Frequency doubling technology perimetry for the detection of glaucomatous visual field loss

Multiple Sclerosis: What Methods are Available for the Assessment of Subclinical Visual System Damage?

We aimed to assess the visual fields and optical coherence tomography (OCT) measurements in patients with multiple sclerosis (MS) to detect subclinical visual system disease. The study included 15 MS patients with previous optic neuritis (Group I), 17 MS patients without previous optic neuritis (Group II), and 14 healthy controls (Group III). Each subject underwent standard automated perimetry (SAP), frequency doubling technology perimetry (FDTP), and OCT. The mean deviation of SAP in Group I was lower than those in Groups II (p = .018) and III (p = .001). The pattern standard deviation of SAP in Group I was higher than those in Group III (p < .0001). The mean deviation of FDTP in Groups I and II was lower than those in Group III (p = .0001 and p = .016, respectively). The temporal quadrant of the retinal nerve fibre layer in Group I was thinner than those in Groups II and III (p = .005 and p = .003, respectively). The mean macular volume in Group I was thinner than those in Groups II and III (p = .004 and p = .002, respectively). A single method is inadequate for establishing early and/or mild visual impairment in MS. All conventional and non-conventional techniques are complementary in demonstrating subclinical visual damage in MS.

Simultaneously performed combined 24-2 and 10-2 visual field tests in glaucoma

Using either 24-2 or 10-2 visual field (VF) testing only is not enough to cover all the various types of glaucomatous VF defects. We investigated the performance of the combined 24-2 and 10-2 perimetry when conducted together and separately using the structure–function relationship. A total of 30 glaucoma patients with isolated peripheral nasal step, 37 patients with isolated paracentral scotoma, and 38 patients with both paracentral and nasal scotoma were included. To create the combined Humphrey VF test, a custom test pattern was established using the built-in custom point options, an example of the X, Y coordinate system. In glaucoma patients with peripheral nasal step, the superotemporal topographic structure–function relationship with peripapillary retinal nerve fiber layer (RNFL) thickness was superior in relation to the combined or 24-2 perimetry relative to the 10-2 perimetry (both P < 0.05). The combined VF test showed more favorable inferotemporal or inferonasal structure–function correlation with the corresponding ganglion cell–inner plexiform layer (GCIPL) thickness when compared with results gleaned using the 24-2 VF test (P < 0.05). Simultaneously performed 24-2 and 10-2 VF tests demonstrated a superior topographic structure–function relationship when compared with them separately performed in some sectors.

Low-cost, smartphone-based frequency doubling technology visual field testing using a head-mounted display

Background

Current visual field screening machines are bulky and expensive, limiting their accessibility, affordability and use. We report the design and evaluation of a novel, portable, cost-effective system for glaucoma screening using smartphone-based visual field screening using frequency doubling technology (FDT) and a head-mounted display.

Methods

Nineteen eyes of 10 subjects with new-onset or chronic primary open angle glaucoma were tested and compared with the Humphrey Zeiss FDT and the newly developed Mobile Virtual Perimetry (MVP) FDT with the C-20 testing pattern. Mann-Whitney, Bland-Altman and linear regression analyses were performed to assess statistical difference, agreement and correlation, respectively, between the two devices.

Results

The average age of the participants was 58±15 years. No statistically significant difference was found between the MVP FDT and the Humphrey Zeiss FDT (p>0.05). Bland-Altman and linear regression analyses demonstrated good agreement and correlation between the two devices.

Conclusion

The MVP FDT is a low-cost, portable visual field screening device that produces comparable results to the Humphrey Zeiss FDT and may be used as an easily accessible screening tool for glaucoma.

Development of a new algorithm based on FDT Matrix perimetry and SD-OCT to improve early glaucoma detection in primary care

Purpose

The purpose of this study was to develop an objective algorithm to discriminate the earliest stages of glaucoma using frequency doubling technology (FDT) Matrix perimetry and spectral domain-optical coherence tomography (OCT) technology to improve primary care detection.

Materials and methods

Three hundred six eyes (mean age 58.67±15.12) from 161 patients were included and classified in the following three groups: 101 nonglaucoma (GI-NG), 100 glaucoma suspect (GII-SG), and 105 open-angle glaucoma (GIII-OAG). All participants underwent a visual field exploration using the Humphrey Matrix visual field instrument and retinal nerve fiber layer evaluation using the Topcon 3D OCT-2000. Pattern deviation plot was divided into 19 areas and five aggrupation or quadrants and ranked with a value between 0 and 4 according to its likelihood of normality, and differences among three groups were analyzed. Principal component analysis (PCA) was also used to extract the most notable features of FDT and OCT, and a logistic regression analysis was applied to obtain the classification rules.

Results

Only area numbers 7 and 12 and the central zone of FDT Matrix showed statistical differences (P<0.05) between GI-NG and GII-SG. The classification rules were estimated by the four PCA obtained from FDT Matrix and 3D OCT-2000 in a separate and combined use. Area under the receiver operating characteristic curve was 78.88% with FDT-PCA, 82.09% with OCT-PCA, and 94.27% with combined use of FDT and OCT-PCA to discriminate GI-NG and GII-SG.

Conclusion

The predictive rules based on FDT-PCA or OCT-PCA provide a high sensitivity and specificity to detect the earliest stages of glaucoma and even better in combined use. These predictive rules may help the future development of software for FDT Matrix perimetry and 3D OCT-2000, which will greatly improve their diagnostic ability, making them useful in daily practice in a primary care setting.

Visual electrodiagnosis in glaucoma screening: a clinical study

BACKGROUND

The aim of the present study was to investigate the value of pattern visual-evoked potentials (pVEP) and pattern electroretinograms (pERG) in early glaucoma diagnosis.

MATERIALS AND METHODS

Thirty-eight eyes of 38 patients were included. Patients were classified into normal control (NC) and glaucoma patient (GP) groups. Patients underwent a detailed clinical ophthalmic examination and an electrodiagnostic examination using steady-state pVEP and pERG. Differences between groups in the amplitudes of the second harmonic of the pVEP and pERG responses to 480' (A480) and 48' (A48) check sizes and the ratio of the above amplitudes (A48/A480) were examined.

RESULTS

Differences in the 48' and 480' pVEP between groups were not statistically significant. The pVEP A48/A480 ratio was significantly higher in NC than in GP. Differences in pERG between groups were statistically not significant for both 48' and 480' check sizes. In contrast, respective differences in pERG A48/A480 ratio were statistically significant.

CONCLUSIONS

Steady-state pVEP and pERG A48/A480 ratio may be of value in glaucoma diagnosis.

The distribution of visual field defects per quadrant in standard automated perimetry as compared to frequency doubling technology perimetry

To test the ability of frequency doubling technology (FDT) perimetry to reveal defects in the same field quadrants as detected by standard automated perimetry (SAP). Ninety-two eyes with open-angle glaucoma and documented visual field defects by threshold SAP (Octopus Dynamic strategy) also underwent threshold FDT testing after successfully passing the FDT screening test. All eyes revealed varying stages of SAP defects while only 80 revealed FDT damage: 31:21 eyes in the early field loss stage, 36:35 in the moderate field loss stage, and 25:24 in the severe field loss stage in SAP versus FDT, respectively. SAP was able to detect abnormalities in 74 and 79% of the superotemporal, and inferotemporal quadrants, respectively, while the corresponding FDT figures were 70 and 69% for the same quadrants (P < 0.05 each). With regards to the nasal hemifield, SAP detected defects in 73 and 81% of the superonasal and inferonasal quadrants, respectively, compared to 69 and 66% for FDT (P < 0.001 each). The test duration per individual eye was significantly shorter with FDT than with SAP (P < 0.05). As well as the already established lower sensitivity of FDT compared to SAP, this study also demonstrated the significantly poorer ability of FDT in detecting the same field quadrant defects, especially in the early stages of glaucomatous damage.

Selective perimetry in glaucoma diagnosis

PURPOSE OF REVIEW

Selective perimetry evaluates visual function by using visual stimuli that attempt to target specific subpopulations of retinal ganglion cells, which is designed to improve sensitivity to detect glaucomatous functional loss. This paper reviews recent studies that have assessed the characteristics of new strategies/programs of selective perimetry.

RECENT FINDINGS

Selective perimetry is usually compared against an existing standard technique--standard automated perimetry. Recent studies did not consider standard automated perimetry results as part of inclusion/exclusion criteria, avoiding selection bias and permitting fair comparisons between perimetry techniques. Furthermore, the Swedish Interactive Threshold Algorithm is replacing Full-Threshold as the standard automated perimetry gold-standard strategy, and comparisons of the diagnostic performance of function-specific perimetry may be influenced by which standard automated perimetry technique is used as the reference. These factors may impact our perception about the role of selective perimetry in glaucoma management.

SUMMARY

The lack of a perfect gold-standard diagnostic test for glaucoma limits the interpretation of results from cross-sectional studies evaluating visual field tests. Nevertheless, evidence suggests that visual dysfunction in eyes with early glaucoma varies significantly between individuals and no single technique is superior to the others in all patients. A multimodal functional assessment may be more effective in detecting/quantifying visual impairment associated with early glaucoma.

Rapid and cost-effective method to assess vision disorders in a population

PURPOSE

The aim was to develop a means of rapidly assessing eye health in a cost- and time-effective way to monitor changes over time.

METHODS

Key features of the five main eye diseases that cause vision loss in Australia were assessed. Participation was volunteer-based from randomly selected Melbourne suburbs. Recruitment was by mail. Anterior segments and fundi were photographed with a digital non-mydriatic fundus camera. Visual fields were tested with Frequency Doubling Technology. A questionnaire collected information about demographics, general health and lifestyle. Findings from this rapid assessment were compared with those from a population-based study.

RESULTS

A total of 1695 people, aged between 70 and 79 years (mean 74), were recruited. The rates and causes of visual impairment were similar between the rapid assessment method and the population-based study. Among the 134 people (8%) with visual impairment at presentation, 98 (73%) had undercorrected refractive error, 17 (13%) had age-related macular degeneration, 11 (8%) had cataract, 2 (2%) had diabetic retinopathy and 2 (2%) had glaucoma. Screening costs per participant were only about AU$145, compared with AU$433 in the Melbourne Visual Impairment Project (VIP). The application of Frequency Doubling Technology as well as the use of a non-mydriatic digital camera for fundus and lens photography resulted in an average examination time of less than half the time needed in the VIP. Data collection took 3 months rather than 4 years in the VIP.

CONCLUSION

The rapid assessment method was efficient in time and cost and produced results comparable to a normal population-based survey. Repeating the study design for a similarly sampled group every 2 years would allow the assessment of changes in the prevalence of undiagnosed eye disease.

Frequency doubling illusion VEPs and automated perimetry in multiple sclerosis

We examined frequency doubling (FD) illusion based automated perimetry (FDT) and dichoptic FD multifocal visual evoked potentials (FDmfVEPs) in Normal and multiple sclerosis (MS) subjects. Contrast thresholds were determined at 17 visual field locations using an FDT perimeter. The stimuli presented to each location were 0.25 cpd gratings presented with rapid (25 Hz) counterphase flicker and thus displayed the spatial FD illusion. Dichoptic mfVEPs were recorded by concurrently stimulating eight regions/eye with FD stimuli presented at 95% contrast. Recordings were obtained from 27 Normal subjects, 26 MS patients who had experienced Optic Neuritis (MSON) and 24 MS patients without a history of ON (MSNON). The FDT thresholds showed enhanced contrast sensitivity for MSON patients (P < 0.0001) but not for MSNON patients. Response amplitudes for the central four regions of the mfVEP stimulus were reduced in both patient groups (P < 0.005). A classification model based upon the FDT thresholds performed at a specificity of 96% for a sensitivity of 97% in MSON patients, but the accuracy (simultaneously largest sensitivities and specificities) was poor (approximately 60%) in MSNON patients. Discriminant models based on the FDT thresholds and FDmfVEPs were able to diagnose more that 90% MSON patients but performed poorly for MSNON patients.

Assessment of optic disc cupping with digital fundus photographs

PURPOSE

To determine the agreement between the assessment of retinal digital images by using an overlay transparency sheet and the Heidelberg retinal tomograph (HRT) in determining cup-disk ratios greater than 0.6.

DESIGN

Diagnostic test comparison.

METHODS

Computerized topographic and monoscopic digital images of the optic disk of 628 people aged 70 to 79 years were assessed. A grader (M.C.) defined the disk margin on HRT images, and the operation software computed the area cup-disk ratio. The same grader also determined whether the vertical cup-disk ratio on retinal images was greater than 0.6 by superimposing a transparency overlay sheet over the images. Findings of a second grader (J.G.F.) were used to establish reliability measures.

RESULTS

The intragrader reliability for the overlay method and HRT was almost perfect (intraclass correlation coefficient [ICC] = 0.96 and 0.99, respectively), whereas the intergrader reliability was good (ICC = 0.77 and 0.92, respectively). A perfect agreement was found on 28 (85%) of 33 eyes between the overlay and HRT methods in determining cup-disk ratios greater than 0.6.

CONCLUSIONS

The overlay transparency method appears to be a reliable and promising alternative in determining cup-disk ratios greater than 0.6 in a community screening setting.

Performance of community-based glaucoma screening using Frequency Doubling Technology and Heidelberg Retinal Tomography

PURPOSE

To assess the performance of a community-based glaucoma screening algorithm in the general population.

METHODS

A total of 659 individuals aged 50-90 years were screened for glaucoma. Presenting visual acuity, family history of glaucoma, FDT perimetry, and HRT tests were assessed. Additional samples of participants served as control groups. Participants identified as glaucoma positive received a full ophthalmic examination. Based on this exam a consensus diagnosis was made which served as the gold standard.

RESULTS

The optimal screening strategy combining visual acuity and family history with FDT and HRT had sensitivities, specificities, positive predictive values and negative predictive values of 96.8%, 89.7%, 31.9%, and 99.8% respectively for detecting glaucoma.

CONCLUSIONS

By combining assessments of presenting visual acuity and family history of glaucoma with Frequency Doubling Technology perimetry and Heidelberg Retina Tomography, we devised a community glaucoma-screening algorithm that showed a high sensitivity and specificity for detecting glaucoma in the general population.

Screening for glaucoma in a general population with the non-mydriatic fundus camera and the frequency doubling perimeter

PURPOSE

To evaluate the usefulness of non-mydriatic fundus camera (NMFu-camera) and frequency doubling perimeter (FDP) for detecting glaucoma in a general population.

METHODS

This prospective observational multicenter study consisted in screening for glaucoma in the populations of three Belgian cities. Intraocular pressure (IOP) was measured with non-contact pneumo-tonometer (NCT) and applanation tonometry (AT) if NCT IOP was > or = 17 mmHg. Visual field was screened with FDP (C-20-5) and digitized optic disc photographs (ODPs) were taken with NMFu-camera. FDP was considered abnormal if at least one defective point was found. ODPs were graded as normal or glaucomatous by consensus of three glaucoma specialists. Optic disc and visual field results were matched per eye. Subjects with known ocular hypertension and/or treated primary open angle glaucoma were excluded from the analysis.

RESULTS

A total of 1620 subjects were included in the study. Their mean age was 63.2 years. AT IOP was > 21 mmHg in 8.2%. A total of 98.1% of ODPs could be interpreted. Glaucomatous optic discs were detected in 3.5% of the subjects. In this group only 24% had an AT IOP > or = 22 mmHg. FDP was abnormal in 44.5%. The sensitivity and specificity of FDP to identify patients with an optic disc graded as glaucomatous were 58.6% and 64.3% respectively.

CONCLUSIONS

The combined use of the NMFu-camera and the FDP is a feasible method for an initial glaucoma mass screening. NMFu-camera may be a useful and quick method to screen for glaucomatous damage in a community. FDP in screening strategy was revealed to be not sensitive enough when setting the cut-off value at one defective test location. IOP measurements were confirmed to be a poor tool to detect glaucomatous damage.

Monocular and dichoptic masking effects on the frequency doubling illusion

The purpose of this paper was to investigate the effects of both monocular and dichoptic masking on the frequency doubling (FD) illusion, using both temporal and spatial masks. Monocular spatial tuning effects occurred around the fundamental FD spatial frequency of 0.25 cycles per degree (c/deg), whereas dichoptic spatial frequency tuning effects occurred at the doubled spatial frequency of 0.50 c/deg. Temporal tuning effects were observed at the FD temporal frequency of 25 Hz, in both monocular and dichoptic paradigms. These results suggest that the FD illusion is cortical in origin and is dominated by a flicker component.

Laterality of the performance of glaucoma mass screening using frequency-doubling technology

PURPOSE

This study investigated laterality during the performance of glaucoma mass screening with a frequency-doubling technology perimetry test.

MATERIALS AND METHODS

A frequency-doubling technology screening mode (C-20-1, version 2.6) test was performed on both eyes of 14,784 persons. Subjects with visual field abnormalities detected by the frequency-doubling technology test or with fixation error underwent retesting without a specified interval for rest. Consequently, 206 subjects who fulfilled the screening criteria of the frequency-doubling technology-based glaucoma screening protocol [FDT-GSP(+)] were further investigated using the Humphrey visual field analyzer (30-2). As a result, 74 right eyes and 57 left eyes were shown to have definite glaucoma.

RESULTS

Frequency-doubling technology data for the left eye demonstrated a significantly (P<0.001) higher rate of artifacts, such as no reproducibility of results between the first and second tests (left/right: 2.4%/1.7%) as well as fixation errors (left/right: 2.8%/1.0%). The false-positive rate of the FDT-GSP for glaucoma was more than 1.5-fold higher in the left eye than in the right eye (16.3%/9.8%). In the case that either eye exhibited FDT-GSP(+), the positive predictive value of the FDT-GSP for definite glaucoma in the left eye was almost half of that in the right eye (28.4% vs. 53.8%). Specificity of the FDT-GSP for detection of definite glaucoma also exhibited a lower trend (P = 0.097) in the left eye (44.6%) than in the right eye (55.3%), but the sensitivity of the test was similar in both eyes (91.2% vs. 90.5%, respectively).

CONCLUSIONS

When frequency-doubling technology-based mass screening is performed on the general population, performance is lower for the left eye than for the right eye. This performance disparity is likely to be primarily associated with a difference in specificity.

Agreement between frequency doubling perimetry and static perimetry in eyes with high tension glaucoma and normal tension glaucoma

AIMS

To investigate the agreement in results between frequency doubling technology (FDT) and the conventional automated static perimeter in eyes with normal tension glaucoma (NTG) and high tension glaucoma (HTG).

METHODS

72 eyes of 36 patients, who had two or more experiences with the Humphrey field analyser (HFA) program C30-2, were examined with the screening C-20-1 program of FDT. The result of FDT at each of the 17 stimulus points was graded as one of four categories. 58 out of 76 test points of HFA were assigned to one of the 17 clusters corresponding to FDT test points. Each cluster was represented as the lowest (scotoma of HFA) or the highest (threshold of HFA) probability symbol of total deviation (TD) of the HFA test points included in the cluster. The agreement between scotoma/threshold of HFA and FDT results was evaluated for NTG and HTG.

RESULTS

In a total of 65 eyes, the Spearman coefficients between the FDT and HFA (threshold/scotoma of HFA) were 0.599 and 0.515 (p<0.0001), respectively. In the HFA mean deviation matched 20 HTG eyes and 20 NTG eyes, the number of points with abnormal FDT results were 102 and 62 in eyes with HTG and NTG, respectively. The eyes with HTG had more abnormal FDT results than NTG eyes (p=0.0014, Mann-Whitney U test). The kappa coefficient between FDT and threshold of HFA in eyes with HTG and NTG was 0.288 and 0.520, respectively, and the agreement between FDT and scotoma of HFA was 0.480 and 0.439, respectively.

CONCLUSIONS

The best agreement of the results of FDT and HFA was observed in eyes with NTG using threshold of HFA. The eyes with HTG showed lower agreement with more abnormal points in FDT results, which suggests enough sensitivity of FDT in eyes with NTG, and higher sensitivity of FDT in eyes with HTG.

Does frequency doubling technology perimetry reliably detect neurological visual field defects?

AIM

To determine the ability of frequency doubling technology (FDT) perimetry to detect visual field defects of neurological origin.

METHODS

A total of 15 eyes of nine patients who all had complete hemianopias or quadrantanopias underwent the FDT 20-5 screening mode test and Humphrey 24-2 SITA Fast visual field test (HFA). The FDT results were scored according to the number of abnormal test locations (out of a maximum of 4) in each affected quadrant. FDT locations showing a defect of P< 2% were considered abnormal.

RESULTS

Of the 15 eyes, six showed complete superior quadrantanopic and nine complete hemianopic field defects on HFA. Of 96 FDT test locations in these quadrants or hemifields only 38 were abnormal on FDT testing (40%). For the quadrantanopic field defects, five out of 24 locations were abnormal (21%). For the hemianopic field defects, 33 out of 72 locations were abnormal (49%). In three eyes (two with quadrantanopias and one with complete hemianopia), FDT perimetry failed to demonstrate any corresponding abnormality.

CONCLUSIONS

The FDT screening test can fail to demonstrate complete hemianopic and quadrantanopic field defects. Users should be aware of this deficiency when using FDT to screen for field defects.

The learning effect in visual field testing of healthy subjects using frequency doubling technology

PURPOSE

To evaluate the presence, duration and magnitude of a learning effect in serial visual field (VF) testing, using the commercially available frequency doubling technology (FDT) instrument.

PATIENTS AND METHODS

21 healthy adults with no prior VF experience underwent 6 serial VF tests, using the full-threshold C-20 program of the Zeiss-Humphrey FDT analyzer, on one randomly chosen eye. Tests were spaced at least two days apart.

RESULTS

The average mean sensitivity was 32.37 +/- 2.6 dB; the average mean deviation (MD) was 1.22 +/- 1.8 dB. The MD at the first examination (0.28 +/- 2.1 dB) was significantly poorer than at any of the other testing sessions (p<0.003). Similarly, the mean sensitivity at the first examination (31.16 +/- 3.0 dB) was significantly lower than any other testing session (p<0.004). The proportion of improvement from the first to the second session was 63% and 65% of the total improvement, for mean sensitivity and MD, respectively. Mean test duration showed a modest reduction, from 4.40 +/- 0.3 minutes in the first session to 4.17 +/- 0.4 minutes in the last session (p = 0.023). A sub-analysis comparison of the different VF segments showed a more prominent learning effect in the peripheral and nasal visual segments (p<0.0001).

CONCLUSION

Baseline measurements should best rely on the second testing session, since MD and mean sensitivity are somewhat poorer when subjects with no prior VF experience are first tested on the FDT instrument. This may be especially true for the purpose of following patients over time.

Performance of glaucoma mass screening with only a visual field test using frequency-doubling technology perimetry

PURPOSE

To report the performance of glaucoma mass screening with only a visual field test utilizing frequency- doubling technology (FDT) perimetry in general populations.

DESIGN

Hospital and population-based cross-sectional study.

METHODS

This study took place in a multicenter setting. One hundred three consecutive glaucomatous patients and 14,814 persons were randomly selected. We had created a glaucoma screening protocol (GSP) using FDT perimetry (FDT-GSP). Frequency-doubling technology-glaucoma screening protocol was tested on consecutive glaucoma patients diagnosed with Humphrey visual field analyzer (30-2 SITA standard), and then FDT-GSP was applied to general populations. Frequency-doubling technology-glaucoma screening protocol positive subjects were ophthalmologically diagnosed. Detection ability of FDT-GSP was determined in consecutive patients, and the positive predictive value (PPV) of FDT-GSP to detect definitive glaucoma was estimated in general populations.

RESULTS

Frequency-doubling technique-glaucoma screening protocol detected 83.3% and 100% of definitive glaucoma patients with an early (mean deviation [MD] > -6 dB) and more advanced stage (MD < or = -6 dB), respectively. In the population-based screening, there were 660 (4.5%) subjects who had positive FDT-GSP, including 512 in whom no visual field abnormalities (VFA) had been pointed out previously. Of them, 370 subjects underwent ophthalmologic diagnosis. Then, 266 (71.9%, 266/370) subjects had a glaucomatous disk and 167 had definitive glaucomatous VFA. Fifty-five (14.9%) and 39 (10.5%) subjects were diagnosed as having other diseases and as normal, respectively. The PPV of FDT-GSP ranged from 32.6% (167/512)-45.1% (167/370).

CONCLUSIONS

Frequency-doubling technology-based screening with only a visual field test showed reasonable performance on mass screening for detection of definitive glaucoma in this study population, considering the glaucoma prevalence.

Comparison of three tests using the frequency doubling illusion to diagnose glaucoma

PURPOSE

The introduction of the FDT perimeter prompted the comparison of three tests employing frequency doubling (FD) stimuli. These measures compared different visual field locations and contrast ranges. Frequency of seeing curves were examined for the method most similar to FDT.

METHODS

For 146 eyes the following were obtained: (i) contrast matches to two suprathreshold FD stimuli (normal subjects, ocular hypertensve suspects, primary open angle glaucoma subjects); (ii) two alternative forced choice (2AFC) thresholds for horizontally versus vertically orientated FD gratings: and (iii) contrast thresholds determined by method of adjustment (MOA) for five different stimulus types.

RESULTS

A model based on the worst of the MOA hemifield thresholds performed best. The suprathreshold contrast matching tests performed worst. Frequency of seeing curves were fitted for the 146 eyes of the 2AFC tests. Although the MOA thresholds were higher than the 2AFC thresholds (for normals mean +/- SE, 8.47 +/- 0.43 dL, P < 0.0000), the best diagnostic concordance was at lower limens (75% or 80% correct) of the fitted frequency of seeing curves.

CONCLUSIONS

There was good diagnostic concordance between the MOA and 2AFC methods although the thresholds were 1.8-fold different on a log-scale. This suggests that the same neural mechanism mediates both thresholds for rapidly flickering, spatially coarse, patterns.

Screening models for glaucoma

For social and economic reasons, glaucoma screening is a useful and necessary task, with possible benefits for individuals and the health care system arising from the early diagnosis and early therapy of patients with glaucoma. Early treatment of patients with glaucoma decreases the probability that those patients will become blind and lowers the direct and indirect costs for patients with glaucoma. Most of the reported studies dealing with glaucoma screening used only one parameter (eg, intraocular pressure) to detect and to discriminate glaucoma patients from healthy subjects. Glaucoma screening devices might be combined to obtain the best specificity and sensitivity. Because the diagnosis of glaucoma is very closely associated with a morphologic change in the optic nerve head, one screening parameter should be the morphology of the papilla. To increase specificity and sensitivity, a combination of morphologic and functional testing might be useful. In this review, we report the context of glaucoma screening in terms of health economics, the testing quality of devices for functional and morphologic screening, and the results of a pilot study.