Woman presents with acute monocular vision loss
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A 28-year-old woman presented to the Tufts Medical Center emergency department with vision loss in the right eye upon waking up in the morning.
She had a mild bifrontal headache that started the day before. She could see only shadows and colors out of the right eye. She also noticed twitching of the right eye, which she had never experienced before. She was diagnosed with strep throat at an urgent care clinic the day before and was taking antibiotics as prescribed.
Source: Julia Watson, MD, and Thomas R. Hedges III, MD
Her medical history included attention-deficit/hyperactivity disorder, anxiety, asthma, depression, substance use disorder in remission for 9 years, alcohol use disorder in remission for 2 years, and migraines. Her regular medications included an albuterol inhaler, which she used as needed, fluticasone and intramuscular medroxyprogesterone. Her family history was noncontributory. She had no known drug allergies. She smoked half a pack of cigarettes daily.
She was not on any ophthalmic medications and had no prior ophthalmic surgeries. She reported being told she had a “lazy eye” as a child but was not sure which eye was affected and did not recall patching. On arrival at the emergency department, a stroke code was activated. She was seen by the stroke neurology team and taken for a STAT CT of the head without contrast and CT angiography of the head/neck, which were unremarkable. Ophthalmology was consulted for further evaluation.
Examination
Near visual acuity was 20/800, not improved with pinhole, in the right eye and 20/40, with improvement to 20/25 with pinhole, in the left eye. Pupils were equally round and reactive to light. IOP measured by Tono-Pen (Reichert) was 15 mm Hg bilaterally. Color vision was full in the left eye by Ishihara color plates, and the patient identified only 1/11 plates in the right eye. Confrontation visual field was severely constricted in the right eye and full in the left eye. Extraocular movements were full with orthotropic alignment. Cranial nerves were otherwise intact. She had a normal optokinetic response in both eyes. Titmus stereopsis testing revealed 40 seconds of arc.
On external exam, she appeared to be actively squinting her right eye. Anterior segment slit lamp exam was unremarkable in both eyes. On dilated fundus exam, the optic nerves appeared pink and sharp with 0.6 cup-to-disc ratio in both eyes. The maculas, peripheral retinas and vessels were normal in both eyes.
Imaging
OCT of the retinal nerve fiber layer (RNFL) (Figure 1) and ganglion cell layer analysis (Figure 2) were unremarkable in both eyes. OCT of the maculas showed normal foveal contours without fluid or photoreceptor disruption. Monocular visual field testing with VisuALL virtual reality platform (Olleyes) showed temporal loss in the right eye and nonspecific constriction in the left eye (Figures 3a and 3b). Binocular visual field testing showed a dense right homonymous hemianopia (Figures 4a and 4b).
What is your diagnosis?
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Acute monocular vision loss
In a young, otherwise healthy woman presenting with acute monocular vision loss, the differential is broad and includes acute etiologies such as typical or atypical optic neuritis, retinal arterial occlusion, retinal detachment or hemorrhage, vitreous hemorrhage, central serous chorioretinopathy, occipital infarction, idiopathic intracranial hypertension and many other diagnoses. The differential also includes more chronic etiologies of vision loss including amblyopia, keratoconus and Leber hereditary optic neuropathy, among others, as the patient may have only just realized one eye was not seeing as well as the other.
Fortunately, most of the aforementioned etiologies can be quickly ruled out with a comprehensive eye exam and basic testing with OCT and visual field testing. If this workup is unrevealing or if the vision loss seems out of proportion to the pathology found, functional or non-organic vision loss should be considered, either as the sole underlying etiology for the vision loss or as an overlay to organic vision loss. In this case, the patient’s ability to see 9/9 circles in the Titmus stereopsis test revealed that her central visual acuity was likely at least 20/40 in both eyes. Visual field testing demonstrated physiologically incompatible results, which further solidified our suspected diagnosis of functional vision loss.
Workup, management and follow-up
The patient was informed that her examination and workup were reassuring against sight-threatening disease, and she was counseled that she had the potential for significant and even full recovery of her vision. At 2-week follow-up, she reported her vision in the right eye had significantly improved the morning before. Her visual acuity was 20/50 in the right eye. On confrontation visual field testing, she had improved diffuse visual field constriction. Again, reassurance was provided, and close follow-up arranged.
Discussion
Functional, or non-organic, vision loss is characterized by a decrease in visual acuity and/or loss of visual field that has no underlying physiologic basis. It is first and foremost a diagnosis of exclusion, and one must be wary of dismissing a patient’s complaints as functional when there may be true underlying pathology. For example, craniopharyngioma can cause decreased vision and psychological dysfunction, which may mimic functional vision loss. True ocular pathology can also have functional overlay. While some patients are malingering, many truly believe they have lost vision. The key is for the treating physician to maintain curiosity and composure and to focus non-emotionally on examination findings.
There are several different tactics to demonstrate that the patient’s vision is better than it appears. Nystagmus induced by optokinetic drum testing indicates at least 20/400 vision. Using a piece of measuring tape, one can use a writing utensil to draw lines three to six inches apart and see if nystagmus can be induced at a distance, which would require 20/20 vision. In a patient with monocular vision loss, performance on stereopsis testing can be correlated to an estimated visual acuity. In order to see nine circles, visual acuity should be in the range of 20/30 to 20/40. One can use a phoropter to fog the better-seeing eye while testing vision in the affected eye. Additionally, while assessing visual acuity, it can be helpful to use a bottom-up approach rather than top-down testing on the Snellen chart. Each ophthalmologist should experiment and find which tests are most easily and consistently reproduced.
As in our case, visual field testing can be helpful in identifying physiologically incompatible field defects, which were supportive of the diagnosis of functional vision loss. Several different patterns of visual field loss may be seen in cases of functional vision loss, especially visual field constriction. Our patient had monocular temporal hemianopia, which was reproduced with binocular testing and was highly suggestive of functional visual field loss. On the other hand, central scotomas are rarely, if ever, functional in origin.
Although it may be tempting to use visual evoked potentials to differentiate between organic and non-organic vision loss, it should be noted that it is possible for patients to voluntarily modify their performance. An experienced technician should perform the test to make sure that the results are not falsely abnormal.
In counseling patients with suspected non-organic vision loss, the key is to focus the discussion on everything that the eye does well and provide reassurance that the eye has the capacity to make a full recovery. It may be tempting to refer these patients to another eye care provider or neurologist; however, in doing so, this can suggest to some patients that there may still be something wrong with their visual pathway that has yet to be elucidated. Many patients may not recover, and continuing follow-up with reassurance may be necessary.
- References:
- Gittinger JW Jr. Am J Ophthalmol. 1986;doi:10.1016/0002-9394(86)90600-8.
- Lim SA, et al. Ophthalmology. 2005;doi:10.1016/j.ophtha.2005.05.009.
- Sitko KR, et al. Ophthalmology. 2016;doi:10.1016/j.ophtha.2015.09.024.
- Thompson HS. Am J Ophthalmol. 1985;doi:10.1016/S0002-9394(14)75008-1.
- For more information:
- Edited by Jonathan T. Caranfa, MD, PharmD, and Angell Shi, MD, of New England Eye Center, Tufts University School of Medicine. They can be reached at jcaranfa@tuftsmedicalcenter.org and ashi@tuftsmedicalcenter.org.
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