FREQUENCY-DOUBLING TECHNOLOGY AND HIGH-PASS RESOLUTION PERIMETRY IN GLAUCOMA AND OCULAR HYPERTENSION

LADA V. KALABOUKHOVA and BERTIL LINDBLOM

Göteborg University, Institute of Clinical Neuroscience, Section of Ophthalmology, Sahlgrenska University Hospital Mölndal, Sweden

Abstract

Purpose

To investigate the correlation between frequency-doubling technology perimetry (FDT) and high-pass resolution perimetry (HRP) in eyes with primary open-angle glaucoma, suspect glaucoma, and ocular hypertension.

Patients and methods

Ninety-five patients (16 3 eyes) were studied. Visual fields were assessed by HRP, FDT screening, and FDT threshold program 20-5. In eyes in which there was a discrepancy between the test results, a comprehensive clinical examination was performed, including optic disc photography and Heidelberg retinal tomography (HRT).

Results

There were 74 glaucomatous eyes, 16 eyes suspected of having glaucoma, 40 eyes with ocular hypertension, and 33 normal eyes. Of the 163 eyes, 75 (46 %) had normal HRP and FDT screening results, while 66 (40.5%) showed abnormal results in both tests. In 12 (7.4%) eyes FDT screening was abnormal, while HRP was within normal limits. Eight of these eyes were judged to have glaucoma based on the clinical examination. In ten eyes (6.1%), FDT was normal while HRP was abnormal. Five of these ten eyes were judged to have glaucoma. Thus, sensitivity and specificity for FDT were 85.0 and 85.4 %, respectively, for the detection of glaucoma.

There was a good correlation between HRP neural capacity and FDT score (both screening and threshold). The correlation coefficients were r1 = -0.73 and r2 = -0.72, respectively (p < 0 .0001).

Conclusions

Good correlation was found between FDT and HRP. FDT is a good screening test for the detection of optic nerve damage in open-angle glaucoma.

Address for correspondence: Lada Kalaboukhova, Institute of Clinical Neuroscience, Ophthalmology Section, Sahlgrenska University Hospital, SE 431 80 Mölndal, Sweden. Email: lada_kalabukhova@ hotmail.com

Perimetry Update 2002/2003, p. 147

Proceedings of the XVth International Perimetric Society Meeting, Stratford-upon-Avon, England, June 26–29, 2002

edited by David B. Henson and Michael Wall

© 2004 Kugler Publications, The Hague, The Netherlands

STANDARD AUTOMATED PERIMETRY SITA AND FULLTHRESHOLD STRATEGIES COMPARED TO SWAP AND FDT IN GLAUCOMA

C. BODEN, P.A. SAMPLE and R.N. WEINREB

Visual Function Laboratory, Glaucoma Center, University of California at San Diego, La Jolla, CA, USA

Abstract

Purpose

To compare full-threshold (FT) and SITA algorithms for standard automated perimetry (SAP) with two commercially available visual-function specific tests: short-wavelength automated perimetry (SWAP)1 and frequency-doubling technology (FDT) perimetry.2

Methods

Sixty-seven patients with glaucomatous optic neuropathy (GON) with SAP (SITA and FT), SWAP and FDT within three months were included (mean ± SD: 18.2 ± 25.6 days). Visual fields were all reliable with ≤ 25% fixation losses, false-positives and false-negatives. Mean deviation, pattern standard deviation (PSD), and number of abnormal points ( p < 5%) on the pattern deviation plot were compared. Hodapp et al.3 criteria were used to rate the severity of visual loss for SAP and SWAP. Severity criteria modified by Sponsel et al. were used for FDT.4 A subgroup of 19 patients with all four follow-up tests (one follow-up test for each of SAP-FT, SAP-SITA, SWAP and FDT) was used to assess the repeatability of pattern deviation defects. Follow-up SAP-FT, SAP-SITA, SWAP and FDT were conducted with a mean ± SD of 16.8 ± 28.2 days of each other. The first visit and follow-up visit were a mean ± SD of 1.4 ± 0.5 years apart.

Results

In the group as a whole (n = 67), there was good agreement amongst the 4 tests (kappa = 0.7-0.8) as to which fields had a PSD with a probability outside normal limits ( p < 5%). Similarly, agreement was generally good on the severity of visual loss (kappa = 0.48-0.61). FDT severity agreed least with SAPSITA (kappa = 0.48 + 0.07) and SAP-FT (kappa = 0.46 + 0.07). Agreement of SAP-SITA with SWAP (kappa = 0.52 + 0.08) was slightly lower than SAP-FT with SWAP (kappa = 0.61 + 0.07), but both were still good. The number of defective pattern deviation points was only compared for SAP-SITA, SAP-FT, and SWAP, since FDT has only 18 test locations compared to the other tests with 52 test locations. SAPSITA tends to show more abnormal pattern deviation (PD) points (mean ± SD:10.7 ± 9.5) than SAP-FT (8.3 ± 9.2) or SWAP (7.5 ± 7.1), although the difference was only significant from SWAP. In the subgroup

Address for correspondence: Pamela A. Sample, PhD, Department of Ophthalmology, University of California, San Diego, 9500 Gilman Drive, La Jolla, CA 92093-0946, USA. Email: psample@eyecenter. ucsd.edu

Perimetry Update 2002/2003, pp. 149–150

Proceedings of the XVth International Perimetric Society Meeting, Stratford-upon-Avon, England, June 26–29, 2002

edited by David B. Henson and Michael Wall

© 2004 Kugler Publications, The Hague, The Netherlands

of 19 patients with follow-up tests, the number of PD points confirmed as normal or abnormal was similar between the tests: 87, 92, and 86% for SAP-SITA, SAP-FT, and SWAP, respectively.

Conclusions

Standard perimetry results with FT and SITA algorithms correlate highly, as has been shown in previous studies.5-7 The relationship of SITA and FT strategies to the visual function specific tests (SWAP and FDT) was generally similar. However, when switching from full-threshold to SITA strategies in longitudinal comparative studies, caution should still be taken in any analysis involving counts of defective pattern deviation points.

Acknowledgment

Financial support: NEI EY08208 (PAS). Proprietary interest statement: none.

References

1.Sample PA, Johnson CA, Haegerstrom-Portnoy G, Adams AJ: Optimum parameters for short-wave- length automated perimetry [see comments]. J Glaucoma 5(6):375-383, 1996

2.Johnson CA, Demirel S: The role of spatial and temporal factors in frequency-doubling perimetry. In: Wall M, Heijl A (eds) Perimetry Update, 1997, pp 13-19. Amsterdam: Kugler Publ 1997

3.Hodapp E, Parrish RK, Anderson SR: Clinical Decisions in Glaucoma. St Louis, MO: CV Mosby Co 1993

4.Sponsel WE, Arango S, Trigo Y, Mensah J: Clinical classification of glaucomatous visual field loss by frequency doubling perimetry. Am J Ophthalmol 125:830-836, 1998

5.Bengtsson B, Heijl A: Comparing significance and magnitude of glaucomatous visual field defects using the SITA and full threshold strategies. Acta Ophthalmol Scand 77(2):143-146, 1999

6.Sharma AK, Goldberg I, Graham SL, Mohsin M: Comparison of the Humphrey Swedish interactive thresholding algorithm (SITA) and full threshold strategies. J Glaucoma 9(1):20-27, 2000

7.Heijl A, Bengtsson B, Patella VM: Glaucoma follow-up when converting from long to short perimetric threshold tests. Arch Ophthalmol 118(4):489-493, 2000

SCREENING VERSUS THRESHOLD FREQUENCYDOUBLING TECHNOLOGY IN EARLY GLAUCOMATOUS DAMAGE DETECTION

PAOLO BRUSINI, CLAUDIA TOSONI and LUCIA PARISI

Department of Ophthalmology, Santa Maria della Misericordia Hospital, Udine, Italy

Introduction

Frequency-doubling technology (FDT) is a non-conventional visual field testing method, which uses low-spatial-frequency sinusoidal gratings (0.25 cycle/degree) undergoing high-temporal-frequency counterphase flicker (25 Hz). Using these parameters, the spatial frequency of gratings appears to be doubled (frequency doubling illusion). FDT selectively analyzes the My cells, a subset of retinal ganglion cells which have a very low redundancy (3-5% of all retinal ganglion cells). A small reduction in their population, as in the initial stages of chronic glaucoma, can cause early functional damage. For this reason, FDT may have a higher sensitivity than standard automated perimetry (SAP) in early glaucoma diagnosis. The test is fast and easy, particularly when using the screening strategy, which proved to be useful in glaucoma damage detection.1-11 The threshold strategy test time is usually four to five times longer than the screening test. As it is very important to use sensitive diagnostic techniques in the early stages of the disease, we investigated the sensitivity of both strategies in detecting slight functional defects in early glaucoma patients. The specificity was also studied in a sample of healthy subjects.

Patients and methods

Thirty-five eyes from 35 patients with early open-angle glaucoma (mean age, 65.1 ± 12.7 years; range, 29-82 years) were tested with FDT (Welch-Allyn, Skaneateles Falls, NY, and Zeiss-Humphrey Systems, Dublin, CA) using both the screening C-20-5 and the threshold C-20 test, which both examine 17 areas in the 20° central visual field. With the screening strategy, stimuli are initially flagged when they reach the p < 5% probability of being normal. The tested points are classified into four classes: p ≥ 5% (within normal limits); p < 5% (mild-relative defect); p < 2% (moderate-relative defect); and p < 1%

Address for correspondence: Paolo Brusini, MD, Via Pordenone 41, 33100 Udine, Italy. Email: brusini@libero.it

Perimetry Update 2002/2003, pp. 151–154

Proceedings of the XVth International Perimetric Society Meeting, Stratford-upon-Avon, England, June 26–29, 2002

edited by David B. Henson and Michael Wall

© 2004 Kugler Publications, The Hague, The Netherlands

(severe defect). Tests were performed in random order on the same day. All patients had a previous Humphrey 30-2 threshold test. We only considered cases of early visual field defect with SAP (glaucoma staging system12 Stages 1 and 2) and those that had good reliability (<33% of fixation losses and false positive or negative rate). Patients with cataract or other ocular diseases and those with a best-corrected visual acuity of less than 16/20 were excluded. When both eyes from the same patient were eligible, one eye was randomly chosen.

We used two different abnormality criteria to define an FDT test as being abnormal: a. at least one abnormal area (p < 5%) in any location; b. at least two abnormal areas (p < 5%) in any location.

The sensitivity of both FDT strategies was then studied, taking SAP as the gold standard. Moreover, we also studied the correspondence of defect location according to the two strategies, subdividing the tests into four groups: 1. no correspondence (only one test abnormal or abnormal areas localized in different quadrants); 2. partial correspondence (at least one abnormal area localized in the same quadrant); 3. good correspondence (same quadrant or same hemifield involved); 4. perfect correspondence (same abnormal areas). Finally, test time was considered.

Specificity (percentage of normal tests) was estimated from a population of 24 normal subjects (mean age, 44.9 ± 11.7 years; range, 26-73 years).

Results

The sensitivity of the FDT screening test was 91.4% using the abnormality criterion a, and 82.9% with criterion b. The FDT threshold strategy gave only slightly better results: 94.3% with criterion a, and 91.4% with criterion b. Differences were not statistically significant (McNemar’s non-parametric test).

In the control sample of healthy subjects, specificity ranged from 91.7-100% (criteria a and b, respectively) using the screening strategy, and from 66.7-87.5% using the threshold test (differences statistically not significant, McNemar’s non-parametric test).

The correspondence between defects detected by the two strategies was as follows: 1. no correspondence: five cases (14.3%); 2. partial correspondence: ten cases (28.6%); 3. good correspondence: 12 cases (34.3%); 4. perfect correspondence: eight cases (22.9%).

Mean test time was 1 minute 16 seconds (range, 42 seconds to 2 minutes) with the screening test, and 4 minutes 49 seconds (range, 4 minutes 14 seconds to 6 minutes 37 seconds) with the threshold test. The difference was statistically significant (p < 0.001, Student’s t test).

Discussion

FDT is a new and potentially useful non-conventional visual field testing method. In this study, the sensitivity of FDT in early glaucoma was similar for the screening C- 20-5 and threshold C-20 tests using two different criteria to define a test as being abnormal.3,6,9 As expected, using the less stringent criteria, the sensitivity was higher

and the specificity lower with both strategies. However, as in other studies,6 the threshold test seems to give slightly better results at the expense of a longer test time (approximately four times as long). The results of FDT threshold tests have previously been shown to be closely related to the Humphrey 30-2 test.13-15 In the majority of cases, the screening strategy, which supplies semi-quantitative information on defect depth, seems to work very well.

The correspondence between defect location was good to perfect in 57.2% of cases (Fig. 1). This means that even the quicker test is not only able to detect a defect, but also to accurately indicate its location within the visual field.

Only in five cases (14.3%) was there no correspondence, but the defects were very small and there may have been sensitivity fluctuations between the two tests (Fig. 2).

The FTD C-20-5 screening test usually takes less than one minute in normal eyes, and rarely exceeds one minute 30 seconds in abnormal cases. The very short test time allows busy ophthalmologists to screen large numbers of patients, with obvious advantages. It would be an ideal test for epidemiological studies on glaucoma prevalence. In conclusion, both the FDT screening and threshold strategies gave good results in early glaucoma.

References

1.Maddess T, Henry GH: Performance of nonlinear visual units in ocular hypertension and glaucoma. Clinical Vis Sci 7:371-383, 1992

2.Johnson CA, Samuels SJ: Screening for glaucomatous visual field loss with frequency doubling perimetry. Invest Ophthalmol Vis Sci 38:413-425, 1997

3.Quigley HA: Identification of glaucomatous visual field abnormality with the screening protocol of frequency-doubling perimetry. Am J Ophthalmol 125:819-829, 1998

4.Brusini P, Busatto P: Frequency doubling perimetry in glaucoma early diagnosis. Acta Ophthalmol Scand (Suppl 227) 76:23-24, 1998

5.Cello KE, Nelson-Quigg JM, Johnson CA: Frequency doubling technology perimetry for detection of glaucomatous visual field loss. Am J Ophthalmol 129:314-322, 2000

6.Burnstein Y, Ellish NJ, Magbalon M, Higginbotham EJ: Comparison of frequency doubling perimetry with Humphrey visual field analysis in a glaucoma practice. Am J Ophthalmol 129:328-333, 2000

7.Trible JR, Schultz RO, Robinson JC, Rothe TL: Accuracy of glaucoma detection with frequencydoubling perimetry. Am J Ophthalmol 129:740-745, 2000

8.Iester M, Mermoud A, Schnider C: Frequency doubling technique in patients with ocular hypertension and glaucoma: correlation with Octopus perimeter indices. Ophthalmology 107:288-294, 2000

9.Casson R, James B, Rubinstein A, Ali H: Clinical comparison of frequency doubling technology perimetry and Humphrey perimetry. Br J Ophthalmol 85:360-362, 2001

10.Paczka JA, Friedman DS, Quigley HA et al: Diagnostic capabilities of frequency-doubling technology, scanning laser polarimetry, and nerve fiber layer photographs to distinguish glaucomatous damage. Am J Ophthalmol 131:188-197, 2001

11.Thomas R, Bhat S, Muliyil JP, Parikh R, George R: Frequency doubling perimetry in glaucoma. J Glaucoma 11:46-50, 2002

12.Brusini P: Clinical use of a new method for visual field damage classification in glaucoma. Eur J Ophthalmol 6:402-407, 1996

13.Sponsel WE, Arango S, Trigo Y, Mensah J: Clinical classification of glaucomatous visual field loss by frequency doubling perimetry. Am J Ophthalmol 125:830-836, 1998

14.Paczka JA, Friedman DS, Quigley HA et al: Diagnostic capabilities of frequency-doubling technology, scanning laser polarimetry, and nerve fiber layer photographs to distinguish glaucomatous damage. Am J Ophthalmol 131:188-197, 2001

15.Serguhn S, Spiegel D: Comparison of frequency doubling perimetry and standard achromatic computerized perimetry in patients with glaucoma. Graefe’s Arch Clin Exp Ophthalmol 239:351-355, 2001