John McSoley

Sensitivity and specificity of the Swedish interactive threshold algorithm for glaucomatous visual field defects.

PURPOSE To determine the sensitivity and specificity of two new visual field algorithms in detecting glaucomatous visual field defects: (1) Swedish interactive threshold algorithm (SITA) standard and (2) SITA fast. DESIGN Prospective observational case series. PARTICIPANTS Ninety normal subjects and 82 glaucoma patients. TESTING Central 30 degrees fields were performed with the Humphrey visual field analyzer 30-2 program (Humphrey Systems, Dublin, CA) using full threshold, SITA standard, and SITA fast algorithms on the same day for two or more sessions within a 1-month period. MAIN OUTCOME MEASURES Sensitivity and specificity in detecting glaucomatous visual field defects with SITA standard and SITA fast using full threshold testing as the reference standard. RESULTS The sensitivity of SITA standard and SITA fast in detecting glaucomatous defects overall was 98% and 95%, respectively. In the subset of mild glaucomatous field defects (26 patients), sensitivity of SITA standard was 92% versus 85% with SITA fast. Sensitivity was 100% for both algorithms in moderate to severe glaucomatous defects. Specificity for glaucoma defects using SITA standard and SITA fast was 96% for both algorithms. SITA standard reduced test-taking time from full threshold by 52% in normal subjects and 47% in glaucoma patients (P < 0.001). SITA fast reduced test-taking time by 72% in normal subjects and 65% in glaucoma patients (P < 0.001). Mean deviation values were 0.4 dB and 0.8 dB better in SITA standard and SITA fast fields, respectively, in normal subjects (P < 0.001), and 0.7 dB and 1.2 dB in SITA standard and SITA fast fields, respectively, in glaucoma patients (P < 0.001) compared with full threshold values. CONCLUSIONS The new algorithms for measuring visual fields, SITA standard and SITA fast, have excellent sensitivity and specificity for glaucomatous visual field loss with considerable savings in time.

Effect of cataract and its removal on signal strength and peripapillary retinal nerve fiber layer optical coherence tomography measurements.

PurposeTo assess the effect of cataract on optical coherence tomography (OCT), signal strength (SS), and peripapillary retinal nerve fiber layer (RNFL) thickness measurements. MethodsPeripapillary RNFL thickness measurements were obtained by Stratus OCT scans using the Fast RNFL thickness (3.4) acquisition protocol before and after cataract extraction in 45 patients with cataract, including 23 glaucoma patients. Cataracts were graded according to the Lens Opacities Classification System III. ResultsThe postoperative RNFL thickness and SS were 9.3% (P=0.001) and 24.1% (P<0.001) higher than before surgery, respectively. There was greater postoperative change in RNFL thickness measurements in patients with lower preoperative RNFL measurements (r=−0.63, P<0.001) and SS (r=−0.59, P<0.001). Eyes with preoperative SS more than 6 had no significant difference between precataract and postcataract surgery RNFL thickness (P=0.14). There was no significant difference in RNFL thickness change between eyes with cataract only (10.9±20.8 &mgr;m) and those with cataract and glaucoma (7.0±14.7 &mgr;m; P=0.81). ConclusionsCataracts may decrease peripapillary RNFL thickness measurements and the SS on OCT scans. Thinning of the peripapillary RNFL suggestive of glaucomatous progression may be the result of artifact from advancing cataract rather than actual structural changes in the peripapillary RNFL. Peripapillary RNFL thickness measurements should be interpreted with caution in glaucomatous eyes with significant cataract, particularly if the SS is attenuated.

Characteristics of optic nerve head drusen on optical coherence tomography images.

BACKGROUND AND OBJECTIVE To describe the characteristics of optic nerve head drusen in optical coherence tomography (OCT) images. PATIENTS AND METHODS Cross-sectional images of the optic nerve were obtained in seven patients with optic nerve head drusen with Stratus and spectral-domain OCT (Carl Zeiss Meditec, Dublin, CA). These were compared to optic disc photographs, autofluorescence, and echography images. For comparison, these tests were performed on four patients with papilledema and three patients with small optic discs. RESULTS Optic nerve head drusen typically elevated the disc surface and appeared as an optically empty cavity, sometimes with a perceptible reflection from the posterior surface. The disc surface was also elevated in cases of papilledema, but had a strong anterior reflectance behind which there was no visible structure. The surface of the small optic nerves was slightly elevated, but with less anterior reflectance. CONCLUSION Optic nerves with drusen showed features in these OCT images that were distinct from cases of papilledema or small optic discs.

Evaluation of decision rules for frequency-doubling technology screening tests.

Purpose. Frequency-doubling technology (FDT) perimetry has shown promise as a screening test for glaucoma. This study investigates different possible decision rules for FDT screening by applying them to groups of normal and glaucoma subjects. Methods. Within three centers, 218 subjects (aged 15–88 years; 78 with glaucoma, 140 without ocular disease) were each tested twice with the screening program of the FDT perimeter. The subjects consisted of 140 normal subjects with no evidence of glaucoma or other ocular disease likely to affect the visual field and 78 subjects with a diagnosis of glaucoma and no other ocular disease. Fifteen decision rules were applied to the data to compare their sensitivity and specificity. Results. Estimated specificities of the different decision rules ranged from 78% to 99%, although with this sample size, the confidence intervals for these estimates are quite large. Estimated sensitivities ranged from 40% to 72%. Suggested criteria for distinguishing normal subjects from those with glaucoma seem to be either a cluster of two or more adjacent locations abnormal at the p < 2% level with at least one location confirmed or a single location very abnormal (p < 1%) and confirmed. Conclusions. Specificity was clearly improved by confirming an apparently abnormal test result by repeating the screening test outweighing the resultant small loss in sensitivity. These findings provide useful information for making an informed choice of decision rules for FDT screening results.

Comparison of matrix with humphrey field analyzer II with SITA

Purpose To study the performance of the Matrix perimeter compared with the Humphrey Field Analyzer II (HFA) with the Swedish Interactive Thresholding Algorithm over the range of contrast sensitivities each machine could estimate. Methods Fifty stable glaucoma subjects at various stages of disease and three normal subjects had visual fields testing done on five different days within 8 weeks with both perimeters. Intraclass correlation coefficient of mean deviation, pattern standard deviation, and the SD of repeat measurements were evaluated. The repeatability of the sensitivity estimates at individual locations and global indices was quantified, as well as their dependence on disease severity. The relationship between sensitivity determinations with the two instruments was explored (principal curve analysis). Results Mean deviation on the HFA ranged from −31 to +2.5 dB. The mean deviation and pattern standard deviation had intraclass correlation coefficients above 0.90 for both instruments. Over most of the useful range (above 20 dB on the HFA), a difference of 1 dB for the Matrix corresponded to a difference of 2 dB for the HFA. The SD of repeat measurements increased with disease severity with HFA, but not with Matrix, except that values of 12 or 34 dB were highly variable on repeat. Variability was reduced for both HFA and Matrix when duplicate sensitivity values were used. A single Matrix test provided only 15 possible sensitivity values, unevenly spaced, but the average of duplicate measurements provided more numerous sensitivity values. A learning effect was detected for Matrix. Conclusions The decibel values reported by the two machines are not equivalent. Variability of sensitivity determinations is affected more by the sensitivity level with HFA than with Matrix. Duplicate measurements for baseline and follow-up evaluation could be important, especially for Matrix. Further information on learning effects is needed, as is commercially available progression software for Matrix.

Head-down Posture in Glaucoma Suspects Induces Changes in IOP, Systemic Pressure, and PERG That Predict Future Loss of Optic Nerve Tissue

Purpose: To obtain pilot data on posture-induced changes of intraocular pressure (IOP), systemic pressure, and pattern electroretinogram (PERG) predictive of future optic nerve tissue loss glaucoma suspects (GSs). Methods: Mean peripapillary retinal fiber layer thickness (RNFLT) was measured with optical coherence tomography 2 times/year in 28 GS aged 58±8.9 years over 5.0±0.73 years. All patients had a baseline PERG, IOP, and brachial blood pressure measurements in the seated and −10 degrees head-down-body-tilt (HDT) position. Outcome measures were seated/HDT PERG amplitude and phase, IOP, mean arterial blood pressure, and estimated ocular perfusion pressure. An additional group of 11 similarly aged controls aged 56.9±13 years was tested for comparison. Results: Although all GS had initial RNFLT in the normal range, 9/28 of them developed significant (P<0.05) loss of mean RNFLT [thinners (T)] over the follow-up period as opposed to 19/28 who did not [nonthinners (NT)]. Significant (P<0.05) differences between similarly aged controls, NT, and T were found in PERG amplitude, PERG phase, mean arterial blood pressure, IOP, and ocular perfusion pressure. A nominal logistic regression using baseline PERG and hemodynamic variables was able to distinguish T from NT with an area under receiving operator characteristic of 0.89 (SE, 0.07). Conclusions: Baseline PERG, IOP, and systemic blood pressure, together with their changes upon HDT, may have predictive value for future loss of optic nerve tissue in GS. This study supports the rationale for a full-scale clinical trial to identify patients at high risk of development of glaucoma.