Probing glaucoma visual damage by rarebit perimetry

Visual Field Tests: A Narrative Review of Different Perimetric Methods

Visual field (VF) testing dates back to fifth century B.C. It plays a pivotal role in the diagnosis, management, and prognosis of retinal and neurological diseases. This review summarizes each of the different VF tests and perimetric methods, including the advantages and disadvantages and adherence to the desired standard diagnostic criteria. The review targets beginners and eye care professionals and includes history and evolution, qualitative and quantitative tests, and subjective and objective perimetric methods. VF testing methods have evolved in terms of technique, precision, user-friendliness, and accuracy. Consequently, some earlier perimetric techniques, often still effective, are not used or have been forgotten. Newer technologies may not always be advantageous because of higher costs, and they may not achieve the desired sensitivity and specificity. VF testing is most often used in glaucoma and neurological diseases, but new objective methods that also measure response latencies are emerging for the management of retinal diseases. Given the varied perimetric methods available, clinicians are advised to select appropriate methods to suit their needs and target disease and to decide on applying simple vs. complex tests or between using subjective and objective methods. Newer, rapid, non-contact, objective methods may provide improved patient satisfaction and allow for the testing of children and the infirm.

Sensitivity and Specificity of New Visual Field Screening Software for Diagnosing Hemianopia

Purpose

To assess the diagnostic accuracy of visual field results generated by the newly developed software (CU-VF) and the standard automated perimetry (SAP) for detecting hemianopia.

Patients and Methods

Forty-three subjects with hemianopia and 33 controls were tested with the CU-VF software on a personal computer and SAP. Hemianopia was defined as the presence of a hemianopic field respecting the vertical meridian on SAP with the corresponding neuroimaging pathology as evaluated by 2 neuro-ophthalmologists. Results of CU-VF were independently evaluated by 2 neuro-ophthalmologists, 1 general ophthalmologist, and 1 general practitioner in terms of the presence of hemianopia. Sensitivity, specificity, and kappa coefficient for inter-observer reliability were calculated. Satisfaction and ease of use were evaluated with a visual analog-scale questionnaire and analyzed using paired t-test.

Results

The sensitivity (95% CI) and specificity (95% CI) of the CU-VF to detect hemianopia was 74.42% (58.53–85.96) and 93.94% (78.38–99.94). Kappa coefficient between neuro-ophthalmologists versus general ophthalmologist and general practitioner were 0.71 and 0.84, respectively. The mean (SD) test duration was 2.25 (0.002) minutes for the CU-VF and 5.38 (1.34) minutes for SAP (p < 0.001). Subjects reported significantly higher satisfaction and comfort using the CU-VF software compared to SAP.

Conclusion

The CU-VF screening software showed good validity and reliability to detect hemianopia, with shorter test duration and higher subject satisfaction compared to SAP.

Screening for Glaucomatous Visual Field Defects in Rural Australia with an iPad

Aim and objective

Developing improved methods for early detection of visual field defects is pivotal to reducing glaucoma-related vision loss. The Melbourne Rapid Fields screening module (MRF-S) is an iPad-based test, which allows suprathreshold screening with zone-based analysis to rapidly assess the risk of manifest glaucoma. The versatility of MRF-S has potential utility in rural areas and during infectious pandemics. This study evaluates the utility of MRF-S for detecting field defects in non-metropolitan settings.

Materials and methods

This was a prospective, multicenter, cross-sectional validation study. Two hundred and fifty-two eyes of 142 participants were recruited from rural sites through two outreach eye services in Australia. Participants were tested using MRF-S and compared with a reference standard; either Zeiss Humphrey Field Analyzer or Haag-Streit Octopus performed at the same visit. Standardized questionnaires were used to assess user acceptability. Major outcome measures were the area under the curve (AUC) for detecting mild and moderate field defects defined by the reference tests, along with corresponding performance characteristics (sensitivity, specificity).

Results

The mean test duration for MRF-S was 1.88 minutes compared with 5.92 minutes for reference tests. The AUCs for mild and moderate field defects were 0.81 [95% confidence interval (CI): 0.75–0.87] and 0.87 (95% CI: 0.83–0.92), respectively, indicating very good diagnostic accuracy. Using a risk criterion of 55%, MRF-S identified moderate field defects with a sensitivity and specificity of 88.4 and 81.0%, respectively.

Conclusion and clinical significance

The MRF-S iPad module can identify patients with mild and moderate field defects while delivering favorable user acceptability and short test duration. This has potential application within rural locations and amidst infectious pandemics.

How to cite this article

Chia MA, Trang E, Agar A, et al. Screening for Glaucomatous Visual Field Defects in Rural Australia with an iPad. J Curr Glaucoma Pract 2021;15(3):125–131.

A novel Bayesian adaptive method for mapping the visual field

Measuring visual functions such as light and contrast sensitivity, visual acuity, reading speed, and crowding across retinal locations provides visual-field maps (VFMs) that are extremely valuable for detecting and managing eye diseases. Although mapping light sensitivity is a standard glaucoma test, the measurement is often noisy (Keltner et al., 2000). Mapping other visual functions is even more challenging. To improve the precision of light-sensitivity mapping and enable other VFM assessments, we developed a novel hybrid Bayesian adaptive testing framework, the qVFM method. The method combines a global module for preliminary assessment of the VFM's shape and a local module for assessing individual visual-field locations. This study validates the qVFM method in measuring light sensitivity across the visual field. In both simulation and psychophysics studies, we sampled 100 visual-field locations (60° × 60°) and compared the performance of qVFM with the qYN procedure (Lesmes et al., 2015) that measured light sensitivity at each location independently. In the simulations, a simulated observer was tested monocularly for 1,000 runs with 1,200 trials/run, to compare the accuracy and precision of the two methods. In the experiments, data were collected from 12 eyes (six left, six right) of six human subjects. Subjects were cued to report the presence or absence of a target stimulus, with the luminance and location of the target adaptively selected in each trial. Both simulations and a psychological experiment showed that the qVFM method can provide accurate, precise, and efficient mapping of light sensitivity. This method can be extended to map other visual functions, with potential clinical signals for monitoring vision loss, evaluating therapeutic interventions, and developing effective rehabilitation for low vision.

Portable Perimetry Using Eye-Tracking on a Tablet Computer-A Feasibility Assessment

Purpose

Visual field (VF) examination by standard automated perimetry (SAP) is an important method of clinical assessment. However, the complexity of the test, and its use of bulky, expensive equipment makes it impractical for case-finding. We propose and evaluate a new approach to paracentral VF assessment that combines an inexpensive eye-tracker with a portable tablet computer (“Eyecatcher”).

Methods

Twenty-four eyes from 12 glaucoma patients, and 12 eyes from six age-similar controls were examined. Participants were tested monocularly (once per eye), with both the novel Eyecatcher test and traditional SAP (HFA SITA standard 24-2). For Eyecatcher, the participant's task was to simply to look at a sequence of fixed-luminance dots, presented relative to the current point of fixation. Start and end fixations were used to determine locations where stimuli were seen/unseen, and to build a continuous map of sensitivity loss across a VF of approximately 20°.

Results

Eyecatcher was able to clearly separate patients from controls, and the results were consistent with those from traditional SAP. In particular, mean Eyecatcher scores were strongly correlated with mean deviation scores (r² = 0.64, P < 0.001), and there was good concordance between corresponding VF locations (∼84%). Participants reported that Eyecatcher was more enjoyable, easier to perform, and less tiring than SAP (all P < 0.001).

Conclusions

Portable perimetry using an inexpensive eye-tracker and a tablet computer is feasible, although possible means of improvement are suggested.

Translational Relevance

Such a test could have significant utility as a case finding device.

Test Conditions in Macular Visual Field Testing in Glaucoma

PURPOSE

The purpose of this study is to evaluate the suitable visual field (VF) test conditions (target size, test type, and eccentricity) for the macular region, we investigated the correlations between the ganglion cell layer (GCL) thickness and 6 VF test results.

METHODS

We tested 32 eyes of patients (61.1±9.2 y) with preperimetric (6), early-stage (16), and moderate-stage (10) glaucoma. The VF tests included 3 SAP (the 10-2 HFA using SITA with target size III [HFA SITA (III)], full threshold with size III [HFA FULL (III)] and size I [HFA FULL (I)]) and 3 visual function-specific perimetry tests (the 10-2 SWAP, 10-2 flicker, and 10-2 Humphrey Matrix). The GCL and inner plexiform layer (GCL+IPL) thickness was measured by Spectral Domain Optical Coherence Tomography (SD-OCT) with a macular 7×7 mm cube scan (3D OCT-2000, Topcon). The coefficient of determination (r) for the correlation between visual sensitivity and the GCL+IPL thickness was calculated for each test at eccentricities 0 to 5 degrees, 5 to 7 degrees, and 7 to 10 degrees using linear and quadratic regressions.

RESULTS

All 6 tests showed the strongest correlation with the GCL+IPL thickness at 5 to 7 degrees. The respective r (linear) and R (quadratic) for HFA SITA (III), HFA FULL (III), HFA FULL (I), SWAP, Flicker, and Matrix were (0.40, 0.50), (0.43, 0.53), (0.44, 0.46), (0.51, 0.51), (0.33, 0.34), and (0.52, 0.52).

CONCLUSIONS

As compared with the frequently-used SAP with a size III, SAP with size I and the function-specific perimetry tests (especially the Matrix) could be more suitable for testing the macular region.

Comparison of Peristat Online Perimetry with the Humphrey Perimetry in a Clinic-Based Setting

Purpose

We determined the receiver operating characteristic (ROC) curves for Peristat online perimetry at detecting varying degrees of glaucoma and the correlation between Peristat online perimetry and Humphrey visual field.

Methods

A prospective, comparative study of Peristat online perimetry (an achromatic static computer threshold testing program) and Humphrey visual field (HVF) 24-2 SITA standard testing was performed by 63 glaucoma patients and 30 healthy controls in random order. The number of total adjacent abnormal test points were identified for each test, and compared with Spearman correlation. Receive operating characteristic curves were generated for Peristat online perimetry detection of mild and moderate-severe glaucoma patients using contrast sensitivity thresholds of −16.7, −21.7, and −26.7 dB.

Results

The area under the ROC curve for glaucoma detection ranged from 0.77 to 0.81 for mild disease (mean deviation [MD], >−6 dB on HVF) and 0.85 to 0.87 for moderate to severe disease (MD, <−6 dB on HVF) depending on contrast threshold. Peristat online perimetry and Humphrey visual field abnormal points were highly correlated with Spearman rank correlations ranging from 0.55 to 0.77 (all P < 0.001).

Conclusions

Peristat online perimetry exhibits a reasonable ROC curve without specialized equipment and exhibited significant correlation with the conventional 24° Humphrey visual field test.

Translational Relevance

Low cost widely available internet-based visual fields may complement traditional office-based visual field testing.

Methodology and reporting of diagnostic accuracy studies of automated perimetry in glaucoma: evaluation using a standardised approach

PURPOSE

To evaluate methodological and reporting quality of diagnostic accuracy studies of perimetry in glaucoma and to determine whether there had been any improvement since the publication of the Standards for Reporting of Diagnostic Accuracy (STARD) guidelines.

METHODS

A systematic review of English language articles published between 1993 and 2013 reporting the diagnostic accuracy of perimetry in glaucoma. Articles were appraised for methodological quality using the 14-item Quality assessment tool for diagnostic accuracy studies (QUADAS) and evaluated for quality of reporting by applying the STARD checklist.

RESULTS

Fifty-eight articles were appraised. Overall methodological quality of these studies was moderate with a median number of QUADAS items rated as 'yes' equal to nine (out of a maximum of 14) (IQR 7-10). The studies were often poorly reported; median score of STARD items fully reported was 11 out of 25 (IQR 10-14). A comparison of the studies published in 10-year periods before and after the publication of the STARD checklist in 2003 found quality of reporting had not substantially improved.

CONCLUSIONS

Methodological and reporting quality of diagnostic accuracy studies of perimetry is sub-optimal and appears not to have improved substantially following the development of the STARD reporting guidance. This observation is consistent with previous studies in ophthalmology and in other medical specialities.

New rarebit vision test captures macular deficits hidden to acuity tests

PURPOSE

Evaluation of a new personal-computer-based vision test aimed for rapid and accurate assessment of macular conditions such as age-related macular degeneration (AMD).

METHODS

The new test depends on segmented digits defined by rarebits, that is, receptive field-size bright dots briefly presented against a dark background. Digit size was fixed at 40 × 50 min of arc. Digit positions were varied at random within a 4.6 × 3.5-degree test field. There were no fixation demands. The number of rarebits per digit segment could be varied between 3 (the minimum needed for veridical perception) and 128, in 11 preset steps. The test task was to find the smallest rarebit number required to recognize the test digits. Thirty-seven patients with various stages of AMD and 25 control subjects participated in the evaluation, which also included a standard acuity test.

RESULTS

Analysis of receiver operating characteristics indicated significantly better discrimination by the rarebit test. Rarebit numbers >16 appeared to reliably indicate the presence of oedema.

CONCLUSION

The rarebit test appeared well suited for fine grading of vision in AMD. The simple set-up and the lack of fixation demands made for practicable examinations of short durations. The test is available for free on the Internet.

Self-Testing of Vision in Age-Related Macula Degeneration: A Longitudinal Pilot Study Using a Smartphone-Based Rarebit Test

Purpose. There is a need for efficient self-tests of vision in patients with neovascular age-related macula degeneration. A new tablet/smartphone application aiming to meet this need is described and its performance is assessed in a longitudinal pilot study. Materials and Methods. The new MultiBit Test (MBT) employs segmented digits defined by rarebits, that is, receptive field-size bright dots briefly presented against a dark background. The number of rarebits per digit segment was varied in a cyclic fashion, in preset steps. There were no fixation demands. Twenty-eight patients with neovascular AMD of varying severity were monitored for an average of 30 weeks. Test scores were evaluated on an individual basis, by contrasting observed trends with the clinical status recorded at independently scheduled clinical examinations. Results. Serial plots of MBT results revealed gradual improvement after successful antineovascular treatment. Recurrences were signalled by gradual deteriorations of results. Test results remained stable during clinically stable time intervals. MBT results agreed well with clinical assessments whereas an acuity test performed at chance level. The MBT was well accepted by all subjects. Conclusions. The MBT appears to have a good potential for effective self-testing of vision in AMD and merits large-scale studies. Exploration of MBT performance with other forms of macula conditions may be worthwhile.

Quantitative measurement of fixation stability during RareBit perimetry and Humphrey visual field testing

PURPOSE

To compare fixation stability and fixation loss between the Humphrey Field Analyzer (HVF, static fixation target) and the RareBit computer-based perimeter (RBP, kinetic fixation target) during visual field testing.

METHODS

Fourteen healthy volunteer subjects wore an ASL Mobile Gaze Tracker as they completed HVF 10-2 and RareBit central field tests in a random order. Fixation stability, defined as the average distance from the fixation target to the subject's gaze location, was calculated using data from the processed video capture. Fixation loss, defined as eye closure or a deviation of >20 degrees from the fixation target, was also measured. All subjects were surveyed regarding test preference.

RESULTS

Use of the RBP kinetic target was associated with 18% improved fixation stability compared with the HVF static target (P=0.02). Nine of 14 study subjects demonstrated better fixation with RBP compared with HVF. Subjects demonstrated decreased fixation loss during RBP (0.9 s) compared with HVF (10.0 s) (P=0.002). Eighty-six percent of study subjects preferred RBP over HVF.

CONCLUSIONS

Use of the RBP kinetic fixation target is associated with consistent fixation stability and decreased fixation loss compared with the HVF static target. This improvement in fixation stability may result from decreased perception interference (Ganzfeld, Troxler, and binocular rivalry effects), and may help account for the greater comfort reported with RBP compared with HVF.

Parallel rarebits: a novel, large-scale visual field screening method

BACKGROUND

Rarebit perimetry (RBP) is a computer-based perimetric testing program with sensitivity and specificity for detection of visual field defects comparable to traditional automated perimetry. To make large-scale screening more efficient, we developed a parallel rarebit perimetric method to screen groups of subjects simultaneously. We then used this method to report the mean hit rate (MHR) among subjects aged 13 to 19 years.

METHODS

Rarebit perimetry was installed on computers in an existing school computer laboratory. All subjects provided medical and demographic information and underwent a basic visual examination. Testing instructions were provided to groups of up to 35 subjects and rarebit perimetry was subsequently administered. Two or three test supervisors answered questions and ensured that subjects were well aligned with their test screens. Mean hit rate, reaction times, error rates and testing time were calculated, and time estimates for rarebit, frequency doubling perimetry and Humphrey 24-2 Swedish Interactive Thresholding Algorithm (SITA) fast test were compared.

RESULTS

A total of 364 rarebit perimetric tests were conducted on 182 subjects. Of these, 154 subjects met our inclusion criteria for the reference range (three testing errors or less and visual acuity 6/9 or better). The average mean hit rate was 94.3 ± 4.63 per cent. Screening of 500 subjects using this parallel rarebit perimetric method would require approximately nine hours, which is far less than an estimated 77 hours required for frequency doubling perimetry C-20 screening tests or an estimated 127 hours required for Humphrey 24-2 SITA fast tests.

CONCLUSION

Using our methods, rarebit perimetry can be administered in parallel to groups of subjects. The mean hit rate was comparable to that reported in previously published studies. This parallel technique may improve the efficiency of large-scale visual field screenings.

Visual field examination using a video projector: comparison with Humphrey perimeter

PURPOSE

To present a method of visual field examination using a video projector. Also, we compare our results with those of a Humphrey perimeter, which is accepted as standard in automated perimetry.

MATERIALS AND METHODS

Software implementing a full-threshold 4-2-step staircase algorithm for the central 30-2 of the visual field (76 points) has been developed and tested in nine eyes of seven patients using an Epson TW 700 video projector. The results were compared to those obtained from the same patients using the Humphrey perimeter.

RESULTS

High correlation between the video projector visual fields and those of the Humphrey perimeter was found. The point-to-point correlation coefficient ranged from 0.75 to 0.90, with P<0.0001 for each eye.

CONCLUSION

Visual field examination results using a video projector have high correlation with those of a Humphrey perimeter. The method is possibly suitable for clinical use.

Rapid assessment of neurovisual integrity using multiple rarebits

OBJECTIVE

Rapid assessments of vision commonly rely on visual acuity testing alone. Although well suited for uncovering optical defects, visual acuity tests may fail to detect dysfunction of the neural substrate. There is a need for a rapid companion test sensitive to neural damage.

DESIGN

Evaluation of diagnostic tests.

PARTICIPANTS AND CONTROLS

Forty-seven patients with optic nerve or visual pathway lesions of low to moderate severities and 30 normal subjects.

METHODS

A new computer-based quick test of neurovisual integrity was developed using segmented digits defined by rarebits, that is, receptive field-size bright dots briefly presented on a dark background.

MAIN OUTCOME MEASURES

The test variable was the number of rarebits per segment; digit size was fixed. The test task was to call out verbally all digits that were seen during an 8-second presentation sequence. Test outcomes were contrasted with the results of an optotype acuity test and automated perimetry.

RESULTS

All subjects easily grasped the test task. The normal subjects read, on average, 5.6 (± 0.5 standard deviation) of the 6 digits contained in the test sequence, whereas the patients averaged 3.3 ± 1.8 digits. The numbers of digits read correlated modestly with the acuity and perimetry results. Analysis of receiver operating characteristic curves indicated that the multiple rarebit test provided the best discrimination.

CONCLUSIONS

The multiple rarebit test seemed to be highly capable of detecting neurovisual dysfunction. Its simplicity and uniquely short duration indicate a useful role in screening settings. The test is available free on the Internet.

FINANCIAL DISCLOSURE(S)

Proprietary or commercial disclosure may be found after the references.

Detection of visual field defects in pre-perimetric glaucoma using fundus-oriented small-target perimetry

PURPOSE

To evaluate the usefulness of automated fundus-oriented small-target perimetry in detecting glaucomatous visual field abnormalities.

MATERIALS AND METHODS

One eye from each of 60 normal, 37 pre-perimetric glaucoma (PPG) and 29 early stage of primary open-angle glaucoma (POAG) persons were included. The new perimeter had two monitors, one for a campimeter and the other for the examiner's operation. A test area within the central 15° was set in the fundus image. The target size was 2.9 min in diameter, and the distance between the two adjacent targets was 60 min. The rate of negative response (RNR) among the age-matched controls, PPG and POAG were compared. The relationship between the RNR and age of the normal or standard automated perimetry (SAP) global indices in PPG and POAG was examined. The areas under the receiver-operating characteristic curve (AROC) to discriminate PPG or POAG versus normal were determined.

RESULTS

The RNR increased significantly with age in normal and differed significantly (P < 0.001) among control (1.8 ± 1.3 %), PPG (9.2 ± 10.4 %) and POAG (21.2 ± 14.3 %). Significant correlation was found between the RNR and SAP global indices. The AROC was 0.89 for PPG and 0.95 for POAG.

CONCLUSION

Fundus-oriented small-target perimetry is useful in detecting visual field abnormalities in PPG.

Rarebit perimetry: normative values and test-retest variability

BACKGROUND

We aim to establish normative values and evaluate test-retest variability for the central and foveal field tests of version 4 of rarebit perimetry.

DESIGN

This was a prospective study undertaken in collaboration between Tan Tock Seng Hospital, Singapore, and Singapore Polytechnic.

PARTICIPANTS

Fifty-four normal subjects were recruited and included in the study.

METHODS

Subjects underwent rarebit perimetry testing, studying the central and foveal fields. All subjects repeated the test within 1 month of the initial visit. The 'mean hit rates' of one eye of every subject were analysed.

MAIN OUTCOME MEASURES

Mean hit rates of subjects were analysed to establish normative values for the central and foveal fields. Test-retest variability was also analysed.

RESULTS

Overall normative mean hit rates were 86.3 ± 13.95% for the central field and 91.6 ± 6.35% for the foveal field. For every increasing year of age, we found a 0.47% decrease in the central mean hit rates (P < 0.001). Normative mean hit rate for central and foveal fields were 90.6 ± 12.3% and 98.2 ± 3.7% respectively, in 'young' subjects, and 81.9 ± 15.6% and 85.0 ± 9.0% respectively, in 'mature' subjects. We found no significant test-retest variability in the foveal field (P = 0.554). There was significant test-retest variability in the central field (P < 0.001), but the difference was a 3.5 unit mean hit rate increase, which may be clinically significant.

CONCLUSIONS

Rarebit perimetry is repeatable and reliable. We have established normative values for two age groups.

Variability of rarebit and standard perimetry sizes I and III in normals

PURPOSE

To compare test-retest variability in rarebit perimetry (RBP) and conventional standard automated perimetry (SAP) using Goldmann size I and III stimuli.

METHODS

Seventeen normal subjects underwent RBP, size I SAP, and size III SAP on five separate visits within a 5-week period. Test-retest variability could not be directly compared because of differences in units. Instead, data were transformed to lie on the same scale by calculating a percentile range to mean ratio for each test.

RESULTS

Percentile range to mean ratio was highest for size I (3.42 ± 0.62), followed by size III (2.29 ± 0.55), and RBP (0.29 ± 0.10). Results for all three tests were significantly different from each other.

CONCLUSIONS

Comparison of tests with different scales is problematic, but RBP's retest variability appears to be significantly less than both sizes I and III SAP in the measurement of normal subjects.

Determining mechanisms of visual loss in glaucoma using Rarebit perimetry

PURPOSE

Evidence for ganglion cell visual dysfunction in human glaucoma is often indirect, being either measured at the cellular level in animal models or being inferred from the pooled responses of a large number of ganglion cells in human observers. Rarebit perimetry (RBP) uses repeated, intense (150 cd/m2) stimuli-whose size is close to the spatial scale of a ganglion cell-to search for small retinal areas with zero sensitivity. Decreasing the stimulus luminance to 64 cd/m2 in normal observers does not alter the percentage of RBP stimuli detected [the mean hit rate (MHR)], and so we hypothesized that a similar response robustness should occur in glaucoma if the elements detecting the RBP target show no signs of visual dysfunction.

METHODS

Nineteen glaucoma subjects and 19 age-matched controls were tested with a customized RBP test at 13 stimulus luminances (10 to 150 cd/m2, 0.14 log unit intervals). A four-parameter (threshold, spread, false positive proportion, and miss rate) cumulative Gaussian psychometric function was fitted to the response rate data from a glaucoma-affected region (glaucoma subjects; MHR >50% and <80%) and from the corresponding region in an age-matched normal control. Our hypothesis would predict that only the miss rates should differ between groups.

RESULTS

Glaucoma subjects showed significantly higher miss rates (0.18 vs. 0.04, p < 0.001), lower false positive proportions (0.009 vs. 0.025, p = 0.004), greater spreads (0.30 vs. 0.19, p = 0.002), and elevated thresholds [1.57 log(cd/m2) vs. 1.13 log(cd/m2), p < 0.001].

CONCLUSIONS

Responses to RBP stimuli are not robust to decreasing luminances in glaucoma. Our results more directly imply the presence of ganglion cell visual dysfunction in human glaucoma than studies using larger targets where contrast sensitivity losses could result through ganglion cell death alone. Such dysfunction may not be detected by Rarebit's MHR given that dysfunctional elements may still respond to the very intense RBP stimulus.

A history of perimetry and visual field testing

Perimetry and visual field testing have been used as clinical ophthalmic diagnostic tools for many years, and this manuscript will provide a brief historical overview of these procedures and the individuals who developed them. Today, we have many different forms of perimetry that are designed to evaluate different locations within the visual pathways and various mechanisms and subsets of mechanisms within the visual system. However, the most widely used method of performing perimetry and visual field testing has not substantially changed for more than 150 years, consisting of detecting a small target superimposed on a uniform background at different locations within the field of view. Although the basic test procedure has remained similar throughout the ages, there have been many advances in test administration, standardization, statistical evaluation, clinical analysis, interpretation, and prediction of outcome based on visual field findings.

The role of standard automated perimetry and newer functional methods for glaucoma diagnosis and follow-up

Automated perimetry has become the mainstream for assessment of functional glaucomatous loss and progressive damage. Recent improvements with the Swedish interactive thresholding algorithm (SITA) strategy and the guided progression analysis (GPA) have further settled standard achromatic perimetry (SAP) as the preferred method for diagnosis and follow-up of functional loss. Although SAP is still considered the gold standard, function-specific perimetry may offer advantages for early diagnosis. Frequency doubling technology (FDT) and short-wavelength automated perimetry (SWAP) have been shown to be helpful, especially when SAP is normal and there is a suspicion of glaucoma. Studies using rarebit perimetry have also shown promising results. Studies have observed that each test identifies a different subset of eyes, and combining the tests may improve sensitivity. Nevertheless, the more sophisticated analyses do not reduce the importance of a correct interpretation of the test results.

Rarebit perimetry for bedside testing: comparison with standard automated perimetry

BACKGROUND

Rarebit perimetry (RBP), a technique developed for the detection of early damage to the afferent visual system, has not been extensively tested at the bedside. This study was designed to test the feasibility of bedside testing with RBP in comparison with standard automated perimetry (SAP) performed in the clinic.

METHODS

We tested 29 eyes of 15 subjects admitted with neurologic or neurosurgical diseases affecting the afferent visual system. RBP was performed on a laptop computer at the bedside. SAP (Humphrey field analyzer) testing was performed later in the clinic. Results were evaluated by a masked neuro-ophthalmologist.

RESULTS

Visual fields corresponded between RBP and SAP in 21(72%) of the 29 tested eyes. RBP detected defects in 5 subjects who had normal visual field results on SAP. All subjects preferred RBP for convenience.

CONCLUSION

RBP is a convenient method of bedside visual field testing and is no less sensitive to visual field defects in this role than SAP.

Rarebit perimetry and fovea test before and after cataract surgery

PURPOSE

To evaluate the effect of cataract on rarebit perimetry and the fovea test.

METHODS

Twenty-five consecutive patients scheduled for cataract surgery (mean age 63.0 +/- 7.9 years) were examined prior to and after cataract surgery with a complete ophthalmological examination. In addition, the rarebit perimetry (RBP) and the rarebit fovea test (RFT) were performed.

RESULTS

Best-corrected visual acuity [BCVA, expressed in minimum angle of resolution (MAR)], RBP and RFT mean hit rate (MHR) improved significantly after cataract surgery. The relative pre-postsurgery difference was larger in the RFT [2.1 standard deviations (SDs)] compared to in BCVA (0.78 SDs). Seven patients had good BCVA (< or = 1.25) and RBP (83-99%) but low RFT (0-66%) before surgery. One patient with low preoperative BCVA (2.5) had a normal RFT (94%).

CONCLUSION

Cataract influenced both the RFT and RBP test, albeit the former more than the latter. The influence of cataract on RFT results, even when visual acuity is decreased only moderately, has to be taken into account when evaluating foveal function in patients with cataract. The larger relative change in RFT compared to BCVA values is thought to indicate that RFT is more sensitive for the effect of cataract. Therefore, RFT appears to be a sensitive test for visual disturbance and can presumably provide additional information at the preoperative evaluation of the patient.

Non-conventional perimetric methods in the detection of early glaucomatous functional damage

PURPOSE

To compare the ability of frequency-doubling technology (FDT), rarebit perimetry (RBP), and pulsar perimetry (PP) in detecting early glaucomatous functional damage.

METHODS

This prospective observational cross-sectional case study included 52 patients with early primary open-angle glaucoma (mean deviation -2.3+/-1.1 dB; pattern standard deviation 3.0+/-1.2 dB) and 53 healthy controls. Visual field (VF) testing included standard automated perimetry (SAP) Humphrey Field Analyzer 30-2, FDT N-30, RBP (version 4.0), and PP T30W. One eye per patient was considered. Sensitivity at fixed specificities and area under the receiver operating characteristic curve (AROC) for discriminating between healthy and glaucomatous eyes were calculated and compared.

RESULTS

The parameters associated with the largest AROC, which were not statistically different (Hanley-McNeil method, P0.42-0.71) were as follows: number of locations in the pattern deviation probability (PDP) plot with P<5% for FDT (0.93); mean hit rate for RBP (0.95); and mean defect for PP (0.94). PP test duration was significantly shorter than FDT and RBP (P<0.002).

CONCLUSIONS

FDT, PP, and RBP are useful non-conventional VF methods in detecting early glaucomatous VF defects with similar AROCs. The methods were rapid and easy, and PP took less than half the time than SAP. These non-conventional testing may prove to be useful in providing additional information in the diagnosis of glaucoma suspect with normal SAP results, in the therapeutic decision-making process of early glaucomatous patients, and in subjects unable to perform VF testing with SAP.

Visual fields and optic disc morphology in very low birthweight adolescents examined with magnetic resonance imaging of the brain

PURPOSE

We aimed to evaluate visual fields (VFs) and optic disc morphology in very low birthweight (VLBW) adolescents compared with age- and gender-matched controls, and to relate the findings to magnetic resonance imaging (MRI) results.

METHODS

Fifty-nine VLBW adolescents and 55 age- and gender-matched controls with normal birthweight were examined. Visual fields were tested using computerized rarebit perimetry (RB). Optic nerve and retinal vessel morphology were evaluated by digital image analysis of fundus photographs. Brain MRI was conducted in the VLBW subjects.

RESULTS

Ten of the 57 VLBW subjects (p = 0.022) had subnormal VF results defined as a mean hit rate below the fifth percentile of the controls (i.e. < 89%). All of these also had significantly lower mean hit rates (p = 0.039) in the inferior hemifield. Sixteen of 57 (28%) VLBW subjects had white matter damage of immaturity (WMDI) on MRI. Six of 15 subjects with WMDI (who underwent VF testing) also had subnormal RB results, compared with four of 39 with normal MRI findings (p = 0.02). The mean neural retinal rim area was 9% smaller (p = 0.018) in the VLBW group than in the control group. The VLBW adolescents had a significantly higher index for tortuosity of arterioles than the controls (p < 0.001).

CONCLUSIONS

In the present study, 18% of all VLBW adolescents and 40% of those with WMDI had subnormal RB VF findings. The VLBW group had increased arterial tortuosity and a somewhat smaller (9%) mean neural retinal rim area than the control group. Thus sequels to VLBW appear to persist in adolescence.

The relationship between Rarebit perimetry and OCT-derived retinal nerve fibre layer thickness in glaucoma

PURPOSE

To examine the association between measures of neuroretinal matrix integrity as determined with Rarebit perimetry and optical coherence tomography (OCT)-derived retinal nerve fibre layer thickness.

METHODS

One randomly selected eye of 30 White primary open-angle glaucoma patients (age: 60.9 +/- 11.7 years; MD: -3.2 +/- 5.1 dB) and 16 healthy White individuals (age: 33.2 +/- 6.4 years; MD: -0.8 +/- 0.8 dB) were included in the study. Participants underwent Rarebit perimetry testing (central field, software version 4) and an OCT fast retinal nerve fibre layer (RNFL) scan. Correlation was investigated between hemifield Rarebit scores and the corresponding RNFL values, as well as between global Rarebit scores and the respective RNFL measures.

RESULTS

Statistically significant correlations of average hit rate (HR) < 90 and mean hit rate (MHR) were detected with Max-Min and average thickness (Pearson's r ranging from 0.393 to 0.474). Number HR < 90 showed a moderate correlation only with Max-Min (r = -0.396, P = 0.030). Regarding the association between hemifield hit rates and the corresponding OCT thickness parameters, only inferior maximum correlated moderately with HR superior (r = 0.385, P = 0.035). A tendency was detected for the relationship of superior maximum with HR inferior (r = 0.345, P = 0.062). For the control group, no significant correlation was found for any of the global or hemifield indices and the corresponding thickness values.

CONCLUSION

Although Rarebit perimetry is based on a physiological principle distinctly different from conventional perimetry, it provides global indicators of neuroretinal matrix integrity that correlate with some OCT-derived RNFL thickness measures.

[Not Available]

Purpose of the study was to compare Rarebit Perimetry (RP) with Standard Automatic Perimetry (SAP) in patients with ischemic retrochiasmal lesions. Seventeen patients with homonymous hemianopia underwent SAP and RP. Correlation between the two techniques was evaluated, congruent defects were quantified in the spared hemifield and residual vision areas were investigated in the blind hemifield. A strong correlation was found between SAP and RP. In the spared hemifield, RP detected congruent defects in a higher percentage of cases. Residual detection function has been found at RP in 69,2 % of perimetrically blind visual field quadrants as assessed by SAP. In conclusion, RP appears to be useful to assess visual function in hemianopic patients. As compared to SAP, it seems able to detect small congruent defects in a higher percentage of cases. Finally, a certain residual function seems to be present at RP in the blind regions of the visual field, however, for this finding further demonstrations are required.

Rarebit perimetry and frequency doubling technology in patients with ocular hypertension

PURPOSE

To test the capability of rarebit perimetry (RP), a recent non-conventional perimetric technique, in detecting early functional damage in subjects with ocular hypertension (OHT) and to compare RP findings with those obtained by frequency-doubling technology (FDT) perimetry.

METHODS

Thirty patients with OHT were matched with 30 healthy subjects. All were tested with RP and FDT. Frequency-doubling technology mean deviation (MD) and pattern standard deviation (PSD), as well as RP mean hit rate (MHR), of the two groups were analyzed. The agreement between the two techniques was tested by Kappa analysis.

RESULTS

In the OHT group the mean (SD) FDT MD was 0.5 (2.1), the mean (SD) FDT PSD was 4.2 (1.6), and the mean (SD) RP MHR was 81.4 (6.7). In the control group, corresponding values were mean (SD) FDT MD 1.1 (1.4), mean (SD) FDT PSD 3.0 (0.3), mean (SD) RP MHR 96.2 (2.0). The differences between the two groups were not significant for the studied indexes. Eleven (36.6%) out of the 30 OHT eyes had abnormal RP results; 12 (40.0%) eyes had abnormal FDT results. Five (16.6%) eyes had abnormal RP and FDT findings. Only 1 eye (3.3%) in the control group had abnormal RP results and 3 eyes (10.0%) had abnormal FDT results. RP and FDT showed a moderate agreement (Kappa=0.43; 95% CI: 0.42 to 0.51).

CONCLUSIONS

RP and FDT showed VF defects not shown in standard automated perimetry in the OHT group. This may be indicative of an increased risk in developing glaucoma, even if a gold standard for detecting subtle defects is not currently available. RP has the additional advantage of not requiring any expensive device to be used. The poor agreement between these techniques in identifying eyes with early damage warrants further investigations. Large longitudinal studies are needed before defining the role of RP in early glaucoma diagnosis.

How robust is the optic chiasm? Perimetric and neuro-imaging correlations

OBJECTIVES

Analysis of form and function relationships with tumour-mediated dislocations and deformations of the optic chiasm.

MATERIALS AND METHODS

Results of magnetic resonance tomography and two forms of quantitative, computerized perimetry were contrasted in 31 patients with pituitary adenomata impinging on the chiasm, prior to treatment.

RESULTS

Perimetric abnormalities ranged from none to modest. High-pass Resolution Perimetry (HRP) produced abnormal results in 10 cases and RareBit perimetry (RBP) in 15 cases. Overall, field defects and qualitative stages of deformation and dislocation of the chiasm were well correlated. Among quantitative indices, the best correlations were obtained by a measure of the cranio-caudal position of the chiasm.

CONCLUSIONS

On average, an elevation of the chiasm by 6 mm will be associated with abnormal visual fields in 50% of the cases. An additional elevation of 5 mm will raise the incidence of field defects to 90%.

Efficiency of Rarebit perimetry in the evaluation of homonymous hemianopia in stroke patients

AIMS

To compare the efficiency of Rarebit perimetry and the Humphrey field analyser (HFA) in detecting the homonymous hemianopia in stroke patients with occipital lobe infarcts.

METHODS

40 patients who suffered from visual complaints caused by acute occipital lobe infarcts underwent visual field analysis on the same day, in random order-first with either Humphrey perimetry 30-2, SITA standard program (Zeiss Humphrey Systems) or Rarebit perimetry. A visual field was classified into four quadrants for right and left eyes: superior temporal, superior nasal, inferior temporal, and inferior nasal. The entire mean hit rate numbers (MHR) and mean deviation and pattern standard deviation (PSD) values were compared for each quadrant of each eye.

RESULTS

The results of Rarebit MHR and HFA mean deviation values for each quadrant of the right and left eyes were highly correlated in all patients with homonymous hemianopia (Pearson's r correlation coefficients for superior temporal, superior nasal, inferior temporal and inferior nasal quadrants of right and left eyes were 0.827, 0.833, 0.843, 0851 and 0.746, 0821, 0882, 0.824, respectively (p<0.001 for all quadrants)). There was a strong correlation between Rarebit MHR and HFA PSD for each quadrant of both eyes.

CONCLUSIONS

Rarebit perimetry is rapid, reliable, and easily performed in patients with homonymous hemianopia. It can be done using a simple software program and simple hardware and it readily detects severe visual loss in patients with occipital lobe lesions.

Perception of very small visual stimuli in the fovea: normative data for the Rarebit Foveal Test

BACKGROUND

Conventional visual tests are not sensitive enough to detect low degree neural damage, as 6/6 (1.0) visual acuity can be upheld with less than two-thirds of the normal number of optic nerve axons. The aim of the current study was to evaluate the physiologic properties of a new computerised test, the Rarebit Fovea Test (RFT), using very small stimuli, by quantifying the effect of age and binocular summation in relation to stimulus luminance.

METHODS

The RFT relies on the perception of very small (less than 0.5 minutes of arc) bright stimuli. Two different experiments were performed. 1. Thirty-five subjects (age 19 to 63 years) were tested with five different stimulus luminances, 158, 64, 53, 41 and 33 cd/m(2). 2. Nineteen subjects (age 19 to 63 years) were tested using binocular stimulation to define the binocular summation.

RESULTS

Significantly reduced median hit rates were observed at luminances of 53 cd/m(2) or below. Age and mean hit rate correlated negatively at all luminance levels below 158 cd/m(2). The mean hit rate from binocular stimulation, compared to the highest value from monocular stimulation in the same subject, was increased by a factor of 1.54 +/- 0.45 (SD). No age effect was found regarding binocular summation.

CONCLUSIONS

The results in the current study indicate that RFT can identify some of the well-known features of the visual system, that is, the effects of age and binocular summation, provided that the stimulus luminance is adequately selected.

Rarebit and frequency-doubling technology perimetry in children and young adults

PURPOSE

To describe the outcome of visual field examinations performed with rarebit (RB) and frequency-doubling technology perimetry (FDT) in children and young adults.

METHODS

Twenty-one children (aged 6.5-12 years) and 30 teenagers and young adults (aged 14-20 years), participated in the study.

RESULTS

Reliable RB examinations were carried out in 76% of the younger group and 90% of the older group. Corresponding values for FDT were 57% and 90-95%, respectively. The RB results were very similar to those previously obtained in adult subjects, while some subjects showed borderline values in FDT, depending on the criteria used. The RB perimetry was preferred by 88% of the examined subjects.

CONCLUSIONS

Rarebit perimetry seems useful for visual field examination in children aged 7 years and over, if age-corrected normative data are established; this test was also preferred by the tested subjects. No adaptation or special instructions were needed and the children found it rather amusing.