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Woman presents with decreased night vision
Exam showed mild arteriolar narrowing and healthy optic nerves.
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A 56-year-old Caucasian woman was referred from an outside office to the Neuro-ophthalmology service at the New England Eye Center for evaluation of decreased night vision. Her symptoms started about 2 months before her presentation, when she noticed spots of her vision were missing in dim lighting. The decreased vision progressed, and at the time of evaluation, she could not see to drive and required assistance with walking at nighttime. In bright lighting and during the daytime, she was asymptomatic. She had similar but milder symptoms about 1 year prior and felt they resolved spontaneously. Her vision was otherwise intact.
Her medical history was significant for obesity, hypertension, diabetes, severe anemia and basal cell carcinoma. Her surgical history was significant for Roux-en-Y gastric bypass in 2005 and then revision with limb distalization in 2013. Her ocular history was significant for corrected myopia and dry eye. At the time of presentation, her only medications were multivitamins, iron infusions and amlodipine.
Examination
Source: Eleni Konstantinou, MD, and Laurel Vuong, MD
Visual acuities were 20/20 in the right eye and 20/20-1 in the left eye. Pupils were equally round and reactive without an afferent pupillary defect. Extraocular movements were full, as well as confrontation visual fields. Color plates were normal in both eyes. IOP was 10 mm Hg in both eyes. Slit lamp examination was unremarkable with no evidence of cataracts. Dilated funduscopic examination showed clear vitreous, mild arteriolar narrowing and pink optic discs with a small cup-to-disc ratio. Retinal examination was unremarkable with no evidence of peripheral pigmentary changes or macular changes (Figure 1). OCT of the macula was unremarkable (Figure 2). Visual fields were normal. Full-field electroretinogram (ffERG) showed abnormal photoreceptor responses, with rods worse than cones (Figure 3).
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Decreased night vision
The differential diagnosis of decreased night vision (nyctalopia) is broad. Most commonly, it could be secondary to uncorrected myopia or cataracts. In cases of true nyctalopia, many congenital disorders can be considered, such as congenital stationary night blindness (CSNB), fundus albipunctatus, Oguchi disease and retinitis pigmentosa (RP). Choroideremia, gyrate atrophy and enhanced cone syndrome disease can also be included in the differential. In congenital disorders, nyctalopia usually presents at birth or at a young age. The fundi in CSNB can be normal, as well as in fundus albipunctatus in the early stages. In choroideremia, fundi have distinctive atrophic hypopigmented areas. Hyperpigmented fundi with lobular loss of the retinal pigment epithelium and choroid are unique for gyrate atrophy. In RP, fundus findings typically consist of arteriolar narrowing, waxy pallor of the disc and variable amounts of bone spicule-like pigment changes. However, pigment changes can be absent in a variant called RP sine pigmento. RP symptoms can also present later in life, but fundi will have the aforementioned abnormalities even in the absence of pigmentation.
Metabolic disorders such as vitamin A deficiency, abetalipoproteinemia and zinc deficiency are involved in acquired nyctalopia secondary to malabsorption and can present with a normal fundus exam. Other causes include paraneoplastic autoimmune retinopathies and autoimmune retinopathies. In the latter disorders, the signs, symptoms and radiographic findings will vary and depend on the antibodies that are generated against different retinal proteins.
Given the patient’s history of Roux-en-Y-gastric bypass surgery in 2005 and revision in 2013, vitamin A deficiency was suspected as the etiology of her visual symptoms. When we explained to the patient that we needed to check her vitamin A levels, she revealed she recently had blood work done that showed her levels were 5 µg/dL (normal levels 15 to 60 µg/dL). Her other lab work was normal. When she learned of the connection between the vitamin A levels and her visual symptoms, she recalled that when she was symptomatic the previous year, her vitamin A level was also low at that time, and after she received supplementation, her visual symptoms resolved.
Discussion
Vitamin A deficiency is the leading cause of childhood blindness in the developing world. In the United States, vitamin A deficiency can be a result of reduced intake (inadequate food supply, alcoholism, mental illness, dysphagia), impaired absorption (Crohn’s disease, celiac sprue, pancreatic insufficiency, short bowel syndrome, chronic diarrhea), disordered transport (zinc deficiency, abetalipoproteinemia) or liver disease. Malabsorption of vitamin A has been documented after bariatric surgery as well.
Vitamin A, a fat-soluble protein, gets absorbed in the small intestine, and it is commonly found in three forms: retinoic acid, retinol and retinaldehyde. Major sources of vitamin A (retinol) are vegetables (as beta carotene or pro-vitamin A) and meat (vitamin A). Within the intestinal mucosal cells, carotene is converted to retinol, and then it is esterified into palmitic acid. The latter travels through the lymphatic system to the liver where it gets stored. Under increased metabolic requirement for vitamin A, retinyl palmitate is hydrolyzed, and the reconstituted retinol travels via the bloodstream, attached to retinol-binding protein (RBP), to the target tissue. In this process, adequate body stores of zinc and protein are necessary for the formation of RBP, without which vitamin A cannot be transported to its target tissues.
Vitamin A has a pivotal role in immunity (activates T and B cells, helps with differentiation and proliferation of B and T cells) as well as in maintenance of specialized epithelium and vision. In the form of retinol or retinaldehyde, vitamin A combines with the protein opsin in the photoreceptors to create rhodopsin and to initiate the visual cycle. Overall, deficiency of vitamin A leads to night blindness with associated visual field changes and a depressed ffERG (abnormal rod and cone system). However, normal visual fields have also been reported.
Symptoms can be subtle initially and rapidly lead to a wide spectrum of ophthalmic manifestations that can occur years after any surgical procedure. Xerophthalmia is a term that is used to describe the spectrum of ophthalmic disorders that occur secondary to vitamin A deficiency. The first symptom is nyctalopia (night blindness). Conjunctival pathology follows. Absence of vitamin A and an inability to maintain a specialized epithelium, leads to loss of conjunctival goblet cells and squamous cell metaplasia. Thus, the conjunctiva becomes dry. Another ocular consequence is the appearance of Bitot’s spots, superficial foamy gray plaques found in the bulbar conjunctiva in the palpebral aperture. Keratomalacia is often associated with preceding systemic stressors such as measles or severe malnutrition. Retinal findings known as xerophthalmic fundus include numerous small yellow dots representing loss of pigment from the retinal pigment epithelium that are seen in the periphery. The WHO classifies the ocular surface changes into three stages: stage 1, conjunctival xerosis without (X1A) or with (X1B) Bitot’s spots; stage 2, corneal xerosis (X2); and stage 3, corneal ulceration involving less than one-third (X3A) or more than one-third (X3B) of the corneal surface. There is also corneal scarring (XS) and xerophthalmic fundus (XF).
The diagnosis is established by measuring the vitamin A levels. The treatment consists of different doses of vitamin A based on age and severity of symptoms. Vitamin A supplementation is given either orally or intramuscularly if there is a concern for severe malabsorption or corneal involvement requiring a faster recovery.
Improvement of Bitot’s spots is seen within 2 weeks of high-dose vitamin A therapy. However, the retinal manifestations of vitamin A deficiency are slower to respond to treatment. Night blindness and dark adaptation problems often persist for up to 4 weeks. Additionally, retinal function recovery varies from days to years after intramuscular supplementation. Cases have shown normalization of ERG testing within 12 days after the initiation of vitamin A therapy, but with a stable abnormal amplitude of macular flicker. This is attributed to the cones being more resistant to the deleterious effects of vitamin A deficiency; thus, it takes longer for full recovery. This finding highlights the importance of regular follow-up even after resolution of symptoms to further assess the visual prognosis and the risk for long- term retinal dysfunction.
Clinical course continued
Our patient experienced resolution of her symptoms within 2 weeks after oral supplementation.
- References:
- Braunstein A, et al. Lancet. 2010;doi:10.1016/S0140-6736(09)61874-2.
- Chae T, et al. Br J Ophthalmol. 2006;doi:10.1136/bjo.2006.092502.
- Genead MA, et al. Doc Ophthalmol. 2009;doi:10.1007/s10633-009-9200-y.
- Hansen BA, et al. Retin Cases Brief Rep. 2018;doi:10.1097/ICB.0000000000000441.
- Lee WB, et al. Ophthalmology. 2005;doi:10.1016/j.ophtha.2004.12.045.
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- For more information:
- Eleni Konstantinou, MD, and Laurel Vuong, MD, can be reached at New England Eye Center, Tufts University School of Medicine. 800 Washington Street, Box 450, Boston, MA 02111; website: www.neec.com.
- Edited by Adam T. Chin, MD, and Omar Dajani, MD. They can be reached at the New England Eye Center, Tufts University School of Medicine, 800 Washington St., Box 450, Boston, MA 02111; website: www.neec.com.