eye was randomly chosen from 48 patients with glaucoma and 60 healthy individuals. All participants were classified using Humprey visual field, program 30-2 (Humphrey Instruments, Inc., San Leandro, CA, U.S.A.); mean deviation, pattern standard deviation, short-term fluctuation, and corrected pattern standard deviation were measured. Superior and inferior mean deviation were calculated. For each participants the mean Heidelberg Retina Tomograph was generated from three 10 degrees Heidelberg Retina Tomograph pictures. The Student t test was used to compare healthy and glaucomatous retinal nerve fiber layer (RNFL) mean degree values every 5 degrees. A global measurement, superior sector (25 degrees-125 degrees), nasal sector (130 degrees-230 degrees), inferior sector (235 degrees-335 degrees), temporal sector (340 degrees-20 degrees), and polar sector (superior + inferior) were calculated. The global, superior, nasal, inferior, temporal, and polar RNFL height (RNFLH) were compared between healthy individuals and patients with glaucoma. The correlation between global, superior, inferior, and polar retinal nerve fiber layer height and visual field was calculated. A significant difference was found for RNFLH mean from 45 degrees to 330 degrees and for the distribution of the means (as reflected by the standard deviation) from 85 degrees to 100 degrees, 260 degrees to 295 degrees, and 335 degrees to 5 degrees. From these data we created three new sectors: new superior sector (from 85 degrees to 100 degrees), new inferior sector (from 260 degrees to 295 degrees), and new polar sector (combining the new superior and the new inferior sector). Comparing the healthy individuals to the patients with glaucoma, the mean RNFLH values for each sector were found to differ significantly (p < 0.001), with the exception of the temporal sector. Significant correlations (p < 0.001) between the global RNFLH and mean deviation (r = -0.36), pattern standard deviation (r = 0.49), and corrected pattern standard deviation (r = 0.48) were found in healthy participants and those with glaucoma. The strongest correlations (p < 0.001) were found between the pattern standard deviation and the corrected pattern standard deviation with the new polar sector (r = 0.60 and r = 0.59, respectively). We found that the strongest correlations with the visual field were with the new polar and new inferior sector.

Peripapillary atrophy in normal and primary open-angle glaucoma.

This study was undertaken in order to determine the value of measuring peripapillary atrophy for the diagnosis and follow-up of patients with glaucoma, and to evaluate how closely peripapillary atrophy is related to structural and functional optic nerve damage in glaucoma. Magnification-corrected morphometry of photographs using a computer graphic program and automated static threshold perimetry were performed in 234 eyes of 141 patients with primary open-angle glaucoma and 139 eyes of 86 normal subjects. The groups were not significantly different in age, refractive error or disc area. Zones alpha and beta were significantly larger, total peripapillary atrophy was significantly more extensive, and zone beta occurred more often in the glaucoma group than in the normal group. The frequency of zone beta increased with advancing glaucoma stage. The areas of zones alpha and beta and total peripapillary atrophy increased significantly with decreasing rim/disc area ratio, rim area, and mean deviation, and with increasing vertical and horizontal cup-to-disc ratios and cup area. Correlation coefficients were generally higher for zone beta than for zone alpha. Peripapillary atrophy was greater in a sector in which the neuroretinal rim loss was more marked. These findings suggest that increases in the extent of peripapillary atrophy are related to the severity of glaucomatous optic nerve damage and visual field defects, and that peripapillary atrophy is useful for the diagnosis and progression of glaucomatous nerve damage.

Reduced intraocular pressure after phacoemulsification and posterior chamber intraocular lens implantation

Purpose: To ascertain whether phacoemulsification with posterior chamber intraocular lens (IOL) implantation causes long-term reduction in intraocular pressure (lop).Setting: Private practice, Kempten, Germany.Methods: Intraocular pressure was measured in both eyes of 120 consecutive patients who were unilaterally phakic after phacoemulsification a mean of 17 months ± 17 (SD) previously. Mean age of the 36 men and 84 women was 76 ± 10 years. Data were analyzed using binomial distribution and the Wilcoxon signed-rank test.Results: The median ratio of IOP in the pseudophakic eye to IOP in the phakic eye was 0.83. The IOP was lower in the pseudophakic eye in 96 patients (80%). The median IOP was 12 mm Hg in the pseudophakic eyes and 14 mm Hg in the phakic eyes (P < .001). As measured by the interquartile range, IOP distribution was more centered in the pseudophakic than in the phakic eyes (3 versus 4). The IOP in the pseudophakic eyes remained lower to the last measurement, 5 years postoperatively, and appeared to be independent of patient age. Lower IOP in the pseudophakic eye was consistently present in patients with higher IOP in the phakic eye (16 to 22 mm Hg).Conclusion: Phacoemulsification with posterior chamber IOL implantation reduced IOP in most but not all patients with a preoperative lop of 22 mm Hg or less. This reduction was maintained over several years, with the cause yet to be established. Lower IOP may decrease the risk of subsequent glaucomatous nerve damage in these patients.

Acquired pits of the optic nerve in glaucoma

An acquired pit of the optic nerve (APON) is a discrete, focal area of depression within the optic cup at the level of the lamina cribrosa. It is an under-diagnosed sign of glaucoma damage due to its subtle appearance. APONs occur more frequently unilaterally and in patients with normal-tension glaucoma (NTG). They often correspond to a deep, sharp-margined scotoma approaching or involving fixation. Given the location and progressive nature of the associated visual field defects, glaucoma patients and glaucoma suspects should be evaluated for this sign of localized optic nerve damage.

Peripapillary fluorescein angiographic findings in primary open angle glaucoma.

Detailed fluorescein angiographic findings in the disc circumference may be useful for evaluating the possible relation of the circumference to glaucomatous nerve damage. Fluorescein angiograms of 25 eyes of 25 subjects with primary open angle glaucoma were observed after they had undertaken Octopus perimetry. Based on the retinotopic projection, disc sectors and corresponding visual field regions were set. Twenty three eyes (92%) showed a zone of no fluorescence around the disc (non-fluorescent zone). Of these, the zone width of the 20 eyes that had visible ciliary vessels within the zone was wider than that of the other three eyes, and showed fluorescein diffusion from the outer boundary of the zone towards the disc. The diffusion reached the disc if the zone was narrow. In those 20 eyes, a standardised difference in the zone width of inferior temporal sector minus superior temporal sector correlated with the difference in mean loss of corresponding visual field regions (r = 0.48, p = 0.0312). The visible ciliary vessels suggest the absence of the choriocapillaris in the non-fluorescent zone, the width of which correlated with the visual field defect and may affect the amount of the fluorescein diffusion to the disc. This suggests that the diffusion might be related to optic nerve damage in glaucoma.

The Heidelberg retina tomograph in glaucoma

Purpose: To establish the ability of the Heidelberg retina tomograph (HRT) to detect morphological change of the optic nerve head in glaucomatous optic neuropathy and to evaluate glaucomatous nerve fibre layer defects.Introduction: The HRT is a confocal laser scanning microscope designed for three‐dimensional imaging and measurement of the in vivo fundus. The light source is a diode laser operating at a wavelength of 670 mm. Thirty‐two single, two‐dimensional sectional images are recorded within 0.032 s with a repetition rate of 20 Hz, digitised in a frame of 25 × 256 pixels. Sequential viewing of the plates permits three‐dimensional resolution of the image. Use of the HRT enables comparison of change in optic nerve head morphology with change in visual function.Methods: The sample consists of 30 early primary open angle glaucoma subjects showing repeatable glaucomatous field defects on Humphrey 30‐2 analysis and 65 glaucoma suspects with normal Humphrey 30‐2 fields but with multiple risk factors for the development of glaucoma. All subjects are evaluated using white‐on‐white and blue‐on‐yellow visual fields as well as HRT analysis of the optic nerve head and retina at three‐month intervals over a 15‐month period.Discussion: We have demonstrated the need for consistent image scaling in prospective follow‐up (Hosking et al., 1995), a facility to be incorporated in the next software revision; the importance of selecting an optimum scan; and that the correction of astigmatism required for quality image acquisition results in image distortion. The application of nerve head analysis software to demonstrate localised wedge‐shaped nerve fibre bundle defects is illustrated and further modification of the software to demonstrate more subtle subclinical nerve fibre layer defects will be discussed.

Theoretical predictions and experimental findings of visual deficits in glaucoma

Purpose: To investigate the motion and colour processing in normal subjects and in patients with primary open angle glaucoma, and to develop theoretical models in order to explain present findings and to understand the processes involved.Methods: Movement processing was investigated using an optical motion projection system, capable of generating continuous motion of a single dot target with controlled speed, displacement and motion direction. Displacement and direction discrimination thresholds (i.e. target displacement at a constant speed needed for 75% probability of detection of motion or correct discrimination of its direction) were measured for both foveal and peripheral stimulus presentations and for a range of speeds. Colour vision was tested using a novel method which employs a random luminance modulation technique to mask out achromatic contrast changes and allowing detection of a spatially structured object based on the processing of chromatic signals only (Barbur et al. 1993).Results: Changes in the parameters of the motion detection model (e.g., delay time and receptor regularity) that was developed to predict the experimental data in normal subjects also predicts an increase in displacement threshold and poorer sensitivity for discrimination of motion direction in glaucoma patients. The results obtained show that patients may report stimulus motion in 80% of presentations whilst performing at chance when required to discriminate the direction of motion. Chromatic discrimination ellipses measured for foveal stimulus presentations in glaucoma patients were often similar to those measured in normal subjects. In the periphery, however, much larger chromatic displacement thresholds were measured in all directions.Conclusions: The technique used to measure the chromatic discrimination ellipses is sensitive to glaucomatous nerve damage and the results suggest a larger threshold elevation in the periphery than at the fovea. The motion model developed to explain performance in normal vision also predicts the experimental findings in glaucoma patients and may be used to predict degraded motion discrimination in patient groups with similar pathologies.

Interobserver Variation in the Measurements of Peripapillary Atrophy in Glaucoma

The purpose of this retrospective study is to compare the measurements of intrapapillary and peripapillary parameters between two observers and test the usefulness of measuring different types of crescents. Optic disc photographs of 23 eyes of 23 patients with glaucoma and 23 age-matched normal eyes were measured in Oulu and in Erlangen using manual planimetric techniques. The authors measured the following magnification corrected intrapapillary and peripapillary areas: optic disc, neuroretinal rim, cup: disc area ratio, scleral ring, central (zone beta), and peripheral peripapillary atrophy (zone alpha). Twenty-one patients with glaucoma had a follow-up of 3.2 years (range, 1.1-4.7 years), and follow-up for 19 control eyes was 3.7 years (range, 2.5-5.9 years). The measurements were performed in a masked fashion for the diagnosis and temporal sequence of the photographs. Central peripapillary atrophy (zone beta) was statistically significantly largest in primary open-angle glaucoma in both centers (Oulu, P=0.003; Erlangen, P=0.004), whereas normal and exfoliative eyes did not differ significantly from each other. The results for peripheral peripapillary atrophy (zone alpha) and scleral ring were less consistent. Despite statistically significant interobserver correlations ranging from r=0.30 (scleral ring area; P=0.0472) to r=0.97 (optic disc area; P=0.0001), the means of all parameters, except for zone alpha and beta, differed statistically significantly between the two observers. The central peripapillary atrophy, or zone beta, is the most reproducible parameter when measuring peripapillary atrophy in glaucoma. Nonetheless, its measurement is of limited usefulness in the recognition of glaucoma or progression of glaucomatous nerve damage.

Blue-on-yellow perimetry

Summary Laboratory based studies which employ foveal stimuli have demonstrated a selective short-wavelength sensitive (SWS) pathway deficit prior to visual field loss in glaucomatous patients. Early glaucomatous visual field loss as revealed by conventional perimetry, however, is generally accepted to occur outside the fovea. Consequently, blue-on-yellow perimetry was developed which permits the assessment of SWS function across the central visual field. This new clinical technique employs a blue stimulus to preferentially stimulate the SWS pathway and a high luminance yellow background to saturate the other receptor types. Clinical studies suggest that blue-on-yellow perimetry reveals early glaucomatous field loss before conventional perimetry which follows a pattern dictated by the anatomy of the retinal nerve fibre bundles. Blue-on-yellow perimetry is particularly prone to attenuation by the ocular media and macular pigment because of the use of a short-wavelength stimulus. Ocular media absorption (OMA) increases with increase in age (approx. a 10 dB increase in mean OMA between 20 and 70 years relative to 410 nm), exhibits a large variation between individuals of the same age (approx. 9 dB) and is exaggerated in diabetics. Both OMA and forward light scatter (LS) result in a diffuse reduction of blue-on-yellow sensitivity. Macular pigment absorption (MPA) does not vary systematically with age (P > 0.05) but exhibits a large variation between individuals (approx. 10 dB relative to 460 nm). MPA results in a symmetrical reduction of blue-on-yellow sensitivity centred on the fovea (mean foveal MPA 4 dB, P < 0.001) with 5° eccentricity. The psychophysical techniques employed to quantify OMA, forward LS and MPA are time-consuming and not suitable as routine clinical procedures. Methods of analysis which avoid the use of absolute sensitivity values need to be employed to identify abnormality in the blue-on-yellow visual field. Such an approach may rely on the identification of change in shape (i.e. pattern standard deviation) or symmetry (i.e. glaucoma hemifield test) of the visual field. Alternatively, the clustering of stimulus locations with markedly reduced sensitivity and the conformity of clusters to recognized patterns of glaucomatous nerve fibre loss should provide sensitive measures of abnormality.

Blue‐on‐yellow perimetry

SummaryLaboratory based studies which employ foveal stimuli have demonstrated a selective short‐wavelength sensitive (SWS) pathway deficit prior to visual field loss in glaucomatous patients. Early glaucomatous visual field loss as revealed by conventional perimetry, however, is generally accepted to occur outside the fovea. Consequently, blue‐on‐yellow perimetry was developed which permits the assessment of SWS function across the central visual field. This new clinical technique employs a blue stimulus to preferentially stimulate the SWS pathway and a high luminance yellow background to saturate the other receptor types. Clinical studies suggest that blue‐on‐yellow perimetry reveals early glaucomatous field loss before conventional perimetry which follows a pattern dictated by the anatomy of the retinal nerve fibre bundles.Blue‐on‐yellow perimetry is particularly prone to attenuation by the ocular media and macular pigment because of the use of a short‐wavelength stimulus. Ocular media absorption (OMA) increases with increase in age (approx. a 10 dB increase in mean OMA between 20 and 70 years relative to 410 nm), exhibits a large variation between individuals of the same age (approx. 9 dB) and is exaggerated in diabetics. Both OMA and forward light scatter (LS) result in a diffuse reduction of blue‐on‐yellow sensitivity. Macular pigment absorption (MPA) does not vary systematically with age (P &gt; 0.05) but exhibits a large variation between individuals (approx. 10 dB relative to 460 nm). MPA results in a symmetrical reduction of blue‐on‐yellow sensitivity centred on the fovea (mean foveal MPA 4 dB, P &lt; 0.001) with 5° eccentricity.The psychophysical techniques employed to quantify OMA, forward LS and MPA are time‐consuming and not suitable as routine clinical procedures. Methods of analysis which avoid the use of absolute sensitivity values need to be employed to identify abnormality in the blue‐on‐yellow visual field. Such an approach may rely on the identification of change in shape (i.e. pattern standard deviation) or symmetry (i.e. glaucoma hemifield test) of the visual field. Alternatively, the clustering of stimulus locations with markedly reduced sensitivity and the conformity of clusters to recognized patterns of glaucomatous nerve fibre loss should provide sensitive measures of abnormality.

Assessment of current visual psycho-physical testing methods with special reference to primary open angle glaucomatous disease (POAGD)

Early diagnosis of glaucoma with standard perimetric technique remains unsatisfactory as the appearance of discernible visual field defects indicates already extensive optic nerve fiber loss. Experimental evidence, reviewed here in detail, indicates that retinal neurons selective for coarse, temporally modulated patterns are most vulnerable in early glaucoma. Applying this data to perimetric techniques the authors have designed a new test measuring paracentral contrast sensitivity. By presenting sinusoidal gratings of 1 cpd four degrees from fixation, contrast sensitivity was determined as a function of stimulus size. They obtained abnormal contrast sensitivity functions in glaucoma suspects with apparently intact visual fields indicating the potential for better detection of hidden glaucomatous nerve damage.