Do Subjective and Objective Indices of Disease Severity Correlate with Perceived Disability in New Glaucoma Referrals?

Research Article

Austin J Clin Ophthalmol. 2015;2(3): 1052.

Do Subjective and Objective Indices of Disease Severity Correlate with Perceived Disability in New Glaucoma Referrals?

Bach A¹, Ogunbowale L², Kotecha A² and Spratt A¹*

1Department of Ophthalmology, Nova Southeastern University, Larkin Community Hospital, Beraja Medical Institute Coral Gables, USA

2NIHR Biomedical Research Centre for Ophthalmology, Moorfields Eye Hospital NHS Foundation Trust and UCL Institute of Ophthalmology, UK

*Corresponding author: Alexander Spratt, Department of Ophthalmology, Nova Southeastern University, Larkin Community Hospital, Beraja Medical Institute Coral Gables, 2550 S Douglas Rd, Coral Gables, Florida, 33134, USA

Received: March 19, 2015; Accepted: June 30, 2015; Published: July 07, 2015


Purpose/Aim: To assess the relationship between newly referred glaucoma patients’ perceived visual disability, visual field parameters of disease severity and an objective index of disease severity derived from scanning laser polarimetry.

Materials/Methods: This is a prospective case series with newly diagnosed and treatment naïve new glaucoma-clinic patients. Self-reported visual disability was assessed using the vision-specific National Eye Institute Visual Function Questionnaire (NEIVFQ-25) and the glaucoma-specific Viswanathan (Vis-Q) questionnaire.. Standard automated perimetry provided psychophysical indices of disease severity, including Mean Deviation (MD) scores and binocular Integrated Visual Field (IVF) scores using Progressor software. Objective, structural measures of the optic nerve and peripapillary retinal nerve fiber layer were made using the scanning laser polarimeter from which the nerve fiber index value was used as an index of disease severity, both monocularly and by binocular summation.

Correlations between questionnaire responses, visual field indices and objective structural indices were assessed using Spearman’s rank correlation coefficient.

Results: Seventy five patients were eligible the study. Monocular and binocular visual field indices showed weak correlations with self-reported questionnaire scores (Spearman’s rho: NEIVFQ-25 ‘worse’ eye MD r=0.23, p=0.05, IVF score r=-0.16, p=0.19; Vis-Q ‘better’ eye MD r=0.30, p=0.009, IVF r=-0.24, p=0.04). Neither monocular nor binocular objective structural indices of glaucoma damage correlated with self-reported questionnaire scores.

Conclusions: Visual field indices show weak correlations with patients’ perceived visual disability. Objective, structural measures of glaucoma severity at the optic nerve do not correlate with patients’ perceived visual disability. Designing wholly objective modes of self-assessment that yield information about patients’ experiences remains an important, but necessary challenge for early diagnosis and treatment of glaucoma.

Keywords: Glaucoma; Patient-reported outcomes; Visual fields; Nerve fiber index


Glaucoma is a progressive optic neuropathy that results in characteristic morphological changes in the Optic Nerve Head (ONH) and Retinal Nerve Fiber Layer (RNFL) as well as corresponding defects within the Visual Field (VF) [1]. Glaucoma is the leading cause of irreversible blindness worldwide [2], and is becoming more prevalent as life expectancy increases [3]. The condition is considered to be asymptomatic in its early stages due to the mid-peripheral location of defects in the VF in addition to preservation of the central VF and Visual Acuity (VA) until its more advanced stages.

Typically, clinical measures of ONH structure and function, such as visual fields, and RNFL thickness, as well as Intraocular Pressure (IOP) are used to diagnose the condition and monitor its progression. These measures provide the clinician with information regarding patient prognosis and management requirements, but they are clinician-based measures of disease severity, and as such probably provide little indication of the true level of patients’ ‘functional ability’ and hence their vision-related quality of life (QoL).

Previous studies have examined the relationship between automated VF parameters of glaucoma patients with their responses to questionnaires that self-assess perceived visual disability. Some authors report a modest association between perceived visual disability and the severity of binocular VF loss [4-6], others report only weak correlations [7,8]. These differences may be explained by the use of assorted questionnaires to quantify perceived visual disability and by inadequacies of the widely employed Esterman binocular VF test strategy when used to assess patients with mild and moderate degrees of glaucomatous VF loss. Other confounding factors may be related to glaucoma-independent causes of poor automated VF performance such as poor understanding of what the test requires, poor concentration and reduced manual dexterity. Combined with the phenomenon of short-term intra-test variability of automated VF performance in glaucoma patients these factors add to the relative subjectivity of this psychophysical test [9].

Structural evaluation of the ONH and RNFL has been the subject of technological advances in recent years. Compared with VF testing, ONH and RNFL technologies offer great potential for precise, quantitative and more objective assessments of disease stage and progression. The scanning laser polarimeter (SLP) is one such device with high sensitivity in the detection of glaucomatous RNFL defects [10,11] and it has support for its use in the screening of glaucoma suspects [12]. The commercially available SLP, the GDx (GDx ECC; Carl Zeiss Meditec Inc., Dublin, California, USA) provides an overall nerve fiber index (NFI) score. This score is indicative of the percentage likelihood that an optic nerve is glaucomatous based on how far its analysis deviates from the normative database. A recent study showed a positive correlation between RNFL thickness and the National Eye Institute Visual Function Questionnaire (NEIVFQ-25) [13]. Perceived visual disability is an extremely important aspect of glaucoma as it may be able to give the clinician a better insight into early progression of the disease.

Accordingly, the purpose of this study is to examine how patients’ own perceived level of visual disability is associated with VF parameters indicative of glaucoma severity and an objective measure of glaucoma severity derived using RNFL imaging technology for newly diagnosed patients. The goal is to be able to have an easy to perform, at home test to help patients realize that they may be having symptoms of glaucoma and to see an eye care professional. We tested the hypothesis that the NEIVFQ-25 would be able to accurately associate perceived visual function with clinical measurements.


We chose to study a cohort of newly referred patients in order to remove the potential impact of diagnosis itself on questionnaire responses obtained. Patients attending the Glaucoma Service at Moorfields Eye Hospital, London, between November 2006 and January 2007 were invited to participate. Patients attending the clinic were a mixture of external tertiary referrals, referrals from other departments within the hospital and optometrist or general-practitioner initiated referrals. Only patients with no prior ophthalmologist diagnosis of glaucoma were eligible for this study.

To be included in the study all patients were required to be native English speakers and have a best corrected Snellen VA of 6/12 or better in each eye. Patients with ocular co-morbdities other than glaucoma were excluded, although the presence of mild cataract was not an exclusion criterion. The inclusion level for Snellen VA was chosen to help prevent the inclusion of patients with significant cataract. Local research ethics committee approval was obtained prior to commencement of the study and informed consent, according to the tenets of the Declaration of Helsinki, was obtained prior to examination from each subject.

Measurement of perceived visual disability

Many different patient-reported outcome questionnaires exist to assess the impact of disease on patients’ perceived general wellbeing and ability to perform multiple tasks of daily living. Visionspecific questionnaires evaluate the impact of eye disease in terms of symptoms, social and physical functioning and the general and mental health perceptions of patients. Surveys were completed by patients, without supervision, prior to seeing an ophthalmologist.

Global ophthalmic function

The 25 question National Eye Institute Visual Function Questionnaire (NEIVFQ-25) is a validated, generic questionnaire designed to measure the impact of ophthalmic disease on patients’ functional ability [14,15]. The NEIVFQ-25 scores range from 0–100; lower scores indicate poorer ability [5,8,16-18].

Glaucoma status

Glaucoma-specific questionnaires take a disease specific approach with the aim of better understanding and quantifying the functional ability of glaucoma patients. The Viswanathan questionnaire (Vis-Q) [4], modified from that of Drance [19], asks 10 questions about such things as finding dropped objects, difficulty with stairs and dark adaptation with a forced binary ‘yes’ or ‘no’ response. Previous research has demonstrated its correlations with VF parameters [20] but it has not been validated formally. For this study, Vis-Q scores were inverted to be comparable with those of the NEIVFQ-25, such that lower scores indicate a greater difficulty with tasks and a poorer perceived functional ability.

Clinical measures of disease severity: visual field assessment

All patients underwent Humphrey Fields Analyser (HFA; Zeiss Humphrey Systems, Dublin, California, USA) testing using the SITA standard threshold 24-2 test strategy. Mean Deviation (MD) scores were recorded for each eye as an index of monocular disease severity. To be included in the data analysis, patients had to display reliable visual field tests, defined as < 33% fixation losses and false positive tests. A binocular visual field score was generated using the Integrated Visual Field (IVF) function of Progressor software (Moorfields Eye Hospital, London, UK / Medisoft Ltd., Leeds, UK) which integrates raw, point-by-point sensitivity data from each monocular HFA to produce a simulated binocular visual field in which patients’ best sensitivity at each corresponding location of the central 24° of visual field is displayed and scored (Figure 1) [21].