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Sudden monocular visual field loss
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A 15-year-old boy accompanied by his mother presented to the eye clinic with sudden-onset hemifield loss in his left eye on the temporal side. He first observed this deficiency 2 weeks prior during a vision screening at school when he had to cover his right eye. To him, the vision in the left eye suddenly went “poof” and was gone. The patient described a vertical, straight line that separated the seeing from the non-seeing part of his vision. He had long-standing floaters, which were stable, and he denied flashes. He also denied any accompanied pain in his left eye.
The boy has a history of periodic headaches for the last 2 years. The pain was typically on the left side of his head and was relieved with ibuprofen. The last headache was 4 days prior, which lasted about 1 hour and was not correlated with any specific task. He had a history of being hit in the back of the head with a soccer ball 3 years ago. At the time he felt dizzy but reported no treatment or hospitalization. His systemic health was positive for asthma for which he used albuterol and fluticasone propionate inhalers.
The vision was 20/20 in each eye, although the patient noted he would lose the letters on the left side of the line during left eye testing as he progressed to the right. His pupils were equal, round and reactive to light with no relative afferent pupillary defect (APD). During testing, the patient was more sensitive to the light in the left eye and noted it appeared brighter. Confrontation fields were full in the right eye and constricted temporally in the left. Color vision and versions were normal in both eyes. Slit lamp findings were normal, and the IOP was 14 mm Hg in both eyes. The pupils were dilated and all findings were normal, including well-perfused optic nerves with sharp borders and a 0.25 cup:disc ratio and an intact retina.
These visual fields were taken Oct. 20, 2010. The right eye was full but unreliable; mean deviation was -1.49. The left eye was reliable with a complete temporal hemianopia respecting the vertical midline; mean deviation was -15.90.
Images: Wood SD
A visual field was ordered.
Differential diagnoses include juxtasellar lesion such as a pituitary adenoma, retinal defect, optic nerve defect and functional vision loss.
Contradicting findings
Sarah Dougherty Wood
As the optic nerves exit the orbit and travel posteriorly towards the chiasm, the temporal and nasal fibers separate. The temporal fibers stay on the ipsilateral side while the nasal fibers cross. Typically a chiasmal lesion will press on the nasal fibers from each eye resulting in a bitemporal hemianopia, which respects the vertical midline. If the lesion grows anteriorly, it can compress the entire optic nerve on one eye and the nasal fibers of the other eye, therefore, resulting in a junctional scotoma. This is a central defect in one eye and a temporal defect in the other. In general, based on the anatomy described, visual field defects that affect only one eye are pre-chiasmal in nature. Also, visual field defects that respect the vertical mid-line are chiasmal or post-chiasmal due to the splitting of the temporal and nasal fibers. How do we reconcile these seemingly contradicting statements for this patient?
What two pre-chiasmal ocular structures could be damaged that could give a monocular hemianopia? That would be the retina and optic nerve. If there were a retinal detachment, for example, located nasally, this would give a temporal field defect in one eye. This is not the case with this patient because his dilated retinal exam was normal. An optic nerve that is congenitally tilted along the vertical axis can possibly give the appearance of a temporal visual field defect. This patient had healthy nerves that were not tilted. Therefore, a pre-chiasmal cause of the field defect seems unlikely.
A chiasmal lesion would need to be very localized to involve only the nasal fibers of one eye due to the close proximity of the structures in this area. This would be an uncommon finding. In a series of patients at the Mayo Clinic with pituitary adenomas, 5% had temporal defects in one eye and they tended to be superior and close to fixation, not a complete hemianopia (Gittinger).
The neuro-ophthalmology department at the Toronto Hospital had 24 patients in a 15-year period with a monocular temporal hemianopia. In their paper, Hershenfeld and Sharpe describe the causes of all the cases. Nineteen of the patients had juxtasellar lesions such as a pituitary adenoma or craniopharyngiomas. Most of the patients had visual acuity loss, optic nerve pallor and/or an APD. Six patients did not have an APD in their group. Of this subgroup, one had a known pituitary adenoma with resection whose bitemporal visual field defect resolved in just one eye. One patient had disc tilting, and two actually had a bilateral defect on retesting. The other two patients were found to have functional vision loss. Therefore, of the patients with monocular field defects and a tumor, all had an APD on the affected side. Recall that our 15-year-old had normal pupil testing.
Note that an APD would be expected in this case with the mean deviation of -1.49 OD and -15.9 OS on the visual field
These visual fields from Nov. 3, 2010, are reliable with a few scattered defects in both eyes but essentially full.
Unusual stressors
After the visual field testing, functional vision loss was the most likely diagnosis based on the above rationale. At this point, further probing of the patient and his mother was done to determine if there were any unusual stressors in the patient’s life such as recent divorce or troubles at school. The mother disclosed that a few months prior the patient had seen a friend drowning at a local lake and tried to save him, unsuccessfully. The patient was reassured that his eyes were very healthy and that perhaps the stress he has been through has temporarily affected his vision and should resolve. The patient was to return in 2 days for a repeat of pupil and visual field testing.
One technique to further separate functional patients from organic disease is to perform a binocular visual field. With this type of testing, a true hemianopia will still be present but much smaller and located in the most peripheral aspect due to the healthy eye filling in most of the defected area. If the patient is malingering, they will not realize there is overlap of the fields and they will still manifest a temporal defect when tested binocularly.
Follow-up, management
The patient did not return for the 2-day follow-up but did return a week later when he noted he forgot about the initial appointment. The patient said he no longer saw black on his left side. Vision and pupil testing were normal. Visual fields were performed first monocularly and were full in each eye, so there was no reason to perform binocularly. His hemianopia had spontaneously resolved in 1 week.
During the follow-up exam, it was learned that the patient’s mother had a retinal detachment in the past, and her first symptoms were a black curtain on her left side. It is possible the patient got the idea for his vision loss from his mother’s experience.
Functional visual loss is not correlated with a true disease process. Such patients need to be reassured their eyes are healthy, and psychological consult should be considered in some cases. Most cases will resolve spontaneously. Careful and thoughtful examination can eliminate the need for unnecessary and expensive neuroimaging.
References:
- Acaroglu G, Guven A, Ileri D, Zilelioglu O. Monocular temporal hemianopia in a young patient. Turkish Journal of Pediatrics. 2004;46:98-100.
- Gittinger J. Functional monocular temporal hemianopia. Am J Ophthalmol. 1986;101:226-231.
- Hershenfeld S. Sharpe J. Monocular temporal hemianopia. Br J Ophthalmol. 1993;77:424-427.
For more information:
- Sarah Dougherty Wood, OD, MS, FAAO, completed a residency at the Kansas City VAMC, and a research fellowship at the Boston VAMC. She currently practices at the Dorchester House Community Health Center in Boston and is adjunct faculty at NECO. She can be reached at sarah.wood@dorchesterhouse.org.
- Edited by Leo P. Semes, OD, a professor of optometry, University of Alabama at Birmingham and a member of the Primary Care Optometry News Editorial Board. He may be contacted at 1716 University Blvd., Birmingham, AL 35294-0010; (205) 934-6773; fax: (205) 934-6758; lsemes@uab.edu.