Hereditary Disease and Horizontal Cells (M1) Flashcards
What is the type of ERG that gives a measure of overall retinal activity? 1. What is the problem with this? 2
- full-field ERG
2. no good at picking up focal defects
What type of ERG uses an algorithm to sort out the ERG for the corresponding retinal areas that were stimulated by each hexagon?
muti-focal ERG
What are electrodiagnostic tests (like EOG and ERG) used for?
diagnosis of hereditary retinal and choroidal diseases and monitor progression
What test is useful for the diagnosis of vitelliform dystrophy (Best’s disease)? 1. What separates this test from the other possible one? 2. What is the inheritance of the disease? 3
- EOG
- EOG is abnormal for adult carriers and ERG is normal for them
- autosomal dominant
During Best’s disease, what deposits in the RPE? 1. When are pigment disturbances usually observed? 2
- lipofuscin
2. 5-10
What is the progression in the appearance of a lesion during Best’s disease?
Look like egg yolk then rupture and hemorrhage and look like scrambled egg
What is the lesion rupture during Best’s disease associated with?
- focal RPE degeneration
2. choroid atrophy
What are the different inheritance types (with the percentage of each) for retinitis pigmentosa?
- autosomal dominant (30-40%)
- autosomal recessive (50-60%)
- X-linked (5-10%)
What percentage of people with RP have no known prior family history?
50%
What are the common symptoms of RP that affects the rods more (rod-cone RP) than the cones?
- nyctalopia
2. loss of peripheral vision
What are the common symptoms of RP that affects the cones more (cone-rod RP) than the rods?
- acuity loss
- photophobia
- photopsia
- color vision concerns
What are the classic fundus findings in RP patients?
- pigment clumping in the peripheral retina (bone spicule)
2. attenuated (narrow) retinal arteries
What tool can help to diagnose RP, by detecting the changes that precede fundus changes, and monitor the progression?
ERG
What type of ERG is typically affected in rod-cone RP? 1. Cone-rod RP? 2
- scotopic ERG
2. flicker ERG and mixed ERG
What gene do the most common defects for autosomal dominant RP occur?
rhodopsin gene
What process do gene defects often affect in RP? 1. What are the genes involved? 2
- photodransduction
2. PDE6, RPE65, CNGA/B
If the visual disturbances associated with RP are present at birth what do they normal characterize it as? 1. What is the gene affected? 2. What is being looked at as a possible treatment for this? 3
- Leber’s Congenital Amaurosis
- RPE65
- gene therapy
What are the retinal disorders in which neurotransmission is altered between photoreceptors and bipolar/horizontal cells called?
Congenital stationary night blindness
What is the presentation of type 1 congenital stationary night blindness? 1. What cells does the defect affect? 2
- complete absence of rod pathway
2. localized to ON bipolar signaling
Where is the genetic defect in x-linked type 1 congenital stationary night blindness?
nyctalopin (in dendrites of ON bipolars)
Where is the genetic defect in autosomal recessive type 1 congenital stationary night blindness?
TRPM1 in mGluR6
What is the presentation of type 2 congenital stationary night blindness? 1. What is the inheritance? 2. Where is the genetic defect? 3
- incomplete form
- x-linked
- specific VGCC found in PRs (ON -related)
What are the symptoms of CSNB?
- nyctalopia
- normal visual acuity (type 2 usually)
- severe reduction is VA (type 1 usually)
What is the appearance of the fundus in CSNB? 1. What is used to help diagnose this? 2
- usually normal
2. ERG
What changes in the ERG reading of a patient with CSNB?
normal A-wave but no B-wave
What is the current treatment of retinitis pigmentosa?
- counseling and low vision regimes
2. vitamin A supplementation
What cells are horizontal cells in strategic position to influence? 1. Where are they located? 2
- bipolar cell responses
2. outer margin of the inner nuclear layer
What makes horizontal cells unique in their neuronal synapes’?
post-synaptic to PRs and act as pre-synaptic terminals
Do horizontal cells depolarize or hyperpolarize to light? 1. Are they an action potential or graded? 2
- hyperpolarize
2. graded
What kind of receptors are found on the dendritic/axon terminals of horizontal cells that respond to glutamate? 1. Are they sign-conserving or inverting? 2
- ionotropic kainate/AMPA-type receptors
2. sign-conserving
What is the area over which stimulation leads to a response in a particular sensory neuron?
receptive fields
What is the photoreceptor receptive field limited by?
width of outer segment
What do horizontal cells have that allow their receptive field to not just be limited by the extent of their dendrites alone?
gap junctions allowing ions and small molecules to pass directly from one cell to another
