Optic Nerve Head Structure Research Articles

Strategies to improve early diagnosis in glaucoma.

Early diagnosis and treatment of glaucoma is important to reduce the risk of progressive and irreversible visual loss. The key to diagnosis is recognition of morphological changes to the optic nerve head and retinal nerve fiber layer, but in some patients, functional abnormalities are detected first. This review describes recent innovations with the potential to improve the early detection of glaucoma. Developments in imaging include novel optic nerve head metrics such as Bruch's membrane opening-minimum rim width, enhanced ability to quantify inner layers of the glaucomatous macula, and ability to image deep optic nerve head structures, including the lamina cribrosa. Developments in detection of early glaucomatous functional loss include novel perimetric tests using frequency-doubling technology and flicker-defined form stimuli. Methods to combine results of structural and functional assessments are also presented that may improve early detection of glaucoma.

Feature selection and classification for automatic detection of retinal nerve fibre layer thinning in retinal fundus images

Glaucoma which is a leading cause of blindness in the world is not a single disease but a group of disorders with diverse clinical manifestations. If not treated at an early stage it leads to loss of vision. Careful evaluation of optic nerve head structure and Retinal Nerve Fibre Layer (RNFL) is extremely important for diagnosis of the disease and subsequent medication. This work focuses on automatic detection of RNFL thinning, an early indication of glaucoma. A texture-based method is proposed in this work. Texture features were extracted from gray-level co-occurrence matrix and the feature set was optimised using Analysis of Variance (ANOVA) method. Radial basis function classifier was used to discriminate between normal and abnormal regions. The classification results were promising with accuracy of 96.41%.

The role of retrobulbar and retinal circulation on optic nerve head and retinal nerve fibre layer structure in patients with open-angle glaucoma over an 18-month period

Background/aimsEvidence suggests that vascular abnormalities play a role in the pathogenesis of open-angle glaucoma (OAG) in some patients. This study aims to assess changes in retrobulbar and retinal blood flow...

Performance Evaluation of Optic Disc Segmentation Algorithms in Retinal Fundus Images : an Empirical Investigation

Careful evaluation of Optic nerve head structure and its documentation is extremely important for diagnosis of Glaucoma, an eye disease which leads to vision loss. This work focuses on automatic segmentation of Optic disc from fundus images, which is an important parameter for disease diagnosis. We investigate and compare performance of five methods used for Optic disc segmentation. These five methods are based on use of algorithms namely; distance regularized level set, Otsu thresholding, region growing, particle Swarm optimization, generalized regression neural network. For ease of comparison all the methods were implemented and tested on a single database. The method using generalized regression neural network best suits the said application. It outperforms the other four due to highest region agreement, lowest non overlap ratio, lowest relative absolute area difference and low execution time.

Extraction of Optic Cup in Retinal Fundus images: A Compartitive Approach

Glaucoma which is a leading cause of blindness in the world is not a single disease but a group of disorders with diverse clinical manifestations. If not controlled at an early stage, it causes irreversible damage to vision. Careful evaluation of Optic nerve head structure and its documentation is extremely important for diagnosis of the disease and to monitor its progression. The optic nerve head comprises of the optic disc and the optic cup. ‘Optic cup’ is one of the imperative and crucial factors in disease diagnosis and monitoring. The aim of the research is to compare various existing optic cup segmentation methods and report their comparative performance. A modification in calculating threshold has been suggested which improves the accuracy.

Optical Coherence Tomography Visualization of Optic Nerve Head Structure Detects Acute Changes in the Intracranial Pressure (P2.293)

Optical Coherence Tomography Visualization of Optic Nerve Head Structure Detects Acute Changes in the Intracranial Pressure (P2.293)

Automated Segmentation of Optic Nerve Head Structures With Optical Coherence Tomography

To quantify and characterize the difference between automated and manual segmentation of optic nerve head structures with spectral-domain optical coherence tomography (SD-OCT). Optic nerve head radial scans in 107 glaucoma patients and 48 healthy controls were conducted with SD-OCT. Independent segmentations of the internal limiting membrane (ILM) and Bruch's membrane opening (BMO) were performed manually with custom software and with an automated algorithm in each radial scan. The minimum distance between BMO and ILM, termed BMO-minimum rim width (BMO-MRW) was calculated with each segmentation method. Absolute differences between automated and manual segmentations of ILM (ΔILM) and BMO (ΔBMO), and the resulting computation of BMO-MRW (ΔBMO-MRW) were computed. Finally, the relationship between image quality score and ΔILM and ΔBMO was explored. The median (interquartile range, IQR) ΔILM was 8.9 (6.5, 13.4) μm in patients and 7.3 (5.3, 9.9) μm in controls. The corresponding values for ΔBMO were 11.5 (6.6, 22.1) μm and 12.4 (6.8, 25.4) μm. Subject-averaged ΔILM was higher in patients than controls (P < 0.01); however, mean ΔBMO was not (P = 0.09). The median (IQR) subject-averaged absolute ΔBMO-MRW was 13.4 (10.6, 16.8) μm in patients and 12.1 (10.0, 16.8) μm in controls and not statistically different (P = 0.21). Mean image quality score was statistically higher in controls than patients (P = 0.03) but not related to subject-averaged ΔILM or ΔBMO. In individual scans, the median difference in ILM and BMO segmentations was <2 and <3 image pixels, respectively. There were no differences between patients and controls in ΔBMO-MRW.

Alterations in the Neural and Connective Tissue Components of Glaucomatous Cupping After Glaucoma Surgery Using Swept-Source Optical Coherence Tomography

To visualize changes in deep optic nerve head (ONH) structures following glaucoma surgery using (3-dimensional [3D]) swept-source optical coherence tomography (SS-OCT) and to determine the clinical and structural factors associated with postoperative lamina cribrosa (LC) and prelaminar neural tissue (PLT) changes. In this prospective observational case series, SS-OCT thin-sliced datasets of the ONH covering a 3- × 3-mm area comprised of 256 B-scans (interval between scans = ∼12 μm) were obtained before and 3 months after the surgery and evaluated in 73 eyes of 73 patients with glaucoma. Bruch's membrane opening (BMO) and anterior LC boundary were manually delineated by two methods; one in every four B-scans (64 B-scans per eye) and 15 equally spaced horizontal B-scans in BMO area, excluding both ends (interval between scans = 96-120 μm). After former delineation, the point with maximum LC depth among 64 B-scans was automatically calculated, and LC depth and PLT thickness were averaged among 5 points adding 4 points 100 μm apart from this point vertically and horizontally. Associations between the percent change in LC depth and other clinical and structural parameters were tested for statistical analysis. Lamina cribrosa depth and axial length significantly decreased and PLT thickness significantly increased after surgery. The percent change of maximum LC depth correlated significantly with the percent change of IOP (P = 0.008), baseline LC depth (P = 0.032), and visual field mean deviation (P = 0.035; at the point with maximum LC depth), while the percent change of axial length correlated with IOP reduction (P = 0.002) but not with visual field mean deviation. Swept-source optical coherence tomography enables 3D analysis of deep ONH structures, and the change in LC depth after glaucoma surgery have association with IOP change and the severity of glaucomatous optic neuropathy.

Automatic method of analysis of OCT images in assessing the severity degree of glaucoma and the visual field loss

IntroductionIn many practical aspects of ophthalmology, it is necessary to assess the severity degree of glaucoma in cases where, for various reasons, it is impossible to perform a visual field test - static perimetry. These are cases in which the visual field test result is not reliable, e.g. advanced AMD (Age-related Macular Degeneration). In these cases, there is a need to determine the severity of glaucoma, mainly on the basis of optic nerve head (ONH) and retinal nerve fibre layer (RNFL) structure. OCT is one of the diagnostic methods capable of analysing changes in both, ONH and RNFL in glaucoma.Material and methodOCT images of the eye fundus of 55 patients (110 eyes) were obtained from the SOCT Copernicus (Optopol Tech. SA, Zawiercie, Poland). The authors proposed a new method for automatic determination of the RNFL (retinal nerve fibre layer) and other parameters using: mathematical morphology and profiled segmentation based on morphometric information of the eye fundus. A quantitative ratio of the quality of the optic disk and RNFL – BGA (biomorphological glaucoma advancement) was also proposed. The obtained results were compared with the results obtained from a static perimeter.ResultsCorrelations between the known parameters of the optic disk as well as those suggested by the authors and the results obtained from static perimetry were calculated. The result of correlation with the static perimetry was 0.78 for the existing methods of image analysis and 0.86 for the proposed method. Practical usefulness of the proposed ratio BGA and the impact of the three most important features on the result were assessed. The following results of correlation for the three proposed classes were obtained: cup/disk diameter 0.84, disk diameter 0.97 and the RNFL 1.0. Thus, analysis of the supposed visual field result in the case of glaucoma is possible based only on OCT images of the eye fundus.ConclusionsThe calculations and analyses performed with the proposed algorithm and BGA ratio confirm that it is possible to calculate supposed mean defect (MD) of the visual field test based on OCT images of the eye fundus.

Effect of myopia and age on optic disc margin anatomy within the parapapillary atrophy area

To evaluate the effect of myopia and age on temporal optic disc margin anatomy within the parapapillary atrophy (PPA) area by use of spectral-domain optical coherence tomography (OCT). Fifty young myopic eyes with PPA (myopic PPA group), 50 aged non-myopic eyes with PPA (aged PPA group), and 50 young non-myopic eyes without PPA (control group) were enrolled. High-definition OCT scanning was used to obtain horizontal cross-sectional optic nerve head (ONH) images. By use of these OCT scans we investigated three temporal optic disc margin structures: the configuration of the border tissue of Elschnig; the cross-sectional ONH structure coinciding with the clinically detected optic disc margin; and the integrity of the retinal layers within the PPA area. The distribution of the configuration of the border tissue of Elschnig and the cross-sectional ONH structure coinciding with the clinically detected optic disc margin of the myopic PPA group differed significantly from those of the control group (P < 0.01) whereas those of the aged PPA group did not (P > 0.05). Other than the photoreceptor layer, the retinal layers within the PPA area were more commonly impaired in the myopic PPA group than in the aged PPA group (P < 0.001). Myopia and aging led to different structural changes in temporal optic disc margin anatomy within the PPA area. This finding implies that different mechanisms may underlie myopic and age-related PPA development.

Visual field defects due to optic disk drusen in children

Optic nerve head drusen (ONHD) are deposits due to abnormalities in axonal metabolism and degeneration. Studies so far have focused on adults. Our aim was to study the effect of ONHD on visual function as well as optic nerve head structure using optical coherence tomography (OCT) in children. Subjects younger than 18 years of age with ONHD and who had a reliable visual field defect in at least one eye due to ONHD were considered for inclusion. All subjects underwent an extensive ophthalmic examination including best-corrected visual acuity (BCVA), funduscopy, and SITA 24-2 standard automated perimetry. OCT scanning was performed using Cirrus-HD Model 4000. Retinal nerve fiber layer (RNFL) thickness data were compared with a group of age-matched healthy children. Fifteen children were included, with a mean age of 13 years (range 7 to 17 years). BCVA was 1.0 in all eyes, except in a child with concomitant esotropia. ONHD were bilateral in 13 children. Among the 28 eyes with ONHD, 12 (43%) were classified as type 1 (buried), eight (29%) as type 2 (ringed) and eight (29%) as type 3 (superficial). All children had a visual field defect in at least one eye, according to the inclusion criteria; however, two eyes (7%) had no defect in spite of the presence of ONHD. Five eyes showed an isolated enlarged blind spot (18%), 15 cases showed a nasal defect (54%), and six eyes showed a constricted visual field (21%). RNFL thickness was higher in type 1 and 2 ONHD than in the control group, although these differences were only significant for the average, superior, and inferior quadrant thicknesses in type 1 and the inferior quadrant in type 2. RNFL thickness was lower in type 3 ONHD than in the control group, although these differences were only significant for the average, superior, and nasal quadrant thicknesses. ONHD may lead to the development of visual field defects, even in children. In initial stages, ONHD produce an increase in RNFL thickness as measured with OCT. As drusen develop and become superficial, the RNFL thickness decreases. The temporal quadrant is often undamaged, probably reflecting the preservation of central visual acuity.

Comparison of enhanced depth imaging and high-penetration optical coherence tomography for imaging deep optic nerve head and parapapillary structures

PurposeTo evaluate and compare the abilities of enhanced depth imaging (EDI) and high-penetration optical coherence tomography (HP-OCT) to visualize the deep optic nerve head (ONH) and deep parapapillary structures.MethodsHorizontal and vertical optic nerve images were obtained using EDI-OCT and HP-OCT, during the same visit, from 24 eyes of 12 patients with glaucoma. Three graders, using a three-point grading system, independently graded the visibility of the deep ONH structures (prelaminar tissue surface, anterior laminar surface, posterior laminar border, and laminar pores) and deep parapapillary structures (intrascleral vessels, cerebrospinal fluid space, and parapapillary choroid). The differences in the visibility scores between the EDI-OCT and the HP-OCT images and among the image locations were analyzed statistically. The agreement in scoring among the graders also was analyzed.ResultsThe visibility of three ONH structures, the anterior laminar surface, posterior laminar border, and laminar pores, was significantly better with EDI-OCT (P = 0.0010, P < 0.0001, and P = 0.0141, respectively). In contrast, the visibility of all parapapillary structures was significantly better with HP-OCT (P < 0.0001, P = 0.0176, and P < 0.0001, respectively). The visibility scores were better in the vertical images compared with the horizontal images and were best in the temporal quadrants. The intergrader agreement was moderate for all parameters examined.ConclusionBoth EDI-OCT and HP-OCT are useful for evaluating the deep ONH and parapapillary structures. The visibility scores of the deep ONH structures were better with EDI-OCT, in contrast to the better visibility scores of the deep parapapillary structures with HP-OCT. Both systems should be chosen depending on the target tissue to observe.

Real-time eye motion compensation for OCT imaging with tracking SLO

Fixational eye movements remain a major cause of artifacts in optical coherence tomography (OCT) images despite the increases in acquisition speeds. One approach to eliminate the eye motion is to stabilize the ophthalmic imaging system in real-time. This paper describes and quantifies the performance of a tracking OCT system, which combines a phase-stabilized optical frequency domain imaging (OFDI) system and an eye tracking scanning laser ophthalmoscope (TSLO). We show that active eye tracking minimizes artifacts caused by eye drift and micro saccades. The remaining tracking lock failures caused by blinks and large saccades generate a trigger signal which signals the OCT system to rescan corrupted B-scans. Residual motion artifacts in the OCT B-scans are reduced to 0.32 minutes of arc (~1.6 µm) in an in vivo human eye enabling acquisition of high quality images from the optic nerve head and lamina cribrosa pore structure.

The Optic Nerve Head as a Robust Biomechanical System

Purpose. Understanding the effects of IOP on the optic nerve head (ONH) is important in understanding glaucoma and ONH structure and function. The authors tested the hypothesis that the ONH is a robust biomechanical structure wherein various factors combine to produce a relatively stable response to IOP. Methods. The authors generated two populations of 100,000 ONH numerical models each with randomly selected values, but controlled distributions, either uniform or Gaussian, of ONH geometry and mechanical properties. The authors predicted the lamina cribrosa displacement (LCD), scleral canal expansion (SCE), and the stresses (forces) and deformations (strains) produced by a 10 mm Hg increase in IOP. The authors analyzed the distributions of the responses. Results. The responses were distributed nonuniformly, with the majority of the models having a response within a small region, often less than 30% of the size of the overall response region. This concentration of responses was more marked in the Gaussian population than in the uniform population. All the responses were positively skewed. Whether a particular case was typical or not depended on the response used for classification and on whether the decision was made using one-dimensional or two-dimensional criteria. Conclusions. Despite wide variations in ONH characteristics and responses to IOP, some responses were much more common than others. This supports conceiving of the eye as a robust structure, particularly for LCD and SCE, which is tolerant to variations in tissue geometry and mechanical properties. The authors also provide the first estimates of the typical mechanical response of the ONH to variations in IOP over a large population of ONHs.

EARLY HISTOLOGIC AND FUNCTIONAL STUDY OF RADIAL OPTIC NEUROTOMY OUTCOMES IN NORMAL RAT EYES

Radial optic neurotomy (RON) has been proposed as a treatment for central retinal vein occlusion. However, it is still under debate whether RON would be an adequate treatment or a dangerous procedure, and persuasive animal studies are lacking. The aim of this study was to analyze the early histologic and functional outcomes of RON in normal rat eyes. Radial optic neurotomy was performed by cutting into the optic nerve edge at the nasal hemisphere, while the contralateral eye underwent a sham procedure. The retinal function was assessed by scotopic electroretinography, and the visual pathway was assessed by flash visual evoked potentials. Intraocular pressure was assessed with a tonometer, the pupillary light reflex was measured after exposing eyes to a 30-second light flash, whereas the optic nerve head structure was examined by histologic analysis. In normal rat eyes, RON provoked minor histologic alterations at the optic nerve head level and a transient decrease in the electroretinography. No changes in visual evoked potentials, intraocular pressure, and pupillary light reflex were observed in rat eyes submitted to RON. To our knowledge, this is the first study describing the early histopathologic and functional consequences of RON in normal rat eyes.

Enhanced Depth Imaging Optical Coherence Tomography of Deep Optic Nerve Complex Structures in Glaucoma

To assess the usefulness of enhanced depth imaging (EDI) optical coherence tomography (OCT) for evaluating deep structures of the optic nerve complex (ONC; optic nerve head and peripapillary structures) in glaucoma. Prospective, observational study. Seventy-three established glaucoma patients (139 eyes) with a range of glaucomatous damage. Serial horizontal and vertical EDI OCT images of the ONC were obtained from both eyes of each participant. Deep ONC structures, including the lamina cribrosa (LC), short posterior ciliary artery (SPCA), central retinal artery (CRA), central retinal vein (CRV), peripapillary choroid and sclera, and subarachnoid space around the optic nerve, were investigated for their visibility and morphologic features. Deep ONC structures identified in EDI OCT images. Visual field mean deviation of 139 included eyes was -11.8 ± 8.6 dB (range, -28.70 to -2.01 dB). The anterior laminar surface was identified in all eyes in the central laminar area and in 91 (65%) eyes in the periphery beneath the neuroretinal and scleral rims or vascular structures. The LC pores with various shapes and sizes were visualized in 106 (76%) eyes, mainly in the central and temporal areas of the LC. Localized LC lesions seen on optic disc photographs were identified as focal LC defects (partial loss of LC tissue) in the EDI OCT images. The locations of the CRA and CRV were identified in all eyes. In the LC, the CRA maintained a straight shape with a consistent caliber, but the CRV (and tributaries) assumed a more irregular shape. The SPCAs, their branches through the emissary canals in the sclera, or both were visualized in 120 (86%) eyes. The subarachnoid space around the optic nerve was identified with varying degrees of clarity in 25 eyes (18%): 17 had high myopia and extensive parapapillary atrophy. Intrachoroidal cavitation or choroidal schisis, which had been unrecognized clinically, was identified in 2 eyes (1%) with high myopia. Enhanced depth imaging OCT was able to visualize a wide variety of deep ONC structures in glaucoma patients and may be helpful in detecting, conceptualizing, and understanding basic and complicated in vivo anatomic and pathologic features of the ONC in glaucoma. Proprietary or commercial disclosure may be found after the references.

Ischemic Tolerance Protects the Rat Retina from Glaucomatous Damage

Glaucoma is a leading cause of acquired blindness which may involve an ischemic-like insult to retinal ganglion cells and optic nerve head. We investigated the effect of a weekly application of brief ischemia pulses (ischemic conditioning) on the rat retinal damage induced by experimental glaucoma. Glaucoma was induced by weekly injections of chondroitin sulfate (CS) in the rat eye anterior chamber. Retinal ischemia was induced by increasing intraocular pressure to 120 mmHg for 5 min; this maneuver started after 6 weekly injections of vehicle or CS and was weekly repeated in one eye, while the contralateral eye was submitted to a sham procedure. Glaucoma was evaluated in terms of: i) intraocular pressure (IOP), ii) retinal function (electroretinogram (ERG)), iii) visual pathway function (visual evoked potentials, (VEPs)) iv) histology of the retina and optic nerve head. Retinal thiobarbituric acid substances levels were assessed as an index of lipid peroxidation. Ischemic conditioning significantly preserved ERG, VEPs, as well as retinal and optic nerve head structure from glaucomatous damage, without changes in IOP. Moreover, ischemia pulses abrogated the increase in lipid peroxidation induced by experimental glaucoma. These results indicate that induction of ischemic tolerance could constitute a fertile avenue for the development of new therapeutic strategies in glaucoma treatment.

Deformation of the Rodent Optic Nerve Head and Peripapillary Structures during Acute Intraocular Pressure Elevation

PURPOSE. To evaluate the effect of acutely elevated intraocular pressure (IOP) on retinal thickness and optic nerve head (ONH) structure in the rat eye by spectral domain-optical coherence tomography (SD-OCT). METHODS. Fourteen adult male Brown-Norway rats were studied under anesthesia (ketamine/xylazine/acepromazine, 55:5:1 mg/kg intramuscularly). Both eyes were imaged by SD-OCT on two baseline occasions several weeks before and again 2 and 4 weeks after the acute IOP imaging session. During the acute IOP session, SD-OCT imaging was performed 10 minutes after IOP was manometrically set at 15 mm Hg and then at 10, 30, and 60 minutes after IOP had been elevated to 50 mm Hg (n = 8) and again 10 and 30 minutes after IOP had been lowered back to 15 mm Hg (recovery). In two additional groups, IOP elevation was set to 70 mm Hg (n = 4) or 40 mm Hg (n = 2). Acute IOP results are reported for a pattern of 49 horizontal B-scans spanning a 20° square and follow-up results for peripapillary circular B-scans. Retinal and retinal nerve fiber layer (RNFL) thicknesses were measured with custom software by manual image segmentation. Friedman and Dunn's tests were used to assess acute and longer-term effects of acute IOP elevation. RESULTS. Acute IOP elevation to 50 mm Hg caused rapid (within seconds) deformation of the ONH and peripapillary structures, including posterior displacement of the ONH surface and outward bowing of peripapillary tissue; retinal thickness decreased progressively from 10 to 30 to 60 minutes by 16%, 18%, and 20% within the area of Bruch's membrane opening (BMO; P < 0.0001) by 8%, 9%, and 11% within the central 10° (excluding the BMO; P < 0.0001) but only by 1%, 2%, and 2.4% beyond the central 10° (P < 0.0001). Recovery was progressive and nearly complete by 30 minutes. Acute IOP elevation to 40 and 70 mm Hg produced similar structural changes, but 70 mm Hg also interfered with retinal blood flow. There were no changes in peripapillary retinal or RNFL thickness (P = 0.08 and P = 0.16, respectively) measured 2 and 4 weeks after acute elevation to 50 mm Hg. CONCLUSIONS. Acute IOP elevation in the rodent eye causes rapid, reversible posterior deformation of the ONH and thinning of the peripapillary retina, with only minimal retinal thinning beyond 5° of the ONH. No permanent changes in peripapillary retinal or RNFL thickness (for up to 1 month of follow-up) were caused by 60 minutes of IOP elevation to 50 mm Hg.

Optical Coherence Tomography of the Swollen Optic Nerve Head: Deformation of the Peripapillary Retinal Pigment Epithelium Layer in Papilledema

PURPOSE. To examine the biomechanical deformation of load bearing structures of the optic nerve head (ONH) resulting from raised intracranial pressure, using high definition optical coherence tomography (HD-OCT). The authors postulate that elevated intracranial pressure induces forces in the retrolaminar subarachnoid space that can deform ONH structures, particularly the peripapillary Bruch's membrane (BM) and RPE layers. METHODS. The authors compared HD-OCT optic nerve and peripapillary retinal nerve fiber layer (RNFL) findings in eyes with papilledema caused by raised intracranial pressure to findings in eyes with optic disc swelling caused by optic neuritis and nonarteritic anterior ischemic optic neuropathy (NAION), conditions without intracranial hypertension. The authors measured average thickness of the RNFL and the angle of the RPE/BM at the temporal and nasal borders of the neural canal opening. The angle was measured as positive with inward (toward the vitreous) angulation and as negative with outward angulation. RESULTS. Of 30 eyes with papilledema, 20 eyes (67%) had positive RPE/BM rim angles. One of eight optic neuritis (12%) eyes and 1 of 12 NAION (8%) eyes had positive angulation. In five eyes with papilledema, RNFL thickening increased, three of which developed positive RPE/BM angles. On follow-up, 22 papilledema eyes had a reduction of RNFL swelling, and 17 of these eyes had less positive RPE/BM angulation. CONCLUSIONS. In papilledema, the RPE/BM is commonly deflected inward, in contrast to eyes with NAION or optic neuritis. The RPE/BM angulation is presumed to be caused by elevated pressure in the subarachnoid space, does not correlate with the amount of RNFL swelling, and resolves as papilledema subsides.

Effect of Chondroitin Sulfate on Intraocular Pressure in Rats

To study the effect of intracameral injections of chondroitin sulfate (CS) on intraocular pressure (IOP), retinal function, and histology in rats. Acute or chronic injections of CS were performed unilaterally in the rat anterior chamber, whereas the contralateral eye was injected with vehicle. IOP was daily or weekly assessed by a tonometer. Retinal function was assessed by scotopic electroretinography (ERG) and the visual pathway by flash visual evoked potentials (VEPs), whereas the retinal and optic nerve head structure were examined by histologic analysis. A single injection of 8 mg (but not 2 or 4 mg) CS induced a significant increase of IOP. The increase of IOP induced by a single injection of 8 mg CS lasted for 7 days, whereas chronic (weekly) administration during 10 weeks induced a significant and sustained increase in IOP compared with eyes injected with vehicle. A significant decrease of scotopic ERG a- and b- wave amplitude was observed after 6 and 10 weeks of CS administration. Moreover, a significant decrease in scotopic flash VEP N2-P2 component amplitude was observed in eyes treated with CS for 6 and 10 weeks. A significant loss of ganglion cell layer cells and optic nerve axons was observed in eyes receiving CS for 10 weeks. These results suggest that exogenous CS simulates the accumulation of CS in primary open-angle glaucoma and that increased amounts of CS could play a key role in the IOP dysregulation characteristic of glaucoma.