Can malabsorption night blindness affect only one eye?

Malabsorption-Related Night Blindness Does Not Affect Only One Eye

No, malabsorption-related night blindness from vitamin A deficiency is a bilateral (both eyes) condition, not unilateral. Vitamin A deficiency affects the entire body's vitamin A stores and impacts both retinas equally, causing symmetric bilateral visual dysfunction 1, 2.

Why Night Blindness from Malabsorption is Bilateral

Vitamin A deficiency from malabsorption is a systemic nutritional deficiency that affects both eyes simultaneously because:

• Serum retinol (vitamin A) circulates throughout the body and supplies both retinas equally 2, 3
• Rhodopsin synthesis, which is essential for rod photoreceptor function and night vision, becomes impaired bilaterally when vitamin A stores are depleted 2, 3
• The pathophysiology involves insufficient substrate for visual pigment regeneration in both eyes, not a localized ocular problem 1, 4

Clinical Presentation Pattern

Night blindness (nyctalopia) presents as the earliest symptom of vitamin A deficiency and affects both eyes 2, 5:

• Patients report progressive bilateral difficulty seeing in dim lighting or at night 5, 6
• Dark adaptation becomes impaired in both eyes, typically reduced by 1-2.5 log units bilaterally 3
• Electroretinogram (ERG) testing demonstrates bilateral scotopic (rod) response abnormalities, ranging from reduced oscillatory potentials to completely extinguished rod responses 5, 3, 6

Important Clinical Pitfall

If a patient presents with unilateral night blindness, vitamin A deficiency from malabsorption is NOT the diagnosis—look for other causes 1:

• Unilateral night vision loss suggests localized ocular pathology (retinal disease, optic nerve disease) or neurological conditions, not nutritional deficiency 1
• Cancer-associated retinopathy (CAR) can mimic vitamin A deficiency but may present asymmetrically and should be considered in patients with malignancy 4
• True vitamin A deficiency always produces bilateral symmetric findings on examination and ERG testing 3, 6

High-Risk Populations for Malabsorption

Patients at highest risk for developing bilateral night blindness from vitamin A malabsorption include 2, 5:

• Post-bariatric surgery patients, especially after malabsorptive procedures (BPD/DS, RYGB) 1, 5
• Short bowel syndrome from intestinal resections 2, 5, 6
• Cystic fibrosis patients 2, 5
• Chronic liver disease and hepatopathy 2, 5
• Patients on octreotide treatment 5
• Crohn's disease with multiple bowel resections 6

Diagnostic Approach When Night Blindness is Reported

When evaluating night blindness in at-risk patients, obtain bilateral assessment 1, 5:

• Check serum vitamin A levels (normal range 400-700 ng/ml or 20-120 µg/dL) 1, 4, 6
• Perform bilateral dark adaptation testing 3, 6
• Obtain full-field electroretinogram showing bilateral scotopic responses 5, 6
• Document visual acuity in both eyes (often remains normal initially, typically 20/20 to 20/40) 5

Treatment Restores Bilateral Function

Vitamin A supplementation reverses night blindness bilaterally when initiated promptly 7, 3:

• Adults with deficiency: 10,000-25,000 IU oral vitamin A daily for 1-2 weeks 7
• Night vision improvement occurs within 7 days of treatment in both eyes 4
• ERG normalization and dark adaptation recovery occur bilaterally over weeks to months 3, 4
• Recheck vitamin A levels at 3 months after treatment 7