|Year : 2003 | Volume
| Issue : 1 | Page : 35-38
Humphrey visual field and frequency doubling perimetry in the diagnosis of early glaucoma.
G Chandrasekhar, V Kunjam, Vallam S Rao, R Nutheti
VST Center for Glaucoma Care, L V Prasad Eye Institute, Hyderabad, India
VST Center for Glaucoma Care, L V Prasad Eye Institute, Hyderabad
| Abstract|| |
Purpose: To compare Humphrey Visual Field Analyzer (HVF) and Frequency Doubling Perimetry (FDP) testing in the diagnosis of early glaucoma.
Methods: We performed HVF (24-2 standard full threshold) and FDP (N-30) evaluations in 34 consecutive patients with early primary glaucoma and 96 normal subjects. Early glaucoma was defined on the basis of disc changes of glaucoma; the mean deviation on white-on-white perimetry had to be no worse than 6 decibels. Glaucomatous optic neuropathy was defined as a combination of cup-disc asymmetry of more than 0.2, notching, excavation, thinning or pallor of superior or inferior neuroretinal rims, retinal nerve fibre layer defects of the wedge or diffuse type and neuroretinal rim haemorrhage. Both the glaucoma patients and normal subjects had vision better than 6/9 with correction. They had no media opacities other than early nuclear sclerosis and no fundus pathology. Further, normal subjects were free of systemic diseases known to affect the retina or optic nerve, The sensitivity and specificity of HVF and FDP were calculated.
Results: There were 44 eligible eyes among the 34 subjects. The glaucomatous disc findings included notch (n=8), pallor (n=21), thinning (n=23) and haemorrhage (n=1) of the neuroretinal rim. The sensitivity and the specificity of the HVF were 52.3% and 57.3% respectively. The sensitivity and the specificity of FDP were 65.9% and 61.5% respectively.
Conclusion: The difference between FDP and HVF in the diagnosis of early glaucoma is not marked.
Keywords: Humphrey visual fields, full threshold perimetry, frequency doubling perimetry, early glaucoma.
|How to cite this article:|
Chandrasekhar G, Kunjam V, Rao VS, Nutheti R. Humphrey visual field and frequency doubling perimetry in the diagnosis of early glaucoma. Indian J Ophthalmol 2003;51:35-8
|How to cite this URL:|
Chandrasekhar G, Kunjam V, Rao VS, Nutheti R. Humphrey visual field and frequency doubling perimetry in the diagnosis of early glaucoma. Indian J Ophthalmol [serial online] 2003 [cited 2013 May 19];51:35-8. Available from: http://www.ijo.in/text.asp?2003/51/1/35/14740
Frequency Doubling Perimetry (FDP) is a relatively new psychophysical test that has good potential in screening for early glaucomatous visual damage. The technique consists in presentation of low spatial frequency sinusoidal grating (<1cyc/deg) undergoing high temporal frequency counterphase flicker at or above
15 Hz. This is perceived as the grating having double the spatial frequency. Kelly initially described this phenomenon as "frequency-doubling illusion'., The frequency doubling illusion is carried by the Magnocellular pathway, specifically the My subset of ganglion cells.,
Quigley et al have shown that 20 - 35% of the retinal ganglion cells could be damaged before a visual field defect develops on the standard white-on-white perimetry (WWP). There is both histological and psychophysical evidence that the ganglion cells of the magnocellular pathway are affected in early glaucoma.,,, Two separate studies have shown the ability of FDP to detect visual field defects before the standard white-on-white field loss.,
The aim of the present study was to compare FDP and WWP in the diagnosis of early glaucoma.
| Materials and Methods|| |
Forty four eyes of 34 patients of primary early glaucoma with suspected optic disc damage, and 96 eyes of 96 normal subjects were evaluated. All subjects underwent a complete ophthalmic examination including slitlamp biomicroscopy, applanation tonometry, and dilated fundus and stereoscopic disc examination. Indentation gonioscopy was performed for all glaucomatous eyes. Some normal eyes with marginally shallow anterior chambers were included only if angles were open on gonioscopy. Patients with angle closure glaucoma were included after peripheral iridotomy. Automated visual field testing (Humphrey perimetry, Carl Zeiss, USA) and Frequency doubling perimetry (FDP, Carl Zeiss, USA), full threshold N-30 program were done on the same day or within an interval of 7 days.
The inclusion criteria common to both groups were absence of systemic diseases known to affect the retina or optic nerve, vision better than 6/9 with correction and no media opacities other than early nuclear sclerosis. An additional inclusion criterion for the glaucoma group was absence of any fundus pathology other than glaucomatous disc changes. Glaucomatous optic neuropathy was defined as a combination of cup-disc asymmetry of more than 0.2, notching, excavation, thinning or pallor of superior or inferior neuroretinal rims or retinal nerve fibre layer defects of the wedge or diffuse type and neuroretinal rim haemorrhages. Achromatic automated perimetry was performed with the Humphrey Field Analyzer (model 750) using the standard full threshold 24-2 program. Achromatic visual fields with mean deviation worse than -6.0 dB were excluded. Reliability criteria included less than 20% fixation losses and less than 25% false-positive and false-negative responses for both achromatic and FDP perimetry. All eyes with unreliable visual fields were excluded.
A glaucomatous field loss on white-on-white perimetry was defined as a cluster of 3 or more points depressed at the 5% level on the pattern deviation plot with one of the points depressed at the 1% level in either hemisphere.
The clinically significant visual field defect on FDP was defined as presence of 2 adjacent points at p<5%, and one of these p<1% deviation in the pattern deviation plot in either hemisphere. The visual fields were evaluated by a single observer and classified into superior or inferior defects depending on their location.
One of the authors (GC) documented the disc findings without any information on the visual fields. Special attention was given to observing and recording the thinning, notching, pallor and haemorrhages of the neuroretinal rim. Any evidence of nerve fibre layer defects were specifically looked for and documented. The disc evaluation was the gold standard for the diagnosis. Both eyes of the patient were included in the glaucoma group if they satisfied the inclusion and exclusion criteria. In the normal patients, one eye was randomly selected, if both the eyes satisfied the inclusion criteria. The visual field and the FDP data were correlated with the disc findings. The sensitivity and specificity of HVF and FDP were calculated conventionally.
| Results|| |
Forty-four eyes of 34 patients were eligible for the study. Twenty four eyes were excluded for one of three reasons: (1) advanced glaucomatous damage (mean deviation <-6dB); (2) the best corrected visual acuity was <6/9; (3) the fields were unreliable.
In 34 glaucoma patients (44 eyes), the diagnosis of primary open angle glaucoma was made in 35 eyes (high pressure glaucoma, 18 and normal pressure glaucoma, 17), juvenile glaucoma in 3 eyes and primary angle closure glaucoma in 6 eyes. Among the normal group all eyes had normal fundus and optic discs. The disc findings in the glaucoma group consisted of notch (n=8), pallor (n=21), thinning (n=23) and haemorrhage (n=1) at the neuroretinal rim. The demographic and visual field characteristics are shown in [Table - 1]. The two groups were similar in respect of gender, mean refractive error and eye laterality. The mean age was significantly less in the control group. The intraocular pressure (IOP) and the visual field indices were, as expected different in the two groups.
[Table - 2][Table - 3] are the two-by-two tables for the HVF and FDP visual field defects in early glaucoma and normal subjects. The sensitivity and the specificity of the HVF were 52.3% and 57.3% respectively. The sensitivity and the specificity of FDP were 65.9% and 61.5% respectively.
| Discussion|| |
FDP was developed as a screening aid for glaucoma. The test can be completed in a couple of minutes in the screening strategy and is considered very useful for this purpose. It has the additional advantages of being unaffected by refractive correction, and having less variability across tests as compared with WWP. As the frequency doubling illusion is carried by the magnocellular pathway, , which is affected early in the disease process,,, there has been an interest in exploring the potential for this technology in the diagnosis of early glaucoma.
In this study we compared the efficacy of FDP and WWP in the diagnosis of early glaucoma. There were no significant differences in the two groups in terms of gender, eye and refractive error. Age was higher in glaucoma group; this can bias the results but usually there is a practical difficulty in enrolling normal subjects in the higher age group.
Two earlier studies have explored the potential of FDP in the diagnosis of early glaucoma. Sample et al evaluated FDP and other psychophysical tests in 136 eyes with glaucomatous optic neuropathy, the diagnosis based on the assessment of stereophotographs. In their study FDP identified a larger number of eyes (70%) as abnormal among the eyes with glaucomatous optic neuropathy compared to the other three tests; WWP (46%), Short Wave Length Automated Perimetry (SWAP) (61%), motion-automated perimetry (52%). Kondo et al compared FDP and WWP in 11 eyes of patients with normal tension glaucoma (NTG) with a hemifield defect on WWP. Scanning laser ophthalmoscopy identified nerve fibre layer defects in 7 of the intact hemifields, 6 of these 7 eyes showed defects on the FDP. Our findings corroborate these results. We were able to demonstrate a marginally better diagnostic capability of FDP than HVF in early glaucoma. The sensitivity of FDP with the full threshold N-30 program was 65.9% compared to 52.3% of HVF. The relative advantage of FDP in early diagnosis may be diluted by the large stimulus size. With a stimulus pattern similar to the 24-2 of the Humphrey Visual Field Analyzer, FDP has greater sensitivity, but takes a longer time.
The sensitivity of FDP in the present study was 65.9%. Earlier studies on FDP have reported sensitivity ranging from 70 to 100% and specificity ranging from 75 to 100 %. ,, This difference is due to the fact that in these studies the gold standard for the presence of disease was WWP, as opposed to the disc morphology in our study. As noted earlier, significant numbers of ganglion cells are lost before a visual field defect develops on WWP. Once there is a field defect on WWP, FDP performs as well as the WWP.
The current study aimed to evaluate the ability of FDP to diagnose visual field defect before its appears on the WWP. The disc examination by an experienced glaucoma specialist was accepted as the gold standard. With this gold standard, the sensitivity of FDP was slightly better than WWP (65.9% Vs 52.3%). If FDP indeed detects glaucoma earlier than the HVF analyser, then its sensitivity must be very high with poor specificity. Since this is not the case, the diagnostic superiority of FDP as compared with the HVF analyser is not very marked in this group of patients with early glaucoma.
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[Table - 1], [Table - 2], [Table - 3]
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