1.0 Introduction
Currently there is a need for research to develop new and more advanced visual field analysis techniques. This is due to the ever-increasing knowledge surrounding visual function in glaucoma and therefore more demand for techniques that are capable of detecting visual field loss at the earliest possible stage in the disease process. The research conducted in this paper aims to identify if a novel type of visual field test can be used by community optometrists as a replacement or alternative for the conventional static Humphrey testing. This involves comparing patients without visual field loss and those with current glaucomatous field losses on both types of equipment.
1.1. Primary Open Angle Glaucoma
Glaucoma is a complex group of diseases in which damage to the optic nerve occurs due to a build-up of pressure within the eye. A fluid known as the aqueous humour, normally flows in and out of the eye and is unable to drain via the trabecular meshwork properly, so creates a this increased intraocular pressure (NHS, 2016) as shown below in Figure 1.1. The result of this generally creates an increased pressure within the eye and as a result, puts pressure on the optic nerve head. If left untreated, it can lead to severe peripheral vision loss due to the loss of nerve fibre ganglion cells at the back of the eye, although the central field is typically not impaired (BERDAHL, J, 2017). The condition can be split into several different categories: primary open angle, primary angular closure, secondary, normal tension and congenital glaucoma (NHS, 2016).
The type that we will focus on in this study (the most common) is Primary Open Angle Glaucoma (POAG) (NHS, 2016). This is a slow progressive form of the disease that affects around 1-2% of Caucasians in the UK who are over 40 years old, increasing to 4-5% in the over-80s (TCO, 2017). It is also predicted that these numbers will rise due to an aging population (TUCK MW. Et al., 1994). Due to the asymptomatic nature of the condition at the early stages, POAG is the second leading cause of blindness in the UK (TCO,2017). As it tends to have a gradual onset, symptoms may appear when there is a substantial amount of peripheral visual field loss. At this point axons are damaged within the retinal fibre layer and therefore irreversible vision loss has occurred. This is why it is crucial that these changes are captured early, as current perimetry methods only identify this once damage has occurred.
Figure 1.1. Glaucoma diagrams: Comparision between a normal eye and glaucomatous eye. From Top Left clockwise: Normal eye, Trabecular Meshwork Being blocked so fluid cannot drain, Pressure in the eye building up as fluid not draining, Optic Nerve being damaged due to pressure.
1.2. Visual Field
Visual Field analysing or Perimetry, is the measurement of peripheral vision. This is an essential part of an eye test as it detects dysfunction in these areas, leading to diagnosis of not just glaucoma, but strokes, brain tumors and other neurological conditions.
Although current VF tests can at pick up faults in the patient's visual field – it is thought that by the time there is a significant defect, while using existing methods, then as much as 60% of the ganglion cells are already dead. It is thought that by developing a test that is more sensitive to VF loss, earlier detection of glaucoma could be enhanced significantly with improved treatment outcome. There are 3 main types of assessing perimetry: the most common being static, however there are kinetic and novel style field assessments too. In this project we will be focusing on comparing a novel style perimeter to a widely used static to see if it can pick up on glaucomatous field losses earlier or provide us with equivalent results.
1.3. Humphrey Visual Field
Static automated perimetry has been the most common method of assessing peripheral vision in patients with conditions relating to the eye and brain since the mid-1970s (ASAOKA, R. et al. 2012). In particular, Humphrey visual fields has become the gold standard method of visual field (VF) testing for glaucoma diagnosis and management. This involves keeping the patients monocular gaze on a fixed orange spot, while a white target of varying intensity is exposed for a short interval in varying locations – on a white background of fixed luminance. The threshold determined is related to a series of established age-related norms, and various software analysers are also incorporated, such as the Glaucoma Hemifield Test (GHT), and a Swedish Interactive Thresholding Algorithm (SITA). These aim to enhance the clinical utility of the system by increasing the processing speed, and to make detection and tracking of visual field changes more reliable. As the patient’s blind spot is mapped out, this also provides us with how reliable the test is with the number of false positives, false negatives, fixation losses recorded automatically by the machine. In patients with primary open angle glaucoma, specific field defects can be shown through the pattern deviation – due to the RNFL thinning. This usually presents aa a distinct nasal scotoma (otherwise known as a “nasal stepâ€) or an arcuate defect on the field plot. In Fig 1.2, this example shows inferotemporal retina damage correlating to an arcuate defect on a field plot.
Figure 1.2. Glaucoma: Retinal damage cause by glaucoma and the corresponding field defect
1.3.1 SITA
SITA is intelligent software inside the Humphrey which can estimate and predict the threshold of the stimulus brightness. It is varied around the best estimate until a threshold is found at the start of the examination. Guesses are based on the probable “Hill of Vision†deemed from foveal thresholds determined by age. This reduces the time taken for the test to be completed, so therefore less likely for the patient to become tired throughout, whilst still maintaining accurate results.
1.3.2 GHT
The Glaucoma Hemifield Test (GHT) however, analyses threshold test results and compares again to a large database to determine if a patient’s field plot is glaucomatous or within normal limits. From a clinician’s point of view this is an easy way to spot instantly (without having to interpret the pattern deviation) if a patient is outside ‘normal’ i.e. non-glaucomatous limits.
1.4. Ring of Sight
The Ring of Sight (ROS) equipment is new portable technology that has recently been brought to the optical market by Ibis Vision (IBIS VISION, 2017). This is a new novel style of perimetry that we hope to find can assist in diagnosing a condition such as POAG quicker than current methods (MYINT, J. et al., 2011). It may also meet the optical market demand for a new affordable option. The company’s main aims themselves are that it will solve a whole host of problems with current perimetry, such encourage patient concentration, and could be more reliable way for perimetry for domiciliary practices.
 
1.5. Aims/Objectives
The access to automated perimeter tests in practices in the UK have increased to over 95% since 1994, with the majority either using a Henson or Humphrey Visual Field Analyser (HVFA), which both involve a static target (MYINT, J. et al., 2011). As these are the current gold standard in testing, one would assume all optometrists use them but this is not the case. Only 36% of POAG-risk patients fields were assessed by optometrists, which suggests there are issues with the current perimetry equipment that could be improved upon (MYINT, J. et al., 2011). One known issue is that patient fatigue through the test can lead to variable VF measurements and noise. As the current test involves a static target, it can be difficult to focus on the same spot for a long period of time. Additionally, there are reports that eye movements during the test are closely correlated to unreliable VF results and under-estimation of VF sensitivity. We hope some of the problems faced by older patients in particular can be resolved, as this is the most likely reason two thirds of clinicians are not taking advantage of static perimetry techniques (MYINT, J. et al., 2011). In addition, it could potentially be an easier solution to children’s perimetry checks, or those with a lack of concentration such as those with a learning disability, as it is more child-friendly and stimulating. Furthermore, the ROS does not involve a chin rest which could mean that people who have mobility issues with the set up on a VFA could find this more comfortable. This project therefore focuses on comparing sensitivities via a standard static (HVFA) and a novel visual field test (Ring of Sight) on a normal cohort and patients with POAG.
 
2.0 Methodology
2.1. Introduction
This study is sought to determine if the novel style ROS can pick up on glaucomatous defects quicker or the same as Humphrey VF. In this section the inclusion criteria, equipment used, methodology and ethics shall all be discussed.
2.2. Participant Criteria: Normals
The 15 normal participants recruited were predominantly students from Glasgow Caledonian University, alongside friends and family of the researchers. These were asked to take part via word of mouth and all were aware they could leave the study at any point. This group mentioned was be used as a control for the study and carried out the two Visual Field (VF) tests. The inclusion criteria for this normal control group was to have no known eye conditions. We also excluded those with visual acuity of worse than 6/12, refractive error of more than ±6 diopters, and astigmatism of more than ±2 diopters.
2.2.1 Participant Criteria: Glaucomatous
For the glaucomatous group, 4 patients with diagnosed glaucoma were recruited, regardless of the type of visual field defect on conventional perimetry. The inclusion criteria were diagnosed open angle glaucoma. The exclusion criteria was any other ocular pathology except mild cataract or uncomplicated phako. We again also excluded those with visual acuity of worse than 6/12, refractive error of more than ±6 diopters, and astigmatism of more than ±2 diopters.
2.3. Ethics
In order to make sure that participants were not ethically harmed, they were briefed prior to being involved in the project. This involved explaining what tests would be carried out, and in particular how this information would be stored. They were also told if they feel uncomfortable and no longer wish to participate, the tests could be stopped. No identifiable information was taken, as those who participated were simply referred to by initials and the year of birth. This study was approved by the Health and Life Sciences Ethics Committee, and all subjects were advised should they feel the need, can withdraw at any time. See Appendix B, C and D for further details.
2.4 Methods
A one hour visit per subject was made where a brief history, some basic vision tests as well as two visual field tests were carried out. Details of the tests are as follows, in which measurements were recorded for each:
2.4.1 History
A couple of questions are asked in order to ensure the volunteer is eligible to take part. This included if they had glaucoma, what type, which eye(s), and if they have any other known eye conditions. These were asked to avoid any interference with the resukts of the test, making it fair as possible. When asked about the known eye conditions, diabetes and cataract were directly asked about as these can affect peripheral vision and contrast sensitivity hence causing unaccounted for factors in the tests.
2.4.2 VA
Participants wear their habitual distance prescription and asked to look at a log MAR chart from 6m away. Their visual acuity can then be measured by their ability to read letters on said chart in a well-lit room. This is then recorded in log MAR format. This is to ensure the patient has a good enough acuity
2.4.3 HFVA
The peripheral vision of each volunteer was measured using a static HVFA which was used as a comparison to the ROS field equipment. The exact equipment used was a Humphrey Field Analyser [HFA] II 740, software version Rev.C 3.1; Carl Zeiss Meditec, Inc. The Sita-Fast 24-2 programme was chosen, and this provides a fixation target in which they must not lose focus. Participants then pressed a buzzer when a white flash was spotted in the periphery. This test was carried out in a darkened room to avoid light interference. The participants habitual distance correction combined with a +3.00 add to account for the 30cm bowl, is placed in the machines lens holder to help with focus (HEIJL, A. et al., 2012).
2.4.4 Ring of Sight
The peripheral vision of each volunteer was again measured, this time with the ROS Equipment. The test is carried out under standard perimetric conditions (background, 10 candela [cd]/m2) with the full-threshold (24-2 equivalent) strategy, as this is currently the only setting available. The subject looks at a visual display unit (VDU) at 50 cm away with their habitual distance glasses on, or varifocals, while they hold a touch pen and tablet. On the VDU, a spinning wheel will appear (which is the first target), then when another wheel appears in the periphery the subject will drag the touch pen to match the target location. This then becomes the new target to look at, and the test repeats in this fashion. Meanwhile a camera monitors the subject, so the researcher can notify the system when a fixation loss is spotted, which then supports the reliability of the test. To end, the ring is moved over the ‘Continue’ icon on screen to display the results (IBIS, 2017).
The other 4 volunteers with primary open angle glaucoma,
These will be used to categorise volunteer’s depending on the results, along with their date of birth for correlation analysis later in the study. The HVFA and the new ROS tests will then be carried out. All of the aforementioned checks are carried out monocularly so two datasets are obtained for each volunteer, as it is possible to have different stages of glaucoma in each eye. The tests are all recorded and input to an excel document with only initials and date of birth being used as identifying factors.
 
3.0 Results and Analysis
From the tests carried out on young normals, a normative database was able to be constructed which allowed to calculate the mean deviation for our glaucoma patients.
Throughout this chapter the results from the study will be displayed and analysed..
3.1 Normal participants comparision
In this study, the mean deviation (MD) were compared for these normal participants with the ROS and the HVFA. This was to assess for evidence of significant difference in average MD at the end of study for patients assigned to the normal group. In order to carry out this experiment, a group of normal participants (n = 15) were recruited, of which some (n=11) were able to be used in the statistics of the experiment. (Why some were unable to be used is mentioned in section ?????) A brief verbal questionnaire was recorded as mentioned in Section ??? to ensure they met the visual requirements for the tests. The MD with the HVFA was .3582 (s.d. = .14056) whereas the mean deviation with the ROS was -.1174 (s.d. = .10197). The descriptive statistics are summarised in table 1 on the following page.