The physics and psychophysics of microperimetry

Structure-function analysis of MP3 microperimetry versus Octopus perimetry in central glaucomatous visual field defects

INTRODUCTION

To compare the structure-function relationship with microperimetry and Octopus perimetry in primary open angle glaucoma (POAG) patients with central visual field (VF) defects.

METHODS

40 eyes of 24 patients with POAG were enrolled. Circumpapillary retinal nerve fiber layer (cpRNFL) analysis measured by spectral-domain optical coherence tomography (SD-OCT) of the superotemporal, temporal, and inferotemporal optic nerve head (ONH) sectors were related to corresponding microperimetric and Octopus VF clusters using the G2 grid-pattern with dynamic strategy, respectively. The structure-function relationships of both devices were assessed via a segmented regression, as well as linear regression across overall SD-OCT cpRNFL values and outside normative (<1%) SD-OCT cpRNFL values.

RESULTS

Linear and segmented regression fits were similar with both devices. Across overall cpRNFL sectorial values, structure-function relations for the superotemporal, temporal and inferotemporal sectors were R2=0.176 (p=<0.001), R2=0.008 (p=0.069), and R2=0.294 (p=<0.001) for microperimetry, and R2= 0.189 (p=<0.001), R2= 0.020 (p=0.002), and R2= 0.326 (p=<0.001) for Octopus perimetry. For corresponding values outside normative limits (<1%), the relationships were R2=0.113 (p=<0.001), R2=0.001 (p=0.836), and R2=0.420 (p=<0.001) for microperimetry, and R2= 0.192 (p=<0.001), R2= 0.002, (p=0.336), and R2= 0.366 (p=<0.001) for Octopus perimetry.

DISCUSSION/CONCLUSION

Structure-function analysis was similar for both devices. Fundus-tracking should be further evaluated in a longitudinal setting in patients affected by glaucoma.

Microperimetry for geographic atrophy secondary to age-related macular degeneration

Geographic atrophy (GA) is a progressive, advanced form of age-related macular degeneration leading to visual function impairment and irreversible vision loss. Standard clinical tests to evaluate visual function in patients with GA provide poor anatomic-functional correlation, whereas fundus imaging does not assess the visual function deficit. Microperimetry is a psychophysical visual function test that spatially maps retinal sensitivity and allows for identification of correlation of anatomic features with visual function. In this review, we present an overview of mesopic microperimetry for GA, including commercially available microperimetry devices, strategies to capture a mesopic microperimetry test, and strategies to assess and interpret microperimetry data in patients with GA. We demonstrate the importance of microperimetry data for assessing GA progression and for evaluating visual function loss through anatomic-functional correlations. Although valuable, current microperimetry tests require an extensive time commitment from the patient and examiner, and the development of faster, more reproducible and accessible methods is important to enable broader use of microperimetry in both clinical and research settings.

Comparisons of Two Microperimeters: The Clinical Value of an Extended Stimulus Range

SIGNIFICANCE

Fundus-guided perimetry is a common clinical tool used to measure visual field sensitivities. Comparisons between perimeters are often made despite relative differences in hardware parameters. We directly compared two perimeters using Weber contrast, which allowed us to assess the clinical gain associated with the extended stimulus range of the macular integrity assessment (MAIA).

PURPOSE

The purpose of this study was to directly compare sensitivity thresholds for two microperimeters, the MAIA and Optos optical coherence tomography/scanning laser ophthalmoscope, using Weber contrast values. We also examined the clinical utility of the extended stimulus range of the MAIA.

METHODS

Six normally sighted adults with no visual field loss and 16 adults with low vision were recruited. Thresholds were measured on the MAIA and Optos using the same threshold algorithm and test points. To compare equivalent units, decibel thresholds were converted to light increments in apostilbs and then to delta increment intensities relative to each instrument's background luminance. Repeatability was assessed for normally sighted adults by testing both instruments on 3 separate days.

RESULTS

For normally sighted observers, mean thresholds were similar on both instruments, and repeatability within microperimeters was high. The MAIA has a 0.3-log lower contrast range and 1.37 higher contrast range. The lower contrast values did not result in lower thresholds for the normally sighted observers on the MAIA. There was a 25% increase in the number of measurable thresholds owing to the higher contrast values in low-vision observers.

CONCLUSIONS

The higher contrast range in the MAIA yielded only a small increase in detectable thresholds for participants with visual field loss.

Inter-device comparison of retinal sensitivity measurements: the CenterVue MAIA and the Nidek MP-1

BACKGROUND

Our aim is to compare retinal sensitivity measurements obtained on two microperimeters: the CenterVue MAIA and the Nidek MP-1.

DESIGN

A prospective study was conducted in a private ophthalmology clinic.

PARTICIPANTS

Seventeen individuals with a range of stable macular function were recruited as participants.

METHODS

Microperimetry in one eye with identical test strategy in both devices, with randomized testing order, is used.

MAIN OUTCOME MEASURES

The main outcome measures include differences in mean sensitivity (MS), point-wise sensitivity (PWS) and duration. Limits of agreement (LoA) in MS and pooled PWS were calculated. Concordance in scotoma assessment was analysed by kappa (κ) agreement of local defect classification (LDC), LoA in number of scotomatous loci detected and congruence in scotoma localization (CSL).

RESULTS

Median (interquartile range) MS of the MP-1 and MAIA was 13.3 (5.6-18.1) and 21.2 (14.5-27.0) dB, (P < 0.05). Mean difference in PWS was 7.3 dB (MAIA > MP-1). Median (interquartile range) duration for the MP-1 and MAIA was 10'28″ (7'17″-11'53″) and 8'46″ (8'30″-9'06″), (P = 0.21). LoA for MS and pooled PWS was 1.4 to 13.3 dB and -3.9 to 18.5 dB. There was moderate agreement between the devices for LDC (weighted κ = 0.55, P < 0.05). LoA in number of scotomatous loci detected was -13 to 18. CSL varied from 0 to 100% and correlated strongly with increasing scotoma size.

CONCLUSIONS

The large LoA and variation in scotoma mapping concordance suggest that the same microperimeter should be used for follow-up examination. We recommend caution in comparing results derived from different types of microperimeters.

Retinal Sensitivity at the Junctional Zone of Eyes With Geographic Atrophy Due to Age-Related Macular Degeneration

PURPOSE

To compare the retinal sensitivity at the junctional zone and uninvolved retina of eyes with geographic atrophy (GA) due to age-related macular degeneration (AMD).

DESIGN

Cross-sectional, observational study.

METHODS

Patients with dry AMD were evaluated by microperimetry and Cirrus optical coherence tomography (OCT). The GA lesion was segmented on en face OCT images and registered to color images with the microperimetric sensitivity values. The junctional zone, a ring 500 μm in width, surrounding the region of atrophy was further subdivided into "subzones": Zone 1 at the precise border of atrophy; Zone 2 as the center of this junctional region; Zone 3 at the border between the junctional zone and adjacent "normal" retina. An additional Zone 4 was defined as "normal" retina, at least 500 μm from the edge of the GA lesion. The mean sensitivities of all stimuli within each of these zones (across the entire cohort) were compared.

RESULTS

In 36 eyes with GA, the mean retinal sensitivity in the various subzones was as follows: Zone 1 = 13.7 ± 4.7, Zone 2 = 20.3 ± 3.9, Zone 3 = 20.9 ± 3.9, and Zone 4= 21.1 ± 4.1 (all in dB). Zone 1 (atrophic margin) sensitivity was significantly lower than all other zones (P < .001 for all comparisons), but there were no differences between the other zones.

CONCLUSION

Retinal sensitivity appears to drop precipitously at the margins of GA lesions. The retinal sensitivity in the bulk of the junctional zone is similar to apparently uninvolved distant regions.

Macular retinal sensitivity using MP-1 in healthy Malaysian subjects of different ages

PURPOSE

To determine the influence of age and gender on macular sensitivity to light in healthy subjects of 4 age groups using the MP-1 microperimeter.

METHODS

A prospective study was carried out on 50 healthy subjects (age range: 18-60 years) divided into 4 age groups; 18-30 years, 31-40 years, 41-50 years and 51-60 years. Full-threshold microperimetry of the central 10° of retina was performed utilizing 32 points with the MP-1. Macula area was divided into four quadrants, which were superior nasal (SN), inferior nasal (IN), inferior temporal (IT) and superior temporal (ST).

RESULTS

Total mean sensitivity at 10° for age groups 18-30 years, 31-40 years, 41-50 years and 51-60 years were 19.46 ± 0.30, 19.40 ± 0.39, 19.47 ± 0.35 and 18.73 ± 0.75 (dB), respectively. There was a significant difference in total mean retinal sensitivity at 10° and at the four quadrants with age but not for gender. The retinal sensitivity was highest in the IT quadrant and lowest in the SN quadrant for all age groups. The linear regression analysis revealed that there was a 0.019 dB, 0.016 dB, 0.022 dB, 0.029 dB and 0.029 dB per year age-related decline in mean macular sensitivity within the central 10° diameter in the SN, IN, IT and ST quadrants respectively.

CONCLUSION

Among normal healthy subjects, there was a linear decline in retinal light sensitivity with increasing age with the highest reduction in the superior nasal quadrant and lowest in the inferior temporal quadrant.

VFMA: Topographic Analysis of Sensitivity Data From Full-Field Static Perimetry

PURPOSE

To analyze static visual field sensitivity with topographic models of the hill of vision (HOV), and to characterize several visual function indices derived from the HOV volume.

METHODS

A software application, Visual Field Modeling and Analysis (VFMA), was developed for static perimetry data visualization and analysis. Three-dimensional HOV models were generated for 16 healthy subjects and 82 retinitis pigmentosa patients. Volumetric visual function indices, which are measures of quantity and comparable regardless of perimeter test pattern, were investigated. Cross-validation, reliability, and cross-sectional analyses were performed to assess this methodology and compare the volumetric indices to conventional mean sensitivity and mean deviation. Floor effects were evaluated by computer simulation.

RESULTS

Cross-validation yielded an overall R² of 0.68 and index of agreement of 0.89, which were consistent among subject groups, indicating good accuracy. Volumetric and conventional indices were comparable in terms of test-retest variability and discriminability among subject groups. Simulated floor effects did not negatively impact the repeatability of any index, but large floor changes altered the discriminability for regional volumetric indices.

CONCLUSIONS

VFMA is an effective tool for clinical and research analyses of static perimetry data. Topographic models of the HOV aid the visualization of field defects, and topographically derived indices quantify the magnitude and extent of visual field sensitivity.

TRANSLATIONAL RELEVANCE

VFMA assists with the interpretation of visual field data from any perimetric device and any test location pattern. Topographic models and volumetric indices are suitable for diagnosis, monitoring of field loss, patient counseling, and endpoints in therapeutic trials.

Reliability and Intersession Agreement of Microperimetric and Fixation Measurements Obtained with a New Microperimeter in Normal Eyes

PURPOSE

To evaluate the reliability and intersession agreement of measurements of retinal sensitivity as well as of the fixation pattern obtained in healthy eyes with a microperimeter integrating the mechanism of the scanning laser ophthalmoscope (SLO) with the static perimetry.

METHODS

This study included a sample of 44 healthy eyes of 44 subjects of a mean age of 27.0 ± 8.5 years. In all cases, microperimetric exams with the MAIA system (Centervue, Padova, Italy) were performed in three different sessions to evaluate the intersession repeatability. The consistency of measurements was analyzed by using the Friedman test and by analyzing the correlation between consecutive measurements. Agreement between the first and third sessions was assessed by using the Passing-Bablok regression analysis. The following parameters were analyzed: average threshold (AT), macular integrity (MI) index, fixation indexes P1 and P2, bivariate contour ellipse area (BCEA), major and minor axes of the ellipse and high preferred retinal locus position (PRLh).

RESULTS

Not statistically significant differences were found in the evaluated parameters between the three sessions (p ≥ 0.193). The correlation between consecutive measurements was moderate to strong for all parameters evaluated (r ≥ 0.49, p < 0.01), except for the MI and the position of the PRLh (r ≤ 0.305, p ≥ 0.05). The Passing-Bablok regression analysis showed a good agreement between the first and third measurement for all parameters, except for the MI and the position of the PRLh.

CONCLUSION

MAIA MP system is able to provide consistent measurements of AT and fixation in normal subjects. MI and the position of PRLh seem to be the least reliable parameters in this group of patients.

Retinal sensitivity is a valuable complementary measurement to visual acuity--a microperimetry study in patients with maculopathies

PURPOSE

To evaluate changes in macular sensitivity, as measured with microperimetry, among patients with maculopathy and stable visual acuity (VA).

METHODS

Macular sensitivity was assessed using the Spectral OCT/SLO™ microperimetry (OCT/SLO, Optos Plc., Dunfermline, UK) in 25 eyes (16 patients) with maculopathy and stable VA (<5 letters change in ETDRS score) at two consecutive clinic visits. To take the limits of the test-retest repeatability of the OCT/SLO into account, coefficient of repeatability (CoR) was employed to estimate the probability of the sensitivity changes being secondary to measurement noise.

RESULTS

The point sensitivity changes were statistically significant (Wilcoxon signed-rank test, P < 0.001). Seventy-seven points (11 %) out of a total of 700 sensitivity points had a genuine sensitivity change, with a mean increase of 8.6 ± 2.6 dB in 35 points and a mean decrease of 7.9 ± 2.2 dB in 42 points.

CONCLUSIONS

Point-to-point change in macular sensitivity can be used as a biomarker of changes in disease activity in patients with maculopathy, and can be more accurate than either mean sensitivity or BCVA in detection of changes in macular function. The measurement variability should be considered when observing the local sensitivity changes.

Assessment of Central Retinal Sensitivity Employing Two Types of Microperimetry Devices

PURPOSE

To compare the retinal sensitivity measurements obtained with two microperimeters, the Micro-Perimeter 1 (MP-1) and the Optos optical coherence tomography (OCT)/scanning laser ophthalmoscope (SLO) in subjects with and without maculopathies.

METHODS

Forty-five eyes with no known ocular disease and 47 eyes with maculopathies were examined using both microperimeters. A contrast-adjusted scale was applied to resolve the different stimuli and background luminance existing between the two devices.

RESULTS

There was a strong ceiling effect with the MP-1 in the healthy group, with 90.1% (1136 of 1260) test points clustered at 20 dB. The mean sensitivity for the corresponding points in the OCT/SLO was 25.8 ± 1.9 dB. A floor effect was also observed with the OCT/SLO in the maculopathy group with 9.7% (128 of 1316) points clustered at 9-dB values. The corresponding mean sensitivity in the MP-1 was 1.7 ± 3.9 dB. A regression equation between the two microperimeters was established in the common 10 to19 dB intervals as: OCT/SLO = 15.6 + 0.564 × MP-1 - 0.009 × MP-1² + k (k is an individual point constant; MP-1 coefficient P < 0.001; MP-1² coefficient P = 0.006).

CONCLUSION

The OCT/SLO and the MP-1 provide two different ranges of contrasts for microperimetry examination. Broadening the dynamic range may minimize the constraint of the ceiling and floor effect. There is a significant mathematical relationship in the common interval of the contrast scale.

TRANSLATIONAL RELEVANCE

Applying a unified and broadened dynamic range in different types of microperimeters will help to generate consistent clinical reference for measurements.

Fundus-driven perimetry (microperimetry) compared to conventional static automated perimetry: similarities, differences, and clinical applications

Fundus-driven perimetry, commonly known as microperimetry, is a technique for measuring visual field sensitivity, whilst simultaneously viewing the fundus. In this article, we review the technique, focusing on the MP-1 microperimeter (Nidek Instruments, Inc, Padua, Italy); we compare it with conventional static automated perimetry, emphasizing the importance of understanding the effects of the different stimulus conditions and data analyses on the interpretation of microperimetry data. The clinical applications of the technique, in the evaluation of functional and structural changes that accompany retinal diseases, are illustrated by its use in patients with age-related macular degeneration, Stargardt disease, and retinitis pigmentosa. In addition, the advantages and limitations of the technique are summarized.