Prism Therapy and Visual Rehabilitation in Homonymous Visual Field Loss

O'Neill, Evelyn C.*; Connell, Paul P.†; O'Connor, Jeremy C.*; Brady, Janice*; Reid, Irene‡; Logan, Patricia§

Optometry & Vision Science:
doi: 10.1097/OPX.0b013e318205a3b8
Original Article

Purpose. Homonymous visual field defects (HVFD) are common and frequently occur after cerebrovascular accidents. They significantly impair visual function and cause disability particularly with regard to visual exploration. The purpose of this study was to assess a novel interventional treatment of monocular prism therapy on visual functioning in patients with HVFD of varied etiology using vision targeted, health-related quality of life (QOL) questionnaires. Our secondary aim was to confirm monocular and binocular visual field expansion pre- and posttreatment.

Methods. Twelve patients with acquired, documented HVFD were eligible to be included. All patients underwent specific vision-targeted, health-related QOL questionnaire and monocular and binocular Goldmann perimetry before commencing prism therapy. Patients were fitted with monocular prisms on the side of the HVFD with the base-in the direction of the field defect creating a peripheral optical exotropia and field expansion. After the treatment period, QOL questionnaires and perimetry were repeated.

Results. Twelve patients were included in the treatment group, 10 of whom were included in data analysis. Overall, there was significant improvement within multiple vision-related, QOL functioning parameters, specifically within the domains of general health (p < 0.01), general vision (p < 0.05), distance vision (p < 0.01), peripheral vision (p < 0.05), role difficulties (p < 0.05), dependency (p < 0.05), and social functioning (p < 0.05). Visual field expansion was shown when measured monocularly and binocularly during the study period in comparison with pretreatment baselines.

Conclusions. Patients with HVFD demonstrate decreased QOL. Monocular sector prisms can improve the QOL and expand the visual field in these patients.

Author Information


FRCSI(Ophth), MD



Department of Ophthalmology (ECO, PPC, JCO, JB, PL), and Department of Orthoptics (IR), Beaumont Hospital, Dublin, Ireland.

Received February 22, 2010; accepted October 25, 2010.

Evelyn O'Neill; Department of Ophthalmology Beaumont Hospital Dublin 9, Ireland e-mail:

Article Outline

Homonymous Visual Field Defects (HVFD) are caused by anterior or posterior lesions of the retrochiasmal visual pathway, are of varied etiology, and have a prevalence of 0.8% in the general population >49 years.1–4 Pathogenesis of lesions resulting in homonymous hemianopia (HH) are variable depending on the population studied and patient selection. The most common causes of HH include stroke (70%), tumors (10 to 15%), and trauma (13%).3,4 About 30% of all stroke patients and 70% of those with strokes involving the posterior circulation suffer hemianopic visual field loss.2 These numbers are likely to increase with an aging population and improved emergency care for stroke victims. Despite these numbers and the increasing importance of the problem, a recent review found few reports researching rehabilitation techniques for the hemianopic patient.2

HVFDs significantly impair visual functioning. They cause difficulty in detection of obstacles on the side of field loss resulting in impaired reading speed, mobility, navigation, and commonly preclude driving. Furthermore, HVFD after stroke are associated with an adverse functional prognosis,5–7 particularly when coupled with visual neglect or sensory inattention.6–8 It has also been shown that HVFD have a significant impact on quality of life (QOL) and specifically, vision-targeted, health-related QOL.9

Visual rehabilitation of HVFDs relies on physiological principles and documented observations: the “blind” hemifield may retain some visual function10 and up to 50% of patients experience varying degrees of spontaneous recovery within 1 month of injury.11 In most cases of HH, if spontaneous improvement is to occur, it is within the first 3 months of injury, with the majority of spontaneous recovery occurring early, as stated.5,11 Despite the prevalence of HVFDs and their impact on independent functioning, rehabilitation options are limited and there is no widely accepted treatment.2

Visual field rehabilitation techniques attempt to maximize remaining visual function through visual training and optical aids. First, the former include oculomotor training for visual field exploration using compensatory eye movements to expand the hemifield,2,12 and, Visual Restoration Training using computer-based training strategies or other methods that stimulate the affected hemifield and improve lost function.13,14 The latter includes prism therapy, mirrors, reverse telescopes, and closed circuit television monitors.2 These expand the visual field or relocate the image. Expansion of the visual field is the preferable option as image relocation merely replaces one scotoma with another, and field expansion results in a wider field of view.2 Field expansion is performed most successfully with prism therapy.

Binocular sector prisms, applied to the hemianopic one-half each lens, are a commonly used technique for treating HVFD.2,3 They relocate images to remaining functional areas of the affected hemifield when gaze is directed into the prism but cause a scotoma in the primary position of gaze.2 Monocular sector prisms provide visual field expansion when the patient fixates within the field of the prism. They are fitted only to the lens on the side of HVFD. When gaze is directed in the primary position they have no field expansion effect, but when directed into the field of the prism confusion and diplopia occur.2 These prisms, with less selective fitting, cause unacceptable central diplopia and are much less effective.15

A successful HVFD aid requires expansion of the field of view in all positions of gaze while avoiding central diplopia. In 2000, Peli16 described such a novel prismatic device; high power 40 dioptre (Δ) monocular sector prisms limited to the peripheral field (superior, inferior, or both) achieved a field expansion of 20°, effective in all positions of gaze.16 This was through the creation of peripheral diplopia and confusion, a feature of normal vision and therefore tolerated well. An optically created peripheral exotropia achieves this. Patients are taught to look through the central, prism free area of the spectacle lens, thus avoiding central diplopia.16 Previous work, using this technique, suggests patients find these monocular sector peripheral prisms helpful for obstacle avoidance and general mobility, with improvement often assessed subjectively.16,17

The primary aim of our study was to assess this novel interventional treatment of monocular peripheral prism therapy on visual functioning in patients with HVFDs of varied aetiologies using specific vision-targeted, health-related QOL questionnaires. Our secondary outcome measures were continued use of the prism treatment and confirmation of monocular and binocular visual field expansion posttreatment.

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The study was performed in a prospective manner. Twenty consecutive patients with HVFDs were evaluated for enrolment from the Department of Neuro-Ophthalmology and Orthoptics at the National Neurosurgical Centre, Beaumont Hospital, Dublin, Ireland. Inclusion criteria were documented HVFD, normal functioning anterior visual pathways with visual acuities of at least 20/50 in each eye. Exclusion criteria were severe unilateral sensory neglect, moderate-severe cognitive decline, aphasia, apraxia, visual agnosia, and severe physical disability. The research was conducted in accordance with the Declaration of Helsinki and local ethics committee guidelines. Informed consent was obtained from all patients.

All patients underwent specific vision-targeted, health-related QOL questionnaire and monocular and binocular Goldmann perimetry before commencing prism therapy. After the treatment period, QOL questionnaire and perimetry were repeated. All questionnaires and visual fields were performed by one person (IR). Patients were assessed at 2 to 3 weeks (postinitial fitting), 6 weeks, 3 months, and 12 months. All were followed for a minimum of 12 months. Comfort and compliance were assessed at each visit (Fig. 1).

Prism therapy was instituted in accordance with the methods described in 2000 by Peli.16 In brief, separate prism segments were used to expand the upper and lower quadrants. Patients were fitted with monocular upper and lower 40Δ press-on Fresnel prism segments. The prisms were fitted on the side of the HVFD with the base-in the direction of the field defect (a base-out prism effect), so objects on the non-seeing side were imaged on the functional side. For an initial trial period of 2 to 3 weeks, patients were fitted with upper segment prisms only. After a successful trial period, lower segment prisms were applied. The prism fitting procedure within the clinic was performed in a stepwise fashion, designed to determine the minimum interprism separation tolerable to the patient. All prisms were fitted by one orthoptist (IR). Tolerability was determined when comfortable single central vision was maintained with no change in head posture when walking, with and without the prisms. Patients with quadrantanopias were fitted with only one segment, either upper or lower depending on the pattern of field loss. Patients were instructed to foveate through the central carrier lens at all times and not through the prism by making vertical head movements. After a period of adaptation, this creates a constant peripheral optical exotropia, peripheral confusion and diplopia, and ultimately field expansion in all positions of gaze.

The National Eye Institute 25-Item, Visual Functioning Questionnaire (NEI-VFQ-25), (interviewer administered format), was used in the study group and has been described previously.18 This is a validated, reliable survey to measure the dimensions of self-reported vision-targeted health status that are most important in persons with chronic eye disease.18 It measures the influence of visual disability and visual symptoms on; generic health domains, specifically emotional and social functioning and task-orientated domains related to daily visual functioning. The NEI-VFQ-25 generates 12 subscales: within the generic health domains: general health, general vision, near vision, distance vision, driving, peripheral vision, color vision, and ocular pain, and within the vision specific domains: role difficulties, dependency, social functioning, and mental health. Subscale scores were computed with published algorithms. Subscales are scored on a 0- to 100-point scale in which a high score represents better functioning. Scores were compared pre- and postprism therapy with the normal reference group from an adult population with no underlying eye disease (n = 122) derived from the NEI-VFQ-25.18

Monocular and binocular Visual Fields were assessed using standard Goldmann perimetry (III-4-e target; Haagstreit, Koeniz, Switzerland). This consisted of standard screening procedure of dynamic mapping and static perimetric probing within identified non-scotomatous areas. One orthoptist (IR) conducted all perimetry, applying the same procedure used for diagnostic perimetric testing.

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For each subscale of the NEI-VFQ-25 and because of the non-parametric nature of the data, Wilcoxon signed rank test was performed and significance confirmed using the paired t-test. These were performed to determine significance of improvement. A p value of <0.05 was taken to indicate statistical significance. Published accepted scoring from normal subjects provided control data for comparison only.

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Twenty patients were assessed for enrolment, of which 12 fulfilled the inclusion criteria. Two of the 12 patients had initiation of therapy before 3-month postinjury, and thus spontaneous recovery could not be out ruled; therefore, their NEI-VFQ-25 scores and degree of visual field expansion were excluded from our data analysis.

Mean age was 40.4 years (range, 18 to 62) and seven were male. All patients had documented HVFDs (Table 1). Fifty-eight percent of patients demonstrated macular sparing. Etiology of field defect included arteriovenous malformations/aneurysms (50%), ischemic cerebrovascular accidents (25%), with neuro-surgical procedures, tumors (including metastatic disease), and traumatic brain injury accounted for the remaining (25%).

The average time delay from insult to initiation of treatment was 15.8 months (range, 1 to 48 months). However, this was negatively skewed by two patients (30 and 48 months), without whom, the average time delay was 11.2 months. All patients were followed for a minimum of 12 months.

Overall, patients demonstrated significant improvements in multiple vision-related, health-targeted QOL functioning parameters of the NEI-VFQ-25 questionnaire (Table 2 and Fig. 2). Most notably, there was significant improvement within the generic health domains of general health (p < 0.01), general vision (p < 0.05), distance vision (p < 0.01), peripheral vision (p < 0.05), and within the vision specific domains of role difficulties (p < 0.05), dependency (p < 0.05); and social functioning (p < 0.05); all parameters were assessed in comparison with baseline, pretreatment scores, and to reference values of a stratified normal reference group18 (Table 2).

Visual field expansion when measured monocularly and binocularly during the study period was demonstrated in most patients in comparison with pretreatment baselines, with an average field expansion of ∼15° (mean visual field expansion, 14.75°; range, 5 to 30°; Table 3). The expansion was in the corresponding quadrants of field of loss. Two patients with delayed initial treatment (30 and 48 months) demonstrated no significant improvement in field expansion and two patients in whom treatment commenced before 3 months had a field expansion of 22 and 48°.

Ten of 12 (83%) patients expressed satisfaction with progress made using the prism therapy, and none complained of difficulties with adaptation. All subjects expressed subjective increased levels of happiness and coping ability with day to day activities while using the prisms. Two patients, those with the greatest initial delay to therapy (30 and 48 months) and for whom there was no expansion of visual field, were unresponsive to therapy and discontinued prism use after the 12-month period because they felt that the prisms had not improved their visual or daily functioning. There were no reported compliance problems during the study period and the prisms were well tolerated.

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HVFD are a disabling physical condition significantly affecting QOL. Patients with HVFDs demonstrate and report problems in activities of daily living that demand the use of peripheral vision. In this study, we compared the QOL indices pre- and postprism therapy for peripheral field expansion, in patients with HVFDs of varied etiology. Vision-targeted QOL as indicated by NEI-VFQ-25 have been shown to be significantly reduced in patients with HVFDs.9 The QOL scores in our group with HVFD's were lower in all subscales both pre- and posttreatment when compared with a normal reference group.9,18 This is in keeping with previous work demonstrating reduced QOL scores particularly in relation to peripheral vision, distance activities, dependency, and social functioning in patients with homonymous defects.9,19

Overall, subjects in our study group demonstrated improvement in their vision-targeted QOL during the study period. Giorgi et al.20 in their series reported clinical success (defined as continued prism wear) in 67% of subjects with HVFDs treated with prism therapy. They found patients reported perceived benefits and improved QOL with improved obstacle avoidance on the hemianopic side with prism wear.

Interestingly, Bowers et al.17 reported, in a multicenter study, that confidence in fitting and training patients to use the prisms may be an important factor in determining success. Success rates, which they defined as a decision for continued wear of prisms and patient ratings of prism helpfulness for obstacle avoidance, varied widely between their clinics (27 to 81%). Higher success rates were found at clinics where more participants were fitted, suggesting experience in fitting and training patients to use the prisms may be an important factor in determining the success of the prism therapy, reflecting our high success rate on objective measurements, with all patients fitted by one highly motivated orthoptist.

Quantitative studies of visual field recovery suggest that spontaneous improvement of HH is seen in 50% of patients within 1 month of injury, and in most cases, the improvement occurs within the first 3 months. After this period, spontaneous field recovery is very rare.3,11 Therefore, spontaneous improvement in the visual field, sufficient to impact on QOL would be unlikely after this time. In our study, no patient received prism therapy until at least 1-month postinsult, and in the majority (10 of 12 patients), treatment was not initiated until 3 months or more postinjury. Thus, it is argued, in this cohort, the improvement achieved represents improvement resultant from therapy and not spontaneous recovery. However, given that 2 of the 12 participants initiated therapy before 3 months and may have experienced some spontaneous recovery, we excluded their NEI-VFQ-25 scores and degree of visual field expansion from data analysis.

This study has several limitations. First, we considered a rather small sample size with a wide range of visual field impairments, and our patient group is not representative of the general HVFD population, with a lower mean age and fewer HVFD because of ischemic cerebrovascular accidents. Second, we do not have a no-intervention control group affecting the applicability of our results to a general HVFD population. It is interesting to note that most reports investigating this novel form of prism therapy do not contain a control group, reflecting difficult recruitment, stringent exclusion criteria, or reticence of included patients to be placed in the non-intervention arm. Third, the time span between brain injury and commencement of prism therapy was not uniform. Fourth, patients may have, outside of our treatment regime participated in other non-vision specific rehabilitation programs during the study period, which could have influenced the improvement in QOL. However, none made this disclosure to us during the study period. Finally, there was potential for possible bias as one researcher conducted both the intervention and administered the outcome questionnaire.

It is important to note that the lack of a control group in this study cohort complicates assigning all the improvements in NEI-VFQ scores to prism effect, most notably, parameters relating to near vision such as social functioning and role difficulties. However, all patients wearing the prisms expressed greater levels of happiness and ability to cope with daily activities while wearing prisms, and 10 of the 12 participants continued to wear them after the minimum 12 months.

Previously, the benefits of rehabilitation were perceived as offering limited gain to patients with HVFDs. To date, training in scanning has offered some benefit to patients with HVFD; however, their main limitation is that they require intentional scanning and therefore did not increase the field of view without eye movements.16,21 Optical treatments, often considered the only true viable option for rehabilitation in this cohort to date have not been optimal with many of the treatments providing no measurable expansion in visual field, causing unacceptable diplopia and in those causing field of view relocation, many resulted in large central scotomas for patients.2,16 The novel method of monocular sector prisms, as described by Peli,16 used in our treatment group and recently assessed in a community-based trial17 has the potential to provide actual field of view expansion and quantitative improvement in vision-targeted QOL in a convenient and inexpensive way.

In conclusion, our results show a reduced QOL among a small sample with HVFDs compared with normative values. The visual disability associated with HVFD significantly affects patients daily functioning and abilities to perform activities of daily living (ADLs) that are valued by patients. We have demonstrated that peripheral monocular sector prisms can improve the QOL in patients with HVFD. It quantifies for the first time, the improvement in vision-targeted QOL in HVFD patients after prism therapy. Further studies will be needed to confirm these findings in a randomized setting.

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The preliminary data from this study was previously presented as a paper at RANZCO 24th November 2008 at The Royal College of Australian and New Zealand Ophthalmologists Annual Congress Meeting, Melbourne, Australia.

The authors have no proprietary or commercial interest in any product or concept discussed in this article.

Evelyn O'Neill

Department of Ophthalmology

Beaumont Hospital

Dublin 9, Ireland


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Fresnel prism; homonymous hemianopia; rehabilitation; visual field; National Eye Institute 25-Item; Visual Functioning Quality of Life Questionnaire

© 2011 American Academy of Optometry