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  • Neuro-Ophthalmology/Orbit

    Spontaneous improvement can occur after homonymous hemianopia,1 although most patients do not enjoy complete resolution. This article describes three suggested strategies for ophthalmologists to try with such patients: the use of spectacle-mounted prisms that shift images from the blind hemifield, compensatory saccadic training to encourage frequent saccades into the hemianopic region and visual restoration therapy to create stimulation along the border of the blind hemifield.

    Homonymous hemianopia results from an injury to the contralateral retrochiasmal visual pathway. Hemifield loss severely reduces quality of life by interfering with reading speed, driving, scene appreciation, object location and navigation. Unfortunately, none of the therapies described above results in visual field restoration, but each can improve quality of life with variable success. Depending upon the cause and extent of the underlying disorder, hemianopic patients may also suffer from hemiplegia, hemi-neglect or aphasia, any of which may reduce the effectiveness of these approaches.

    Spectacle-mounted Prisms

    Researchers have investigated the use of various spectacle-mounted prisms by homonymous hemianopia patients. Prisms have ranged in size from 15 to 57 prism diopters (PD), with partial or complete coverage of one or both spectacle lenses using both temporary stick-on and permanent ground-in prisms.2,3

    Recent studies have examined the effects of monocular 40 PD prisms mounted 1 to2 mm above and below the visual axis on the eye ipsilateral to the hemianopia, with the prism base placed toward the hemianopic side. Prism use can expand the visual field by up to 20 degrees. Patients report functional mobility improvements.3 A multicenter, placebo-controlled, masked crossover trial comparing an oblique monocular 57 PD prism to sham prism therapy is currently being conducted. 

    The cons of spectacle-mounted prisms include difficulty locating objects, image jump, motion sickness and diplopia. The prisms neither improve reading speed nor allow patients to resume driving. Costs range from $25 to $50 for stick-on prisms to several hundred dollars for the ground-in variety.

    Compensatory saccadic training

    Patients with homonymous hemianopia normally move their eyes into the blind hemifield. Saccadic training purposes to train these movements to improve the accuracy of saccades, search strategies, reading speed and scene registration. Most saccadic training involves having the patient identify objects randomly presented throughout both the blind and seeing hemifield.4,5

    In one randomized, sham-controlled trial, patients experienced improvements in scene exploration, search times and quality of life. Reading speed and visual field size did not change in either patient group.4 Occupational therapists perform this type of training, and health insurance often covers the cost.  

    Patients with right-sided hemianopias often experience problems with reading secondary to difficulty generating efficient reading saccades (hemianopia alexia). Patients receiving optokinetic therapy read text that moves from right to left on a computer screen for 400 minutes during a four-week period. This forces patients to engage in saccadic movement to the right. Patients enjoyed increased reading speeds compared with baseline and following placebo random saccadic training.6 Free moving text programs can be accessed at the Read-Right Web site.

    Visual restoration therapy

    Visual restoration therapy (VRT) putatively works by restoring lost visual field along the hemianopic border, whereas spectacle-mounted prisms and compensatory saccadic training aim to maximize the use of the seeing hemifield. During VRT, customized suprathreshold stimuli are presented along the defective side of the visual field border. In a manner similar to conventional perimetry, the patient presses a button upon stimulus detection. VRT generally requires twice-daily sessions of 30 to 60 minutes each for several months. Proposed mechanisms for this training include activation of potentially viable, damaged neurons at the edge of the insult or neuroplastic remodeling of synaptic maps to undamaged cortex.7-9

    Studies have shown that VRT may shift the visual field border by five to 10 degrees, as measured using a suprathreshold perimeter. This has not borne out with threshold perimetry, which showed no substantive change after VRT.7 Much concern exists that subclinical saccades into the blind hemifield may explain the improvements noted in suprathreshold perimetry. Scanning laser ophthalmoscopy (SLO) with microperimetry allows the investigator to observe simultaneously a display of the retina, a fixation cross and the presented stimulus. As the patient fixates on the cross, the examiner can present the stimulus to the patient along the hemianopic border. Any saccades away from the cross are discarded to guarantee absolute fixation control.

    A study of SLO microperimetry conducted both before and after patients underwent VRT reported that there was no change in the absolute field defect.10 This suggests that the observed visual field gains due to VRT may result from tiny saccades into the blind hemifield that remain undetected by external monitoring. Regardless of the reason, 66 to 72 percent of patients describe subjective improvements in reading, navigation and confidence, which indicates that VRT may have some benefits.9

    The primary obstacle to the use of VRT remains its out-of-pocket price tag of several thousand dollars. VRT's cost may outweigh its benefits unless the therapy is definitively proven to be superior to compensatory saccadic training and spectacle-mounted prisms.

    This article was supported by an Unrestricted Grant from Research to Prevent Blindness, New York, N.Y., and the Minnesota Lions (MSL).


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