Does patient education result in more reliable initial visual fields? |
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Does patient education result in more reliable initial visual fields? |
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DOES PATIENT EDUCATION RESULT IN MORE RELIABLE INITIAL VISUAL FIELDS?
BAL MANOJ, DINESH RATHOD, YEE F. CHOONG, NAPOLEON DEVERAJAN, SUSAN PICKERING, JUDITH ELPHICK, IRIS RICHARDS and
MICHAEL W. AUSTIN
Department of Ophthalmology, Singleton Hospital, Swansea, UK
Introduction
Many departments have introduced technician-led ‘fast-track’ type assessment clinics to differentiate between ‘glaucoma’ and ‘non-glaucoma’. Traditionally, an evaluation of the visual field has formed part of this initial assessment. Various factors may contribute to an equivocal first perimetric result in a significant number of patients, who might otherwise be diagnosed on other clinical features. This not only confounds attempted early discharge, but may also delay definitive treatment. As patient anxiety is usually higher at first consultation than for subsequent visits, it has been suggested that delaying perimetry until later in the evaluation process might improve reliability. The aim of this study was to investigate whether an increased yield of reliable visual fields could be obtained by changing the timing of initial perimetry with postponement until after firstly assessment, education and counseling by a specialist nurse, and secondly a consultation with and further explanation from an ophthalmologist.
Patients and methods
In a prospective study, 196 patients referred with a possible diagnosis of glaucoma were divided into two groups. Group 1 (n = 103) had visual fields at first assessment visit. Group 2 (n = 93) had an assessment visit followed by a physician consultation plus counseling and education, followed by a third visit for visual fields alone. All patients underwent perimetry using Humphrey Visual Field Analyzer Mark I (24-2 Fastpac). The fields were assigned as ‘normal’, ‘abnormal’, ‘equivocal-probably normal’ and ‘equivocal-probably abnormal’, based on the reliability indices, presence of any artifact and the pattern of any defect (three contiguous locations with a defect of
Address for correspondence: Mr. Michael W. Austin, Consultant Ophthalmologist, Department of Ophthalmology, Singleton Hospital, Sketty Lane, Swansea SA2 8QA, UK. Email: maustin@globalnet. co.uk
Perimetry Update 2002/2003, pp. 47–50
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
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greater than or equal to 5 dB, reaching Statpac probability at the 5% level in the pattern deviation plot for non-edge points). For each patient, the reliability indices of the ‘study eye’, i.e., the eye that determined into which category the patient fell, were used for statistical analysis. Fields were defined as equivocal if any of the following occurred; fixation losses greater than 20%, false positives greater than 33%, false negatives greater than 33%1 or if a ‘defect’ were thought to be artifactual (e.g., from the trial lens rim, lid-brow effects or inattention).
Results
Demographic details for the groups are shown in Table 1. There were no significant differences between the groups for age or gender.
Table 1. Demographics
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Group 1 (perimetry at |
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Group 2 (perimetry after |
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technician and doctor consultation) |
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Sex |
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male |
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(44.7%) |
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p = 0.49 |
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female |
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(55.3%) |
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(60.2%) |
(chi square) |
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Age (years) |
64.2 |
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65.4 |
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p = 0.55 |
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mean |
(range 15–88) |
(range 28–87) |
(Mann-Whitney U test) |
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Fig. 1. Reliability indices for visual fields of groups 1 and 2. FL: fixation losses; F+ves: false positives; F-ves: false negatives.
Does patient education result in more reliable initial visual fields? |
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Fig. 2. Subgroup analysis of perimetric diagnoses of groups 1 and 2. N: normal; AB: abnormal; EqN: equivocal-probably normal; EqAb: equivocal-probably abnormal (p > 0.2 for all inter-group comparisons, chi-square test).
Reliability indices for the two groups are shown in Figure 1. A feature of note is the magnitude of the standard deviation for all measures, reflecting lack of homogeneity for reliability in both groups. Contrary to our expectation, group 2 (delayed perimetry) had significantly more fixation losses than group 1 (p = 0.05). There were no other significant differences between the groups for other catch trial errors. Subgroup analysis based on our perimetric results (Fig. 2) did not reveal any statistically significant differences between the group having fields at first visit (group 1) and those having education and counseling prior to perimetry (group 2). Equivocal fields were produced by 66% of patients in group 1 and 60% in group 2.
Discussion
Performance in many psychophysical tests of visual function tends to improve as the subject gains experience with the test.2 This phenomenon is termed the ‘learning effect’ and is well documented.3-9 An ideal screening test provides conclusive evidence of ‘normality’ in a single test. Difficulty occurs when patients produce equivocal results during their first visual field test. This may be due to catch trial errors (fixation losses, false positives or negatives) and various artifacts or defects of inexplicable configuration. Performance effects (motivation, fatigue, drugs, etc.) also contribute.
Conventionally, patients have undergone repeated testing until they produce reliable results or are deemed incapable of performing the test. This process may take up to three or more visits.9 Often a diagnosis has been ‘all but made’ prior to perimetric outcome being known. Hence, valuable resources in health systems are being deployed ineffectively.
We had hoped that, by increasing patient awareness and motivation (by alleviating
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anxiety through counseling at first screening visit and subsequent ophthalmologist consultation), patients would perform better. Unfortunately, our educational intervention did not result in a higher proportion of reliable first fields. A possible explanation for the higher number of fixation losses in group 2 might be that, given their increased knowledge of glaucoma and the possibility of visual field defect, they were in fact more anxious to detect the stimuli and ‘went looking for them’ to a greater degree than the patients in group 1.
We do not dispute the role of visual fields in the diagnosis and follow-up of patients with glaucoma and ocular hypertension. Rather, we question the value of serial equivocal perimetry for those with normal intraocular pressures and normal optic discs. Ideally it should be possible for such patients to be discharged early as ‘normal’, thereby improving access for other patients in a resource-limited NHS. Given the availability of improved methods of evaluating optic discs for the diagnosis of glaucoma,10,11 it may be argued that the time has come to remove ‘exhaustive’ perimetric testing from new patient assessment.
References
1.Humphrey Systems: Evaluating reliability. In: Humphrey Visual Field Analyzer User’s Guide, pp 6.4-6.6. Dublin, CA: Humphrey Systems 1998
2.Aulhorn E, Harms H: Visual perimetry. In: Jameson D, Hurvich LM (eds) Handbook of Sensory Physiology. VII/4: Visual Psychophysics, pp 102-145. Berlin: Springer-Verlag 1972
3.Wood JM, Wild JM, Hussey MK, Crews SJ: Serial examination of the normal visual field using Octopus automated perimetry. Evidence for a learning effect. Acta Ophthalmol Scand 65:326-333, 1987
4.Gramer E, De Natale R, Leydhecker W: Training effect and fluctuations in long-term follow-up of glaucomatous visual field defects calculated with program Delta of the octopus perimeter-201. New Trends Ophthalmol 1:219-228, 1986
5.Katz J, Sommer A, Witt K: Reliability of visual field results over repeated testing. Ophthalmology 98:70-75, 1991
6.Werner E, Adelson A, Krupin T: Effect of patient experience on the results of automated perimetry in clinically stable glaucoma patients. Ophthalmology 95(6):764-767, 1988
7.Heijl A, Lindgren G, Olsson J: The effect of perimetric experience in normal subjects. Arch Ophthalmol 107:81-86, 1989
8.Heijl A, Bengtsson B: The effect of perimetric experience in patients with glaucoma. Arch Ophthalmol 114:19-22, 1996
9.Johnson CA, Keltner JL et al: Baseline visual field characteristics in the Ocular Hypertension Treatment Study. Ophthalmology 109:432-437, 2002
10.Chouhan BC, McCormick TA, Nicolela MT, LeBlanc RP: Optic disc and visual field changes in a prospective longitudinal study of patients with glaucoma: comparison of scanning laser tomography with conventional perimetry and optic disc photography. Arch Ophthalmol 119(10):1492-1499, 2001
11.Wollstein, G, Garway-Heath DF, Hitchings RA: Identification of early glaucoma cases with the scanning laser ophthalmoscope. Ophthalmology 105:1557-1563, 1998