This week, we are sharing another USMLE® Step 1-style practice question to test your knowledge of medical topics. Today’s case focuses on a 21-year-old man who has noticed some difficulty reading textbooks or viewing text on his laptop screen. Can you figure it out?
A 21-year-old man presents to his primary care physician for a routine evaluation. The patient has noticed some difficulty seeing presentation slides during his college lectures. He has not experienced difficulty reading textbooks or viewing text on his laptop screen. He is otherwise healthy and does not take any medications. Vital signs are within normal limits, and visual acuity is noted to be 20/30 bilaterally. Which of the following is the most likely diagnosis?
A. Hyperopia
B. Acute closed-angle glaucoma
C. Astigmatism
D. Presbyopia
E. Myopia
The correct answer to today’s USMLE® Step 1 Question is…
E. MyopiaBefore we get to the Main Explanation, let’s look at the incorrect answer explanations. Skip to the bottom if you want to see the correct answer right away!
Incorrect answer explanations
The incorrect answers to today’s USMLE® Step 1 Question are…
A. Hyperopia
Incorrect: Hyperopia is defined by the presence of farsightedness. This patient, on the other hand, has difficulty seeing distant objects and likely has myopia (nearsightedness).
B. Acute closed-angle glaucoma
Incorrect: Acute closed-angle glaucoma often presents with severe eye pain, eye redness, and a dilated pupil.
C. Astigmatism
Incorrect: Astigmatism is an abnormal curvature of the cornea. The condition manifests with difficulty seeing both near and far objects.
D. Presbyopia
Incorrect: Presbyopia, also termed age-related nearsightedness, occurs due to changes in the lens’s curvature, a decline in lens elasticity, and a decrease in ciliary muscle strength. Symptoms of presbyopia generally manifest around the age of 40 and can be treated with magnifying reading glasses. In contrast, this patient is in his 20s and is unlikely to have presbyopia.
Main Explanation
This young adult presents with difficulty seeing distant objects but not near objects. He likely has myopia, which can be treated with the application of concave lenses.
Normally, as light enters the eye, the lens bends the light so that the optical image is clearly focused on the retina. When the cornea and lens fail to optimize this focus, a distortion or blurring of the image can occur. With hyperopia (far-sightedness), the axial length of the eye is too short for the refractive power of the cornea and lens. Thus, the image is focused behind the retina. This refractive error can be corrected with a convex (converging) lens. In contrast, myopia (near-sightedness) occurs when the axial length of the eye is too long for the refractive power of the cornea and lens. These abnormalities cause the image to be focused in front of the retina. Treatment for myopia involves the application of a concave (diverging) lens.
Lastly, astigmatism refers to an abnormal curvature of the cornea, which causes light rays entering the eye along different planes to be focused unevenly, resulting in distortion of vision at all distances. Treatment involves the application of a cylindrical lens.
Major Takeaway
Myopia occurs when the eye’s axial length is too long for the refractive power of the cornea and lens. The condition results in difficulty seeing distant objects since the image ends up being focused in front of the retina. Treatment involves the application of a concave lens.
References
Daiber, H.F., Gnugnoli, D.M. (2020) “Visual acuity”. StatPearls [Internet]. Web Address: https://www.ncbi.nlm.nih.gov/books/NBK563298/.
Lawrence, M.S., Azar, D.T. (2002) Myopia and models and mechanisms of refractive error control. Ophthalmology Clinics of North America. 15(1),127-133. Doi: 10.1016/s0896-1549(01)00002-5.
Wallman, J., Winawer, J. (2004) Homeostasis of eye growth and the question of myopia. Neuron. 43(4), 447-468. Doi: 10.1016/j.neuron.2004.08.008.
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