Eye histology Flashcards
What are the 3 layers of the eye?
- corneoscleral (tunica fibrosa)
2, uvea (tunica vasculosa)
- retinal layer (tunica internal/nervosa)
What are the refractive medias of the eye?
cornea
lens
suspenory ligaments
aqueous humor
vitreous body
(these are all the structures light passes through to hit the retina)
What are the 3 chambers of the eye?
anterior (between cornea and iris)
posterior (between iris and lens
vitreous (vitreous body)
What are the 2 general portions of the corneoscleral layer of the eye?
cornea (makes up anterior 1/6)
sclera (posterior 5/6 = whites)
What are the 5 layers of the cornea?
- corneal epithelium
- Bowman’s membrane
- Substantia propria
- Descernet’s membrane
- Corneal endothelium
What connective tissue makes up the sclera?
it’s dense fibrous CT with elastic and collagenous fibers
What muscles insert into the sclera of the eye?
the tendons of extrinsic eye muscles
What happens to the sclera layer at the optic nerve region? What is it called?
it forms something like a sieve for the nerve fibers to pass through
it’s called the lamina cribrosa
What do you call the corneo-scleral junction?
the limbus
At the limbus, what does the corneal epithelium becomes continuous with?
the bulbar conjunctiva
What important blood vessles are located at the limbus?
those that supply the cornea
What does the corneal endothelium form at the limbus?
the trabecular meshwork and the canal of schlemm where the aqueous humor drains into the epsicleral veins
What sort of epithelium makes up the corneal epithelium?
stratified squamous, non-keratinizing. 5-6 cell layers thick
What makes up the substantia propria (90% of the cornea)?
transparent, regulat CT made of regularly arranged collagen
the fibrils occur in layers of lamellae, with adjacent lamellae at 90 degree angles to each other with interdigitation holding layers together
fibroblasts are located between the lamellae
glycosaminoglycans liks chondroitin, keratan and hyaluronic acid help hold the collagen together and contribute to transparency by maintainign proper water contenct
What are the three components of the uvea layer?
- choroid
- ciliary body (made of the ciliary processes and ciliary muscle)
- iris
What are the characteristics of the choroid?
It’s highly vascularized and pigmented
loose CT
several layers
Where is the ciliary body located?
it girdles the eye anterior to the ora serrata (triangular in shape)
What do the ciliary processes do?
form the aqueous humor
What are the two layers of the ciliary epithelium and what are they continuations of?
the deep, pigmented layer (continuation of the RPE layer of the retina)
superficial, non-pigemtned layer (a non-nervous continuation of the inner 9 layers of the retina)
What lies at the center of the ciliary processes?
the stromal cores with numerous capillaries - these are probably the source of aqueous humor)
Describe the flow of aqueous humor.
ciliar processes - posteior chamber - anterior chamber - trabecular meshwork - canal of schlemm - venous system
What attaches the lens to the ciliary processes?
the suspensory ligaments (zonule)
What type of muscle are the ciliary muscles?
smooth
What are ciliary muscles super important for? What happens when they contract vs. relax?
super importnat for accommodation
contraction - releases rension on lens, so the lens is thinner - far vision (sympathetics)
relaxation - increases tension on lens - lens is fatter - near vision (parasympathetics)
What does the iris contain?
endothelial surface
underlying CT (with chromatophores to determine eye color)
smooth muscle
What is the iris’ two types of smoother muscle and what is their innervation?
the sphincter - parasympathetic
dilator - sympathetic
What is the posterior layer of the iris made of?
it’s two rows of cuboidal cells that are heavily pigmented in everyone - regardless of eye color
For the retina, the sensitive portion continues anteriorly only to what…
the ora serrata
after that it continues as non-nervous pars ciliaris
What are the 10 layers of the retina?
- pigmented epithelium (RPE)
- rods and cones
- external limiting membrane (outer end of muller cells)
- outer nuclear layer (nuclei and cell bodies of rods and cones)
- outer plexiform layer (synapses between photoreceptors and bipolar cells)
- Inner nuclear layer (cell bodies and nuclei of bipolar cells, horizonal cells, amacrine cells and muller cells)
- Inner plexiform (synapses of bipolar onto ganglion)
- Ganglion cell layer
- Nerve fiber layer
- Inner limiting membrane (inner end of muller cells)
What is the RPE responsible for?
It holds the pigmented portion of the rods and cones
recycles the pigment discs as they age
synthesizes melanin to absorb light after it has sensitized the receptor so that they do get saturated
vitamin A transport and esterification for forming rhodopsin
ion transport
For the photoreceptors, what is contained in the outer segment? In the inner segment?
the outer segment has the pigment discs
the inner segment has all the organelles
(they’re connected by a thin structure called the cilium)
How many rods supply each ganglion cell compared to the cones?
rods = 100 per ganglion
cones: 1-10 per ganglion
Bipolar cells extend from what two layers of the retina?
from the outer to the inner plexiform layers
What do the horizontal and amacrine cells likely do?
the horizontal cells connect groups of cones and rods together - probably integrates information from the connected cells
the amacrine cells are primarily associated with ganglion cells and their funciton is likely integration as well, but it’s poorly understood
What is the function of the muller cells?
mostly supportive - they’re the retinal glial cells basically
What is the macula lutea? How is it related to the fovea centralis?
it’s an area of the retinal lying directly in the optic axis, about 5 mm in diameter
in this area, the rods gradually disappear and cones become increasingly slender and numerous
the fovea centralis is at the center of the macula and it made entirely of cones - this is the area of clearest vision and greatest acuity
Where is the blind sport of the retina?
the optic disc where the nerve fibers make the optic nerve - there are no photoreceptors here.
WIthin the optic disc, what is the optic papilla and what is the physiological cup?
the optic paplila is the portion fo the disc that is raised slightly due to heaping up of the nerve fibers
the physiologic cup is a small central depression through which the artery and vein of the retain emerge
What are the layers of the lens? (layers might be a bad term…makeup?)
the capsule is the outermost layer, made of a basal lamina; type 4 collagen - this is what the zonular fibers attach to
the subcapsular epithelium - a single layer of cells on the anterior surface
at the equator, the subscapular epithelium cells are transformed into lens fibers and move towards the center
WHat happens to the lens with age?
graduall loses water and becomes less elastic, meaning the lens is less able to accommodate
THe lens fibers located at the center are __ than those located on the periphery.
older
What fibers make up the zonule?
thin collagen and fibrillin
What glands are located in the eyelid?
sebaceous glands: meibomian (embedded in tasrsl plates) and zies (associated with hair follicles)
sweat glands (glands of Moll)
what type of gland is the lacrimal gland?
compound tubuloalveolar gland (serous secreting - lots of myoepithelial cells)
