**Abstract**

Age-related macular degeneration (AMD) is a common, chronic, and progressive eye disease that is considered the leading cause of visual loss among the elderly in developed countries. Advanced AMD, including choroidal neovascularization (CNV) or geographic atrophy (GA), is associated with substantial and progressive visual impairment that can lead to a significant reduction in functional independence and quality of life (QoL) for affected individuals, whose number is expected to increase in the coming years in line with population growth and ageing. In this context, while an important part of medical care is focused on preventing the progression of the disease, Visual Rehabilitation (VR) aims to address its consequences by providing these patients with a number of strategies to achieve their goals and participate autonomously, actively and productively in society. This chapter aims to provide an update on evidence-based practices in the field and how modern technologies play an important role in the development of new VR approaches.

**Keywords:** age-related macular degeneration, visual rehabilitation, management, technology, practice, trends

## **1. Introduction**

Age-related macular degeneration (AMD) is a prevalent, progressive eye disease that is characterized by a late-onset neuro-degeneration of the photoreceptors (light-sensitive retinal cells) and their supporting tissues [1].

It is considered a highly disabling disease, as the macula (part of the eye responsible for sharp, clear vision) is the most damaged area of the retina, causing a gradual loss of central vision with subsequent difficulties in many activities of daily living (ADLs) for those affected, such as reading, driving, mobility or face recognition.

Globally, AMD is responsible for approximately 7% of blindness and 3% of visual impairment, making it the third most common cause of vision loss worldwide, and the first in industrialized countries [2, 3].

In economic terms, the total cost due to AMD is estimated to be approximately \$343 billion, including \$255 billion in direct healthcare costs (due to scheduled medical visits, treatment, rehabilitation, vision-related equipment, etc.) and \$88 billion in indirect costs (due to injury, depression, loss of productivity, and social dependence as a consequence of blindness caused by the disease) [4]. Furthermore, the progressive growth and ageing of the population suggests that the magnitude of this issue will increase in the coming years, with the global prevalence of AMD expected to rise from 199 million people in 2020 to 288 million in 2040 [5].

From a clinical perspective, AMD can be classified into early and late stages. Patients with early AMD are usually asymptomatic and present yellowish drusen and pigmentary alterations in the macular area on fundus examination (**Figure 1**), while late stages of the disease, responsible for most visual loss attributed to AMD, are defined by the presence of signs indicating choroidal neovascularization (CNV) or geographic atrophy (GA) [6].

#### **Figure 1.**

*Large drusen appearing as yellowish subretinal spots present in a patient with early AMD from the Blue Mountains Eye Study [7] (A) and progression of both drusen size and area involved over 5 years (B) [6].*

In CNV (wet) AMD, abnormal blood vessels grow and break through to the neural retina (**Figure 2**). These new blood vessels are fragile and tend to leak blood, fluid and lipids, which can accumulate under the macular area, elevating it and distorting vision and eventually leading to the formation of fibrous scarring.

**Figure 2.**

*Recent-onset neovascular AMD on colour photography (left), spectral-domain optical coherence tomography (middle), and optical coherence tomography angiography showing appearance of choroidal new vessels (right) [8].*

On the other hand, in atrophic (late dry) AMD, a gradually deterioration of the retinal pigmentary epithelium (RPE), choriocapillaris, and photoreceptors occurs (**Figure 3**). As both AMD forms progresses, detail in front of central visual field is lost and over time a blind spot (scotoma) may appear in the central visual field of the patient [8].

*Evidence-Based Practice and Trends in Visual Rehabilitation for Patients with Age-Related… DOI: http://dx.doi.org/10.5772/intechopen.96817*

**Figure 3.**

*Large soft drusen surrounding an area of GA on colour fundus photography (left), fundus autofluorescence imaging (middle), and fluorescein angiography (right) [8].*

Although the initial cause of AMD remains unclear, several risk factors have been linked to the development of the disease, such as age (>60 years), lifestyle (smoking, diet), cardiovascular disease and genetic markers [9].

This suggest that the pathogenesis of AMD is the result of a complex multifactorial interaction between environmental, functional, genetic and metabolic factors involving multiple biological pathways, including inflammation, angiogenesis, remodeling of the extracellular matrix, lipid metabolism and transport regulation, etc. [10–12].

In recent years, several epidemiological studies have reported a decrease in blindness and visual impairment associated with AMD [13, 14], which is likely to be attributed to improved diagnostic procedures, earlier diagnosis, slowing disease progression through micronutrient supplementation [15, 16], and the introduction of new therapies based on suppression of vascular endothelial growth factor (VEGF) [17].

Unfortunately, despite all this progress in AMD management, there is currently no effective treatment to cure the disease or reverse its course. However, in most patients, peripheral vision is preserved, allowing them to retain a certain level of autonomy.

On this basis, visual rehabilitation (VR) aims to provide these people with a range of strategies and behaviors to achieve the full potential of their remaining vision, improving their self-confident and independence and enabling them to return to a visually active life as much as possible. This philosophy aims at increasing awareness in low-vision patients, so they do not just focus on their loss or their impairment.

### **2. Visual rehabilitation as part of AMD care**

People who do not have AMD (e.g., family members, caregivers, and even some healthcare providers) often underestimate the effect of this condition, particularly in terms of visual function and quality of life (QoL) [18].

According to the World Health Organization' (WHO), disability must include both the impairment of bodily structures or functions and the difficulty or limitation in performing a task and in participating in life situations [19].

This approach implies that the rehabilitation process cannot only focus on the aspects that directly affect the person, but must also deal with the society in which they live and the context that makes it possible for them to develop, in order to have a successful life.

Paying attention to this, comprehensive AMD care should give attention not only to the structural and functional condition of the eye, but also to the patient's functioning in his or her specific surrounding. In this sense, the main difference between VR and other ophthalmic sub-specialties is that most of these sub-specialties are anatomically defined, while VR is functionally defined (**Figure 4**) [20].


**Figure 4.**

*Comprehensive AMD care diagram showing the areas of influence and differences between medical and rehabilitative care. Adapted from: [20].*

To adequately cover all these aspects, the participation and collaboration of different professionals is necessary, since different goals often require different interventions [21]. This can be observed in the US and Europe models, where a wide range of professionals, varying from continent to continent, work together to achieve a successful rehabilitation.

Multidisciplinary low-vision teams usually require an ophthalmology, an optometrist, an occupational therapist and a rehabilitation teacher among other professionals specially trained in the evaluation of the patient's remaining vision and the prescription of different low-vision aids (LVAs) [22]. However, prescription of these aids is only the first step in learning how to use them effectively, as training and continuous practice are essential to help the patient feel comfortable and get the most out of them [23]. To this end, different techniques can be employed, often using both office- and home-based exercises with the device while performing a specific activity for a few hours in different sessions [24–26].

Besides prescription of LVAs and training on their correct use, VR also contemplates assessment of the home environment, as well as psychological and social worker support. Despite this, it should not be ignored that, according to the Veterans Affairs Low Vision Intervention Trial II (LOVIT II), basic low vision services are sufficient for most people with low vision, although basic services combined with VR programs are most effective for people with a visual acuity of 20/200 or less [27].

### **3. Visual rehabilitation for AMD patients**

VR in AMD patients has largely focused on reading [28] and for this purpose many LVAs have been used. But, today, individuals with AMD demand wider

#### *Evidence-Based Practice and Trends in Visual Rehabilitation for Patients with Age-Related… DOI: http://dx.doi.org/10.5772/intechopen.96817*

objectives that include, apart for reading, being able to participate in other activities and carry out their daily life and travels independently. If we add to this the fact that modern technologies have greatly expanded access to information for people with low-vision, we get that VR encompass a variety of resources to ultimately fit the person's goals, needs and demands.

Reading is a sophisticated activity of great importance for the life of the individual in its personal, educational or professional aspects. Conditions compromising the condition of the macula, such as AMD, can greatly affect this ability, which adequate performance largely depends on the reception of central visual information. Depending on the degree to which the scotoma is affected, the reading speed in these patients can be between 25 and 130 words per minute (wpm), while the average reading speed of a person without visual impairment is usually around 200-250 wpm [29].

In everyday life, everyone needs to be able to read texts whose size covers a range from newspaper print to headlines. People with normal vision perform this task with a speed that favors comprehension and comfort. However, AMD patients find that reading speed is compromised as the font size becomes smaller. In general, this population needs magnification of the text to achieve a reading speed that allows them to read effectively, although this will always be lower than that of people without AMD.

In individuals with central field loss (CFL), eccentric fixation is necessary, and the oculomotor pattern differs when reading. Eye movements in people with severe visual impairment tend towards continuous refixation, i.e., fixation stability is weak, and not always stable and functional [30]. Consequently, letter recognition is slower and more difficult [31]. Sometimes, it is difficult to recognize a word with a single fixation, being necessary several saccades within the same word [32]. Visual field loss close to fixation can also affect everyday activities, such as face recognition or shopping [33].

With this in mind, most functional adaptations in these cases are based on training in the use of a preferred retinal locus (PRL) to make eye movements remain in a functional area of the peripheral retina. This PRL is empowered to assume the macular function and thus restore the lost vision-related skills, so assessing its location and characteristics is an essential part of any reading rehabilitation program [34]. In this context, microperimeters offer the most accurate method for PRL assessment (**Figure 5**).

#### **Figure 5.**

*Microperimetry using a standard grid (52 points) in a study of ranibizumab effects on functional vision in patients with advanced AMD [35] showing the non-visual area of the retina (red points), the normal sensitive retina (green points) and the patient's fixation target (cross) [36].*

The subject's ability to make visual movements so that the target is held in the PRL correlates with reading speed, as do more intense saccadic movements and stability of fixation [37]. In addition to holding the target on the retina, the eye must move rapidly towards objects further away in the field of vision (saccadic movements). The angle at which the movement to fix the image in the PRL must be made will affect the fixation, the stability of which is crucial for reading and proper perception.

After eccentric viewing training, the location of the retinal area used for fixation may change, but not the fixation stability [38]. Moreover, the person does not always use the same PRL, and may use several depending on the target position. Some authors report that these PRLs may appear untrained in patients in the first six months of disease [38]. Many patients with AMD adopt an PRL on the left area of the scotoma, although more information is obtained from the right area during reading. For this reason, Rubin [39] suggests that it is preferable to use the right area of the scotoma to the left.

The benefits of eccentric viewing training on the reading performance of patients with AMD have been supported by several studies. For example, Nilsson et al. [40] trained 20 patients with neovascular AMD, an absolute central scotoma, and a mean best-corrected visual acuity (BCVA) of 20/475 in the use of a new and more favorable PRL for reading, observing that, after a mean training time of 5.2 hours, 90% of the participants learned to use eccentric viewing, which correlated with a significant improvement in reading speed from 9.0 ± 5.8 words per minute (wpm) to 68.3 ± 19.4 wpm.

A larger sample study evaluating the influence of eccentric viewing training in 242 individuals with a central scotoma concluded that, after an average training time of 3.8 hours, reading speed increased from 48.0 wpm to 71.9 wpm, the size of Arial font that could be read fluently could be reduced from 14.3 to 11.5, the duration of comfortable reading improved from 1.7 to 15.8 min, and the mean percentage of material that was understood by patients could be increased from 73.7 to 92.7% [41].

In addition, when compared with other interventions in the literature, such as a microperimetric biofeedback and microscope teaching program, eccentric viewing training has been found to offer greater benefit in terms of improved reading speed among patients with AMD [42].

It can be said that reading is significantly slower in patients who have not been trained in the use of the retinal locus, but, according to the findings of Watson et al., this does not mean that PRL training should not be further investigated [43].

But different oculomotor pattern is not the only factor that explains the lower reading speed in patients with macular degeneration. Cheong et al. concluded that in patients with AMD the visual processing of letter recognition is also lower, thus negatively influencing reading speed, reading comprehension and enjoyment while reading, as well as resistance in avoiding visual fatigue [44].

Another factor that can determine the efficiency of reading in patients with AMD is the number of characters that can be recognized in each fixation or visual span. This, in addition to the slower visual processing observed in these patients, forces more frequent eye movements. According to Chung [45], training can lengthen the visual lag in normal peripheral vision, although this benefit is less pronounced in older people.

For some researchers, contrast sensitivity is shown to be a critical factor in explaining the future reading efficiency of the patient with AMD over other factors such as scotoma size or BCVA [46]. In general, it can be said that individuals with AMD require contrast enhancement to achieve their optimal reading speed level [47, 48].

*Evidence-Based Practice and Trends in Visual Rehabilitation for Patients with Age-Related… DOI: http://dx.doi.org/10.5772/intechopen.96817*

Lighting is another key component involved in the reading rehabilitation process for people with AMD, as the negative effect of uncontrolled illumination hinders vision. In this context, it is known that people with AMD often require high levels of illumination [49]. According to Bower et al., [50] at least 2000 lux are necessary to improve reading performance in patients with AMD, although Seiple et al. [51] indicate that this benefit can only be considered for small font sizes.

Finally, it should be pointed out that various studies have tried to establish the degree of importance the way the text is presented has on reading performance in AMD patients.

Chung is one of the researchers who has dedicated her work to this, although she states that there is not enough evidence that typography or text formatting (e.g., page formatting, Rapid Serial Visual Presentation: RSVP, scrolling text) improves reading speed, except in some cases of RSVP [52, 53]. In clinical practice, these are factors that may affect visual comfort and the subjective perception of improved reading or reduced visual fatigue differently from person to person.
