|Year : 2023 | Volume
| Issue : 2 | Page : 465-467
Peli prism fitting for homonymous hemianopia: Case series for fitting variations
Ranindita Saha1, Vivek Reshamwala2, Prem Nandhini Satgunam1
1 Brien Holden Institute of Optometry and Vision Sciences; Hyderabad Eye Research Foundation, L V Prasad Eye Institute, Hyderabad, Telangana, India
2 Brien Holden Institute of Optometry and Vision Sciences, L V Prasad Eye Institute, Hyderabad, Telangana, India
|Date of Submission||01-Aug-2022|
|Date of Acceptance||12-Dec-2022|
|Date of Web Publication||28-Apr-2023|
Prem Nandhini Satgunam
Prof. Brien Holden Eye Research Center, L V Prasad Eye Institute, Road No. 2, Banjara Hills, Hyderabad - 500 034, Telangana
Source of Support: None, Conflict of Interest: None
Peli prisms are Fresnel prisms for visual field expansion in homonymous hemianopia. They can be dispensed as temporary (press-on) or permanent prisms. In this case series, we discuss the general fitting techniques and report fitting Peli prisms in four unusual scenarios. We show that children and one-eyed patients can be fit with Peli prism. Peli prism can be fit over safety goggles, but fitting in progressive addition lenses can be challenging. Careful counseling, setting realistic goals, giving a proper Peli prism trial, orienting for spatial mislocalization, and demonstrating the visual field expansion are all key ingredients to achieve success.
Keywords: Field expansion, Fresnel prism, homonymous hemianopia, peripheral awareness
|How to cite this article:|
Saha R, Reshamwala V, Satgunam PN. Peli prism fitting for homonymous hemianopia: Case series for fitting variations. Indian J Ophthalmol Case Rep 2023;3:465-7
|How to cite this URL:|
Saha R, Reshamwala V, Satgunam PN. Peli prism fitting for homonymous hemianopia: Case series for fitting variations. Indian J Ophthalmol Case Rep [serial online] 2023 [cited 2023 Jun 6];3:465-7. Available from: https://www.ijoreports.in/text.asp?2023/3/2/465/374910
Peli prisms (also known as peripheral prism, expansion prism, or Peli lensTM) are Fresnel prisms prescribed for homonymous hemianopia for field expansion. The prism base is oriented to the field loss direction (i.e., prism base is on left in left hemianopia). Peli prisms are available in 40 and 57 prism diopters (PD) magnitude that provides visual field expansion for about 20° and 30°, respectively. The 40 PD prism is available as both press-on and permanent prism, whereas the 57 PD prism is available only as a permanent prism. Upon visual field expansion, the patient's ability to navigate and avoid obstacles is found to improve, along with visual attention. Patients with hemianopic field loss, preferably of more than 6 months duration, can undergo a Peli prism trial. Any recovery in the visual field, particularly from neurological insult, could happen within this time frame. This time duration also allows patients to assess their functional difficulty or their ability to adapt and manage.
The Peli prisms have been extensively studied in clinical trials in research settings with strict inclusion criteria, but there is a lack of reporting from clinical settings. In this paper, we describe fitting these prisms in four patients who had unique requirements. Informed written consent to publish photograph was obtained from all patients or parents (in case of a child). The spectrum of these different fittings discussed here will help broaden the practice of Peli prism fitting.
General Fitting Guidelines
Peli prisms are best suited for vertical midline respecting dense homonymous hemianopia. The patient along with the practitioner should set realistic expectations and goals before embarking on the Peli prism-fitting trial. History of functional vision difficulties (e.g., navigation difficulty) should be enquired. Binocular confrontation perimetry can be reflective of the patient's functional visual field. If the patient can appreciate any movement on the “blind” side (Riddoch's phenomenon) or can relatively localize to some objects on the blind side, the patient may not find the Peli prism very beneficial. However, in the absence of such appreciation, the Peli prism will be suitable.
For the trial, the press-on Peli prism (40 PD) is positioned on the patient's spectacle close enough to the pupil to appreciate the visual field expansion inferiorly and superiorly, but not too close to elicit central double vision (see references, for fitting guidelines). The recommended inter-prism distance is about 12 mm, to start the trial. Upon fitting, the visual field expansion can be verified with a quick confrontation perimetry. Next, the spatial mislocalization with prism should be demonstrated by having the patient touch the examiner's wiggling fingers in both the seeing and non-seeing visual fields. The patient should be made aware that the real object is in the blind field, and that he/she needs to move his/her head to localize to the correct position. Following this orientation, the patient is made to walk around with supervision to explore the environment. Feedback on the patient's navigation can be obtained from both the patient's attender and the patient. If benefit is observed, the final Peli prism can be ordered and dispensed.
| Case Series|| |
We prescribed a Peli prism for a 15-year-old boy with left homonymous hemianopia following surgery for pilocytic astrocytoma at the age of 5 years. Peli prism trial on children has not been reported before. The child had 20/20 visual acuity in both eyes. The child was able to appreciate the field expansion and was prescribed 40 PD temporary prism. In a subsequent visit 2 years later, the patient was keen to take the 57 PD oblique prism [Figure 1]. The oblique prism base is oriented down and out in the upper segment and up and out in the lower segment. Such an orientation would facilitate detecting objects closer to the central visual field.
|Figure 1: (a) Patient dispensed with 40 PD horizontal temporary Peli prism for his left homonymous hemianopia in his first visit. (b) Same patient prescribed with permanent 57 PD Peli prism with oblique base direction in a subsequent visit 2 years later|
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A 61-year-old female with right homonymous hemianopia was referred for Peli prism trial from the neuro-ophthalmology clinic. The patient had a history of ventriculoperitoneal shunt because of increased cerebrospinal fluid pressure. She had hypertensive retinopathy. Her best-corrected visual acuity was 20/30, N6 with her progressive addition lenses (PAL). We attempted fitting Peli prisms in this patient over her PAL, since she was not willing to change to bifocal spectacles. In case of bifocals, the Peli prism is mounted above the bifocal segment, so that it does not interfere with reading. However, PAL pose two problems: there is no clear demarcation line for the near and intermediate addition power and PAL's peripheral aberrations can also be shifted with the prisms. The patient was able to appreciate the field expansion with the Peli prism and was given a home trial for 2 weeks. The patient returned to the clinic after 15 days and reported that she was uncomfortable and wanted to discontinue the Peli prism. The Peli prisms were removed and she was advised head scanning to manage her hemianopia.
A 69-year-old man with left homonymous hemianopia following a cerebral stroke wanted Peli prisms to improve his mobility and driving. He had 20/20 unaided visual acuity. The patient wanted the Peli prism over his safety goggles for driving.
The patient appreciated the field expansion with the trial. The Peli prisms were fit over his safety goggles and dispensed [Figure 2]. Patient was cautioned for driving. The field expansion experienced by this patient will be smaller due to the larger vertex distance of the safety goggles [Figure 3].
|Figure 2: Patient with temporary Peli prism spectacles (40 PD with base in horizontal direction) prescribed in his safety goggles for left homonymous hemianopia|
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|Figure 3: Illustration of the effect of vertex distance on the area through which the visual field expansion is appreciated. The expected area (B) of visual field expansion using the Peli prism (P) becomes lesser (B') if the vertex distance increases from A (13 mm) to A' (15 mm). NP= nodal point, 7.08 mm from the corneal plane; height of the Peli prism segment is 8 mm, then α=21.7°, in the case of increased vertex distance, α' will reduce to 19.8° and so will the expected area (B') of visual field expansion|
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As a convention, Peli prism fitting is done over the eye that corresponds to the side of the visual field loss. However, these prisms can also be fit over any eye, with the base pointing to the direction of the field loss. We fit a Peli prism for a one-eyed patient (42-year-old man). The patient had traumatic third nerve palsy with no light perception in the left eye. Temporal hemianopia was observed in the right eye (20/20, N6).
The patient was prescribed the Peli prism for his right eye and in a follow-up visit after 5 years (in 2022), he came for a replacement. He was given a temporary 40 PD with oblique base direction. The oblique directions are found to show better expansion than the horizontal direction. 1 Field expansion was also documented with the tangent screen perimeter [Figure 4].
|Figure 4: (a) Patient with temporary Peli prism spectacles (40 PD with base in oblique direction) prescribed for right homonymous hemianopia. (b) Visual field isopter is obtained with the tangent screen perimeter. The visual field isopters with Peli prism (broken line) and without Peli prism (solid line) are shown|
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A decrease in superior visual field was observed in this patient after the Peli prism fit [Figure 4]b. This is because of the prism scotoma (area covered by the prism was not visible). If the other eye had been functional, this scotoma area would have been compensated.,
| Discussion|| |
Peli prism fitting can be modified as per the patient's requirement. The prisms can be helpful for children and one-eyed patients. The choice of the spectacle design is important. The present recommendation is to fit oblique base directions, regardless of whether the patient would drive or not. In our clinical practice, we have now recently shifted to prescribing the oblique Peli prisms. Studies on driving have demonstrated better detection of objects and pedestrians with the Peli prisms., The driving rules and requirements in India need to be investigated and revised. Optometrists and ophthalmologists already practicing prism prescriptions can now add Peli prisms into their repertoire to help patients with homonymous hemianopia.
| Conclusion|| |
Through the case series below, we also discuss the Peli prism fitting in some unusual scenarios.
The authors acknowledge the Hyderabad Eye Research Foundation and DBT grant (BT/PR32404/MED/30/2136/2019) for supporting the time of author PNS. The authors have no financial interest in the optical aid described here.
Declaration of patient consent
The authors certify that they have obtained all appropriate patient consent forms. In the form the patient(s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.
Financial support and sponsorship
Hyderabad Eye Research Foundation, DBT grant (BT/PR32404/MED/30/2136/2019).
Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2], [Figure 3], [Figure 4]