Internal Medicine Board Review: Ophthalmology

Ophthalmology is one of the topics to understand for the USMLE Step 3, ABIM, and on other medical exams where internal medicine is a major focus. The following is an excerpt out ofCracking the USMLE Step 3.

Ophthalmology is a very specialized field that can get very complicated very quickly.  This field is full of a variety of pathology affecting the eye.  However, we have gone through all these disease states and have compiled the following diseases that are most common and have a higher likelihood of appearing on the USMLE Step 3 examination.  We have also included high quality pictures to add another dimension to this chapter.  Please read and enjoy.

Macular Pathology 

Age-Related Macular Degeneration (ARMD)

 

Exclusive visual from the Knowmedge QVault

• Painless loss of central vision
• See drusen (i.e., yellow deposits) in the macula on ophthalmoscopic exam
• Treatment is low-vision aids, antioxidants and sometimes laser photocoagulation to delay loss of vision in exudative macular disease

Optic Disc Pathology  

Closed-Angle Glaucoma (Acute Glaucoma)

• Acute onset -Typical history is person sitting watching a movie in dark theater with sudden blurry vision that is usually unilateral
• Signs and symptoms include:
  • Tender, hard eye
  • Red eye
  • Dilated pupil that is semi-responsive to light
• Obtain stat ophthalmologic consult
• Conduct tonometry (i.e., measure pressure in the eye) for diagnosis
• Treat with IV acetazolamide or acetazolamide eye drops
  • Carbonic anhydrase inhibitors – decrease the production of bicarbonate
• Can also give β blocker eye drops (i.e., timolol)
• Consider cholinergic eye drops (i.e., pilocarpine)
  • Never give anticholinergics to patients with glaucoma
• Definitive treatment is laser iridotomy

Open-Angle Glaucoma (Chronic Glaucoma)

• Occurs more gradually as vision is lost
• Painless
• Treatment is to decrease intraocular pressure with topical eye drops (i.e., acetazolamide, timolol, or pilocarpine)
  • Never give anticholinergics
• Definitive treatment is laser iridotomy

Lens Pathology 

Cataracts

• Clouding of the lens
• Patients may present with loss of visual acuity
• Requires ophthalmologic follow-up with slit-lamp examination
• Treatment is usually surgical if vision loss is progressive and discomforting

Presbyopia

• Difficulty for lens to focus
• Decrease in near-sightedness
• Presbyacusis – loss of hearing with age (i.e., usually high frequency sounds)

  Vessel Pathology 

Central Retinal Artery Occlusion

 

Exclusive visual from the Knowmedge QVault

• May be from emboli
• May be from atherosclerosis or Diabetes
• Sudden blurry vision or loss of vision in one eye
• Painless -May respond poorly to light, but will constrict abruptly when light shined in other eye
• See cherry red spot on the macula and a pale fundus
• Treat with thrombolysis if within 8 hours since symptom onset
• Consider IV acetazolamide or timolol to decrease intraocular pressure
• Prescribe aspirin daily
• If suspect may be secondary to temporal arteritis, start IV prednisolone immediately and schedule temporal artery biopsy

Central Retinal Vein Occlusion

• Visual loss is painless and occurs gradually
• Ophthalmologic exam is critical
  • Dilated tortuous veins
  • Retinal hemorrhages
  • Cotton-wool spots
  • Macular edema
• Treat with laser photocoagulation
  • Especially for diabetic retinopathy with neovascularization and branch retinal vein occlusion
• Prescribe aspirin daily

Amaurosis Fugax

 

Exclusive visual from the Knowmedge QVault

• Sudden, transient loss of vision
• Usually unilateral
• Described as a curtain coming down vertically over the visual field
• Caused by transient ophthalmic artery (i.e., branch off internal carotid artery) occlusion
• Ultrasound carotids to detect degree of stenosis
  • If greater than 70 % stenosis with symptoms (i.e., amaurosis fugax), carotid endarterectomy is indicated
• May also do Stenting or balloon angioplasty
• If carotid stenosis greater than 60 % and patient asymptomatic, carotid endarterectomy indicated
• Prescribe aspirin daily

NeuroOphthalmology 

Lesions along Visual Processing Circuit

• Lesion of Right Optic Nerve
  • Blindness in right eye
  • No reaction to light in right eye
  • Left eye does not constrict with light in right eye
• Lesion at Optic Chiasm
  • Patients present with bitemporal hemianopsia
  • Seen in pituitary tumors, craniopharyngiomas, or Rathke’s cleft cyst
• Lesion of Right Optic Tract
  • Causes a contralateral homonymous hemianopsia with loss of macular vision
• Lesion of Right Optic Tract in Meyer’s Loop in Temporal Lobe
  • Causes a left superior quadrantonopsia (i.e., “pie in the sky”)
• Lesion of Right Optic Tract in Parietal Loop in Parietal Lobe
  • Causes a left inferior quadrantonopsia
• Lesion in Right Occipital Lobe
  • Causes a left homonymous hemianopsia with macular sparing  Seen in posterior cerebral artery (PCA) distribution infarctions

  Tumor/Cancer 

Retinoblastoma

• Autosomal recessive
• Mutation of RB1 gene(Tyrosine kinase)
• Mutation on chromosome 13
• Most distinctive sign is leukocoria
  • White spot present in the patient’s pupil upon light testing
  • If detected on ophthalmoscopic exam, treatment is stat ophthalmology consult
• Treatment is enucleation

This post was originally posted on the Knowmedge Blog.