Harmohina Bagga

Scanning laser polarimetry with variable corneal compensation and optical coherence tomography in normal and glaucomatous eyes

PURPOSE To evaluate the relationship between visual function and retinal nerve fiber layer (RNFL) measurements obtained with scanning laser polarimetry with variable corneal compensation (SLP-VCC) and optical coherence tomography (OCT). DESIGN Cross-sectional analysis of normal and glaucomatous eyes in a tertiary care academic referral practice. METHODS A commercial GDx nerve fiber analyzer was modified to enable the measurement of corneal polarization axis and magnitude so that compensation for corneal birefringence was eye specific. Complete examination, SLP with fixed corneal compensation (FCC) and variable corneal compensation (VCC), optical coherence tomography (OCT) imaging of the peripapillary RNFL, and automated achromatic perimetry were performed in all subjects. Exclusion criteria were visual acuity less than 20/40, diseases other than glaucoma, and unreliable perimetry. RESULTS Fifty-nine patients (59 eyes; 29 normal, 30 glaucomatous) were enrolled (mean age, 56.7 +/- 20.3 years, range, 20-91). All eyes with glaucoma had associated visual field loss (average mean defect, -8.4 +/- 5.8 dB). Using SLP-FCC, nine of 12 retardation parameters (75%) were significantly less in glaucomatous eyes. Using SLP-VCC, 11of 12 retardation parameters (92%) were significantly less in glaucomatous eyes. Multiple regression models constructed for each retardation parameter with visual field demonstrated that the following VCC parameters were statistically significant whereas FCC parameters were not: ellipse average (FCC, P =.28, VCC, P =.001), superior average (FCC, P =.38, VCC, P <.001), inferior average (FCC, P =.10, VCC, P =.008), average thickness (FCC, P =.30, VCC, P =.031), and superior integral (FCC, P =.43, VCC, P =.001). Similar results were obtained for multiple regression models constructed with OCT-derived RNFL thickness: ellipse average (FCC, P =.99, VCC, P =.002), superior average (FCC, P =.90, VCC, P <.001), inferior average (FCC, P =.61, VCC, P =.007), and superior integral (FCC, P =.92, VCC, P <.001). CONCLUSIONS Compared with fixed compensation, mean-based SLP parameters generated with SLP-VCC have greater correlation with visual function and RNFL thickness assessments obtained with OCT.

Macular symmetry testing for glaucoma detection

To evaluate structural asymmetry in the macula using optical coherence tomography (OCT) in glaucomatous eyes with visual field defects localized to one hemifield. Methods:Complete examination, standard automated perimetry (SAP), and OCT imaging (512 A-scans) of the peripapillary retina and macula were performed. Exclusion criteria were visual acuity <20/40, diseases other than glaucoma, and SAP defects localized to both hemifields. Macular OCT images were obtained using four 5-mm radial scans centered on the foveola and passing obliquely through the macula (15° superotemporally and inferotemporally). Macular measurements temporal to the fovea (T) were sub-divided into nasal (T1) and temporal (T2) segments. Macular symmetry testing (MST) was performed in T, T1, and T2 segments by comparing the mean macular thickness of the perimetrically abnormal and perimetrically normal hemi-zones (macular thickness in perimetrically normal hemi-zone/macular thickness in perimetrically abnormal hemi-zone × 100), and superior and inferior hemi-zones in normal subjects (macular thickness in superior hemi-zone/macular thickness in inferior hemi-zone × 100). MST measurements were considered to be abnormal if they exceeded the 95% limits of normal variability. Results:Forty eyes of 40 patients (20 normal, 20 glaucoma) were enrolled (mean age 60 ± 19 years, range 21-89). All eyes with glaucoma had associated hemifield defect (average MD = −7.23 ± 4.8 dB, range −0.9 to −15.4). In glaucomatous eyes, mean retinal thickness in T, T1, and T2 within the perimetrically abnormal hemi-zone (222 ± 14 μm, 224± 17 μm, 221 ±13 μm, respectively) was significantly less (P = 0.002, 0.008, 0.001, respectively) than the corresponding segments in the perimetrically normal hemi-zone (235 ± 17 μm, 237 ± 18 μm, 233 ± 17 μm, respectively). Normal eyes showed no difference (P = 0.17, 0.20, 0.35) in T, T1, and T2 measurements within the superior hemi-zone (254 ± 11, 249 ± 14, 258 ± 14) and inferior hemi-zone (252 ± 11, 250 ± 13, 255 ± 13), respectively. MST values in glaucomatous eyes were outside 95% limits of normal variability in 17/20 (85%) T segments, 16 /20 (80%) T1 segments, and 16/20 (80%) T2 segments. Conclusion:Localized macular thickness changes exist in glaucomatous eyes with regional visual field loss. The MST may represent a novel strategy for glaucoma diagnosis.

Predicting subsequent visual field loss in glaucomatous subjects with disc hemorrhage using retinal nerve fiber layer polarimetry

Purpose:To predict progression of visual field loss after an episode of disc hemorrhage in glaucoma patients on the basis of retinal nerve fiber layer (RNFL) GDx polarimetry measurements analyzed by wavelet-Fourier analysis (WFA). Methods:Retrospective GDx data from 16 subjects (10 progressors and 6 non-progressors based on visual fields) obtained near the time of disc hemorrhage were analyzed to predict which patients would have visual field progression. Polarimetry scans throughout a follow-up period (31 months average) were also analyzed to compare field progression to RNFL thickness change after the hemorrhage. Mean RNFL thickness inferred from the polarimetry data at sixteen 22.5° sectors at distances of 1.6, 1.7, and 1.8 disc diameters were used. Data were analyzed by applying to appropriate regions of disc hemorrhage patients a structural analysis (WFA) we had developed previously. A linear discriminant function (Fischer) was produced and a leave-one-out method using separate training and test data was used to assure validity of the results. Results:Patients who subsequently progressed were successfully predicted with moderate success (sensitivity / specificity was 0.77 / 0.88 with ROC area = 0.858). A separate analysis comparing pre- and post-hemorrhage RNFL sector thickness revealed clear evidence of RNFL thinning at the inferior and superior sectors before progression of visual field. The thinning of RNFL thickness was not restricted to regions corresponding to the location of the hemorrhage. Conclusion:Wavelet-Fourier analysis can differentiate progressors from non-progressors with moderate accuracy. Comparison to a prior study of this same cohort emphasizes that relatively small regions must be considered (as opposed to larger quadrants) to see these significant changes in RNFL.

Clinical variables associated with glaucomatous injury in eyes with large optic disc cupping.

BACKGROUND AND OBJECTIVE To characterize the range of retinal nerve fiber layer (RNFL) and standard automated perimetry damage in eyes with large vertical cup-disc ratio (VCDR). PATIENTS AND METHODS Complete examination, standard automated perimetry, scanning laser polarimetry with variable corneal compensation, and optical coherence tomography (OCT) of the RNFL and optic nerve head were performed. Large VCDR was defined as > or = 0.80 using stereoscopic disc examination and OCT optic nerve head analysis. Structural and functional characteristics were assessed separately in eyes with a disc area of less than 2 mm2, 2 to 2.5 mm2 and greater than 2.5 mm2. RESULTS Fifty-seven eyes of 57 subjects were enrolled. A broad range in mean deviation (2.0 to -32.8 dB) and mean RNFL thickness with OCT (24.3-100.4 microm) and scanning laser polarimetry with variable corneal compensation (24.0-61.7 microm) was identified. Predictors of standard automated perimetry severity using multiple linear regression were mean RNFL thickness using OCT (P = .001) and scanning laser polarimetry (P = .001), OCT-vertical cup diameter (P = .003), temporal, superior, nasal, inferior, temporal standard deviation (P = .03), and OCT-disc area (P = .04). Eyes with an OCT-disc area of less than 2 mm2 demonstrated significantly greater standard automated perimetry damage, RNFL loss using OCT and scanning laser polarimetry, and OCT-rim area (P = .002, .0007, .03, and < .0001, respectively) compared with eyes with a disc area of greater than 2.5 mm2. CONCLUSIONS Eyes with large VCDR have a wide range of RNFL atrophy and standard automated perimetry damage. Small optic discs are associated with more advanced glaucomatous injury.

Retinal nerve fiber layer assessment using scanning laser polarimetry

There is mounting evidence that retinal nerve fiber layer (RNFL) loss precedes detectable visual field loss in early glaucomatous optic neuropathy. However, examination and photography of the RNFL is a difficult technique in many patients, is subjective, qualitative, variably reproducible, time consuming, operator dependent, and has limited sensitivity and specificity. Scanning laser polarimetry provides automated, objective, and quantitative measurements of the RNFL. Such assessments are highly reproducible and show good agreement with clinical estimates of optic nerve head structure and visual function. This report will review the historical development, technological principles, reproducibility, sensitivity and specificity, capacity to detect glaucomatous progression, strengths, and limitations of this technology.

Blood Flow Studies and Serological Testing in the Diagnostic Evaluation of Glaucoma: A Pilot Study

BACKGROUND AND OBJECTIVE To evaluate the prevalence of hemodynamically significant carotid artery stenosis, peripapillary blood flow, and serologic abnormalities in a pilot study among patients with glaucoma. PATIENTS AND METHODS All subjects underwent complete eye examination, standard automated perimetry, carotid Doppler ultrasonography, serum laboratory testing, and scanning laser Doppler flowmetry (SLDF). Subjects were subdivided into two groups based on glaucoma subtype (normal-tension vs primary open-angle glaucoma) and severity (mild vs moderate-advanced). RESULTS Twenty eyes of 20 patients with associated glaucomatous visual field loss were enrolled. No significant differences in age, gender, intraocular pressure, systemic comorbidity, number of antiglaucoma medications, and prior filtration surgery were observed between the groups based on the type and severity of glaucoma. The prevalence of clinically significant (> 70%) carotid stenosis, mean peripapillary blood flow assessed by SLDF, mean erythrocyte sedimentation rate, mean hematocrit, mean hemoglobin, and positive FTA-ABS was similar in both groups. Severity of glaucomatous damage as determined by visual field mean defect did not correlate with the degree of carotid artery stenosis (R2 < 0.0001, P = .99) or peripapillary blood flow derived from mean SLDF (R2 = 0.0005, P = .92). CONCLUSION Data from this pilot study demonstrate that the prevalence of hemodynamically significant carotid stenosis, peripapillary blood flow, and serologic abnormalities are similar in patients with normal-tension and primary open-angle glaucoma, and do not correlate with glaucoma severity.