Differences in Static and Kinetic Perimetry Results are Eliminated in Retinal Disease when Psychophysical Procedures are Equated

Standard automated perimetry for glaucoma and diseases of the retina and visual pathways: current and future perspectives

Static automated perimetry (SAP) remains a mainstay of functional assessment of the visual field in diseases of the visual pathway, such as glaucoma and age-related macular degeneration. The fundamental psychophysical task of responding to stimuli of different levels of contrast has remained minimally changed since its inception in the 1980s, and this is potentially the root of several unresolved issues involving the technique. Enduring issues include the optimisation of SAP parameters for maximising defect detection, the influence of subjective behaviour on the response, structure-function discordance, and ageing- and disease-related changes of the visual pathway. Addressing these issues has been a focus of our research program and is the subject of this manuscript. We will review some of the basic psychophysical principles and methods that have contributed to the development of SAP and their contributions to its output measurements. Parameters that are interrogated include stimulus size and background luminance and their modification to improve defect defection in glaucoma and age-related macular degeneration. We propose frameworks for optimising testing parameters and leveraging the results for changing clinical care. In our pursuit of optimising the structure-function relationship in the eye, several areas of research have been developed and explored, including: the reconciliation of subjective responses in perimetry; by minimising sources of biases, such as Method of Limits we have been able to equate static and kinetic perimetry outputs in relation to underlying structural loci. This also formed the basis for our clustering framework, which groups together statistically similar structural and functional test locations to maximise structure-function concordance. Throughout the manuscript, we review the scientific underpinnings of clinical measurements, framing application into real-world patients to improve clinical practice.

A SYSTEMATIC LITERATURE REVIEW OF DISEASE PROGRESSION REPORTED IN RPGR -ASSOCIATED X-LINKED RETINITIS PIGMENTOSA

PURPOSE

Retinitis pigmentosa GTPase regulator-associated X-linked retinitis pigmentosa ( RPGR -associated XLRP) is a rare and severe form of retinitis pigmentosa, resulting in progressive visual impairment; however, disease progression data are limited. A systematic literature review was conducted to assess available data on disease progression in RPGR -associated XLRP.

METHODS

PubMed, Embase, and select congress abstracts were evaluated through June 2022. Eligible studies included results specific to RPGR -associated XLRP or populations with ≥80% of patients with retinitis pigmentosa carrying disease-causing RPGR variants. End points of interest included visual acuity, visual field, ellipsoid zone width, progression to blindness, and patient-reported outcomes.

RESULTS

Fourteen studies met ≥1 end point of interest. Progressive declines in visual acuity, visual field, and ellipsoid zone width were reported across studies. Nearly all publications reported annual declines in visual acuity (3.5%-8.2%). Annual visual field declines ranged from 4.2% to 13.3%. Changes in retinal structure were also observed (ellipsoid zone width changes: -177 to -830 µ m/year). Most studies measured blindness using visual acuity; visual field-based definitions resulted in blindness by age ∼25 years. Patient-reported outcome data were limited.

CONCLUSION

Published evidence shows that patients with RPGR -associated XLRP experience progressive decline in visual acuity, visual field, and ellipsoid zone width, eventually resulting in blindness. Additional longitudinal data with standardized end points and expanded collection of patient-reported outcomes are needed to assess visual decline in RPGR -associated XLRP.

Kinetic Perimetry on Virtual Reality Headset

OBJECTIVE

We present a portable automatic kinetic perimeter based on a virtual reality (VR) headset device as an innovative and alternative solution for the screening of clinical visual fields. We compared the performances of our solution with a gold standard perimeter, validating the test on healthy subjects.

METHODS

The system is composed of an Oculus Quest 2 VR headset with a clicker for participant response feedback. An Android app was designed in Unity to generate moving stimuli along vectors, following a standard Goldmann kinetic perimetry approach. Sensitivity thresholds are obtained by moving centripetally three different targets (V/4e, IV/1e, III/1e) along 24 or 12 vectors from an area of non-seeing to an area of seeing and then transmitted wirelessly to a PC. A Python real-time algorithm processes the incoming kinetic results and displays the hill of vision in a two-dimensional map (isopter). We involved 21 subjects (5 males and 16 females, age range 22-73 years) for a total of 42 eyes tested with our proposed solution, and results were compared with a Humphrey visual field analyzer to test reproducibility and efficacy.

RESULTS

isopters generated with the Oculus headset were in good agreement with those acquired with a commercial device (Pearson's correlation values r > 0.83 for each target).

CONCLUSIONS

we demonstrate the feasibility of VR kinetic perimetry by comparing performances between our system and a clinically used perimeter in healthy subjects.

SIGNIFICANCE

proposed device leads the way for a portable and more accessible visual field test, overcoming challenges in current kinetic perimetry practices.

Current Review of Traumatic Optic Neuropathy and Traumatic Brain Injury among Military Service Members

Traumatic optic neuropathy (TON) is a form of optic nerve damage that while rare in the general population, is commonly associated with traumatic brain injury (TBI). With increasingly high rates of TBI in the military community, our service members and veterans represent a population where traumatic optic neuropathy is prevalent. Parachute jumpers have been identified as a high-risk group for under-reported head injury and therefore many cases of TBI are easily overlooked. With recent insights into the limitations of the veteran's disability exam, we review the current understanding of TON and propose an updated protocol for TON evaluation. We also urge for development of safer helmet design to reduce and prevent further cases of TBI, mTBI, and TON in our military personnel.

Electrophysiological Analysis of Traumatic Optic Neuropathy and Traumatic Brain Injury Among Active Military

Background

Traumatic Optic Neuropathy (TON) can cause persistent visual deficits and is a known sequala of Traumatic Brain Injury (TBI). Little is known regarding appropriate diagnosis, management, and treatment.

Methods

we performed a prospective cohort study with 356 active military personnel using electrophysiological Visual Evoked Potential (VEP) testing for TON in the context of known or suspected TBI. This was done with the intent to review and revise management protocol for patients who are susceptible to TON. This new VEP protocol was incorporated with kinetic and static visual field testing to uncover occult cases of TON previously missed in the current disability examination, as well as aid in evaluation of patients with borderline concussive cases that do not meet current diagnosis of mild, moderate, or severe TBI by the Veteran's Disability Exam.

Results

80 patients were diagnosed with TON. Average age of TON patients was 37.4 years, with most patients being male. Of those patients with TON, 45% had reported TBI, whereas an additional 54% had suspected history of concussion. Patients presented with bilateral TON (65.8%, n=52), while unilateral TON cases occurred less frequently (35.4%, n=28). Visual field defects were apparent in both static and kinetic visual field testing in 54% of cases. VEP sensitivity in our study was 88%. Military parachute jumpers (paratroopers) represent the highest risk group for undiagnosed TBI and TON.

Conclusions

we recommend periodic static and kinetic visual field testing in high-risk individuals working in fields with high concussion rates. Focused collaboration for safer helmet design is imminent. By improving helmet design, we can reduce mTBI and related TON, as well as reduce costly medical care and disability payments after military discharge.

Functional characteristics of glaucoma related arcuate defects seen on OCT en face visualisation of the retinal nerve fibre layer

Purpose

To assess continuity of perimetric defects corresponding to arcuate defects seen on optical coherence tomography (OCT) en face reflectance images of the retinal nerve fibre layer (RNFL) in patients with glaucoma.

Methods

Seven patients with glaucoma who had arcuate structural defects on OCT RNFL en face images were recruited. Static suprathreshold stimuli were presented along different meridians to localise perimetric defects in the corresponding hemifield. Then two contrasts, one 6 dB greater than the other, were used with kinetic perimetry to assess the slope of the defect. Findings with kinetic and 24‐2 perimetry were compared.

Results

Static perimetry found that regions of perimetric abnormality spatially corresponded with the regions of en face RNFL hyporeflectivity. Kinetic perimetry found that the slopes of the edges of the defects ranged from 3–12 dB degree⁻¹, and that the functional abnormalities were continuous with the physiologic blind spot even when the 24‐2 protocol only showed paracentral defects.

Conclusions

Perimetric abnormalities and arcuate RNFL en face defects were spatially correspondent. Perimetric testing guided by OCT en face reflectance images can reveal greater functional detail of glaucomatous abnormality than 24‐2 testing.

A Strategy for Seeding Point Error Assessment for Retesting (SPEAR) in Perimetry Applied to Normal Subjects, Glaucoma Suspects, and Patients With Glaucoma

PURPOSE

We sought to determine the impact of seeding point errors (SPEs) as a source of low test reliability in perimetry and to develop a strategy to mitigate this error early in the test.

DESIGN

Cross-sectional study.

METHODS

Visual field test results from 1 eye of 364 patients (77 normal eyes, 178 glaucoma suspect eyes, and 109 glaucoma eyes) were used to develop models for identifying SPE. Two test cohorts (326 undertaking Swedish interactive thresholding algorithm [SITA]-Faster and 327 glaucoma eyes undertaking SITA-Standard) were used to prospectively evaluate the models for identifying SPEs. Global visual field metrics were compared among reliable and unreliable results. Regression models were used to identify factors distinguishing SPEs from non-SPEs. Models were evaluated using receiver operating characteristic (ROC) curves.

RESULTS

In the test cohorts, SITA-Faster produced a higher rate of unreliable visual field results (30%-49.7%) compared with SITA-Standard (10.8%-16.6%). SPEs contributed to most of the unreliable results in SITA-Faster (57.5%-64.9%) compared with gaze tracker deviations accounting for most of the unreliable results in SITA-Standard (40%-77.8%). In SITA-Faster, results with SPEs had worse global indices and more clusters of sensitivity reduction than reliable results. Our best model (using 9 test locations) can identify SPEs with an area under the ROC curve of 0.89.

CONCLUSION

SPEs contribute to a large proportion of unreliable visual field test results, particularly when using SITA-Faster. We propose a useful model for identifying SPEs early in the test that can then guide retesting using both SITA algorithms. We provide a simplified framework for the perimetrist to improve the overall fidelity of the test result.

Validation of a novel functional test for assessing metamorphopsia using epiretinal membranes as a model

Current tests for assessing metamorphopsia do not account for confounders such as perceptual filling-in and spatial redundancy, which affect its sensitivity and repeatability. This proof-of-concept study aimed to assess the performance of a novel laboratory-based psychophysical test (Line Sag Test, LST) which addresses these issues for quantification of metamorphopsia in idiopathic epiretinal membranes. The LST quantifies perpendicular metamorphopsia at three eccentricities (3°, 6°, and 9°) along eight meridians (45° steps). Metamorphopsia was assessed using the LST and Amsler grid and the hit rates of both tests for detecting metamorphopsia were compared. Normal metamorphopsia scores using the LST did not differ significantly from 0 and fell within one step-size (p = 0.500). The LST detected significantly more cases of metamorphopsia than the Amsler grid (14/21 versus 3/21) (p = 0.003). Similarly, significantly more cases of visual distortions in asymptomatic iERMs were detected using the LST than the Amsler grid (11/18 versus 0/18) (p = 0.008). The LST has a higher hit rate compared to the Amsler grid (67% versus 14%). This work demonstrates a psychophysically-robust functional test addressing perceptual confounders is more sensitive for quantifying and localising metamorphopsia in macular disease, particularly in asymptomatic disease.

Clinical Evaluation of Swedish Interactive Thresholding Algorithm-Faster Compared With Swedish Interactive Thresholding Algorithm-Standard in Normal Subjects, Glaucoma Suspects, and Patients With Glaucoma

PURPOSE

To compare the visual fields results obtained using the Swedish interactive thresholding algorithm-Standard (SS) and the Swedish interactive thresholding algorithm-Faster (SFR) in normal subjects, glaucoma suspects, and patients with glaucoma and to quantify potential time-saving benefits of the SFR algorithm.

DESIGN

Prospective, cross-sectional study.

METHODS

One randomly selected eye from 364 patients (77 normal subjects, 178 glaucoma suspects, and 109 patients with glaucoma) seen in a single institution underwent testing using both SS and SFR on the Humphrey Field Analyzer. Cumulative test time using each algorithm was compared after accounting for different rates of test reliability. Pointwise and cluster analysis was performed to determine whether there were systematic differences between algorithms.

RESULTS

Using SFR had a greater rate of unreliable results (29.3%) compared with SS (7.7%, P < .0001). This was mainly because of high false positive rates and seeding point errors. However, modeled test times showed that using SFR could obtain a greater number of reliable results within a shorter period of time. SFR resulted in higher sensitivity values (on average 0.5 dB for patients with glaucoma) that was greater under conditions of field loss (<19 dB). Cluster analysis showed no systematic patterns of sensitivity differences between algorithms.

CONCLUSIONS

After accounting for different rates of test reliability, SFR can result in significant time savings compared with SS. Clinicians should be cognizant of false positive rates and seeding point errors as common sources of error for SFR. Results between algorithms are not directly interchangeable, especially if there is a visual field deficit <19 dB.

Optimising the Structure-Function Relationship at the Locus of Deficit in Retinal Disease

Technologies such as optical coherence tomography have facilitated the visualization of anatomical tissues such as that of the retina. The availability of in vivo retinal anatomical data has led to the hypothesis that it may be able to accurately predict visual function from anatomical information. However, accurate determination of the structure-function relationship has remained elusive in part due to contributions of non-retinal sources of variability, thus imposing potential limitations in the fidelity of the relationship. Furthermore, differences in manifestation of functional loss due to different retinal loci of change (inner retina or outer retinal elements) have also been the subject of debate. Here, we assessed the application of a novel, more objective psychophysical paradigm to better characterize the relationship between functional and structural characteristics in the eye. Using ocular diseases with known loci of anatomical change (glaucoma, inner retinal loss; and retinitis pigmentosa, outer retinal loss), we compared conventional more subjective psychophysical techniques that may be contaminated by the presence of non-retinal sources of variability with our more objective approach. We show that stronger correlations between underlying retinal structure and visual function can be achieved across a breadth of anatomical change by using a more objective psychophysical paradigm. This was independent of the locus of structural loss (at the ganglion cells for glaucoma or photoreceptors for retinitis pigmentosa), highlighting the role of downstream retinal elements to serve as anatomical limiting factors for studying the structure-function relationship. By reducing the contribution of non-retinal sources of variability in psychophysical measurements, we herein provide a structure-function model with higher fidelity. This reinforces the need to carefully consider the psychophysical protocol when examining the structure-function relationship in sensory systems.