|Year : 2022 | Volume
| Issue : 3 | Page : 744-746
A case report of rehabilitation of bilateral inferior field defect with Peli prisms: A novel fitting
Shruti Nishanth, Alphia Rehman, Henderson Henry, M Nivean, M Nishanth, Pratheebadevi Nivean
M.N Eye Hospital, Chennai, Tamil Nadu, India
|Date of Submission||12-Nov-2021|
|Date of Acceptance||21-Mar-2022|
|Date of Web Publication||16-Jul-2022|
Dr. Shruti Nishanth
Paediatric Ophthalmologist, M.N Eye Hospital, Chennai - 600 021, Tamil Nadu
Source of Support: None, Conflict of Interest: None
Bilateral inferior visual field loss (BIVFL) is a rare entity, and rehabilitation of such patients can be challenging. Peli prisms are a good option for visual rehabilitation in horizontal homonymous hemianopias. Here we present an interesting case of BIVFL with macular sparing, successfully rehabilitated with a novel vertical orientation of Peli prism.
Keywords: Inferior field loss, vertical Peli prism, visual field restoration
|How to cite this article:|
Nishanth S, Rehman A, Henry H, Nivean M, Nishanth M, Nivean P. A case report of rehabilitation of bilateral inferior field defect with Peli prisms: A novel fitting. Indian J Ophthalmol Case Rep 2022;2:744-6
|How to cite this URL:|
Nishanth S, Rehman A, Henry H, Nivean M, Nishanth M, Nivean P. A case report of rehabilitation of bilateral inferior field defect with Peli prisms: A novel fitting. Indian J Ophthalmol Case Rep [serial online] 2022 [cited 2022 Dec 3];2:744-6. Available from: https://www.ijoreports.in/text.asp?2022/2/3/744/351156
Bilateral inferior visual field loss (BIVFL) or inferior hemianopsia is mainly associated with non-arteritic anterior ischemic optic neuropathy (NA-AION), retinal lesions (choroiditis and coloboma) or optic nerve lesions (glaucoma, optic disc drusen and optic nerve hypoplasia). All of these affect the structures anterior to the optic chiasm. Retro chiasmal pathology may be a rare presentation.
BIVFL with macular sparing is one of the presentations of occipital lobe lesion, which can be due to penetrating injury or due to blunt trauma to the bilateral occipital lobe in the area of the superior calcarine fissure. If the insult affects the area inferior to the calcarine fissure, it may result in a superior field defect. BIVFL may also be caused by cerebrovascular accidents of the posterior circulation, which supplies the inferior part of the occipital lobe.
We present a case of BIVFL with macular sparing in our patient due to traumatic gliosis in the bilateral occipital lobe in the region of superior calcarine fissure, successfully rehabilitated with a vertical orientation of Peli prism.
| Case Report|| |
A 40-year-old lady, a teacher by profession, presented with complaints of defective vision on looking down and to her side for 4 months. She gave a history of a road traffic accident involving a fall from a bike which lead to a blunt injury to her occipital region.
Her best-corrected visual acuity was 20/20 and N6 in both eyes. Anterior and posterior segment evaluation was normal in both eyes. The patient was orthophoric. Worth four dot test showed binocular fusion. Colour vision was normal. Extraocular movements were full and free. Visual fields (30-2) showed BIVFL defect with macular sparing.
T1-weighted MRI brain showed hyperintensity in the region of bilateral superior calcarine fissure in the occipital lobe suggestive of gliosis.
A diagnosis of BIVFL with macular sparing due to bilateral calcarine fissure gliosis was made. On literature search, there were no reports of rehabilitation of such an inferior field loss. Amidst reports of successful rehabilitation of temporal hemianopias with the help of Peli prisms, a trial was initiated for this patient with the latter.
Peli prisms are stick-on high-power Fresnel prism of 40 prism diopter (PD), which are segments in the size of a rectangle. In cases of horizontal temporal hemianopias, the two Peli prisms are usually oriented in horizontal fashion 6 mm above and below the pupillary reflex, on the side of the hemianopia. The base of the prisms would be oriented towards the side of the hemianopia. This will ensure the image is projected from the non-seeing temporal field to the seeing nasal field. They help in providing visual clues to the patient from the non-seeing field, without compromising on the central vision. With that clue, the patient can turn his/her head to visualize the object in his seeing field.
In this particular case, the field loss was inferior and bilateral. Hence a novel approach of Peli prism orientation was attempted. In both the eyes, the prisms were vertically attached with their base down (base towards the side of the defect). As a result of which, the non-seeing infero-temporal field was projected onto the supero-temporal seeing field.
Prism trial was given as follows. Baseline visual fields were performed. The examiner was seated opposite the patient (to eliminate parallax error) and a torchlight was used to elicit the pupillary reflex. With the help of a scale, a mark was made on the temporal aspect of the glasses using an ink marker, at 5, 5.5, 6, 6.5 and 7 mm from the reflex. The prism was then placed on the patient's existing glasses, base down, with the centre of the nasal border of the prism at 5 mm from the pupillary reflex. A confrontation test was done to see if the patient could perceive the fingers shown in the infero-temporal field and the supero-temporal field. When the patient could not perceive the fingers, the prism was placed in a similar fashion at 5.5 mm and so on, until the patient showed recognition of the fingers projected in her infero-temporal and supero-temporal field of vision. When the prism was placed at a distance of 6.5 mm from the pupillary reflex [Figure 1], the patient showed the perception of the fingers in her supero-temporal field. A visual field test was repeated with the Peli prisms placed at 6.5 mm and it showed an expansion of field by 20° on the infero-temporal aspect.
|Figure 1: Press on 40 PD Fresnel peripheral prism segments placed base down, with the centre of the nasal border of the prism at 6.5 mm from the pupillary reflex|
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The patient underwent 2 h of training in the office to adjust to the prisms and 1 week of training at home. Visual fields were then repeated for the patient and a good improvement was noted in the infero-temporal vision in both eyes [Figure 2]a and [Figure 2]b. Two days following prism training, the patient had difficulty in adjusting to the prism in situ. The patient underwent another session of in-office training and on 1-week follow-up reported comfort in mobility and orientation. On further follow-up at 1 month, the patient reported sustained visual field expansion and was comfortable with the modified spectacles.
|Figure 2: (a) Octopus visual fields of right eye pre (A, C and E) and post (B, D and F) Peli prism rehabilitation. Pre-prism visual fields (A, C and E) showed an inferior visual field defect with macular sparing. An expansion of 20° in the temporal field of vision can be observed in the visual field after rehabilitation with Peli prism (B, D and F). A, C and E: pre-prism greyscale, age normal deviation and age normal probability, respectively. B, D and F: post-prism greyscale, age normal deviation and age normal probability, respectively. (b) Octopus visual fields of pre (A, C and E) and post (B, D and F) Peli prism rehabilitation of left eye. Pre-prism visual field (A, C and E) showed an inferior visual field defect with macular sparing. An expansion of 20° in the inferior field of vision can be observed in the visual field after rehabilitation with Peli prism (B, D and F). A, C, E: Pre-prism greyscale, age normal deviation and age normal probability, respectively. B, D and F: Post-prism greyscale, age normal deviation and age normal probability, respectively|
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| Discussion|| |
Most scientific literature primarily focuses on three therapeutic modalities (approaches) for rehabilitation of visual field loss, namely restorative training, compensatory training and optical aids. The first approach is directed at the restoration of vision to the non-seeing visual field using a prolonged training technique. This technique includes vision restoration therapy in which the subject is instructed to fix gaze at a central point. Visual stimuli are then repeatedly presented in the border between non-seeing and the seeing field (the transition zone) during the procedure. The overall duration for this training is for 6 months, consisting of 1-h sessions per day. The second approach is compensatory training which attempts in alleviating the resulting disability by technically educating the subjects in making efficient and effective eye movements.
The use of optical aids (prisms) is the third method for visual field rehabilitation. Here, the prisms are fitted on the temporal half of the spectacles on the side of the non-seeing field. It aims to shift visual stimuli from a non-seeing field to the seeing one. There are differences among the prisms as well; for instance, the monocular Fresnel prisms provide an expansion of the visual field when placed on the temporal aspect on the side of the hemianopia. However, it can cause central scotoma as the prism runs through the pupillary zone. A new set of spectacle mounted prisms was introduced by Peli, in which monocularly fitted sector prisms spare the central aspect but extend across the entire width of the spectacle lens. Peripheral prism segments placed above and below the line of sight have been the most successful in increasing the usable visual field while avoiding diplopia in the primary gaze. Peli prisms are usually placed unilaterally on the upper and lower parts of the spectacle lens and can provide up to 20° visual field expansion on the hemianopic side while maintaining clear central vision. This property is known as vision multiplexing and this helps in achieving field expansion without central scotoma. They have also been observed to improve mobility and help in the avoidance of obstacles., There have been several advances in the prism, including a perioscopic design that helps in better field expansion.
In our case, we considered using the Peli prism for visual field loss rehabilitation as it spares the central field. The vertical orientation could provide a good expansion of the infero-temporal visual field for the patient, which could help her address her students in the class. The fitting required chair time and training for 1 week period for the adaptation.
Some of the unique features of this case were that it was a BIVFL, which is rare, and rehabilitation of these patients is challenging. Peli prisms have only been tried for horizontal homonymous hemianopias so far. In our case, we have tried a unique fitting of the Peli prisms in a vertical orientation to enable the infero-temporal non-seeing field to be mirrored onto the seeing supero-temporal field. As a result, there was an unobstructed central vision in this patient. To the best of our knowledge, this vertical fitting of Peli prisms has not been tried before. This fitting method can be applied to other conditions that can manifest with a BIVFL, such as AION where a positive scotoma may be perceived. It can be a useful rehabilitative tool in patients with positive scotoma.
| Conclusion|| |
This is a unique case of successful rehabilitation of inferior visual field loss through vertical orientation of Peli prisms. Further studies can be done, to assess the role of the vertical orientation of Peli prisms in patients with other causes of BIVFL such as AION.
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
Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2]