A Road Less Travelled: Technical Advances in Eccentric Viewing

Low vision care is primarily provided to people with age related macular degeneration (AMD) and associated central vision loss. This is because reduced macular function has a greater impact on quality of life than other forms of vision loss. Vision impairment caused by central vision loss can significantly hinder independence for activities of daily living and impede social inclusion.^1-4 

I have been witness to the profound difference this training has on mental health, self confidence and the restoration of independence in many of my patients

The premise of low vision practice is to optimise residual vision in order to improve quality of life. Low vision rehabilitation for people with macular dysfunction is commonly addressed by introducing magnification using optical and/or electronic devices. The use of optical character recognition is also gaining popularity. Education in lighting and enhancing contrast function complements adaptive technology. While these intervention options hold merit, the use of eccentric viewing is commonly overlooked and underutilised.

Literature has documented that eccentric viewing training (EVT) has a greater potential than magnification to maximise visual performance in those with bilateral macular loss or reduced foveal function.^5,6 Therefore, eye care professionals should strongly consider their approach to low vision intervention for those with central vision loss. In the wise words of Robert Frost, “two roads diverge in a wood, and I took the one less travelled by, and that has made all the difference”.

ECCENTRIC VIEWING

Eccentric viewing is a technique that enables a person with central field loss to look slightly off centre or past the object of interest, so the image seen falls on the unaffected peripheral retina. This compensatory viewing strategy may result in one or multiple eccentric points.7 Additionally, inconsistent and unstable eccentric fixation is noted when people intuitively find their preferred retinal loci (PRL).^8,9 Consequently, poor fixation stability at the PRL adversely affects visual function and functional ability.^10,11 Therefore, guided training from an eye professional, such as an orthoptist, will help the individual establish the biological processes that occur when eccentrically viewing.

A number of studies have reported that participants who have undergone EVT using a structured program, improved their near acuity and reported significant improvements in stabilisation of fixation, reading ability (including fluency and speed) and contrast sensitivity.^12-14 Research participants who did not undergo EVT showed no change in their visual function.4

RINCIPLES OF ECCENTRIC VIEWING

The foundation of EVT is to identify the most viable paramacula area as an alternative retinal focal point. A re-fixation movement is then made so the image seen is projected onto this functional retinal area. When a professional chooses an eccentric point using clinical means, this location is known as the trained retinal locus (TRL). Identification of the TRL requires an assessment of macular integrity, which incorporates three major components: scotoma characteristics, preferred retinal locus, and oculomotor control.

Traditionally, either kinetic or static perimetry is used to establish the size, shape, and location of the central scotoma. The TRL is then identified once the scotoma characteristics have been established. However, results from a standard visual field test can be unreliable because central fixation is relatively unstable. Additionally, naturally occurring microsaccades, tremors and drifts used to help maintain fixation – can compound fixation instability and impact the reliability of the visual field result.^15,16 

Furthermore, the isolated use of a traditional visual field test fails to comprehensively assess macular integrity. A considerable amount of information pertaining to the location of the PRL and oculomotor control is foregone.

Knowledge relating to the PRL is important to help either reinforce a PRL or create a paramacula TRL. The location of the eccentric locus underpins the reeducation of the visual system to a new visual fixation condition. In this way, it endorses cortical plasticity.¹⁴ 

Information about oculomotor control provides insight into fixation stability. Visual fixation is the ability for the eye to stay still at a single retinal location so the image can be seen. When there is damage to the macular region, fixation stability degrades and this compounds the vision loss. People with poor fixation stability describe the image as “jumping” or moving around.

The introduction of microperimetry technology enables the simultaneous assessment of macular integrity across all three major characteristics.

Microperimetry, also known as fundus related perimetry, has slowly been infiltrating clinical practices around the world since the late 20th century. However, the clinical use of microperimetry is still relatively novel to Australia.

Microperimetric technology incorporates analysis of retinal morphology alongside retinal function. During a standard automatic perimetry assessment, the microperimeter concurrently incorporates fundus imaging, macular sensitivity topography, and fixation analysis.^13,14 The most prominent asset of this technology is the ability to record and monitor fixation stability by plotting fixation points and graphing the amplitude of eye movements.

The various modalities of the microperimeter can be used for the purposes of EVT. Initially, this instrument can be used to establish all characteristics of macular integrity. Once the TRL has been identified, microperimetry biofeedback can be employed for low vision rehabilitation purposes.

MICROPERIMETRIC BIOFEEDBACK ECCENTRIC VIEWING TRAINING (MB-EVT)

Vision Matters, which I established, is the first Australian low vision practice to employ microperimetric biofeedback technology for the purposes of eccentric viewing training.

There have been a number of EVT techniques that have been created and their efficacy has been validated multiple times over. Systematic reviews evaluating the effectiveness of EVT found no conclusive evidence to reveal which particular method of EVT was superior.¹⁷ However, it is difficult to draw this conclusion as no studies have directly compared each technique against the other.

In order to investigate the effectiveness of MB-EVT against other methods, I conducted a comparative data analysis. I evaluated the data from my patients who underwent MB-EVT against data published by Vukicevic and Fitzmaurice (2002), who used the home kit and EccVue18 techniques (Figure 1). Data from each EVT cohort represented participants with age related macular degeneration. Each patient group had the equivalent number of participants; their near acuity was measured using an identical clinical test; and they participated in the same number of training sessions.

Figure 1 shows that participants who underwent training using the home kit and EccVue had a 51% and 40% (respectively) improvement in their near acuity. Those who underwent MB-EVT showed a significant improvement of 70% in their near acuity.

The introduction of microperimetry technology enables the simultaneous assessment of macular integrity across all three major characteristics

Further analysis of patients who completed the MB-EVT at Vision Matters revealed that overall, patients had a greater improvement in fixation stability than in near acuity. This is in keeping with studies that show improved fixation stability strongly correlates with improved visual acuity.^15,16

Figure 2 outlines the fixation success rates of the first nine patients who underwent MB-EVT at Vision Matters. A closer analysis of the graph shows that patients with poorer fixation stability pre-training had greater improvements in their fixation success post training. For example, patient two improved from 32% fixation success pre-training to 96% post training. Similarly, patient five began the EVT with 12% fixation stability and on completion achieved 94% fixation success post training.

THE CASE OF MRS AB

Literature pertaining to the success of EVT on quality of life is inconclusive.^3,4,17 This is in part because of the paucity of research investigating this area and also because of the lack of consistent standard of practice. Nevertheless, anecdotally the majority of my patients who have completed the program have reported significant improvements in their quality of life.

One such patient is Mrs AB who was 85 years old when she presented with extensive bilateral macular scarring due to geographic age related macular degeneration. Previous ocular history entailed bilateral post vitrectomy and pseudophakia.

Mrs AB sought low vision services because she had continuous difficulty reading small print despite having an electronic magnifier. She had also given up playing Bridge, which was her primary social activity.

Mrs AB’s pre and post training fixation stability measures are outlined in Figures 3 and 4. At the start of the training Mrs AB was legally blind (2/60) with poor fixation stability (Figure 3). At the completion of the training, Mrs AB’s distance acuity improved to 6/60. There was also a significant improvement in her near acuity from N80 to N8. The improvements in acuity correlate to her substantial improvement in fixation stability (Figure 4).

Post training, Mrs AB returned to reading the newspaper without the aid of low vision equipment. She also reported increased confidence and efficiency when playing Bridge and noted that she was more readily able to recognise faces. Mrs AB’s son also reported his mother to be more confident and generally happier since completing the training.

BROADER APPLICATIONS

EVT is commonly targeted to those with AMD. However, this training can be applied to other pathologies affecting the macula such as diabetic maculopathy, Stargardt’s disease, foveomacular vitelliform dystrophy, myopic macular degeneration, and chorioretinal atrophy.

On multiple occasions, I have been witness to the profound difference this training has on mental health, self confidence, and the restoration of independence in many of my patients.

Eye health care professionals should consider EVT as an important low vision intervention option for those with central vision loss. This training may currently be the road less travelled, however it will “make all the difference” to patients’ lives.

Natalia Kelly B.Orth&OphthSc, PGDiplHltResMthds has been a registered and accredited low vision orthoptist since 2003. She has provided clinical supervision, clinical risk evaluation, mentoring and professional development to numerous orthoptists practicing in various Australian states and territories.

Ms Kelly established Vision Matters to integrate ophthalmic technology with low vision intervention. Aside from private practice, she is part of the orthoptic teaching team at LaTrobe University, Department of Clinical Vision Sciences. Ms Kelly has a special interest in neurological visual impairment, paediatric low vision and eccentric viewing. She is based in Melbourne and is committed to providing excellence and offering innovative practices that are at the forefront of low vision care.

For further visit www. visionmatters.com.au. 

References: 

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