Sima Shakiba

Bio: Sima Shakiba is an academic researcher from University of California, San Diego. The author has contributed to research in topics: Glaucoma & Nerve fiber layer. The author has an hindex of 4, co-authored 4 publications receiving 863 citations.

Comparison of the GDx VCC scanning laser polarimeter, HRT II confocal scanning laser ophthalmoscope, and stratus OCT optical coherence tomograph for the detection of glaucoma.

Abstract: Objective: To compare the abilities of current commercially available versions of 3 optical imaging techniques: scanning laser polarimetry with variable corneal compensation (GDx VCC), confocal scanning laser ophthalmoscopy (HRT II [Heidelberg Retina Tomograph]), and optical coherence tomography (Stratus OCT) to discriminate between healthy eyes and eyes with glaucomatous visual field loss. Methods: We included 107 patients with glaucomatous visual field loss and 76 healthy subjects of a similar age. All individuals underwent imaging with a GDx VCC, HRT II, and fast retinal nerve fiber layer scan with the Stratus OCT as well as visual field testing within a 6-month period. Receiver operating characteristic curves and sensitivities at fixed specificities (80% and 95%) were calculated for parameters reported as continuous variables. Diagnostic categorization (outside normal limits, borderline, or within normal limits) provided by each instrument after comparison with its respective normative database was also evaluated, and likelihood ratios were reported. Agreement on categorization between methods (weighted ) was assessed. Results: After the exclusion of subjects with unacceptable images, the final study sample included 141 eyes of 141 subjects (75 with glaucoma and 66 healthy control subjects). Mean±SD mean deviation of the visual field test result for patients with glaucoma was �4.87±3.9 dB, and 70% of these patients had early glaucomatous visual field damage. No statistically significant difference was found between the areas under the receiver operating characteristic curves (AUCs) for the best parameters from the GDx VCC (nerve fiber indicator, AUC=0.91), Stratus OCT (retinal nerve fiber layer inferior thickness, AUC=0.92), and HRT II (linear discriminant function, AUC=0.86). Abnormal results for each of the instruments, after comparison with their normative databases, were associated with strong positive likelihood ratios. Chance-corrected agreement (weighted ) among the 3 instruments ranged from moderate to substantial (0.50-0.72). Conclusions: The AUCs and the sensitivities at high specificities were similar among the best parameters from each instrument. Abnormal results (as compared with each instrument’s normative database) were associated with high likelihood ratios and large effects on posttest probabilities of having glaucomatous visual field loss. Calculation of likelihood ratios may provide additional information to assist theclinicianindiagnosingglaucomawiththeseinstruments.

Ganglion cell losses underlying visual field defects from experimental glaucoma

Abstract: PURPOSE. To investigate the relationship between ganglion cell losses and visual field defects caused by glaucoma. METHODS. Behavioral perimetry and histology data were obtained from 10 rhesus monkeys with unilateral experimental glaucoma that was induced by argon laser treatments to their trabecular meshwork. After significant visual field defects had developed, the retinas were collected for histologic analysis. The ganglion cells were counted by light microscopy in cresyl violet-stained retina sections, and the percentage of ganglion cell loss (treated to control eye counts) was compared with the depth of visual field defect (treated to control eye thresholds) at corresponding retinal and perimetry test locations. Sensitivity losses as a function of ganglion cell losses were analyzed for Goldmann III, white and Goldmann V, and short- and long-wavelength perimetry test stimuli. RESULTS. The relationship between the proportional losses of ganglion cells and visual sensitivity, measured with either white or colored stimuli, was nonlinear. With white stimuli, the visual sensitivity losses were relatively constant (approximately 6 dB) for ganglion cell losses of less than 30% to 50%, and then with greater amounts of cell loss the visual defects were more systematically related to ganglion cell loss (approximately 0.42 dB/percent cell loss). The forms of the neural-sensitivity relationships for visual defects measured with short- or long-wavelength perimetry stimuli were similar when the visual thresholds were normalized to compensate for differences in expected normal thresholds for white and colored perimetry stimuli. CONCLUSIONS. Current perimetry regimens with either white or monochromatic stimuli do not provide a useful estimate of ganglion cell loss until a substantial proportion have died. The variance in ganglion cell loss is large for mild defects that would be diagnostic of early glaucoma and for visual field locations near the fovea where sensitivity losses occur relatively late in the disease process. The neural-sensitivity relationships were essentially identical for both white and monochromatic test stimuli, and it therefore seems unlikely that the higher sensitivity for detecting glaucoma with monochromatic stimuli is based on the size-dependent susceptibility of ganglion cells to injury from glaucoma.

Detecting early glaucoma by assessment of retinal nerve fiber layer thickness and visual function.

Abstract: PURPOSE. To compare the abilities of scanning laser polarimetry (SLP), optical coherence tomography (OCT), short-wavelength automated perimetry (SWAP), and frequency-doubling technology (FDT) perimetry to discriminate between healthy eyes and those with early glaucoma, classified based on standard automated perimetry (SAP) and optic disc appearance. To determine the agreement among instruments for classifying eyes as glaucomatous. METHODS. One eye of each of 94 subjects was included. Healthy eyes (n = 38) had both normal-appearing optic discs and normal SAP results. Glaucoma by SAP (n = 42) required a repeatable abnormal result (glaucoma hemifield test [GHT] or corrected pattern standard deviation [CPSD] outside normal limits). Glaucoma by disc appearance (n = 51) was based on masked stereoscopic photograph evaluation. Receiver operating characteristic (ROC) curve areas, sensitivities, and specificities were calculated for each instrument separately for each diagnosis. RESULTS. The largest area under the ROC curve was found for OCT inferior quadrant thickness (0.91 for diagnosis based on SAP, 0.89 for diagnosis based on disc appearance), followed by the FDT number of total deviation plot points of ≤5% (0.88 and 0.87, respectively), SLP linear discriminant function (0.79 and 0.81, respectively), and SWAP PSD (0.78 and 0.76, respectively). For diagnosis based on SAP, the ROC curve area was significantly larger for OCT than for SLP and SWAP. For diagnosis based on disc appearance, the ROC curve area was significantly larger for OCT than for SWAP. For both diagnostic criteria, at specificities of ≥90% and ≥70%, the most sensitive OCT parameter was more sensitive than the most sensitive SWAP and SLP parameters. For diagnosis based on SAP, the most sensitive FDT parameter was more sensitive than the most sensitive SLP parameter at specificities of ≥90% and ≥70% and was more sensitive than the most sensitive SWAP parameter at specificity of ≥70%. For diagnosis based on disc appearance at specificity of ≥90%, the most sensitive FDT parameter was more sensitive than the most sensitive SWAP and SLP parameters. At specificity ≥ 90%, agreement among instruments for classifying eyes as glaucomatous was poor. CONCLUSIONS. In general, areas under the ROC curve were largest (although not always significantly so) for OCT parameters, followed by FDT, SLP, and SWAP, regardless of the definition of glaucoma used. The most sensitive OCT and FDT parameters tended to be more sensitive than the most sensitive SWAP and SLI' parameters at the specificities investigated, regardless of diagnostic criteria.