0–20 % 4–63 %

0–7 %

Fig. 19.6 Direction of scotoma shift: (a). Summarized results of several studies: mostly the scotoma is shifted upwards or to the right, i.e. fixation is below or left of the scotoma [12–15] (b). On the retina the eccentric retinal fixation loci are accordingly located mostly above or left of the lesion, i.e. in the left upper quadrant in both eyes [12]

Table 19.2 Clinical assessment of fixation

•Gaze direction: corneal reflexes

•Perimetry: localization of the blind spot

•Fundus image: fixation of a fixation target in direct ophthalmoscopy

•By means of the corneal reflexes the gaze direction can be assessed at a glance. When the patient is asked to fixate the eyes of the investigator, the patients views to the hairline for example (Fig. 19.5 bottom right).

•By perimetry: The position of the blind spot indicates the fixation behaviour. Eccentric fixation can be diagnosed by a thorough perimetry. In a manual perimetry, the shift of the blind spot can be shown clearly Fig. 19.4a. In an automated perimetry, the blind spot can be ‘lacking’ (due to the shift). A shift can only be proven with a dense test-point grid. In case of alternating PRLs, the blind spot sometimes can be shown in 2 different locations.

•At the fundus the fixation locus can be determined using the fixation star in the direct ophthalmoscope.

19.3.4 Motor Aspects

Fig. 19.7 SLO-fundus image of a patient with AMD: she reads the text with an eccentric retinal locus above the lesion. She is fixating the ‘i’. The patient sees the text upright. The movement of the fovea along the text can be recorded in the SLO-video

stage of the disease, when the central seeing island has disappeared and eccentric fixation becomes possible. ‘Eccentric viewing training’ can be helpful in such cases [19].

Some patients are able to change their fixation locus depending on the task: They fixate small stimuli, such as single optotypes, centrally, but broad stimuli, such as words, eccentrically. They are able to read with the corresponding magnification. Thus, these patients show a discrepancy between visual acuity and magnification need [12].

19.3.3 Examination of Fixation Behaviour

Fixation behaviour can often be diagnosed with easy methods (Table 19.2):

Fixation stability plays an important role for eccentric reading. Unstable fixation is unfavourable [20].

Eye movements during reading show impaired reading patterns in patients with AMD as a consequence of their sensory deficit. In patients with early macular degeneration, the reading pattern is preserved in principle, reading speed is reduced, the number of forward saccades is increased. In patients with advanced macular degeneration, the reading pattern is no longer regular. Reading speed is markedly decreased, the number of forward and backward saccades markedly increased [6, 21].

19.4Methods to Examine Reading Ability

1.Refractive error, accommodation range, visual acuity for far and near: These are necessary as a basis for later adaption of visual aids.

2.Magnification need: A simple and valuable method to examine the potential reading ability in a patient with foveal vision loss is the determination of

magnification need. Special reading charts for lowvision patients (e.g. MN-Read charts) provide texts in different magnifications compared to normal newspaper print. In a defined distance, the magnification need can be determined directly. This test does not only tell, if magnification is helpful at all, but also what amount is necessary. This is the basis for the selection and application of a magnifying visual aid.

3.Reading speed: Reading speed should be measured with standardized paragraphs of text to be read aloud. Paragraphs instead of single sentences are preferable for a more accurate measurement of speed. Reading aloud provides additional information about fluency, mistakes and understanding. Newly developed texts in 17 languages are available: ten equivalent texts in each language for repeated measurements, all of them were elaborated for equal length, difficulty and linguistic complexity (International Reading Speed Texts, IReST, http://www.amd-read.net) [22, 23]. This evidence-based method allows a standardized documentation of the success during treatment and rehabilitation interventions.

4.Parafoveal contrast sensitivity (Fig. 19.8): It can be easily and quickly tested by the Macular Mapping Test [24] with different contrast levels. It is suitable for monitoring the course of the AMD, for assessing treatment effects and can be helpful for early detection [25].

5.Central visual field: Visual field defects in the centre, i.e. involving the reading visual field, cause reading impairment. Additionally, the position of the blind spot provides information about fixation behaviour.

6.Fixation behaviour: Knowledge about fixation behaviour (central or eccentric) is important in cases of

discrepancies between good visual acuity and reading disability as in ring scotoma.

7.Eye movement recording: Recording of eye movements during reading provides additional information about the reading strategy, especially for scientific investigations [6, 21].

19.5Rehabilitation Approaches to Improve Reading Ability

The aim of rehabilitation is optimization of residual function and support of compensatory processes (Table 19.3). For improving reading ability a wide pallet of magnifying visual aids is available (see Chap. 20 and Table 19.4). In an own study of 835 AMD patients an improvement of reading speed occurred in 94% of the patients. The mean improvement was 45 words per minute (Fig. 19.9) [26, 27].

Another crucial measure is training to handle the visual aids.

Additionally, reading speed can be further improved by specific reading training with computer training programs, as we showed in a randomized and controlled study in patients with central scotoma due to juvenile maculopathy Stargardt [28]. The patients could improve their reading speed by additional 20 words per minute and they were also able to apply their newly learned strategy in everyday life during page reading.

Regarding ‘eccentric viewing training’ positive results have been reported [19], but there is still considerable controversy about methods and criteria for choosing the optimal area [29].

Table 19.3 Rehabilitation: aims

•Optimization of the residual function

•Reading and orientation ability

•Independence, mental agility, quality of life

Table 19.4 Rehabilitation measures for reading disorders

Visual aids (see Chap. 20)

•Magnifying, contrast enhancing

•Illumination

Training

•Handling of the visual aids (crucial!)

•Specific reading training; sensory and motor (recommendable)

•Use of the best fixation locus: ‘eccentric viewing training’ (controversial)

Social counselling

Reading speed before adaptation of visual aids (words/minute)

Fig. 19.9 Reading speed before adaptation of magnifying aids in words per minute (abscissa) compared to the reading speed after adaptation of visual aids (ordinate) in 835 AMD patients. An improvement occurred in 94% of the patients with an average increase of 45 words per minute (Modified after [26, 27])

Table 19.5 Conclusions: preconditions for reading ability in AMD

Sensory

•Sufficient size of the reading visual field and sufficient resolution of the retinal area used for reading. In eccentric fixation, the insufficient resolution can be compensated by magnification of the text.

Motor

•Stable fixation and regular reading eye movements

General

•Motivation

•Cognitive ability

•Manual skills

Summary for the Clinician

›Loss of reading ability is the most serious functional impact in AMD.

›The preconditions for reading ability in patients with AMD are concerned with three areas (Table 19.5):

›Sensory: A sufficient size of the reading visual field and a sufficient resolution of the retinal area used are necessary. In eccentric fixation, the insufficient resolution can be compensated by text magnification.

›Motor: Stable fixation and regular reading eye movements are favourable.

›General: The motivation of the patient and his cognitive abilities are of importance. Additionally, manual skills play a role for handling the visual aids and computer software programs.

›For examination of reading ability standardized tests are available. The determination of visual acuity is not sufficient as this measures only recognizing one optotype at a time. The knowledge of the central visual field and the fixation locus are especially important in patients with a ring scotoma, who show a discrepancy between good visual acuity and high magnification need. Determination of magnification requirement is crucial for further rehabilitation measures. Assessment of reading speed with standardized texts allows a quantitative and evidence-based procedure for diagnostics, monitoring the course and for documentation of success after treatment and rehabilitative interventions.

›RehabilitationisverysuccessfulinAMDandallows an improvement of reading ability in most patients.

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