Spatial and chromatic interactions in the human pattern electroretinogram

The Relation of White-on-White Standard Automated Perimetry, Short Wavelength Perimetry, and Optic Coherence Tomography Parameters in Ocular Hypertension

PURPOSE

The purpose of this study is to examine the demographics, clinical properties, and the relation between white-on-white standard automated perimetry (SAP), short wavelength automated perimetry (SWAP), and optical coherence tomographic (OCT) parameters of patients with ocular hypertension.

MATERIALS AND METHODS

Sixty-one eyes of 61 patients diagnosed with ocular hypertension in the Ankara Numune Education and Research Hospital ophthalmology unit between January 2010 and January 2011 were included in this study. All patients underwent SAP and SWAP tests with the Humphrey visual field analyser using the 30.2 full-threshold test. Retinal nerve fiber layers (RNFL) and optic nerve heads of patients were evaluated with Stratus OCT.

RESULTS

Positive correlation was detected between SAP pattern standard deviation value and average intraocular pressure (P=0.017), maximum intraocular pressure (P=0.009), and vertical cup to disc (C/D) ratio (P=0.009). Positive correlation between SWAP median deviation value with inferior (P=0.032), nasal (P=0.005), 6 o'clock quadrant RNFL thickness (P=0.028), and Imax/Tavg ratio (P=0.023) and negative correlation with Smax/Navg ratio (P=0.005) were detected. There was no correlation between central corneal thickness and peripapillary RNFL thicknesses (P>0.05).

CONCLUSIONS

There was no relation between SAP median deviation, pattern standard deviation values and RNFL thicknesses and optic disc parameters of the OCT. By contrast significant correlation between several SWAP parameters and OCT parameters were detected. SWAP appeared to outperform achromatic SAP when the same 30-2 method was used.

Relation between blue-on-yellow perimetry and optical coherence tomography in normal tension glaucoma

OBJECTIVE

To assess the relation between blue-on-yellow perimetry (B/YP) indices and optical coherence tomography (OCT) parameters in normal tension glaucoma (NTG) patients and to investigate the diagnostic ability of B/YP and OCT in discriminating NTG from normal eyes.

DESIGN

Cross-sectional study.

PARTICIPANTS

Eighty normal subjects (80 eyes) and 80 NTG patients (80 eyes) were enrolled in the study.

METHODS

All patients underwent white-on-white perimetry, B/YP, and OCT measurement. The correlation between B/YP indices and OCT parameters was analyzed. The area of the receiver operating characteristic (ROC) curve was calculated to discriminate NTG patients from normal subjects.

RESULTS

A highly significant correlation was found between B/YP mean deviation (MD) and average thickness of the retinal nerve fibre layer (r2 = 0.707, p = 0.000), and a moderately significant correlation was found between B/YP MD and temporal average (r2 = 0.437, p = 0.010) in the early NTG patients. A mildly or moderately significant correlation was found between B/YP MD and average thickness, inferior average, temporal average, superior maximum, and maximum-minimum (r2 = 0.212-0.498, p = 0.001-0.048) in the moderate or late NTG patients. The area under the ROC curve at the B/YP MD was 0.896, and the 3 OCT parameters with the widest area under the curve were average thickness (0.957), inferior average (0.932), and superior average (0.913). Average thickness showed the highest sensitivity (93%) with specificities at 90% and 80%.

CONCLUSIONS

The significant correlation between B/YP indices and OCT parameters in NTG patients suggests that the 2 tests detect similar areas or amounts of NTG damage and could be used for NTG early diagnosis.

Correlation between blue-on-yellow perimetry and scanning laser polarimetry with variable corneal compensation measurements in primary open-angle glaucoma

OBJECTIVE

To investigate the correlation between blue-on-yellow perimetry (B/YP) indices and scanning laser polarimetry with variable corneal compensation (GDx VCC) parameters in primary open-angle glaucoma (POAG) patients, and to evaluate whether the two tests can detect similar glaucomatous damage.

METHODS

One eye each of 86 patients with POAG was chosen. All patients were examined with the Octopus 101 automated perimetry dG2 program using the dynamic strategy/normal method (white-onwhite perimetry, W/WP), with the dG2 program using the dynamic strategy/BY method (blue-on-yellow perimetry, B/YP), and with GDx VCC. Findings were analyzed by using Pearson's correlation analysis.

RESULTS

Of the 42 early glaucoma patients, 28 had both B/YP visual field loss and retinal nerve fiber layer (RNFL) defects detected by the GDx VCC measurements, and in 85.7% (24/28) of patients the regions of B/YP visual field defects corresponded to the RNFL defects detected by GDx VCC. All moderate and late glaucoma patients had both B/YP visual field loss and RNFL defects detected by GDx VCC, and in 95.5% (42/44) the regions of B/YP visual field defects corresponded to the RNFL defects detected by GDx VCC. A statistically significant correlation was found between B/YP mean sensitivity (MS) and the temporal-superior-nasal-inferior-temporal (TSNIT) average (r2>0.191, P>0.047) in the early glaucoma group, but no significant correlation was found between the W/WP indices and GDx VCC parameters. In the moderate to late glaucoma group, a low or moderate, but significant, correlation was found between B/YP MS and GDx VCC parameters (r2>0.286-0.405, P>0.001-0.01), with the most correlative parameter with B/YP MS being the TSNIT average. A low but significant correlation was also found between the B/YP mean defect (MD) and TSNIT average, superior average, inferior average, and nerve fiber indicator (NFI) (r2>0.188-0.271, P>0.013-0.044), and a low or moderate significant correlation was also found between the W/WP MS and MD and the GDx VCC parameters.

CONCLUSION

The presence of significant correlations between some B/YP indices and the GDx VCC parameters in glaucoma patients suggests that the two tests can detect similar areas and amounts of glaucomatous damage. These findings raise the possibility that both techniques can be used in clinical examinations to yield convergent data.

Temporal analysis of the topographic ERG: chromatic versus achromatic stimulation

The topographic electroretinogram evoked by multi-focal exchange of black and white or red and green stimuli was analysed into linear and non-linear Wiener kernels. The first-order (temporally linear) response showed a biphasic waveform which inverted as the luminance ratio of the exchanged colours passed through unity (established both psychophysically and photometrically). A short latency non-linearity which was dependant on luminance contrast was observed in both chromatic and achromatic ERG. However, in the chromatic second-order response, a long-latency non-linearity, foveally prominent, with a distinct skew in power towards the nasal retina, appeared around the isoluminant point, between the points of silent substitution for the L and M-cone types. Modelling of the second-order responses showed that over a wide range of luminance ratios, the chromatic ERG is well described by a linear combination of the achromatic (contrast-dependent) component and the response at isoluminance. The difference in second-order response between coloured and black and white stimulation, at the same luminance contrast, showed that the long-latency non-linearity is recorded when the red and green cone types are operating out of phase and peaks in amplitude at a green/red luminance ratio of 0.8. This interpretation was confirmed by the lack of the long-latency non-linearity in colour-anomalous subjects (whether deficient in the L or the M-cone type). A marked similarity exists between the properties of the long-latency non-linearity and the frequency-doubled response generated in the ganglion cells of the magnocellular pathway.

Large-field S-cone flicker test

BACKGROUND

Disturbances of blue color vision and of temporal contrast sensitivity can indicate early damage in glaucoma. For the present study a quick and easy test was devised which examines both functions at one time by testing the temporal contrast sensitivity of a blue flickering light on an intense yellow background.

METHODS

Large coextensive background and test fields (85 degrees) are used, making fixation uncritical. Detailed experiments were made in two normal subjects to derive spectral sensitivity curves from flicker-fusion frequency (FFF) versus intensity functions and to obtain complete temporal contrast-sensitivity (De Lange) curves under different levels of adaptation and test lights. After selection of appropriate luminances and one stimulation frequency from these experiments, test-retest variability was studied in four subjects in five repetitions. In addition, normal values were collected from 22 subjects.

RESULTS

Spectral sensitivities for two levels of FFF (15 Hz and 44 Hz) agree with Stiles' pi 1 at the low and with pi 4 at the high FFF. Temporal contrast-sensitivity curves show a low-frequency section with peak sensitivity at 1 Hz and a high-frequency section with a peak at around 4 Hz. From the basic experiments the following conditions for the clinical examination were selected: Background luminance 2600 cd/m2, test luminance at 451 nm 0.8 cd/m2, stimulation frequency 4 Hz. The test-retest variability showed an acceptable intraclass correlation co-efficient (0.6).

CONCLUSIONS

The present experiments carried out with a very large stimulus led to meaningful results which are in rather good agreement with results reported in the literature on small-field stimuli. The blue-on-yellow flicker test carried out under the conditions mentioned above is a quick and easy test which could be helpful in improving early glaucoma diagnosis.

The effect of stimulus size on human cortical potentials evoked by chromatic patterns

The effect of stimulus size on the pattern onset-offset visual evoked potential elicited with stimuli of two different wavelengths is studied under intensive yellow adaptation: (1) The onset response obtained with a 460 nm pattern is of negative polarity (N1) and saturates in amplitude with a stimulus radius of 7 deg. The onset response obtained with a 550 nm pattern is of positive polarity and continues to increase up to the maximum size (32.2 deg). (2) The peak time of N1 (460 nm) decreases with increasing stimulus size, that of P1 (550 nm) remains constant. These results are discussed as reflecting either varying retinal and brain anatomy, or cone activity, color-opponent activity, or luminance contrast activity.

Pattern-reversal electroretinogram in response to chromatic stimuli: I. Humans

We have studied the steady-state PERG in human subjects in response to red-green plaid patterns modulated either in luminance or in chromaticity or both. By varying the relative luminance of the red and green components, a value could be obtained at which the PERG amplitude was either minimum or locally maximum. This always occurred at equiluminance, as measured by standard psychophysical techniques. PERG amplitude and phase were measured as a function of spatial and temporal frequency of sinusoidal contrast reversal. In both space and time, the response to chromatic patterns was low-pass, while that to luminance was band-pass, and extended to higher spatial and temporal frequencies. The phase of the PERG to chromatic stimuli was systematically lagged compared with that to luminance stimuli, by an amount corresponding to about 20 ms under our experimental conditions. The variation of phase with temporal frequency suggested an apparent latency of about 67 ms for color contrast compared with 47 ms for luminance. These estimates were confirmed with separate measurements of transient PERGs to abrupt contrast reversal. For both luminance and chromatic stimuli, the amplitude of PERGs increases with increasing stimulus contrast. By summing vectorially the responses to appropriate luminance and chromatic contrasts, we were able to predict with accuracy the response as a function of color ratio (ratio of red to total luminance). The above findings all agree with those reported in the accompanying paper for the monkey PERG (Morrone et al., 1994), and indicate that the differences in response latency and integration time of luminance and chromatic stimuli observed by psychophysical and VEP techniques may arise at least in part from the properties of retinal mechanisms.

The origins of luminance and pattern responses of the pattern electroretinogram

A luminance response is spatially insensitive and dependent upon temporal contrast. The contribution of luminance to the pattern onset electroretinogram (PERG) can be estimated from the temporal contrast of a pattern's illuminance profile on the retina. A profile can be computed for different spatial frequencies by resynthesising the Fourier transform of the pattern after it has been filtered by the eye's MTF. A pure luminance response does not fully account for the amplitude of the PERG. The residual response is called "pattern specific". After the effects of spatial contrast degradation have been corrected for the response is spatially bandpass tuned with a peak that changes with eccentricity. An optimum foveal stimulus is estimated to be 3.5' arc. The pattern specific response component shows a correlation with inner nuclear and ganglion cell volumes. When the relationship of the luminance ERG with temporal contrast was explored empirically it was found to behave in good approximation to the theoretical predictions.

Interactions of spectral, spatial, and temporal mechanisms in the human pattern visual evoked potential

The human pattern onset-offset visual evoked potential (VEP) was studied with different colours and spatial frequencies presented on a steady homogeneous intensive yellow background. Under this condition a broad, late negative wave (N2) dominated by the blue-sensitive mechanism and a sharper earlier positive wave (P1) dominated by the red-green-sensitive mechanism can be observed. With a 460 nm pattern N2 shows a strong amplitude tuning at low-medium spatial frequencies. With 550 nm an early negative component (N1) is added showing an amplitude tuning at high spatial frequencies. Different spatial resolutions of the two colour mechanisms are thus indicated. With pattern-reversal stimuli the 550 nm stimulus shows a higher temporal resolution than the 460 nm stimulus.