There are about 9 different etiologies that contribute to eye pathology. See if you can recall them.
Other (organs, etc)
Try to recall the components of the eye exam.
How is the pediatric eye exam approached?
Visual acuity & fields, pupil exam, extraocular movements, intraocular pressure, slit-lamp and fundus exams.
Done under anesthesia (good luck getting a 2yo to fixate). Also get corneal thickness, ultrasound (OCT?), and dilated fundus imaging.
Recall the five layers of the cornea.
What functions does it serve?
Epithelium > Bowman's membrane > Stroma > Descemet's membrane > Endothelium
It must be transparent, provides the majority of refraction (~50D), and helps maintain structure.
What is the composition of the corneal stroma?
What function is served by the corneal endothelium?
Type 1 collagen and keratinocytes, arranged in parallel bundles to preserve transparency.
Pumps out water from the corneal stroma.
How does the cornea respond to a superficial injury?
What is the outlook for a deep corneal injury?
Epithelial hyperplasia and full repair.
The outlook for any injury that penetrates the stroma is bad--the repair response will form a scar (Type 4 collagen, blood vessels) that will reduce or destroy vision.
Describe the different subtypes of Peter's anomaly.
Type I - Iridicorneal adhesions
Type II - Corneolenticular adhesions
"Peter's-Plus" - In association with syndrome of short stature, delayed development, characteristic facial features...
*All feature corneal opacification, often bilateral.
What corneal structure is most damaged in Peter's anomaly?
What can cause it?
The endothelium & Descemet's membrane.
Can be sporadic, but sometimes seen with PAX6 mutations.
Describe the epidemiology of Fuch's corneal dystrophy.
What would be seen on histology?
Autosomal dominant inheritance, yet has a female predilection. Disease onset in 50s.
Proliferation of endothelium/descemet's membrane (guttae), eventually progressing to endothelial loss. Thickened cystic stroma, hazy overall.
Describe the structure and function of the lens.
The lens is a transparent and biconcave structure suspended by zonule fibers. It is divided into an epithelium, capsule, and fiber cells.
It functions in accommodation--can change shape to facilitate focusing.
Describe the internal composition of the lens.
What is a cataract?
Contains highly organized, long & thin cells full of crystallin. Older cells found centrally.
A cataract is a clouding of the lens.
What are the ocular consequences of a prenatal rubella infection?
Rubella can infect the fiber cells, causing inappropriate proliferation.
Cataract forms (initially focal, then complete).
Retinopathy results from RPE damage ("Salt & pepper", vision OK)
Other anomalies (deafness, heart disease, microcephaly, hepatomegaly...review lecture on TORCH)
Besides congenital Rubella infection, what else can cause cataracts?
Age (from UV radiation; more or less inevitable!)
What is the function of the retina?
Try to recall its layered structure.
The retina converts light into neuronal impulses. It's the "seeing" part of the eye.
Comprised of 11 layers (probably don't need to know them, but: Internal limiting membrane, nerve fiber layer, ganglion cell layer, inner plexiform layer, inner nuclear layer, outer plexiform layer, outer nuclear layer, external limiting membrane, photoreceptor outer & inner layers, retinal pigment epithelium)
What is the RPE?
What functions does it serve?
Retinal pigment epithelium; the dark squamous layer deep to the photoreceptor layer.
Absorbs stray light, forms the blood-retinal barrier, supplies nutrients and eliminates waste. Also involved in the retinal cycle (restores all-trans-retinal to 11-cis-retinal by phagocytosing PR outer segments)
Besides photoreceptors, what other neurons are present in the retina?
What structures do they ultimately signal to?
Bipolar cells, ganglion cells, horizontal cells, amacrine cells, and Muller cells (glia).
The thalamus, hypothalamus, midbrain, and lateral geniculate nuclei
What is retinitis pigmentosa?
What is the most common defect caused?
A broad collection of heritable retinal degenerative conditions.
Discussed in class was a mutation in rhodopsin in which the opsin protein misfolded, reducing outer segment cycling.
What is the inheritance pattern of retinitis pigmentosa?
What is it associated with?
As this is a heterogeneous disease, there are variants with just about every inheritance type.
May be isolated, syndromic (eg Usher's disease), or secondary to other diseases (eg Refsum's disease)
What is the difference between dry and wet AMD?
Dry: Drusen form in the outer retinal layers, causing loss of RPE and photoreceptors.
Wet: Choroidal vessels breach Bruch's membrane to enter retina, can cause bleeding and further loss.
Describe the pathophysiology of Retinopathy of Prematurity.
How can it be treated?
The anterior retina is normally supplied by the central retinal artery; premature birth before this can occur causes abnormalities of the extending vessels which can bleed or cause retinal detachment.
Treatment: Laser therapy (burn the retina in place), anti-VEGF therapy (bevacizumab, presumably)
In diabetic retinopathy, hyperglycemia leads to loss of _____ which promotes bleeding--this manifests on fundus imaging as ________. Areas of nonperfused retina produce ______ causing spread of vessels, which may ultimately contract causing ________.
Microaneurysms, dot-blot & flame hemorrhages
Central retinal artery occlusion, also known as CRAO, tends to result from what conditions?
How is its outlook?
Atherosclerosis, especially of the internal carotid artery.
Not great; vision rarely recovers and it signals increased morbidity due to the atherosclerosis.
What is the only discussed retinal tumor?
Distinguish between the sporadic and hereditary forms.
What are the distinctive clinical and pathologic findings?
Sporadic is usually unilateral, while hereditary (AD) can be bilateral. Note that both result from loss of the Rb gene on chr 13 ("retinoblastoma is unlucky")
White pupil reflex and Flexner-Wintersteiner rosettes.
What is contained within the optic nerve & tract?
Through what does it exit the orbit?
About a million ganglion fibers, plus glia.
The optic canal/foramen (not the superior orbital fissure)
What are some causes of traumatic optic neuropathy?
What can be found on pathology?
Direct or indirect injury (MVAs, falls, assault) as well as hemorrhagic infarcts.
Loss of the axons. Microgliosis (not astrocytosis?)
Dreadful--the optic nerve does not regenerate.
What is glaucoma?
How does it happen?
Increased intraocular pressure.
Increased aqueous humor production or decreased outflow. Note the difference between open-angle and closed-angle (emergency!)
Increased IOP compresses the lamina cribrosa through which the nerve fiber exits, causing ganglion fiber loss there.
What are some risk factors for glaucoma?
How can the disease severity be assessed?
IOP (duh), age, race, and corneal thickness apparently.
Assess IOP with tonometry, and retinal function with microperimetry.
Guttae are seen in which disease?
Bevacizumab can be used to treat which diseases?
Guttae are a hallmark of Fuch's Corneal Dystrophy.
Bevacizumab can be used in retinopathy of prematurity, AMD, DR, actually an assload of retinal pathologies.
What protein facilitates the transparency of the cornea? The lens?
What disease can present with "salt & pepper" retina on fundoscopy?
What is the most common cause of cataracts?
Type 1 Collagen in cornea, Crystallin in lens.
Congenital rubella infection
Review of Neurophys & Anatomy
Describe the pathway taken by retinal impulses to reach the visual cortex.
What extracortical sites receive retinal input?
What would result from lesion of the right optic tract?
Temporal impulses decussate at the optic chiasm. Once at the LGN, fibers segregate by altitude (superior/inferior) and continue through the dorsal or ventral (Meyer's) radiations to reach the visual cortex.
Pretectal nuclei (part of the pupillary reflex pathway), suprachiasmatic nucleus, and presumably 3-4 other sites.
Right optic tract lesion would cause a contralateral homonymous hemianopia (ie Left half of vision is lost)
Review of Neurophys & Anatomy
What do the horizontal cells of the retina do?
Light turns a photoreceptor (ON/OFF), this in turn switches a bipolar cell (ON/OFF), which combine with other bipolar cells to turn a ganglion cell (ON/OFF).
What are the two arterial supplies of the retina?
Horizontal cells are involved in reciprocal inhibition--one photoreceptor being turned on turns off its neighbors.
ON, OFF, ON.
The choroidal arteries and central retinal artery (both branches of the ICA).