Histology of the Eye and Visual Tracts (Dennis) Flashcards
What are tarsal glands?
What are sebaceous glands
What are lacrimal glands?
Special sebaceous, secretion results in evaporation of tears (blockage = chalazion) Eyelash gland (infection = stye) Produces tears
Where is the palpebral and bulbar conjunctiva?
Palpebral is on the lid, bulbar is on the outer surface of the eye itself
Label the chambers of the eye (also on anatomy drawing):
Ok
What is included in the fibrous tunic of the eye? What are they made of ?
Sclera - dense irregular
Cornea - two epithelium layers with connective tissue sandwiched in between
What is included in the vascular tunic/uvea of the eye? What are they made of?
Choroid - vascularized areolar connective tissue
Ciliary body - ciliary smooth muscle and ciliary processes covered with secretory epithelium
Iris - 2 layers of smooth muscle (dilator and sphincter pupilae) and connective tissue + central pupil
What is included in the retina of the eye? What are they made of?
Pigmented layer - pigmented epithelial cells
Neural layer - photoreceptors, bipolar neurons, ganglion and supporting Muller cells
Properties of the sclera and the cornea
Sclera has fibrous opaque layer
Cornea has 5 layers and is continuous with sclera
What is the corneal epithelium?
Layer 1 of cornea - nonkeratinized stratified squamous
What is the bowman’s membrane?
Layer 2. sandwiched between the anterior basement membrane and the corneal epithelium
What is the corneal stroma?
Layer 3 of the cornea. Avascular
What is the Descemet’s membrane?
Layer 4 of cornea. Sandwiched between the posterior basement membrane and the corneal endothelium, very thick
What is the corneal endothelium?
Layer 5. simple squamous facing the anterior chamber
Vascular coat of the eye includes ….
Choroid, ciliary body and iris
Choroid features:
Has an inner vascular layer called the choriocapillary
Bruch’s membrane (ECM layer)
Ciliary body features:
Has ciliary muscle (lens accommodation) and ciliary process (secretes aqueous humor, forms the suspensory ligaments of the lens)
Iris features:
Is a contractile diaphragm in front of the lens, has dilator (radial band) and sphincter (circular band) pupillae
Lens components
Transparent and avascular
Capsule - made of elastic ECM
Subcapsular lens epithelium - periphery cells migrate to make mature lens fiber cells
Lens fibers - has cystallins and lost all organelles
Describe accommodation
Adjustment of the eye for seeing objects at various distances.
Ciliary muscle controls the lens (via flattening or thickening) for near and far vision.
Flat lens - see further (sympathetic)
What is presbyopia?
Loss of lens elasticity with age
Retinal pigmented layer (RPE)
Made of simple cuboidal epithelial cells resting on the Bruch’s membrane of choroid, thus serves as barrier between neural retina and blood from choroid
Functions of RPE
Phagocytose discs shed from the rods and cones, transforms all-trans-retinol to 11-cis-retinal to give back to photoreceptors
Neural retina
Contains the photosensory cells and has no lymphatics
What is the optic disc?
Blind spot in retina where optic nerve exits
Layers of the Retina
Photoreceptor layer
Outer limiting membrane
Outer nuclear layer
- has ends of the rods and cones
- has miller cells on the apical end
- has the cell bodies of the rods and cones
Layers of the Retina:
Outer plexiform layer
Inner nuclear layer
Inner plexiform layer
- processes connecting photoreceptors and non-photoreceptors
- cell bodies of non photoreceptors
- processes of the interconnecting ganglion, amacrine, bipolar and horizontal cells
Layers of the retina:
Ganglion layer
Layer of optic fibers
Inner limiting membrane
- cell bodies of ganglion cells
- processes of ganglion cells
- basement membrane of Miller cells
Properties of rods and cones
Rods more sensitive to light than cone cells
3 classes of cones: blue, green and red
Rods have rhodopsin while cones have iodopsin
Not present at the optic disc
Describe the general structure of rods and cones:
Outer segment = photosensitive, has discs connected to inner segment via cilium
Connecting stalk = has the cilium body
Inner segment = contains the major organelles
How are the photoreceptor discs recycled?
Shed during normal functioning and phagocytosed by the RPE cells
Features of fovea centralis
Highest cone concentration, sharpest visual acuity at the fovea, drops around the periphery of the retina
Avascular, no cell bodies, axons
Features of the macula lutea
Surrounds the fovea and protects the cones in the fovea
Features of the optic disc:
Where ganglion axons of retina converge
No photoreceptors. Blind spot
Features of the optic nerve
Contains axons of the retinal ganglion cells. Axons are myelinated as they pass through the sclera (via oligodendrocytes).
Axons penetrate the sclera and choroid and travel to brain
Central retinal artery is main blood supply to retina
How are images on the retina made?
Rods and cones react to light > send info to ganglion cells > visual pathway > thalamus > primary visual cortex
Difference between visual and retinal fields
Visual field: area you can see when both eyes are fixed in one position
Retinal field: image on the retina from the visual field
Where is the object of attention focused at in the retina?
Fovea and macula. Optic disc is medial, retinal axons leave eye as optic nerve
Binocular vs monocular zones:
Binocular: central region seen by both eyes
Monocular zones: R/L region seen by corresponding eye
Retinal hemifields:
Refers to the nasal and temporal halves of retina
Divided into upper and lower quadrants
How is retinal image projected?
Inverted in both lateral and vertical dimensions
Significance of the Optic nerve decussation
Contralateral delivery of info on both sides of the optic tract
Helps bring together info from comparable areas of the retinas = depth perception
Features of the lateral geniculate nucleus
6 layers with myelinated fibers sandwiched in between
What are optic radiations?
Myelinated secondary fibers from the LGN
Each individual fiber carries info from 1 eye
Optic radiation fibers that carry information from the lower quadrant of the contralateral retina (Baums)
Originate from…
Passes through …
Targets …
Dorsomedial portion of the LGN
Retrolenticular limb of the internal capsule
Superior bank of the calcarine sulcus (on cuneus)
Optic radiation fibers that carry information from the upper quadrant of the contralateral retina (Meyers)
Originate from…
Passes through….
Targets…
Ventrolateral portion of the LGN
Forms the Meyer loop on the temporal lobe
Inferior bank of calcarine sulcus (on lingual gyrus)
Optic radiation fibers that carry information from the macula and fovea ….
Come from central LGN and pass through caudal portions of the visual cortex
Hemianopia:
Quadrantopia:
- Blindness in one half of the visual field
- Blindness in quadrant of visual field
Homonymous visual fields:
Heteronymous visual fields:
Cannot see in the same halves of each eye (e.g. blind in right half of left and right eye)
Cannot see in different halves of each eye (e.g. blind in right of left eye and left of right eye)
Congruous vs incongruous lesion and relationship to the visual cortex
Vision loss on the same side of the visual field
Usually this type of lesion is closer to visual cortex.
- Lesion closer to optic tract or radiations are likely to be incongruous
Damage before the chiasm =
Damage at the chiasm =
Damage after the chiasm =
Affects ipsilateral eye
Causes heteronymous deficits
Homonymous deficits
