Pathogenesis of Disorders Leading to Blindness Flashcards
Cornea
Clear dome covering the iris and the pupil, does most of the focusing of light; covers the anterior chamber, dryer than bone.
Anterior chamber angle
the angle formed between the cornea and the iris where the aqueous fluid drains from the eye.
Crystalline lens
does the remainder of light focusing and in the long can change or thicken to focus something at near.
Ciliary body
supports the lens and produces aqueous fluid
Vitreous
jelly filling the back of the eye
Retina
many specific neural layers creating an electrical signal form light
Optic nerve
transmits light and images to the brain
Cataracts
A reduced transparency of the crystalline lens, which can result in a change in color (brown cataract), change in refractive index, or an increase in light scattering (opacification).
NOT A FILM ON THE CORNEA OF THE EYE.
The lens fiber continues thickening and can turn yellow; it cannot focus light, it scatters light instead, which decreases the light reaching the retina.
Cannot be treated with a laser, but are completely cured with surgery.
Leading cause of blindness worldwide; REVERSIBLE BLINDNESS.
Risk Factors: increased age (most common), smoking, diabetes, trauma or inflammation of the eye, exposure to sun and UV rays, corticosteroid medication, previous eye surgery.
Symptoms: normally slow and painless, decreased vision, glare, myopic shift (2nd sight), double vision when looking with one eye because of cataract, poor night vision, blurred vision, halos around objects, lack of color contrast or faded colors.
Observation and glasses can correct changes in refractive error.
Definitive treatment is surgery.
Age Related Macular Degeneration (AMD)
A gradual deterioration of the central retina (macula) with subsequent loss of function. It is also a major cause of IRREVERSIBLE BLINDNESS.
It only affects central vision and does not cause total blindness.
Dry ARMD: slow changes over time, few symptoms at first, mild progressive decrease in vision, end stage shows areas of no vision (geographic atrophy)-lost cells.
Cannot reverse.
Blood vessels from choroid leak under Bruch’s membrane into the retinal tissue.
As Bruch’s membrane thins, breaks, and becomes leaky, the retinal pigment epithelium goes.
Pigment clumping and geographic atrophy.
Drusen accumulation: waste products that weaken the wall.
Anti-oxidants and zin reduced likelihood of progression of intermediate and advanced degrees.
Blood vessels haven’t popped through yet.
Wet ARMD
Results from blood or serum leaking from newly formed blood vessels beneath the retina, which scar and lead to visual problems.
Blood vessels take advantage of the breaking membrane and pop through and lead and bleed.
Straight lines look wavy-metamorphopsia; main presenting symptom; dry AMD becomes wet AMD.
Treatment: intravitreal injection; inject patients with medication that makes blood vessels shrivel and go away.
Thermal laser, photodynamic therapy (cold laser).
Poor prognosis, limited recovery and high recurrence rate.
Risk Factors for AMD: Age above 50, cigarette smoking, Family history (strongest, although not inherited in Mendelian fashion), increased exposure to UV, white race and light eyes, hypertension and CV disease, lack of dietary intake of antioxidants and zinc.
Glaucoma-Optic Nerve Disease
The ciliary bodies make fluid that goes around helens and the surface of the iris and creeps out a structure called the angle; the angle between the cornea and the iris.
Caused by increase pressure i the anterior chamber of the eye that is precipitated by an alteration in the natural flow of aqueous humor out of the anterior chamber.
Open-angle Glaucoma: Blocked aqueous fluid flow causes an increased intraocular pressure, which damages the optic nerve and leads to vision loss.
There is a place for the fluid to draw, it is just blocked up.
Pressure cups out the nerve at the back of the eye.
Little hemorrhage on the nerve.
No signs/symptoms in he early stages.
Loss of peripheral vision in earlier stages.
Irreversible diminished visual activity at the end stages; it goes from tunnel vision to black.
Closed-angle glaucoma: Results from the angle of the iris obstructing the drainage of the aqueous fluid, which increases the intraocular pressure and leads vision changes.
The iris is pushed up and blocking the angle.
Can result from dialing drops, systemic meds, certain lighting conditions.
Sudden onset of severe eye pain.
Unilateral headache
Halos around lights
Nausea and vomiting
Blurred vision
Photophobia
This is an ophthalmic emergency!
Dilated pupil because the the muscle is ischemic from so much pressure.
Risk factors: small anterior chamber (closed), increased intraocular pressure (both), older than 60 (both), family history of glaucoma (open), African American ancestry (open), Far-sightedness (close) because the eye is small, compact, and short and there is little space in the anterior chamber.
Treatment: can be maintained for life with drops, laser to clean out drain or accessory drain by surgery if laser doesn’t work.
Diabetic Retinopathy
A response to poor blood glucose control that is seen eventually in most individuals with diabetes mellitus.
Occurs from microvascular disease of the eye, which impairs the transportation of oxygen and nutrients into the eye.
Background diabetic retinopathy or non-proliferative diabetic retinopathy-blindness can results from leakage of serum into the macular retina (diabetic macular edema).
The blood vessels in the eye become damaged from diabetes.
Hemorrhages, cotton wool spots (ischemic white spots), micro aneurysms, which leak and impair vision.
Lipoprotein that leaks out.
Proliferative diabetic retinopathy-characterized by the growth of abnormal new vessels on the surface of the retina, these can bleed into the retina or vitreous.
Damaged blood vessels from diabetes least retinal ischemia, which decreases the blood and nutrient supply to the retina.
New blood vessels form where they aren’t supposed to be, which are very fragile and leak, so vision is obscured.
The blood vessels are not int he retina, they often grow up into the vitreous jelly cavity; hemorrhage here and get back blotches of blood clots here.
Risk factors: duration of disease, hyperglycemia (poor control), proteinuria (renal disease), hypertension, gender, race, genetics, age at exam, age at diagnosis, serum lipids, pregnancy, smoking cigs, alcohol, SES.
Leading cause of blindness underage 65, 2nd leading cause of new blindness.
Symptoms: progressive disease, gradual vision loss, generalized blurring, areas of focal vision loss (big black blotches).
Major causes of vision loss: Macular edema (NPDR)
Vitreous hemorrhage (PDR)
Treatment: very treatable! Laser surgery, you kill off the peripheral retina, so there is less retina to need oxygen and less of a drive to make new blood vessels in PDR.
Injected steroids or anti vegF antibodies, Regular eye exam, Hgb A1c every 3 months for tight glycemic control, hyperlipidemia treatment, smoking cessation, bp control.
Ocular Tumors
Ocular melanoma is the most common primary ocular tumor in adults.
It can metastasize with fatal results.
Treatment is controversial with enucleation vs radiotherapy.
Retinoblastoma is the most common childhood ocular tumor; white pupil.
See rosettes: islands of blue tumor in a sea of pink necrosis; tumor is not good at getting a blood supply, so it dies off when it is far from it.
Potentially fatal
If detected early, enucleation and chem associated with a good prognosis for long term survival.
Metastatic other tumors elsewhere in the body can metastasize to the eye through the choroidal circulation typically; visual loss can be a presenting problem with ths.
Primary neoplasms can also occur in the orbit, lacrimal gland, and eyelids.
Infectious Causes of Worldwide blindness
Trachoma- mycoplasmal conjuctivitis carried by flies; causes scarring and inward turning of the eyelids with eventual corneal scarring; if caught early, can be treated with antibiotics; caused by chalmidya bacteria, also causes pink eye (conjunctivitis); scar which causes blindness in trachoma.
Onchocerciasis or river blindness; prevalent in sub-Saharan Africa; a worm infestation carried by flies.
Onchocerca volvulus; worm, parasite, infected blackfly, so much inflammation when the worms crawl across the eye that you get the scarring problem that can progresso blindness.
HIV- in and of itself can cause retinopathy like non-proliferative diabetic retinopathy; ischemic and hemorrhage spots.
Opportunistic infections in AIDS: CMV (cytomegaloviral) retinopathy: most common serious ocular complication of AIDS and can lead to total blindness though it can be controlled with antiviral medications.
Retinal detachments due to CMV can now be treated surgically.
Herpes zoster
Herpes Simplex
Toxoplasmosis
Xerophthalmia is a loss of mucus-screting conjunctival goblet cells caused by childhood vitamin A deficiency.
Trauma: bleeding (front, fluid, jelly, under in retina), blunt trauma, penetrating trauma.
Age Related eye changes
Corneal endothelium is lost; these cells pump fluid out of the cornea to keep it clear; if there is accelerated loss of these cells with findings of gluttata= Fuch’s dystrophy.
The lens becomes more dense (produces lens fibers), more brunescent (brown and opaque), and thicker; much less pliable resulting in presbyopia (inability to see as one ages).
