Retina general info and findings Flashcards
Know the layers of the retina on OCT.
Which layers appear as dark bands?
Inner nuclear layer, outer nuclear layer, inner photoreceptor segm., and outer photoreceptor segm.
What are the two landmarks that we use in the retina and what are their sizes?
Optic nerve: =1DD =1.5-2mm in size (also 500 microns is about 0.33 DD)
Vessels: 1st vein is approx. 120 microns
What are the sizes for the parts of the macula/fovea?
foveola - floor of the fovea 0.35mm
fovea rod-free zone - 0.57mm
fovea - 1.5 mm across (shallow depression in the center of the macula)
parafovea - retinal bipolar and gg cells highest 0.5mm
perifovea - gg cells go from 4 thick to 1 cell thick 1.5mm
macula - 4mm across
How many mm ora to ora?
32mm
Posterior pole size and macula location?
Posterior pole is about 45 degrees, and the macula is about 11.8 degrees temporal from the optic disc
What are the 5 layers of Bruch’s Membrane?
Posterior to Anterior:
- Basement membrane of choriocapillaris
- Outer collagenous layer
- Elastic lamina
- Inner collagenous layer
- Basement membrane of the RPE
Which layer do drusen first accumulate in?
the inner collagenous layer of Bruch’s membrane
Which structures make up the blood-retina barrier?
basement membrane of the RPE, and endothelial cells of the retinal vessels
What is a main difference between the vessels in the choroid compared to the vessels in the retina?
Choroid has no tight junctions, vessels are fenestrated!
Retinal vessels are not fenestrated and make up part of the blood-retina barrier.
Which layers in the choroid have small vessels vs larger vessels?
Sattler’s layer has small vessels, Hallers layer has large vessels
Know normal retinal blood supply. What does the ACA supply?
anterior uvea and anterior choriocapillaris
What artery supplies the inner retina?
Central retinal artery
What do the SPCAs supply?
nasal and temporal choriocapillaris that supplies the posterior ⅔ of the outer retina (up to the ONL, including OPL, ELM, photoreceptors, RPE)
What do the LPCAs supply?
peripheral choriocapillaris, one nasal and one temporal, supplies the anterior ⅓ of the outer retina (up to the ONL, including OPL, ELM, photoreceptors, RPE)
Which layer of the retina has the branches of the CRA running through?
branches run through the nerve fibre layer with adhesions to ILM. superficial capillary network runs in NFL and GCL, deep capillary network runs in the INL.
What is autoregulation in the retina?
retina autoregulates its blood flow and depends on the CO2/O2 level. decrease in O2 causes high CO2 and vessels will dilate trying to increase flow. increase in O2 and low CO2 causes vessels to constrict and have decreased flow and increased resistance and pressure. If pressure gets too much, the vessels will change tone (myogenic response) to resist the change in IOP.
this fluctuation concept is what leads to diabetic retinal vessel findings
Differences between retinal arteries and veins:
arterioles lie in the NFL or GCL, they are strong and not easily affected by external forces (should not see spontaneous pulse), smooth muscles, no elastic lamina
venules are thin-walled, distensible, compressable, allows for SVP
In between which layers is a pre-retinal (subhyaloid) hemorrhage found? and where does the blood come from?
posterior to ILM and anterior to NFL
blood comes from the superficial capillary bed
Which hemorrhage is affected by gravity?
pre-retinal hemorrhage
Which hemorrhage clears up the fastest? (When seen is always bright red and fresh)
pre-retinal hemorrhage, clears in days to 1 month
What might a pre-retinal heme be a sign of?
peripheral vascular disease/arterial disease
Does a pre-retinal heme lie in front of, with, or behind the visible retinal vessels?
Pre-retinal hemorrhage occurs in front of the vessels, obscures underlying vessels, blocks NFL and choroid and everything behind it (affects vision)
Which type of hemorrhage follows the NFL pattern?
Flame shape hemes
What might flame-shaped hemes be a sign of?
most commonly associated with retinal vein occlusions and hypertensive retinopathy
Which layer are flame hemes found in and where does the blood come from?
post-arteriolar superficial capillary bed, in RNFL same as other vessles and so sometimes can appear in front of, within or behind the retinal vessels
Other findings that are associated with a flame heme finding:
roth spots within flame heme
drance heme = flame heme at the disc
Which layer are dot/blot hemes found in and where does the blood come from?
pre-venule deep capillary bed in the OPL
What does dot/blots hemes signal and what conditions are they associated with?
signals venous congestive disease, and are most associated with diabetic retinopathy and ocular ischemic syndrome
How long do dot/blot hemes take to resolve?
slower, 6 months to years
Which layers are sub-retinal hemorrhages found and what are they secondary to/caused by?
found between RPE and sensory retina, breakthrough of deep hemorrhages, secondary to CNVM (AMD), deep bleed and so retinal vessels can be seen above the heme. These bleeds are also more purple than superficial pre-retinal hemes
What is the classic description of a sub-RPE hemorrhage seen on OCT and in which layers is it located between?
grey/green/almost black, located between the RPE and Bruch’s membrane, very deep and are dark when viewing fundus, common in wet AMD and also a result of CNVM
What are some reasons for vitreous hemorrhage?
a break in ILM can cause, results from NVD, NVE, PVD with retinal break, macroaneurysm, or wet AMD
Microaneurysms may look like dot/blot hemes but what are the differences otherwise?
Microaneurysms are active leakages and can be visualized on FA, they will shine white, while dot/blots will be dark as they block NaFl.
What causes microaneurysms?
Microaneurysms are leakage from parafoveal capillaries that have weakened cell walls (pericytes) or caused by active cellular response to hypoxia, forms in response to ISCHEMIA!
When does venous beading occur?
constriction/dilation of vein lumen, more common in chronic cases, non-specific sign of ischemia, and one of the strongest predictors of if a patient will develop neovascularization
What does IRMA stand for?
Intra Retinal Microvascular Abnormalities
What is IRMA and in what layer is it found?
intraretinal shunting through vascular channels from pre-existing capillary bed, located in OPL, these are not new vessels and so are not fenestrated and not leaking (different from neo), the vessels may look tortuous and may lead to neo eventually as it indicated retinal non-perfusion
If you see IRMA in a diabetic, is it PDR or NPDR?
NPDR still!
What can FA be used to confirm?
FA is needed to confirm leaking vs. leaked. Can differentiate microaneurysms from dot/blot heme and differentiates IRMA from neo
What is drusen and at what level is it found?
drusen is an accumulation of metabolic waste products from rods receptor outer layer, collecting in the RPE, appear as small round yellow lesions, can be hard, calcified, soft and/or confluent, creating an abnormal thickening of inner Bruch’s membrane
What are the sizes of drusen and how do they affect AMD development?
small drusen <64 microns are well defined and focal with a 1.3% risk of AMD development
intermediate drusen 65-124 microns with an 18% risk of AMD development and also greater risk of RPE abnormalities and atrophy
large drusen >125 microns greater risks
Which type of drusen has the least risk of progression to CNVM?
Hard drusen, discrete, well demarcated
What are exudates and what level are they found at?
lipid laden macrophages, waxy yellow lesions at the level of OPL, more superficial compared to drusen (drusen are deep) and so exudates are brighter yellow
What is circinate retinopathy?
exudates form a circle, indicating leaking microaneurysms or choroidal neovascularization, accumulation of lipid from these leaks, edema
What were cotton wool spots previously called and why is it wrong classification?
used to be called soft exudates which is wrong as CWS are not leaking!
What are cotton wool spots and what to they indicate?
fluffy, white, swelled up axons from a sudden arteriolar microinfarct at level of NFL, indicates hypoxia
What conditions might CWS indicate and when is it okay to have CWS?
it is never okay to have even one cotton wool spot, must look for the cause of it!
can be associated with DM, RVO, HTN, Lupus or HIV/AIDS
What is an RPE window defect?
white/yellow, round, well-circumscribed areas with no surround of reactive RPE hyperplasia, lesion is a result of an absence of melanin in the RPE (seeing underlying sclera), it is benign and pt is born with it. includes cobblestone finding.
What are the differences between window defects and atrophy?
atrophy develops over time and something caused it, we need to investigate, likes to be need macula, more disorganized, associated with hyperplasia, makes up a chorioretinal scar
window defect is there when patient is born and nothing needs to be done besides documentation, can happen anywhere in the retina, more organized, distinct looking, can be found in a CHRPE and have hypertrophy alongside
Window defect vs atrophy goes with hyperplasia or hypertrophy?
window defect — hypertrophy
atrophy — hyperplasia
What is white without pressure?
gray-white translucent area with scalloped borders, usually bilateral, can be mistaken for RD especially on OPTOS, but it is flat, often found in the temporal periphery, with 30% incidence in general population and 10x more common in dark-skinned individuals
What are myelinated nerve fibres and how do you differentiate from CWS?
often come from the disc in RNFL pattern, usually doesn’t extend beyond posterior pole, has NO visual or clinical significance! CWS are usually more round
What is a chorioretinal scar?
usually white to yellow intraretinal fibrosis with accompanying RPE hyperplasia, itself is benign but may have been causes by previous inflammation or trauma and may lead to RD (monitor yearly and look for retinal tears)
(common cause is toxoplasmosis)
What is fibrosis and what may cause it?
response to injury (mechanical vs hypoxia driven), gliosis (neo/angiogenesis driven) blood rubs with glia causing it to proliferate including fibroblasts. associated with DM, PVR, ROP, AMD
What is the number one cause of tractional retinal detachments?
Fibrosis, pulling on retina
What does A,B,C,D,E stand for when describing retinal lesions?
Asymmetry, Borders, Colour, Diameter, Evolution/Elevation
What are lacunae?
a diagnostic finding of window defect inside a CHRPE, (the white area that is not the hypertrophy)
What is CHRPE vs bear tracks
Congenital hypertrophy of the RPE, both involve enlargement of RPE cells, well-demarcated, round, can be solitary or multiple, brown or black, flat or scalloped margins, bear tracks don’t have lacunae and are associated with colorectal cancer and familial adenomatous polyposis
What is the difference between hypertrophy and hyperplasia by definition
hypertrophy means enlarged cells but same number, hyperplasia means more number but no change in size
What might be the cause of RPE hyperplasias
RPE hyperplasia represents RPE cells invading the sensory retina, may be in response to injury, retinal tear, retinal detachment, lattice degeneration, etc., appears black, forms in chorioretinal scars, irregular shaped areas with variable size, indicative of a process that has been ongoing 60 to 90 days. self limiting but must investigate the cause of the retinal insult
What is another name for benign choroidal melanoma and what is it?
Choroidal nevus, it is a benign melanocytic tumor of the posterior uvea (accumulation of atypical but benign melanocytes), flat, slate gray lesion of variable size, monitor if <2mm, assume malignancy if >5mm
What are the distinguishing features of choroidal melanoma vs nevi
nevi have drusen, melanoma has lipofuscin which is more orange. drusen represents stability, while lipofuscin represents an active growth (it is an intermediate metabolite), often nevi are <2mm and flat while melanoma is >2mm and elevated, melanoma may also have vessels visible in the tumour dome, and non-uniform colour
