Invest Ophthalmol Vis Sci. 2016 Nov 1;57(14):6158-6166. doi: 10.1167/iovs.16-19458.

Activity Limitation in Glaucoma: Objective Assessment by the Cambridge Glaucoma Visual Function Test

Simon E Skalicky MBBS, BSc (Med), MMed, MPhil1,2,4,5

Colm McAlinden MB BCh, BSc (Hons), MSc, PhD6,7,8

Tasneem Khatib MBBS2

Louise May Anthony MBBS2

Sing Yue Sim MA MB BChir2

Keith R Martin DM2,3

Ivan Goldberg AM, MBBS, FRANZCO, FRACS1,9,10

Peter McCluskey PhD1,10

 

1Discipline of Ophthalmology, University of Sydney, Sydney, Australia

2Addenbrookes Hospital, Ophthalmology Department, Cambridge, UK

3Cambridge NIHR Biomedical Research Centre, University of Cambridge, UK

4Departments of Ophthalmology and Surgery, Royal Melbourne Hospital, University of Melbourne, Australia

5Centre for Eye Research Australia, Royal Victorian Eye and Ear Hospital, University of Melbourne, Australia

6Abertawe Bro Morgannwg University Health Board, Swansea, UK

7School of Ophthalmology and Optometry, Wenzhou Medical University, Wenzhou, Zhejiang, China

8Flinders University, Bedford Park, Adelaide, South Australia, Australia

9Eye Associates, Sydney Australia

10Glaucoma Unit, Sydney Eye Hospital, Sydney Australia.

Correspondence: seskalicky@gmail.com

 

ABSTRACT

The Cambridge Glaucoma Visual Function Test (CGVFT) is a newly designed computerized objective test that may simulate daily visual function related to glaucoma. Administered to 70 glaucoma patients and 14 controls it was evaluated for fit to the Rasch model; following removal of misfitting items it had good fit with acceptable targeting and precision. The CGVFT was successfully assessed using criterion and convergent validity tests. Computer based simulations lie the CGVFT may have a greater role in future assessment and clinical management of glaucoma patients.

PMID: 27835712

 

SUPPLEMENT

Patients with glaucoma of worsening severity have increasing difficulty performing visually demanding tasks requiring light/dark adaptation, contrast discrimination and peripheral-vision dependent activities.1 As glaucomatous optic neuropathy progresses it can impact walking, driving, venturing from home, seeing at night, adjusting to different levels of illumination, reading, judging distances and seeing peripheral objects.2, 3 Visual tests currently used in routine clinical practice (eg visual field testing, visual acuity, contrast sensitivity) may not reflect real-world conditions. For example, multiple visual distractions, changing illumination and head and eye movements are artificially controlled in routine clinical testing.4 Such limitations could potentially be overcome by objective simulation of real-world functional visual ability. A performance-based assessment of functional ability related to vision, the Assessment of Visual Disability Related to Vision (ADREV) has previously been engineered and validated; this is physical and can be challenging to implement in the clinic.5, 6 We hypothesised that objective visual functional testing could be improved using simpler, more reproducible computer-simulated activities – as such patients can still be tested in real-life simulations while seated safely, under timed conditions.

Patients aged over 40 years with open angle glaucoma and no other visual morbidity were enrolled. Visual field parameters, visual acuity, contrast sensitivity, sociodemographic information and Glaucoma Activity Limitation-9 (GAL-9) and Visual Function Questionnaire Utility Index (VFQUI) questionnaire responses were recorded.

The Cambridge Glaucoma Visual Function Test (CGVFT) was designed taking inspiration from daily challenges described by glaucoma patients as well as ADREV items.3 Thirteen tasks, each with three to four difficulty levels were included (Figure 1), simulating:

  1. Identifying objects in a busy street scene
  2. Identifying individuals in a group or crowd
  3. Identifying unique daily objects surrounded by similar objects
  4. Identifying creatures in camouflaged environments
  5. Identifying cutlery in a cluttered cutlery drawer
  6. Identifying objects within a cluttered room
  7. Identifying hazardous furniture in a dimly illuminated room
  8. Identifying an article in a sheet of newspaper
  9. Identifying an ‘x’ within a set of ‘+’s
  10. Identifying a match for a sock
  11. Identifying moving balls coming to the centre from the periphery in multiple directions
  12. Reading with progressively reduced contrast
  13. Performing a road hazard-perception driving-simulation test

 

Testing was undertaken with strict lighting and invigilation conditions. The computer image was projected onto a 1 x 3 m white screen at a distance of one metre reflecting a binocular horizontal visual field of 60o . Each image represented a specific task that the participant was asked to complete by the test administrator. Each image has a central fixation point of a rotating gold star, and participants were asked to begin each task by looking specifically at the fixation point but were subsequently permitted eye and/or head movements to complete the task. Most items within the test were timed. Results were recorded for untimed tasks in a pass/fail manner.

The initial CGVFT had 139 pilot items of which 59 fit well to the Rasch model. Following removal of misfitting items it had acceptable precision (person separation index 2.13) and targeting. CGVFT (logit) scores increased between controls (-0.20 ±0.08) and mild (-0.15 ±0.08), moderate (-0.13 ±0.10) and severe glaucoma patients (-0.05 ±0.10) (p<0.001, ANOVA) demonstrating good criterion validity. Correlation coefficients of 0.455 (p<0.001) between CGVFT and Glaucoma Activity Limitation-9 (GAL-9) person measures and 0.399 (p=0.005) between CGVFT and (Visual Function Questionnaire Utility Index) VFQUI person measures indicated convergent validity (Figure 2). Lower better eye mean deviation and greater age were associated with worsening CGVFT person measures (p≤0.001) on multivariable analysis.

The CGVFT has potential limitations. The test requires specific hardware (eg a computer, projector) as well as specific lighting and patient adaptation criteria. One cannot be certain if the CGVFT really reflects real-life tasks experienced by the patient; such tasks are impossible to precisely recreate and measure scientifically, and like all clinical tests the CGVFT is at best a potential sample of visual difficulties that might be experienced by glaucoma patients.

Patients were invigilated to begin each task by gazing on the rotating central golden star, but then allowed to break fixation to complete the task. This is not the same as true fixation control typically used for computerized visual field testing. Future studies may be required to determine if the use of initial gaze centration enhances or detracts from the validity of this test, or if the length of time prior to making the first eye movement (generally a saccade) and its speed and accuracy may have influenced participants’ ability on the CGVFT.4 Potential avenues for improvement include the use of gaze-tracking technology, conversion into a tablet- smartphone-based app, or virtual reality software that can be used to measure patients’ ability to navigate a simulated three-dimensional environment from a remote observer computer screen.

The Cambridge Glaucoma Visual Function Test is a computer-based test administered to a cohort of glaucoma patients and controls. This tool may benefit glaucoma patients, carers, health care providers and policy makers, providing increased awareness of activity limitation due to glaucoma.

 

 

Figure 1. Each image was projected onto a large screen requiring 600 of horizontal visual field. Tasks include: A. find a raspberry among the cherries; B. find a fork among the spoons, and a spoon among the forks; and to correctly match the sock in C. with one in D.

 

Figure 2. Scatterplots: A. Cambridge Glaucoma Visual Function Test (CGVFT) versus Glaucoma Activity Limitation-9 person measures; B. CGVFT versus Visual Function Questionnaire Utility Index person measures; C. CGVFT person measures versus better eye mean deviation (decibels).

 

 

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4. Smith ND, Glen FC and Crabb DP. Eye movements during visual search in patients with glaucoma. BMC ophthalmology. 2012; 12: 45.
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