Retina anatomy Flashcards
Ganglion cells
Magnocellular, parvocellular, and koniocellular describe three subtypes of ganglion cell layers.
M cells = large diameter axons, subserve a larger area of the visual field, and are more sensitive to light and motion than P cells. M cells therefore play more of a role in dim lighting conditions.
P cells = 80% of ganglion cells, are concentrated in the central retina, have smaller-diameter axons, serve a smaller area of the visual field, and play more of a role in color and acuity.
Koniocellular cells were the last cells to be recognized and are thought to play an important role in blue / yellow discrimination. Koniocellular ganglion cells are also believed to be the first affected by glaucoma. This theory ties into using short wavelength automated perimetry (SWAP) to detect early glaucoma. SWAP is essentially analogous to a Humphrey visual field with a blue stimulus on a yellow background. Most modern Humphrey visual field machines can perform SWAP.
VEGF - pathological
4 major isoforms of the VEGF protein. They are created by alternate splicing of the VEGF gene on chromosome 6.
VEGF 165 is the isoform thought to be most involved in neovascular AMD and is the primary target of the anti-VEGF drug pegaptanib (Macugen).
Vortex veins
4-5 vortex veins that drain from the equator into the superior ophthalmic vein, which then passes through the superior orbital fissure, and drains into the cavernous sinus.
field of view
Binocular indirect ophthalmoscopy advantages (over direct ophthalmoscopy): wider field of view and stereopsis.
The correct order (from highest field of view to lowest) is: 30 D > 28 D > 20 D. The order in terms of magnification is the opposite (i.e. 20 D has the highest magnification).
Please remember that the magnification obtained with an indirect lens is: the power of the eye / power of the lens
Thus, a 20 diopter lens for an emmetropic eye would give a magnification of:
60 D / 20 D = 3
Where does the vitreous attach most strongly?
vitreous base is a zone that extends 2 mm anterior to and 4 mm posterior to the ora serrata. Vitreous in this area cannot be separated from the underlying retina or pars plana epithelium without tearing them.
Laser lenses
High plus power laser lenses provide wider, less sharp views of the retina that are optimal for broader applications of laser energy such as for PRP
Mnemonic: think - if you are a positive (+) person, you probably eat more and are fatter (wider) and less sharp) - and you have the big picture (PRP)
retinal findings that carry an increased risk for retinal tear and subsequent detachment
increased risk for retinal tear and subsequent detachment including cystic retinal tufts, zonular traction retinal tufts, lattice degeneration, meridional folds, enclosed ora bays, and peripheral retinal excavations.
Mnemonic: PRE-EO CZaR Mi(L)F
peripheral retinal excavations/Enclosed ora/
Cystic or zonular traction retinal tufts
meridonal (lattice) folds.
Peripheral retinal findings that do not predispose to retinal tears or RD:
noncystic retinal tufts (they are noncystic because there is no vitreous traction)
cobblestone degeneration (aka paving-stone degeneration MC located INFERIORLY),
RPE hyperplasia/hypertrophy
peripheral cystoid degeneration ( zones of microcysts in the far peripheral retina, almost all pts have this)
MFs = folds of redundant peripheral retina that project into the vitreous. They are either aligned with a dentate process or with the middle of an ora bay. MFs are most commonly found in the superonasal quadrant. They are present in approximately 20% of all eyes.
laser terms
Photocoagulation: when tissue absorbs light energy delivered by a laser and converts this to heat causing tissue coagulation.
Photoablation occurs when laser pulses selectively ablate small areas of tissue without harming adjacent tissue. It is much less destructive than photocoagulation. Excimer lasers use photoablation in corneal refractive procedures because it allows selective ablation of tissue without resulting in damage or subsequent scarring of adjacent corneal tissue.
Photodisruption occurs when laser energy is used to rupture or explode tissue. YAG lasers used in posterior capsulotomies and laser iridotomies utilize photodisruption.
Lens (at SLE) and magnification
Volk Super 66 gives a 1:1 image magnification. Thus, the size of a retinal lesion can be read directly off of the reticule (in this case 1.0 mm).
The magnification correction factors for some other slit-lamp biomicroscopy lenses are:
Volk 60 D: 0.88 Volk 78 D: 1.11 Volk 90 D: 1.33 Nikon 60 D: 1.03 Nikon 90 D: 1.63
Retinal vascularization
retinal vascularization is complete in the nasal quadrants at 36 weeks and on the larger temporal side at 40 weeks. Memorize these values!
Also remember that the process of retinal vascularization begins at 4-5 months of gestation and involves the outward spread of mesenchymal cells from the optic disc.
However, mature vascularization is not achieved until 3 months after birth.
Lincoff’s rule
“Lincoff’s rules” help localize the causative retinal break in the case of a rhegmatogenous RD.
Rule #1: for superior temporal or nasal RDs, the primary break lies within one-and-a-half clock hours of the highest border of the RD.
Rule #2: for total or superior RDs that cross the 12 o’clock, the primary break is at 12 o’clock or in a triangle (the apex of which is at the ora serrata and where the sides extend one-and-a-half clock hours to either side).
Rule #3: for inferior RDs, the higher side of the RD indicates on which side of the optic disc the primary break is located.
Rule #4: for “inferior” bullous RDs, the primary break is located superiorly.
PDT and photosensitivity
most serious side effect of PDT is photosensitivity skin reactions that can lead to serious skin burns.
photosensitivity period for verteporfin is 48 hours, but some retinal specialists will advise patients to stay out of intense sunlight for at least 5 days.
These reactions occurred in 3.5% of patients in the TAP (Treatment of Age-Related Macular Degeneration with Photodynamic Therapy) study.
Meridonal folds
Redundant peripheral retina that projects into vitreous. Aligned with dentate process or in middle of ora bay. MC found in superonasal quadrant. Present in ~20% of eyes. Assoc/w/increased risk of RD
Meridonal complex
Ciliary process with meridonal fold
= when a dentate process and ciliary process occur within the same meridian. The involved dentate and ciliary processes are typically abnormally large, combined with a meridional fold, and usually associated with peripheral retinal excavation along the same meridian.
Pathological vs high myopia
pathologic myopes typically have a spherical equivalent of >= -8.00 D and an axial length of >= 32.5 mm.
“High myopes” usually have a spherical equivalent >= -6.00 D and an axial length of >= 26.5 mm.
Other pathologic myopia findings: optic disc tilting with extensive peripapillary atrophy lacquer cracks posterior staphyloma atrophy of the RPE and choroid elongation/atrophy of the ciliary body lattice, cystoid, paving-stone degeneration choroidal neovascularization peripheral retinal holes.
Hruby’s lens
Hruby lens is a high-powered planoconcave lens (-55 D) that is typically attached to the slit-lamp for convenience. Unlike most other slit-lamp biomicroscopy lenses, it gives a direct (non-inverted) image.
Ex of when to use: macular laser Rx (would want to use a negative planoconcave lens to obtain an upright, higher resolution image)
Disadvantage = field of view is very restricted (~5-8 degrees or about one disc diameter).
Mnemonic: negative person: being morally superior (upright + superior resolution) - fine detail (macula)
What forms the Blood-? Barrier
inner retinal-blood barrier: tight junctions between the nonfenestrated endothelial cells of the retinal blood vessels
outer blood-ocular barrier: junctional complexes between the APICES of the retinal pigment epithelial cells (aka “zonulae occludentes.”)
blood-aqueous barrier: tight junctions between cells of the nonpigmented epithelium of the ciliary body
FAZ foveola
FAZ = part of the retina that is said to be free of capillaries. Its location is approximately the same as the foveola and is roughly 250 to 600 microns in diameter. The FAZ may increase in size in certain disease states, like diabetic macular ischemia (>1K)
foveola = (CON-ING)where the inner nuclear and ganglion cell layers are absent. photoreceptors in the foveola are all cones.
umbo: partially responsible for the retinal light reflex. defined histologically as the central concavity of the floor of the foveola.
Macula - histologic definition
The macula is defined histologically as the area of the posterior retina with ≥ 2 layers of ganglion cells. It is approximately 6 mm in diameter and is centered vertically between the temporal vascular arcades.
Foveola vs fovea
foveola is defined histologically as the central floor of the fovea where the INL and GCL are absent. Clinically, the foveola is defined as the area within the fovea, approximately 0.35 mm in diameter, which corresponds to the foveal avascular zone.
(4.0 mm temporal and 0.8 mm inferior to the optic nerve. The foveola is 350 microns in diameter. The fovea is 1.5mm in diameter (the size of one optic disc).
fovea is defined histologically as the depression in the inner retinal surface where the photoreceptor layer consists entirely of cones
Blood supply of choroid
derived from the short posterior ciliary arteries. There are approximately 20 short posterior ciliary arteries (and 10 short posterior ciliary nerves) that enter the globe in a ring around the optic nerve.
The arterial pressure in the choroidal vasculature is much lower than that arriving via the short posterior ciliary arteries because the blood is rapidly re-distributed by a network of choroidal vessels. The outer layer of (large-diameter) choroidal vessels is called the Haller layer while the inner layer of (smaller-diameter) choroidal vessels is called the Sattler layer.
