Visual loss pathology

Question 1

Major causes of vision loss

Answer 1

• Age-related macular degeneration
• Glaucoma
• Cataracts
• Diabetic retinopathy

Question 2

Age-related macular degeneration (AMD)

Answer 2

• Senescence and dysfunction of the retinal pigment epithelium (RPE), accompanied by sub retinal drusen deposits, and occasional choroidal neovascularization
• Vision loss due to dysfunction of photoreceptors (receive nutrients from choroid along w/ RPE)
• 2 types: dry and wet (exudative) AMD
• Symptoms: blurry vision, mostly in central vision (central scotoma)

Question 3

Dry AMD

Answer 3

• 90% of AMD cases
• Drusen deposits accumulate btwn RPE and bruch’s membrane near macula
• Atrophy of RPE results in visual loss (photoreceptor dysfunction), areas of atrophy result in coalescing “geographic atrophy” around macula
• Rx: antioxidants, regular exams, stem cell Rx in the works

Question 4

Wet AMD

Answer 4

• 10% of AMD cases
• New abnormal vessels grow from choroidal circulation into subretinal space
• These form choroidal neovascular membranes (CNVM)
• Subretinal fluid accumulates and subretinal hemorrhage and scaring occurs
• All lead to loss of photoreceptors and vision
• Rx: anti-VEGF, lasers

Question 5

Glaucoma

Answer 5

• Increase in intraocular pressure (IOP) that eventually leads to damage to ganglion cell axons at the optic nerve head and resultant vision loss
• Results from an obstruction of flow for the aqueous humor (usually around the canal of schlemm)
• 2 types: primary open angle (POAG) and acute closed angle (ACAG)

Question 6

Primary open angle glaucoma (POAG)

Answer 6

• Slow progression (chronic), asymptomatic until late stage
• Due to blockage of schlemm or trabecular meshwork leading to inability to drain aqueous humor
• Increase IOP, damages ganglion cells and vascular supply
• Generally bilateral
• Symptoms: visual field loss and blurry vision, halos around lights
• Rx: decrease aqueous humor production w/ beta (b1) blockers, carbonic anhydrase inhibitors, a1 agonists
• Can also increase outflow by using cholinergics and prostaglandin analogs

Question 7

Acute closed angle glaucoma (ACAG)

Answer 7

• Acute and abrupt blockage of aqueous outflow
• Shallow anterior chamber predisposes to this, since iris is in close proximity to cornea
• Pupillary dilation can precipitate an attach because it increases tightness of contact btwn iris and lens
• Fluid must flow btwn lens and iris, around iris, then btwn iris and cornea. A blockage anywhere in this path results in ACAG
• Symptoms: nausea, vomiting, pain
• Rx: cholinergics to constrict pupil, osmotic agents (glycerol, mannitol) to decrease IOP, laser iridectomy to increase outflow

Question 8

Cataracts 1

Answer 8

• Due to lens opacities that impede vision
• Cortical degeneration: opacities that radiate around the periphery of the lens, caused by swelling and liquefaction of younger cortical fiber cells
• Nuclear sclerosis: opacity of central area of lens often w/ lens discoloration, caused by deterioration of older lens fibers

Question 9

Cataracts 2

Answer 9

• May result from systemic diseases (diabetes) and are correlated w/ UVB exposure
• Present w/ blurry vision and glare, double vision (monocular diplopia), near-sightedness (myopia), and second sight (need for reading glasses disappears due to myopia)
• Management: extraction of lens and replacement when severe and affecting daily lives

Question 10

Diabetic retinopathy (DR)

Answer 10

• Diabetes affects retinal vasculature (specifically the venous side of retinal capillary beds), and is a venous occlusive disease
• The resulting damage to retina leads to visual loss
• 2 types: proliferative and non-proliferatvie
• Both are chronic diseases
• Sx: blurry vision, dark floaters, visual field loss, poor night vision

Question 11

Non-proliferative DR

Answer 11

• Venous dilation accompanied by micro aneurysms in venous capillaries (+ exudate)
• Microaneurysms result in dot-blot appearance of retina as veins are deep in the retina (AV nicking)
• Cotton wool spots: patches of lost retina
• Macular edema (loss of central vision, lost vision can be in patches)
• Rx: controlling diabetes/HTN, lasers

Question 12

Proliferative DR

Answer 12

• Areas of retinal neovascularization which extend into vitreous and bleed
• Vitreous scaffolds areas of neovascularization
• Accompanied by exudates
• Retinal detachment may occur
• Also may get recurrent vitreous hemorrhage
• Rx: anti-VEGF and lasers, along w/ controlling diabetes