A patient presents with a gradual loss of night vision and peripheral vision. What is the most likely diagnosis based on fundoscopy findings? er

Correct Answer: C. Retinitis pigmentosa

Retinitis pigmentosa (RP) is a progressive, inherited dystrophy of photoreceptors characterized by the pathognomonic triad of night blindness (nyctalopia), progressive peripheral visual field loss, and bone-spicule pigmentation on fundoscopy. The disease begins with rod photoreceptor degeneration, causing early night vision loss, followed by progressive cone involvement leading to central vision loss and color blindness in later stages. Fundoscopy reveals the classic "bone-spicule" appearance—dark pigmentation in a bone-spicule pattern in the mid-periphery, waxy optic disc pallor, and attenuated retinal vessels. The patient's presentation of gradual night vision loss followed by peripheral vision loss is the hallmark natural history of RP. Electroretinography (ERG) shows extinguished or severely reduced responses, confirming photoreceptor dysfunction. RP is often associated with systemic conditions (Kearns-Sayre syndrome, Refsum disease, Usher syndrome) and requires genetic counseling. Indian prevalence is approximately 1 in 4,000 live births, making it a significant cause of inherited blindness in the Indian population.

Why the other options are wrong

A. Diabetic retinopathy — Diabetic retinopathy typically presents with microaneurysms, dot-blot hemorrhages, and hard exudates rather than bone-spicule pigmentation. Vision loss in diabetes is usually central (from macular edema) or sudden (from vitreous hemorrhage), not the insidious peripheral-then-central pattern of RP. Night blindness is not a feature of diabetic retinopathy. This is a common trap because both are progressive retinal diseases, but the fundoscopic findings and symptom pattern are entirely different. B. Retinal hemorrhage — Retinal hemorrhage is an acute or subacute event causing sudden vision loss or floaters, not gradual progressive night blindness and peripheral field loss over months to years. Fundoscopy shows red or dark hemorrhagic areas, not pigmentary changes. Hemorrhage is a sign of another disease (diabetes, hypertension, trauma, vascular occlusion), not a primary progressive dystrophy. The chronic, progressive nature of the patient's symptoms rules out hemorrhage as the primary diagnosis. D. Hypertensive retinopathy — Hypertensive retinopathy presents with flame hemorrhages, cotton-wool spots, hard exudates, and papilledema in acute malignant hypertension, or mild arteriolar narrowing in chronic disease. Night blindness and bone-spicule pigmentation are not features. Vision loss in hypertensive retinopathy is usually related to macular involvement or optic nerve head changes, not peripheral field loss from photoreceptor degeneration. The absence of systemic hypertension signs and the specific pattern of night blindness followed by peripheral loss excludes this diagnosis.

High-Yield Facts

Mnemonics

RP Triad: N-P-B** Night blindness (early), Peripheral field loss (progressive), Bone-spicule pigmentation (fundoscopy). Use this to recall the classic presentation and fundoscopic findings in one breath. RP vs Diabetic: SPICE vs MEAD RP = Spicule pigmentation, Peripheral loss, Inherited, Cone later, ERG extinguished. Diabetic = Microaneurysms, Exudates, Acute/central, D**iabetes history. Quick way to differentiate at the bedside.

NBE Trap

NBE often pairs progressive vision loss with diabetic retinopathy because both are common and progressive; students may confuse the symptom pattern. The key discriminator is that RP starts with night blindness and peripheral loss, while diabetes causes central/macular loss first and sudden vision loss from hemorrhage. The bone-spicule pigmentation is pathognomonic for RP and absent in diabetes.

Clinical Pearl

In Indian clinical practice, a young patient (often <30 years) presenting with night blindness and asking "why can't I see at dusk?" should immediately raise suspicion for RP, especially if there is consanguinity or family history of blindness. Early diagnosis allows genetic counseling and family screening, which is crucial in the Indian context where autosomal recessive RP is most common.

_Reference: Robbins Ch. 29 (Retina); Harrison Ch. 427 (Disorders of Vision); Bailey & Love Ch. 37 (Ophthalmology)_