A 19-year-old man presented with worsening peripheral visual field loss in his right eye greater than his left eye over 8 months. He also complained of hemeralopia and photophobia. His medical history was otherwise negative, and his medications included cetirizine and montelukast sodium for seasonal allergies. The family history was negative for ocular disease, and social history was negative for drug and alcohol use. He had undergone a thorough evaluation including contrasted, fat-suppressed magnetic resonance imaging of the brain and orbits, computed tomographic angiography, cerebrospinal fluid analysis, and multiple hematological studies.
The visual acuity was 20/20 in each eye with normal color vision. Automated visual fields showed generalized constriction in the right eye and a temporal defect in the left eye (Fig. 1). Pupils were isocoric at 5 mm with normal reactivity and no relative afferent pupillary defect. Ocular motility and trigeminal and facial nerve functions were normal. Anterior segment and funduscopic examinations showed no abnormality (Fig. 1). Visual evoked potentials were normal. Multifocal electroretinography (mfERG) showed well-preserved local responses in the central retina and severely reduced responses in the perifoveal retina (Fig. 1) corresponding to the visual field defects. Full-field ERG disclosed normal scotopic responses in both eyes but diminished photopic amplitudes (Fig. 2). Macular optical coherence tomography with autofluorescence revealed loss of the intensity of the ellipsoid zone in the macula corresponding to the regions of signal loss on the mfERG (Fig. 3). The ABCA4, BEST1, ELOVL4, PROM1, RDS–sequencing panel using polymerase chain reaction amplification for Stargardt disease was negative. The patient was diagnosed with peripheral cone dystrophy.
Cone dystrophy refers to a group of genetically heterogeneous disorders with fundus appearance ranging from normal to mild pigmentary mottling to bull's eye maculopathy (1). Patients typically experience a progressive decline in visual acuity and color vision and aversion to bright light. On ERG, the cone system initially is affected; and in advanced disease, the rod system becomes involved (1). Cone dystrophy can be further subdivided into central and peripheral forms. In both, the cone system is predominately impaired with preservation of the rod system and lack of fundus changes on ophthalmoscopy (2). Central cone dystrophy, also named occult macular dystrophy, may be sporadic or dominantly inherited and affects only the macular cones, sparing the macular rods (2,3). Peripheral cone dystrophy, the rarer of the 2 types, involves only the perifoveal cones, sparing the central cones (1).
Peripheral cone dystrophy, like central cone dystrophy, presents with photophobia, hemeralopia, and visual field loss. Because the peripheral cones are affected, visual acuity and color vision are preserved.
Because of its rarity, peripheral cone dystrophy may be misdiagnosed as acute idiopathic blind-spot enlargement or functional visual loss. Recent technological advances, particularly mfERG, have facilitated the diagnosis of peripheral cone dystrophy (1–3). Our case illustrates a striking correlation between visual field depression and mfERG attenuation in the peripheral retina whereas central recordings are preserved in the setting of a normal fundus (Fig. 1). Peripheral cone dystrophy should be kept in the differential diagnosis of patients with peripheral field loss who complain of hemeralopia and photophobia. With clinical suspicion and wider access to mfERG, this entity may no longer be a diagnostic improbability.
1. Lam BL. Electrophysiology of Vision: Clinical Testing and Applications. Boca Raton, FL: Taylor and Francis Group, 2005.
2. Kondo M, Miyake Y, Kondo N, Ueno S, Takakuwa H, Terasaki H. Peripheral cone dystrophy: a variant of cone dystrophy with predominant dysfunction in the peripheral cone system. Ophthalmology. 2004;111:732–739.
3. Mochizuki Y, Shinoda K, Matsumoto CS, Klose G, Watanabe E, Seki K, Kimura I, Mizota A. Case of unilateral peripheral cone dysfunction. Case Rep Ophthalmol. 2012;3:162–168.