Use of scanning laser ophthalmoscopy to monitor papilloedema in idiopathic intracranial hypertension

AIMS: To determine the sensitivity of confocal scanning laser ophthalmoscopy (SLO) in detecting clinically significant changes in papilloedema secondary to idiopathic intracranial hypertension (IIH) and the correlation with visual field loss. METHODS: Eight patients--three new, two recurrent, and three chronic cases of IIH--were examined over a 9 month period with SLO (Heidelberg retina tomograph) of optic nerve head and 30-2 Humphrey visual fields (six cases). Optic disc swelling (volume) was assessed in each eye using a circular contour line placed around the swollen optic nerve head on the mean image of three topographic images. Nine volume measurements from single images in each eye of every patient were performed on one occasion to assess repeatability. RESULTS: In the five acute cases optic disc volumes (range 1-16 mm3) decreased with treatment to stable, normal levels. Three of these had mild, reproducible, field defects which resolved. Two chronic cases had stable or fluctuating disc volume with no detectable change in grade of papilloedema and mild field loss. In one case which underwent theco-peritoneal shunting both disc volume and field worsened, indicating therapeutic failure. Both improved postoperatively. CONCLUSIONS: SLO has a high sensitivity for detecting small changes in disc volumes and correlates closely with visual field change in the short term. It can confirm therapeutic failure by detecting stable or increasing disc volume. Decreasing volume may indicate resolution of papilloedema or secondary optic atrophy, so accompanying funduscopy and visual fields remain essential.     

Change in optic disk topography after trabeculectomy

PURPOSE: To investigate the relationship between optic disk topography and intraocular pressure before and after trabeculectomy with confocal scanning laser ophthalmoscopy. METHODS: The eyes of 49 consecutive patients undergoing trabeculectomy at a university-based glaucoma practice underwent preoperative and postoperative imaging using a confocal scanning laser ophthalmoscope (Heidelberg Retina Tomograph). Three images of one eye of each patient were obtained with a 15-degree field of view. Preoperative images were obtained approximately 2 months before surgery (mean +/- SD, 2.4 +/- 1.6 months). Postoperative images were obtained at least 3 months after surgery (mean, 4.5 +/- 2.6 months). RESULTS: Mean preoperative intraocular pressure, postoperative intraocular pressure, and percent change in intraocular pressure respectively were 23.1 +/- 6.8 mm Hg, 12.7 +/- 7.1 mm Hg, and 43.8% +/- 29.9%. A significant association (P < .01) was found between percent decrease in intraocular pressure and decreases in cup area, cup volume, and cup/disk area ratio as well as between percent decrease in intraocular pressure and increases in rim area, rim volume, mean height contour, retinal cross-section area, and height in contour. Between 11.7% and 31.2% of the variability (R2) in these parameters was explained by the percent change in intraocular pressure. Topography changes were more strongly associated with percent change than with mean change in intraocular pressure. We found no association between percent decrease in intraocular pressure and reference plane height or maximum cup depth. CONCLUSIONS: Changes in optic nerve topography were associated with reduction in intraocular pressure after trabeculectomy.     

Diagnosis of malaria--an overview

PURPOSE: To examine the anterior optic nerve vasomotor effects of nonselective and relatively beta-1-selective beta-adrenergic antagonists in rabbits, because different influences on optic nerve blood flow with these medications have been suggested. METHODS: After topical therapy for 30 days with either timolol maleate 0.5% (six rabbits), betaxolol hydrochloride 0.5% (six rabbits), or placebo (two rabbits), the microvasculature of the optic nerve was examined with an intraluminal microvascular corrosion casting technique. The investigators were masked to both the medication group and the treated eye. The constriction, in percent of the downstream vessel caliber, was measured at the vascular branching point of arterioles supplying the anterior optic nerve. An average constriction was calculated and compared between the medication groups and between the treated and the contralateral, untreated eyes. RESULTS: Constriction values from a total of 218 arterioles supplying the anterior optic nerve were obtained for the 14 rabbits. The means of the average constriction on the treated side were comparable between the groups treated with timolol maleate, betaxolol hydrochloride, and placebo (one-way analysis of variance, P = .64), as well as between the treated and untreated eyes (two-tailed t-test for paired variables, P = .68 for timolol maleate and P = .42 for betaxolol hydrochloride). The statistical power to find a difference of 5% or more average constriction was at least 90%. CONCLUSIONS: Both relatively selective and nonselective beta-adrenergic antagonists produce no observable optic nerve vasomotor effects in the rabbit eye.     

Prosthetic arteriovenous fistulas and venous anastomotic stenosis: influence of a high flow velocity on the development of intimal hyperplasia

OBJECTIVE: To search a sensitive parameter for the early diagnosis of primary open angle glaucoma (POAG). METHOD: A system of computerized image analysis was used to acquire images of the optic nerve head of patients with POAG, suspect glaucoma (SG) and of normal persons. Each of these groups contained 31 eyes of 31 cases. The mean relative depths of disc rim and cup at different areas in the optic nerve head were measured. All these patients were followed up for four to six months, and the changes of the mean depths of every sector were compared between each pair of the three groups with statistic analysis. RESULTS: The mean depth of the neural rim and cup of each sector and that of total rim and total cup of POAG and SG patients were all deeper than that of normal controls. The mean depths of neural rim of the superior sector, inferior sector and the total rim area of POAG were deeper than that of SG patients. Compared to their first measurements, the changes of mean depths of neural rim of superior sector and total neural rim area of POAG patients were more prominent than that of normal controls and SG. We also compared the relative depth of the total rim area in the different areas in the optic nerve head with other two dimensional optic disc parameters such as cup/disc ratio, etc. CONCLUSION: Our study suggests that three-dimensional stereoscopic measurement of the surface of optic nerve head and follow-up be of paramount importance in the early diagnosis of POAG patients.     

Effect of the contour line on cup surface using the Heidelberg Retina Tomograph

BACKGROUND: Significance of topometric follow-up examinations of the optic nerve head in glaucomatous eyes depends on the reproducibility of the calculated parameters. Since the definition of the standard reference plane in software version 1.11 of the Heidelberg Retina Tomograph has been changed, intrapapillary parameters depend directly on the position of the contourline in the sector between -10 degrees to -4 degrees, and therefore on the observer variability to determine the disc border. We evaluated intra- and interobserver variability and present a simple approach to increase reproducibility. METHOD: The disc border of 4 glaucomatous eyes, 3 ocular hypertensive eyes and 3 eyes of healthy subjects were traced by two observers, 5 times using the free draw mode and 5 times by the addition of contourline circles. RESULTS: We found a median variability of the mean disc radius in sector -10 degrees to -4 degrees of 51 microns, which defines the position of the standard reference plane, resulting in a median variability of the position of the standard reference plane of 33 microns which caused a variability of 81 microns2 of the cup area. Addition of contourline circles smoothing the final contourline along the border of the optic disc resulted in a decrease of the coefficient of variation of the standard reference plane of 3.76% (6.76% vs. 3.0%), of the cup area of 2.34% (3.87% vs. 1.53%) and of the rim volume of 3.41% (9.75% vs. 6.34%). CONCLUSION: The calculation of the cup area using software version 1.11 of the Heidelberg Retina Tomograph depends on observer variability. The addition of contourline circles to define the final contourline along the disc border increases reproducibility. However, in follow-up of topometric examinations of the optic nerve head the software supported transfer mode should be used. Comparing topometric data of an individual optic disc in follow-up suppose the same definition of the contourline. Therefore, topometric data evaluated using software version 1.10 or earlier needs to be recalculated.     

Cytological studies on the developing vitreous as related to the hyaloid vessel system

The embryonic development of the cell population of the mammalian vitreous has been traced to two sources: the undifferentiated mesenchymal cells of the eye primordium and the primitive reticular cells of the bone marrow. Undifferentiated mesenchymal cells invade the future vitreous space in two ways: through the annular opening between the rim of the optic cup and the lens primordium, and through the open embryonic fissure. They differentiate into prevascular cells, hemangioblasts, and fibrocytes located in the area of the optic nerve head. From the very beginning of fetal development, another ameboid-type cell of mesenchymal origin makes its entrance into the vitreous through the hyaloid vessels; these monocyte-like cells differentiate into hyalocytes and populate a well-defined area of the cortical vitreous close to the retina and to the ora serrata. Gamma-irradiation (600 rads) of newly born rabbits and cats decreases the number of migrating amebocytes in their vitreous; 24 h later, however, they are replaced by monocytes from the hyaloid vessels.     

Evaluation of coexisting optic nerve head drusen and glaucoma with optical coherence tomography

OBJECTIVE: Optic nerve head drusen often make evaluation of the nerve head difficult to interpret. In addition, visual field defects are known to occur in patients with optic disk drusen, resembling glaucomatous damage. The authors report two cases of coincident optic nerve head drusen and glaucoma, in which the use of optical coherence tomography (OCT) in evaluating the nerve fiber layer was beneficial. PARTICIPANTS: Two patients with both optic nerve head drusen and glaucoma, one with primary open angle glaucoma, the other with pseudoexfoliation glaucoma were evaluated. Both patients had asymmetric optic disk drusen, with clinically visible drusen only in one eye. INTERVENTION: Ophthalmologic examination, color and red-free photography, automated Humphrey visual field testing and OCT were performed. RESULTS: Nerve fiber layer loss as measured by OCT was found to be greater than expected by the appearance of the optic nerve head and red-free photography, with visual fields consistent with findings in case 1. In case 2, visual fields were full, despite nerve fiber layer thinning seen by OCT and red-free photography. CONCLUSIONS: There can be significant nerve fiber layer thinning in patients with both glaucoma and optic disk drusen, despite the appearance of the optic nerve head in these patients. The cup margin may be obscured by the drusen, giving rise to a falsely full-appearing disk. In such cases, OCT may provide a useful means to quantitatively measure the nerve fiber layer thickness and to aid in the management of these patients by detecting nerve fiber layer thinning earlier than would otherwise be possible.     

Laser scanning tomography of the optic nerve head in ocular hypertension and glaucoma

BACKGROUND: This study evaluated the ability of laser scanning tomography to distinguish between normal and glaucomatous optic nerve heads, and between glaucomatous subjects with and without field loss. METHODS: 57 subjects were classified into three diagnostic groups: subjects with elevated intraocular pressure, normal optic nerve heads, and normal visual fields (n = 10); subjects with glaucomatous optic neuropathy and normal visual fields (n = 30); and subjects with glaucomatous optic neuropathy and repeatable visual field abnormality (n = 17). Three 10 degrees image series were acquired on each subject using the Heidelberg retina tomograph (HRT). From the 14 HRT stereometric variables, three were selected a priori for evaluation: (1) volume above reference (neuroretinal rim volume), (2) third moment in contour (cup shape), and (3) height variation contour (variation in relative nerve fibre layer height at the disc margin). Data were analysed using analysis of covariance, with age as the covariate. RESULTS: Volume above reference, third moment in contour, and mean height contour were significantly different between each of the three diagnostic groups (p < 0.001). Height variation contour showed no significant difference among the three diagnostic groups (p = 0.906). CONCLUSIONS: The HRT variables measuring rim volume, cup shape, and mean nerve fibre layer height distinguished between (1) subjects with elevated intraocular pressures and normal nerve heads, and glaucomatous optic nerve heads, and (2) glaucomatous optic nerve heads with and without repeatable visual field abnormality. This study did not directly assess the ability of the HRT to identify patients at risk of developing glaucoma. It is hypothesised that the greatest potential benefit of laser scanning tomography will be in the documentation of change within an individual over time.     

The cumulative normalised rim/disc area ratio curve

BACKGROUND: The assessment of the cup of the optic disc depends, among other criteria, on the disc area. A small cup in a small optic disc can indicate an advanced glaucomatous lesion, while on the other hand a large cup in a large optic disc can be normal. Therefore, a cumulative normalised rim/disc area ratio curve could help to distinguish between glaucomatous and normal optic cups. The aim of our study was to calculate normalised rim/disc area ratio curve. METHODS: Heidelberg Retina Tomograph examinations of the optic nerve head of 100 randomly selected eyes of 100 normal subjects were evaluated. We calculated the disc area-adjusted normalised rim/disc area ratio in sectors of 10 degrees. The 95th, 90th and 50th percentiles of each of the 36 sectors were displayed in descending order. RESULTS: In relation to the normal percentile curves, it is possible to display an individual normalised rim/disc area ratio curve. We obtained such curves for a normal optic disc, optic nerve heads with moderate and advanced lesions and a small optic disc with glaucomatous damage. CONCLUSION: We present a new display mode for the results of Heidelberg Retina Tomograph optic nerve head examination, which may be helpful for easy and reliable assessment of the local, diffuse and combined components of glaucomatous optic nerve head damage depending on optic disc size.     

Neuronal death in glaucoma

Glaucoma is recognized to have its major detrimental effect upon the eye by killing retinal ganglion cells. The process of cell death appears to be initiated at the optic nerve head, though other sites of injury are possible but unsubstantiated. At present the injury at the nerve head seems related to the level of the eye pressure, but its detailed mechanism is as yet unexplained. There is a greater loss of ganglion cells from some areas of the eye, and this feature of glaucoma seems related to the regional structure of the supporting connective tissues of the optic nerve head. Larger retinal ganglion cells have been consistently shown to have somewhat greater susceptibility to injury in glaucoma, though all cells are injured, even early in the process. Ganglion cells die by apoptosis in human and experimental glaucoma, opening several potential areas for future therapies to protect them from dying. Neurotrophin deprivation is one possible cause of cell death and replacement therapy is a potential approach to treatment.     

Influence of optic disc size on the sensitivity of the Heidelberg Retina Tomograph

PURPOSE: The aim of this study was to evaluate the influence of optic disc size on the ability of variables generated by the Heidelberg Retina Tomograph, software version 1.11, to distinguish glaucoma patients from normals in a cross-sectional study. PATIENTS AND METHODS: For evaluation of the optic disc with the Heidelberg Retina Tomograph, eyes of 87 normals and 61 glaucoma patients were selected. Disc area, volume above reference, rim area, cup area, cup volume, third moment in contour and the mean retinal nerve fibre layer thickness at the border of the optic disc were selected for evaluation. The sensitivity at 80% specificity of these variables was calculated under three conditions: (1) no correction for disc size; (2) calculation in the following disc size ranges: class I (1.0-2.0 mm2), class II (2.0-2.5 mm2), class III (2.5-3.15 mm2) and class IV (3.15-5.0 mm2); (3) calculation globally, taking into account the different disc sizes of the four classes. RESULTS: Neuroretinal rim area, cup area and volume, third moment and nerve fibre layer thickness were significantly and positively correlated with optic disc size in normals. Neuroretinal rim volume measurements were statistically independent of optic disc size. Sensitivity was lowest when the size of the optic disc was not considered. Sensitivity increased when evaluated in four optic disc size classes. With growing optic disc size sensitivity of the retinal nerve fibre layer increased and third moment value decreased. Cup volume and area had their lowest sensitivity for large optic discs. The area of the neuroretinal rim was the only variable which showed similar sensitivity values under all three conditions. CONCLUSIONS: The sensitivities of HRT variables varied with optic disc size. Evaluation of their sensitivity requires the definition of optic disc classes or statistical correction for the size of the optic disc.     

Effects of topical nipradilol, a beta-blocking agent with alpha-blocking and nitroglycerin-like activities, on aqueous humor dynamics and fundus circulation

PURPOSE: To study the effects of nipradilol, a nonselective beta-blocker with alpha 1-blocking activity and nitroglycerin-like activity, on aqueous humor dynamics and optic nerve head (ONH) circulation in albino rabbits. METHODS: Experiments were carried out during the dark phase, in conscious rabbits conditioned to a schedule of alternating 12-hour periods of light and dark. The blood-aqueous barrier permeability and the aqueous flow rate were determined fluorophotometrically. The effect on outflow to general blood circulation and uveoscleral outflow were determined by using the fluorophotometric Diamox technique, and the effect on the uveoscleral outflow was further assessed by using the anterior chamber perfusion method. The ONH circulation was estimated by using the laser speckle method. RESULTS: Unilateral topical administration of 0.25% nipradilol solution lowered intraocular pressure (IOP) with relatively weak contralateral effects in a dose-dependent manner with a maximum reduction of 6 mm Hg and an effect duration of 6 hours. Twice-daily instillation for 14 days showed no attenuation of the effects. Single instillation of 0.25% nipradilol showed no significant effect on blood-aqueous barrier permeability and decreased aqueous flow rate in the treated eye (17%; P < 0.01) and in the contralateral eye (9%, P < 0.05). Nipradilol produced no significant effect on outflow facility to general blood circulation, whereas it substantially increased uveoscleral outflow. Twice-daily 0.25% nipradilol instillation increased ONH tissue blood velocity by 13% (P < 0.01), which was probably attributable to locally penetrating drug. CONCLUSIONS: Because of its ability to lower IOP and to increase uveoscleral outflow and optic nerve head circulation in rabbits, further studies are warranted to determine whether nipradilol has potential as an antiglaucoma agent in humans.     

Association between watershed zone and visual field defect in normal tension glaucoma

In order to evaluate the association between the watershed zone and glaucomatous optic damage, we performed indocyanine green fluorescence angiography with a scanning laser ophthalmoscope in 54 eyes of 27 patients with normal tension glaucoma. The visual field indices were measured with a Humphrey Field Analyzer. We identified 8 eyes (14.8%) of 7 patients with a watershed zone not including the optic nerve head (type I), 32 eyes (59.3%) of 20 patients with the zone partially including the optic nerve head (type II), and 14 eyes (26.0%) of 10 patients with the zone including the optic nerve head (type III). Of the total of 27 patients, 10 patients (37.0%) had different types in each eye. In these patients, the mean deviation (MD) of visual field indices was worse in the eye with the watershed zone which included a larger part of the optic disc than in the contralateral eye (p < 0.05). Conversely, the eye with worse MD than the contralateral eye had a watershed zone which included a larger part of the optic disc than the other eye (p < 0.05). The location of watershed zone appeared to influence the progression of the visual field defect.     

Quantification of optic nerve blood flow changes using magnetic resonance imaging

PURPOSE: To evaluate the possibilities of magnetic resonance imaging (MRI) for quantification of pharmacologically induced changes in optic nerve microcirculation. METHOD: T2-weighted MRI sequences were used to image the eye, optic nerve, and frontal cortex in rats. Two sets of control images before and one set during Gd (DTPA) infusion were recorded. Blood flow values for two regions of the optic nerve (an anterior part, including the optic nerve head, and a more posterior part) and the frontal cortex were calculated by image analysis from the change in signal intensity, as already reported for cerebral blood flow. For each rat, a control experiment before drug administration and a second experiment 30 minutes after subcutaneous injection of either placebo (n = 7), timolol (n = 7), or SDZ GLC-756, a dopamine D-1 antagonist and D-2 agonist (n = 7), were carried out in a double-blind fashion. RESULTS: Mean basal blood flow values were found between 29.4 and 45.6 ml/100 g per minute in the anterior part of the optic nerve, 38.3 and 42.9 ml/100 g per minute in the posterior part of the optic nerve, and 68.0 and 75.0 ml/100 g per minute in the frontal cortex. Placebo and timolol did not cause significant changes. SDZ GLC-756 significantly increased blood flow by 238% +/- 65% in the anterior part and by 87% +/- 40% in the posterior part of the optic nerve. CONCLUSIONS: These results suggest that MRI provides quantification of optic nerve blood flow and that dopaminergic substances increase optic nerve blood flow.     

Aging changes of the optic nerve head in relation to open angle glaucoma

AIMS: To determine the age related changes in optic nerve head structure in a group of normal subjects and assess the significance of any changes in relation to those found in open angle glaucoma. METHODS: A group of 88 white volunteers and friends and spouses of patients with a normal visual field and normal intraocular pressure was studied. Two different imaging and measurement devices were used (computer assisted planimetry and scanning laser ophthalmoscopy), and the results from each were compared. Measurements were made of the optic disc, optic cup, and neuroretinal rim areas, and the vertical optic disc diameter and cup/disc diameter ratio. RESULTS: Neuroretinal rim area declined at the rate of between 0.28% and 0.39% per year. Vertical optic cup diameter and optic cup area increased with age. The mean cup/disc diameter ratio increased by about 0.1 between the ages of 30 and 70 years. CONCLUSIONS: Age related changes are significant and measurable, and should be taken into account when assessing the glaucoma suspect, and when estimating the rate of progression of glaucomatous optic neuropathy in patients with established disease.     

Pentoxifylline suppression of TNF-alpha mediated axonal degeneration in the rabbit optic nerve

In AIDS patients, axonal degeneration in the optic nerve occurs as a histopathological manifestation of the optic neuropathy. Direct infection of neurons by HIV is unlikely, and the axonal injury may be an indirect effect mediated by cytotoxic factors such as tumor necrosis factor-alpha (TNF-alpha) which we have previously demonstrated to cause axonal degeneration in the rabbit optic nerve. To test the suppressive effects of pentoxifylline in preventing TNF-alpha-mediated axonal degeneration, we applied pentoxifylline to an established rabbit model that demonstrates an AIDS-like optic neuropathy using intravitreal TNF-alpha injections. Degenerated axonal profiles were numerous in control rabbit optic nerve (mean 1879) and reduced in rabbits receiving the medium dose of pentoxifylline (300 mg PO BID, mean 439, p < 0.001) and the highest dose of pentoxifylline (600 mg PO BID, mean 120, p < 0.007). High dose pentoxifylline reduced TNF-alpha-induced axonal losses to less than 10% that seen without pentoxifylline pretreatment. Lower doses of pentoxifylline had a lesser but significant protective effect. Our results suggest that TNF-alpha-mediated axonal degeneration can be suppressed by high doses of pentoxifylline. Pentoxifylline may therefore be useful in AIDS patients demonstrating neurological or neuro-ophthalmological symptoms.     

Eye- and head movements in freely moving rabbits

1. Eye- and head movements were recorded in unrestrained, spontaneously behaving rabbits with a new technique, based upon phase detection of signals induced in implanted coils by a rotating magnetic field. 2. Movements of the eye in space were exclusively saccadic. In the intersaccadic intervals the eyes were stabilized in space, even during vigorous head movements. Most of this stability was maintained in darkness, except for the occurrence of slow drift. 3. Many saccades were initiated while the head was stationary. They were accompanied by a similar, but slower head rotation with approximately the same amplitude. The displacement of the eye in space was a pure step without appreciable under- or over-shoot. The deviation of the eye in the head was mostly transient. 4. Other saccades were started while the head was moving and were possibly fast phases of a vestibulo-ocular reflex. The time course of the eye movement in space was identical for all saccades, whether the head was moving prior to the saccade or not. Eye movements without any head movement were not observed. 5. Saccades were mostly large (average 20-6 +/- 12-4 degrees S.D.) and never smaller than 1 degree. The relations of maximal velocity and duration to amplitude were similar to those reported for man. 6. Visual pursuit of moving objects, when elicited, was only saccadic and never smooth. 7. It is concluded that the co-ordination and dynamics of the rabbit's head- and eye movements are similar to those of primates. In the absence of foveal specilization, the eye movements are restricted to a rather global redirection of the visual field, possibly in particular of the binocular area.     

Bacillary angiomatosis associated with myositis in a patient infected with human immunodeficiency virus

PURPOSE: To report a patient with optic nerve avulsion caused by forceful rotation of the globe that occurred when his thumb penetrated the orbit while he was diving. METHODS: A 17-year-old boy was initially examined for sudden loss of vision after jumping feet first from a bridge 50 feet above a river. Upon hitting the water, he felt his right thumb push into his right globe. The patient underwent ophthalmologic and imaging examination. RESULT: Examination disclosed a tear of the optic nerve head from the sclera temporally in the right eye. CONCLUSION: Optic nerve avulsion occurs secondary to forceful rotation of the eye with tearing of the optic nerve as it exits the globe.     

Measurement of optic disc compliance by digitized image analysis in the normal monkey eye

PURPOSE: To characterize the compliance of the normal monkey optic disc under conditions of induced short-term fluctuations in intraocular pressure (IOP). METHODS: In 10 monkeys, one eye was compliance tested on three separate days followed by a single test of the contralateral eye (40 compliance tests). In a testing session, the optic disc was imaged at 2 and 47 minutes (baseline time point) after IOP was lowered to 10 mmHg; then at 2, 17, 32, and 47 minutes after IOP was elevated to 45 mmHg; then at 2, 47, and, in some cases, 92 minutes after IOP was lowered back to 10 mmHg. Eight digitized images were analyzed at each time point, yielding two parameters to characterize the position of the disc: the Mean Position of the Disc (MPD) and the Change from MPDBaseline (the value of MPD at a given time point minus the value for MPD at the baseline time point of that testing session). Analysis of variance (ANOVA) testing was used to evaluate the overall effect of IOP on both parameters while taking into account the effects of variability due to different monkeys and repetitions of the test as well as differences between the two eyes of an individual monkey. With the addition of data from 11 compliance tests performed on eight additional monkeys, the overall results were calculated in terms of the mean Change from MPDBaseline at each time point for a total of 51 compliance testing sessions. RESULTS: The mean Change from MPDBaseline was -28 microns (95% confidence interval, -23 to -33 microns) 47 minutes after elevation of IOP. The disc surface returned to its baseline position 92 minutes after IOP was lowered back to 10 mmHg. Elevation of IOP within a compliance test had a significant effect on the position of the optic disc surface (P = 0.0002, ANOVA), as characterized by the parameter Change from MPDBaseline. Neither the difference in the amount of movement between the two eyes of an individual monkey nor the variability within the three repetitions of the test in a given eye was statistically significant. CONCLUSION: Small, reversible (elastic) posterior deformations of the optic disc surface follow acute elevations of IOP in the normal monkey eye. Detection of acute IOP-induced deformations of the optic disc surface may represent a means by which to mechanically test the deeper load-bearing tissues of the optic nerve head.