WBR0149

Author	[[PageAuthor::Rim Halaby, M.D. [1]]]
Exam Type	ExamType::USMLE Step 1
Main Category	MainCategory::Biochemistry
Sub Category	SubCategory::General Principles
Prompt	[[Prompt::A 35-year-old female presents to her ophthalmologist for a decrease in vision. Over the past month she has experienced increasing difficulty distinguishing objects, especially when driving home from work at night. She denies any family history of ocular disease, reporting only hypertension in her father and dyslipidemia in her mother. Physical exam is unremarkable except for dry skin and fine hair. What is the most likely diagnosis?]]
Answer A	AnswerA::Diabetic retinopathy
Answer A Explanation	[[AnswerAExp::Diabetic retinopathy is the most severe retinal complication of diabetes. Up to 80% of all diabetics who have had diabetes for more than 18 years develop diabetic retinopathy. It is the leading cause of non-traumatic blindness in adults. People with untreated diabetes are 25 times more likely to develop blindness than the general population. However, this patient is young and neither her medical history nor her symptoms suggest the presence of diabetes.]]
Answer B	AnswerB::Glaucoma
Answer B Explanation	[[AnswerBExp::Glaucoma is a group of diseases of the optic nerve involving loss of retinal ganglion cells in a characteristic pattern. Although raised intraocular pressure is a significant risk factor for developing glaucoma, there is no established threshold intraocular pressure that causes glaucoma. One person may develop nerve damage at a relatively low pressure, while another person may have high eye pressure for years and never develop damage. Untreated glaucoma leads to permanent damage of the optic nerve and resultant visual field loss, which can progress to blindness. This patient has no history of conditions such as ocular trauma or uveitis that would increase clinical suspicion for glaucoma.]]
Answer C	AnswerC::Cataract
Answer C Explanation	[[AnswerCExp::A cataract is an opacity that develops in the crystalline lens of the eye or in its envelope. Cataract can be caused by advanced age and diabetes among other causes. However, this patient is young and the history does not suggest the presence of cataract.]]
Answer D	AnswerD::Nutritional deficiency
Answer D Explanation	[[AnswerDExp::Night blindness is one of the first signs of vitamin A deficiency. Vitamin A deficiency is common in developing countries but rarely seen in developed countries.]]
Answer E	AnswerE::Genetic disease
Answer E Explanation	[[AnswerEExp::Genetic causes of blindness include: Leber's congenital amaurosis, Leber's hereditary optic neuropathy, retinoblastoma and albinism. This patient has no family history of blindness or albinism. Furthermore, she is older than the typical age of onset of all of the above conditions.]]
Right Answer	RightAnswer::D
Explanation	[[Explanation::The patient in this vignette is suffering from Vitamin A deficiency. Vitamin A deficiency is common in developing countries but rarely seen in developed countries. Night blindness is one of the first signs of vitamin A deficiency. Vitamin A is a critical precursor involved in the synthesis of rhodopsin, the eye pigment responsible for sensing light. Rhodopsin is composed of retinal (an activated form of vitamin A) and opsin (a protein). When vitamin A is not present in sufficient quantities, deficiency of retinal leads to deficiency of fully assembled rhodopsin. The eye is now more poorly suited to adapt to low-illumination scenarios, resulting in night blindness. In addition to its essential structural role in rhodopsin, vitamin A is necessary for cellular differentiation in the immune system and maintenance of the skin epithelium. As a result, vitamin A deficiency is associated with dry, thickened skin and increased risk of infection, particularly with measles. The role of vitamin A in cellular differentiation is highlighted most clearly by the fact that acute promyleocytic leukemia is caused by a translocation of the retinoic acid (a metabolite of vitamin A) receptor, which induces a differentiation block in myeloid progenitors. This condition can be treated successfully with a combination of all-trans-retinoic acid and arsenic. Educational Objective: Vitamin A deficiency is associated with night blindness, skin changes and increased risk of measles. References: First Aid 2014 page 92]]
Approved	Approved::Yes
Keyword	WBRKeyword::Eye, WBRKeyword::Opthalmology, WBRKeyword::Blindness, WBRKeyword::Vitamin, WBRKeyword::Nutrition, WBRKeyword::Vision loss
Linked Question	Linked::
Order in Linked Questions	LinkedOrder::