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New visual field indices of disharmony for early diagnosis of glaucoma, alone or associated with conventional parameters

PURPOSE

To evaluate the specificity of new perimetric indices based on harmony, alone and in combination with structural data, for glaucoma detection.

METHODS

In this prospective observational cross-sectional study, one eye of 105 healthy subjects and 97 early and suspect glaucomas were sequentially included and examined with Cirrus optical coherence tomography, twice with OCULUS Smartfield perimeter (SPARK strategy) and twice with Humphrey Analyzer (24-2 SITA-Fast) at the Ophthalmology Department from the University Hospital La Candelaria. Disharmony in the visual field was evaluated including vertical threshold symmetry, threshold rank), and homogeneity (threshold standard deviation from its maximum) using the patient himself/herself as a reference. We also evaluated disharmony in combination with the mean deviation and the pattern standard deviation in a single index (mismatch) and various combinations of morphological and functional indices. Combinations used a new score based on values above certain critical cut-off levels of each index.

RESULTS

For 95% specificity, the highest sensitivities were as follows: vertical cup/disc ratio: 28.9%; SPARK threshold rank: 29.9%; and SITA-Fast threshold standard deviation: 28.9%. For the combined indices and 100% specificity, they were 5 SPARK indices mismatch: 10.3%; 5 SITA-Fast indices mismatch: 11.3%; 8 optical coherence tomography indices: 21.9%; 13 SPARK and optical coherence tomography indices: 27.8%; and 13 SITA-Fast and optical coherence tomography indices: 32.0%.

CONCLUSION

Disharmony combined with normative value-based indices and/or optical coherence tomography indices is useful for very specific early diagnosis of glaucoma.

Franz Fankhauser: the father of the automated perimeter

Franz Fankhauser is known as the father of automated perimetry and of the q-switched Nd:YAG laser knife. His 15-year journey to computerize perimetry started in 1958 with unsuccessful attempts to automate kinetic perimetry. The switch to using static perimetry resulted in a breakthrough in 1973, and in 1975 the OCTOPUS perimeter came on the market. At the same time Fankhauser was working on the use of light sources for the treatment of ocular tissues. During his career, Fankhauser worked in very close collaboration with mathematicians, physicists, engineers. One of the most astonishing characteristics of Fankhauser was his ability to find and to motivate young scientists to work as a cohesive group for his projects.

Age-dependent normative values for differential luminance sensitivity in automated static perimetry using the Octopus 101

PURPOSE

To determine age-dependent normative differential threshold values for the Octopus 101 instrument and to create a smooth mathematical model characterizing the age-dependency and asymmetry of the hill of vision.

METHODS

Static automated perimetry within the central 30 degrees visual field (VF) was conducted with the Octopus 101 (background luminance 10 cd/m(2)) in 81 eyes of 81 ophthalmologically healthy subjects (11-12 per decade of age) aged 10-79 years. A 4-2-2 staircase strategy with three reversals was run. The test point grid consisted of 68 concentrically arranged points with test point condensation towards the VF centre, representing the approximately rotation-symmetrical 30 degrees hill of vision. Thresholds of differential luminance sensitivity (DLS) were estimated by the maximum likelihood method. A smooth mathematical model was fitted to the normative data.

RESULTS

The model fit was satisfactory (r(2) = 0.74). Covariables were: age, eccentricity, angle and subject. Total random standard deviation (SD) was 1.75 dB. The residual SD exceeded 1.75 dB in the border region, was 1.5 dB within the centre and fell below 1.25 dB in a ring around the centre. Average thresholds of DLS varied with age quadratically. It is close to constant for the 10-40-year-old age group and declines ever more steeply thereafter. The effect of age on DLS in the VF increased with eccentricity. The greatest drop was located in the peripheral superior hemifield: at 25 degrees eccentricity the superior DLS was estimated to be 5.5 dB higher in 10-year-olds than in 75-year-olds.

CONCLUSIONS

This new smooth model allows for the prediction of age-related normal threshold values for any stimulus location within the 30 degrees VF and thus for the calculation of global and local measures of defect such as mean defects or p-values for any type of stimulus.

Stabilization and comparison of TOP and Bracketing perimetric strategies using a threshold spatial filter

BACKGROUND

To evaluate a new perimetric spatial filter that takes into account relations of dependence between regions of the glaucomatous visual field.

METHODS

51 glaucoma patients and 30 controls were examined using the Octopus 1-2-3 on four occasions using program 32; two with TOP and two with Bracketing (BRA) strategy. Each threshold was replaced by a filtered threshold, calculated as the mean of its own value and the four points best correlated with it, weighted with the correlation coefficient (r) that relates them.

RESULTS

Application of the filter had minimal effect on the absolute mean defect (MD) but reduced the square root of loss variance (sLV) by 17.6% in TOP and 28.8% in BRA, increasing the similarity between their results. Filtered TOP and BRA thresholds were more similar than those obtained in the two unfiltered BRA examinations. Filtering reduced the value of short fluctuation by 28.6% in TOP and 45.4% in BRA and reduced sLV fluctuation by 14.3% in TOP and 24.2% in BRA, thus harmonizing the two strategies for these two parameters (p > 0.05). The influence of filtering on MD fluctuation was minimal (p > 0.05). In normal subjects the number of points beyond 5 dB of normality (not reproducible false scotomas) reduced from 1.5% to 0.2% in TOP and from 4.9% to 1.6% in BRA, while in glaucoma patients changes were minimal.

CONCLUSIONS

The proposed spatial filter stabilized perimetric results, acting with greater effect on BRA than on TOP, making their results more similar.

Comparison of Diagnostic Ability between a Fast Strategy, Tendency-Oriented Perimetry, and the Standard Bracketing Strategy

PURPOSE

To compare the diagnostic abilities of the standard bracketing strategy (BR) and a fast strategy, the tendency-oriented perimetry (TOP).

METHODS

Seventy-seven controls and 91 eyes from patients with glaucoma were analyzed with the strategies TOP and BR. Sensitivity (Se), specificity (Sp), the area under the receiver operating characteristic (ROC) curve (AC) and the optimum cutoff value (CO) were calculated for the visual field indices mean defect (MD), the square root of the loss variance (sLV) and the number of pathological points (NPP).

RESULTS

In the glaucoma group, the mean MD value using TOP and BR was 7.5 and 8.3 dB, respectively. The mean sLV value using TOP and BR was 5.0 and 5.3 dB, respectively. Indices provided by TOP had higher ROC values than the ones provided by BR. Using TOP, the index with the best diagnostic ability was sLV (Sp = 94.8, Se = 90.1, AC = 0.966, CO = 2.5 dB), followed by NPP and MD. Using BR, the best results were obtained for MD (Sp = 92.2, Se = 81.3, AC = 0.900, CO = 2.5 dB) followed by sLV and NPP.

CONCLUSIONS

A fast strategy, TOP, had superior diagnostic ability than the standard BR. Although TOP provided lower LV values than BR, the diagnostic ability of this index was higher than that of the conventional strategy.

Threshold variation in automated perimetry

A physiologic fluctuation in threshold levels exists in automated perimetry, which is greater in glaucoma and ocular hypertensive patients than in normal subjects. Fluctuation increases with greater eccentricity from fixation and in areas of reduced retinal sensitivity. Other factors related to automated perimetry testing potentially may influence threshold fluctuation including: a learning effect, reliability, pupil size, age, and the mode of stimulus presentation. Statistical software may aid in analyzing both the single field and the changes between successive fields. However, statistical programs cannot replace physician judgment, and all factors that may influence threshold levels should be considered when interpreting automated visual fields.

The distribution of normal values in automated perimetry

From 354 visual fields of 137 normal subjects, various components of variance were calculated separately for each test location of the Octopus automated-perimetry program J0. The method of component analysis of variance was used. The following components were analyzed: interindividual variation (variation of visual-field measurements in different subjects), long-term fluctuation (variation of different visual-field measurements in the same subject), differences between the right and left eyes and fluctuation within one visual field test in one subject, i.e., short-term fluctuation. The results show increased variations at the center relative to the paracentral area and a slight increase with eccentricity.

Full threshold versus quantification of defects for visual field testing in glaucoma

Nineteen glaucoma patients, 17 ocular hypertensives, and 16 normal subjects underwent visual field testing on the Humphrey Field Analyzer using two programs: full threshold (thresholding of all test points with double-crossing technique) and quantification of defects (thresholding only points that deviated more than 6 dB from a presumed normal retinal contour). The purpose of the study was to compare the diagnostic value of information gained by the latter, less time-consuming test with that of the full threshold procedure. The average time requirement per eye was 13 min 11 s for full thresholding and 4 min 22 s for quantification of defects. Of the 104 sets of fields, the diagnosis was at variance in 18. The differences were most often due to shallow defects in otherwise normal fields or shallow defects surrounding deeper scotomas that had been detected by both programs. The shallow defects placed the fields in more advanced diagnostic categories and were all detected with the full threshold technique.

Comparison of quantitative testing with the Octopus, Humphrey, and Tübingen perimeters

Meridional threshold testing was used to compare the quantitative abilities of the Octopus 201, Humphrey 620, and Tübingen perimeters. In 40 patients with mild to moderate glaucomatous visual field defects, the perimeters provided comparable results, and only small differences could be identified. Manual Tübingen testing identified slightly fewer defects, and scotomas were plotted as narrower and shallower than on the two automated devices, which were nearly equivalent in performance.

Neuropathies of the optic nerve and visual evoked potentials with special reference to color vision and differential light threshold measured with the computer perimeter OCTOPUS

The contrast evoked potentials (VEPs) to different check sizes were recorded in about 200 cases of discrete optic neuropathies (ON) of different origin. Differential light threshold (DLT) was tested with the computer perimeter OCTOPUS. Saturated and desaturated tests were applied to evaluate the degree of acquired color vision deficiency. Delayed VEP responses are not confined to optic neuritis (RBN) alone and the different latency times obtained from other ON are confluent. The delay may be due to demyelination, to an increasing dominance of paramacular VEP subcomponents or to an increasing dominance of the upper half-field responses. Recording with smaller check sizes has the advantage that discrete dysfunctions in the visual field (VF) center are more easily detected: a correlation between amplitudes and visual acuity is best in strabismic amblyopias, is less expressed in maculopathies of the retina and weak in ON. The absence or reduction of amplitudes to smaller check sizes, however, is an important indication of a disorder in the VF center of ON in an early or recovered stage. Acquired color vision defects of the tritan-like type are more confined to discrete ON, whereas the red/green type is reserved to more severe ON. The DLT of the VF center is reduced in a different, significant and non significant extent in discrete optic neuropathies and the correlation between DLT and visual acuity is weak. A careful numerical analysis is needed in types of discrete ON where the central DLT lies within normal statistical limits: a side difference of the DLT between the affected and the normal fellow eye is always present. Evaluation of visual fatigue effects and of the relative sensitivity loss of VF center and VF periphery may provide further diagnostic information.