Understanding structure and function in glaucoma

OBJECTIVE: Glaucomatous optic neuropathy (GON), defined as definitive damage to the optic-nerve head (ONH) and retinal-nerve-fiber layer (RNFL), involves structural changes in the ONH and RNFL and functional losses in the central visual field. Due to the unique anatomic distribution of the nerve fibers as they enter the ONH, there are specific changes in the ONH correlated with specific findings in the visual-field characteristic of GON. The evaluation of these changes is discussed. METHODS: There are qualitative and quantitative methods in the structural examination of the ONH and RNFL, and quantitative techniques in the functional assessment of the central visual field. They are correlated to one another their strengths and limitations are discussed. RESULTS: Clinical evaluation of the ONH and RNFL consists of five basic rules: (1) identify the limits of the optic disc and determine its size, (2) identify the s of the neuroretinal rim, (3) examine the RNFL, (4) examine the region for parapapillary atrophy, and (5) look for retinal and optic-disc hemorrhages. These steps are simple to use and comprise a portion of the comprehensive eye evaluation. Without proper documentation of the changes in glaucoma progression may be missed. Computer-based digital-imaging technology exemplified by the HRT II, GDx, OCT, provides fast, reproducible, objective measurements of the ONH and RNFL, allowing for more precise diagnosis and monitoring of glaucoma. These changes have good correlation to functional assessments exemplified by the standard automated perimetry (SAP) and the selective perimetry (FDT, SWAP). Typical glaucomatous visu field defects include nasal step, paracentral scotoma, and arcuate defects which follow the RNFL pattern. Progression of these defects is monitored over time and needs to be differentiated from long-term fluctuation. CONCLUSION: The clinician should perform both structural and functional assessments to diagnose and monitor glaucoma. Both examinations provide complimentary information and each has its own place in the clinical care of glaucoma patients. The newer imaging devices and selective perimetry augment the diagnostic armamentarium of the clinician and should, therefore, be used appropriately.

Risk of visual loss in advanced glaucoma after trabeculectomy and combined cataract surgery

OBJECTIVE: This study determined the risk of postoperative visual loss and the factors affecting the decrease in visual acuity in patients with advanced glaucoma who underwent trabeculectomy or combined cataract surgery. METHODS: Charts of patients with advanced glaucoma who underwent trabeculectomy or combined cataract surgery were reviewed for the following parameters: visual acuity (VA), intraocular pressure (IOP), and visual-field indices of the Humphrey perimetry. Eyes that lost 2 or more Snellen lines or worsened one category two months after surgery were identified. Central vision was lost (wipeout) when best corrected VA was less than 20/200, characterized as a sudden, permanent, and unexplained visual loss within 2 months post-operatively. Analysis of variance (ANOVA) determined the differences between groups and logistic regression analyzed the factors affecting the decrease in visual acuity postoperatively. RESULTS: Ninety-eight eyes of 92 patients aged 18 years and older were included in the study. The incidence of postoperative visual loss 2 months after surgery was 20 percent (20/98), of which 3 percent (3/98) was considered "wipeout." Factors affecting the decrease in VA postoperatively include the presence of surgical complications (p = 0.04) and increase in postoperative IOP at two months (p = 0.05). CONCLUSION: The incidence of wipeout among patients with advanced glaucoma who underwent trabeculectomy or combined cataract surgery is low and generally occurs in patients with central-splitting fixation. Surgical complications play a major role in causing postoperative decrease in VA.

The diagnostic properties of a nerve-fiber analyzer in glaucoma: potential use as a screening or diagnostic tool

Methods: Patients with and without glaucoma underwent a complete eye evaluation, automated perimetry, scanning laser polarimetry with the GDx 400, and opticdisc photography. Two glaucoma experts graded each study eye. Two-by-two tables were constructed for 5 GDx parameters (average thickness, superior average, inferior average, ellipse average, and ellipse modulation) and the CDx number. Receiver operating characteristic (ROC) curves were generated. Results: The study included 355 patients (171 normal, 184 glaucoma). The mean values of the 5 GDx parameters were lower for the glaucoma than for the normal group. The sensitivity and specificity of the GDx 400 were 45.4 percent and 91.9 percent if the cut off level of the GDx number was 71. Ellipse modulation (EM) measures have the best ROC curve with area under the curve of 0.725. Conclusion: The GDx 400 nerve-fiber analyzer is primarily used as a screening tool to detect the presence or absence of glaucoma. Its accuracy can be improved with use of continuous corneal compensator.

Retinal nerve fiber measurements in glaucoma suspects

Purpose: To determine the proportion of glaucoma suspects with abnormal nerve fiber layer measurement using GDx nerve fiber analyzer Methodology: The study population consisted of glaucoma suspects between ages 30-70 years, who underwent glaucoma workup including retinal nerve fiber layer measurement (GDx NFA) Results: 35 eyes of glaucoma suspects were analyzed. 28/35 were found to have normal NFL thickness; 5/35 have 1 abnormal GDx parameters; 1/35 with 3 abnormal GDx parameters; 1/35 with 3 GDx abnormal parameters. Linear regression analysis showed no correlation between C:D and GDx parameters Conclusion: This study confirms that superior maximum is useful to the other parameters but there is a need to collect more samples. (Author)

Cup to disc ratio and optic disc size in screening for glaucoma

PURPOSE:To determine the cup and disc areas using computer-aided imaging. METHODOLOGY:Case-control study using the computer-aided imaging as a screening test in a given population. RESULTS:There is a wide variability in cup and disc areas among glaucoma suspects and normal. CONCLUSION:C:D alone has a poor predictive value for diagnosing glaucoma.Optic disc size with C:D is just as sensitive and specific in screening for glaucoma.Cup and disc areas are positively correlated for normal and glaucoma suspects.