A 17-year-old boy is brought to the clinic due to poor vision at night. The patient developed mild difficulty seeing at night about 4 months ago, and it has slowly worsened. Visual field examination shows visual loss in the midperiphery. External eye examination reveals normal tear formation. Funduscopic examination shows bilateral optic disc pallor, attenuation of retinal vessels, and areas of dark discoloration in the retina. Which of the following is the most likely mechanism of this patient's visual impairment?

Question

A 17-year-old boy is brought to the clinic due to poor vision at night.  The patient developed mild difficulty seeing at night about 4 months ago, and it has slowly worsened.  Visual field examination shows visual loss in the midperiphery.  External eye examination reveals normal tear formation.  Funduscopic examination shows bilateral optic disc pallor, attenuation of retinal vessels, and areas of dark discoloration in the retina.  Which of the following is the most likely mechanism of this patient's visual impairment?

Quizplus · Accepted Answer

11ec160b_3b16_e4bb_9249_9d104a1c04cf_MD0001_00 This patient has poor night vision, visual field loss, and funduscopic changes (eg, pigment accumulation, optic disc pallor, retinal vessel attenuation) consistent with retinitis pigmentosa, a genetic disease characterized by progressive dystrophy of the retinal pigmented epithelium and photoreceptors (eg, rods, cones). Rods, which are highly metabolically active and most prevalent in the periphery, are affected first, leading to the initial manifestations of progressive night blindness and loss of peripheral vision. Early funduscopic changes include retinal vessel attenuation (ie, narrow vessels likely due to alterations in retinal metabolic demand) and a waxy, pale optic disc (due to optic nerve atrophy and gliosis). In advanced disease, loss of cones (most prevalent in the central retina) causes decreased central visual acuity. Degeneration of retinal pigmented epithelial cells releases pigment, which deposits in a characteristic bone-spicule pattern over the course of the disease. (Choice A) Retinoblastoma, which is caused by inactivation of both alleles of the RB1 gene (ie, 2-hit hypothesis), typically presents in the first 3 years of life with leukocoria (ie, white pupillary reflex), strabismus, and a creamy-white mass on funduscopic examination. (Choice C) Increased intracranial pressure can be associated with transient visual obscuration and decreased visual acuity. However, other symptoms (eg, headache, vomiting) are also typically present and papilledema with blurred optic disc margins would be seen on funduscopy. (Choice D) Angle-closure glaucoma occurs due to narrowing of the angle between the iris and the cornea, which blocks aqueous outflow. Patients typically have acute eye pain and vision loss with conjunctival erythema, cornea edema, and a mid-dilated, poorly reactive pupil. Optic nerve atrophy secondary to chronically increased intraocular pressure results in optic nerve cupping on funduscopy. (Choice E) Central retinal artery occlusion typically presents with unilateral painless acute vision loss in patients age >40 with thromboembolic risk factors (eg, hypertension). Retinal whitening and a cherry-red macula are the characteristic funduscopic changes. Educational objective: Retinitis pigmentosa is a genetic condition resulting in progressive dystrophy of retinal pigmented epithelium and photoreceptors. Patients typically present with progressive night blindness and loss of peripheral vision due to early loss of rods, which are highly metabolically active. Funduscopic examination may show dark pigments deposited in a bone-spicule pattern in addition to retinal vessel attenuation and optic disc pallor. __________ References: Retinitis pigmentosa. (http://www.ncbi.nlm.nih.gov/pubmed/30137803)

A 17-Year-Old Boy Is Brought to the Clinic Due to Poor