Reading disorders due to visual field defects: a neuro-ophthalmological view

Abstract

Background: Reading disorders can be caused by visual field defects. Analysis of the reading process provides important information about perceptual preconditions and cortical adaptive strategies, which are also of significance for rehabilitation. Methods: Reading performance was examined using a scanning laser ophthalmoscope (SLO), which allows the simultaneous assessment of the preferred retinal locus (PRL) in relation to the stimuli and the eye movements. Visual fields were measured using Tuebingen perimetry and a self-developed SLO perimetry, attentional fields using the Test of Sustained Attention. Results: Patients with absolute central scotomas are only able to read if they learn to use an eccentric PRL. With a ring scotoma, reading ability depends on the size of the intact central island and the fixation behavior. With hemianopia, it is crucial whether there is macular splitting or sparing. Without sparing, reading performance depends on adaptive strategies such as predictive saccades or eccentric fixation.The latter causes a shift of the field border towards the hemianopic side in conventional perimetry. Locations of high attentional capability during central fixation (early stage of maculopathy) correspond to the later eccentric PRL during follow-up. Conclusions: Reading performance depends on the size of the perceptual area and the resolution of the PRL used for reading. Compensating strategies are crucial for regaining reading ability. Eccentric fixation causes a shift of the sensory and oculomotor reference, indicating high cortical plasticity. There is evidence that the location of a future PRL is influenced by sustained attention -a mechanism that could be utilized for specific training. Reading disorders are strongly connected with neuro-ophthalmological issues.

Reading strategies in Stargardt's disease with foveal sparing

“…Such a condition is of particular interest with regard to its functional implications. As previously reported [ 3 - 5 ], subjects with a ring scotoma fixate small stimuli with the central locus, but wider stimuli with the eccentric locus. The alternation between central and eccentric fixations was found in 8 out of 40 eyes of patients with Stargart's disease [ 6 ], and it was suggested that this fixation pattern was a phase in the transition from foveal to eccentric fixation [ 7 ].…”

Reading strategies in Stargardt's disease with foveal sparing

“…Such a condition is of particular interest with regard to its functional implications. As previously reported [ 3 - 5 ], subjects with a ring scotoma fixate small stimuli with the central locus, but wider stimuli with the eccentric locus. The alternation between central and eccentric fixations was found in 8 out of 40 eyes of patients with Stargart's disease [ 6 ], and it was suggested that this fixation pattern was a phase in the transition from foveal to eccentric fixation [ 7 ].…”

Binocular Inhibition of Reading in Macular Telangiectasia Type 2

“…For fluent reading, a perceptual span of approximately 58 in the reading direction is required in order to guide the next saccade to the following text location and organize the switch between fixation and saccades during the reading process. 21 When reading from left to right, the visual field to the right appears to be of higher importance for reading performance than the visual field to the left side. 22 Scotomas of the left eye are projected on the right side of the fixated letter/word and hence in reading direction, thus interrupting the perceptual span required for reading (Figs.…”

Accounting for visual field abnormalities when using eye-tracking to diagnose reading problems in neurological degeneration

“…On the other hand, some authors have indicated that reading performance in patients with hemianopia depends on adaptive strategies such as predictive saccadic movements or eccentric fixation. The latter causes a displacement of the edge of the field towards the hemianopic side in conventional perimetry ( 42 ).…”

“…This results in an altered visual field shift to the hemianopic side in conventional perimetry and in enlarging the functional visual field ( 42 ).…”

“…Eccentric fixation and frequent saccadic movements to the hemianopic side cause a visual field edge shift on conventional perimetry, which can be misinterpreted as macular sparing or even visual field improvement ( 42 ).…”

Reading strategies in Stargardt's disease with foveal sparing

“…Such a condition is of particular interest with regard to its functional implications. As previously reported [ 3 - 5 ], subjects with a ring scotoma fixate small stimuli with the central locus, but wider stimuli with the eccentric locus. The alternation between central and eccentric fixations was found in 8 out of 40 eyes of patients with Stargart's disease [ 6 ], and it was suggested that this fixation pattern was a phase in the transition from foveal to eccentric fixation [ 7 ].…”

Binocular Inhibition of Reading in Macular Telangiectasia Type 2

“…For fluent reading, a perceptual span of approximately 58 in the reading direction is required in order to guide the next saccade to the following text location and organize the switch between fixation and saccades during the reading process. 21 When reading from left to right, the visual field to the right appears to be of higher importance for reading performance than the visual field to the left side. 22 Scotomas of the left eye are projected on the right side of the fixated letter/word and hence in reading direction, thus interrupting the perceptual span required for reading (Figs.…”

Accounting for visual field abnormalities when using eye-tracking to diagnose reading problems in neurological degeneration

“…On the other hand, some authors have indicated that reading performance in patients with hemianopia depends on adaptive strategies such as predictive saccadic movements or eccentric fixation. The latter causes a displacement of the edge of the field towards the hemianopic side in conventional perimetry ( 42 ).…”

“…This results in an altered visual field shift to the hemianopic side in conventional perimetry and in enlarging the functional visual field ( 42 ).…”

“…Eccentric fixation and frequent saccadic movements to the hemianopic side cause a visual field edge shift on conventional perimetry, which can be misinterpreted as macular sparing or even visual field improvement ( 42 ).…”

Reading strategies in Stargardt's disease with foveal sparing

“…Such a condition is of particular interest with regard to its functional implications. As previously reported [ 3 - 5 ], subjects with a ring scotoma fixate small stimuli with the central locus, but wider stimuli with the eccentric locus. The alternation between central and eccentric fixations was found in 8 out of 40 eyes of patients with Stargart's disease [ 6 ], and it was suggested that this fixation pattern was a phase in the transition from foveal to eccentric fixation [ 7 ].…”

Binocular Inhibition of Reading in Macular Telangiectasia Type 2

“…For fluent reading, a perceptual span of approximately 58 in the reading direction is required in order to guide the next saccade to the following text location and organize the switch between fixation and saccades during the reading process. 21 When reading from left to right, the visual field to the right appears to be of higher importance for reading performance than the visual field to the left side. 22 Scotomas of the left eye are projected on the right side of the fixated letter/word and hence in reading direction, thus interrupting the perceptual span required for reading (Figs.…”

Accounting for visual field abnormalities when using eye-tracking to diagnose reading problems in neurological degeneration

“…On the other hand, some authors have indicated that reading performance in patients with hemianopia depends on adaptive strategies such as predictive saccadic movements or eccentric fixation. The latter causes a displacement of the edge of the field towards the hemianopic side in conventional perimetry ( 42 ).…”

“…This results in an altered visual field shift to the hemianopic side in conventional perimetry and in enlarging the functional visual field ( 42 ).…”

“…Eccentric fixation and frequent saccadic movements to the hemianopic side cause a visual field edge shift on conventional perimetry, which can be misinterpreted as macular sparing or even visual field improvement ( 42 ).…”