Ophthalmology General Flashcards
Chalazion
impacted material in the meibomian gland, bursting leading to granuloma formation
Internal Hordeolum
Infected meibomian gland (stye)
Glands of Zeiss and Moll
less important glandsassociateo with skin hairs and cilia
if infected -> external stye (external hordeolum)
Tarsal plate
poorly developed fibrous structure running along upper and lower eyelids, meibomian glands in it. surgical landmark and holding layer for sutures.
Musculature of the eye
Orbicularis oculi - eyelid closure
Levator palpebral superioris - lifting upper eyelid
Mullers muscle -maintains upper eyelid
Nasolacrimal system
Tears -> medial canthus, collected in the puncta.
Caniliculi
Lacrimal ducts
Lacrimal sac
Upper portion of nasolacrimal duct into which 2
Nasal punctum
- opening of the nasolacrimal duct in to the nasal cavity
Lacrimal gland
- below dorsolateral orbital rim, produces 70% tears
tear film
- mucous layer secreted by corneal epithelial cells and goblet cells of conjunctiva
- aqueous layer, water and solutes, defense mechanism (Igs and lactoferrin)
- lipid layer secreted by meibomian glands, prevents evaporation
Layers of the cornea
> epithelium - shed as squamous cells in 1 week cycle - basal cells at limbus = stem cells > stroma - collagen - lamella layers > uDescement's membrane - during progressive ulceration of the cornea, before perforation develops, forms a descemetocele (surgical emergency) > endothelium - v thin - keeps cornea dehydrated via NaK pumps - no regenerative capacities
Limbus
transition between cornea and limbus (may be pigmented)
Sclera
white of the eye, continuous with limbus and cornea
- covered by subconjunctival connective tissue (episclera/Tennon’s capsule)
- v thin at equator and near optic disk
- lamina cribs where axons of ganglion cells exit the eye to form the optic nerve
Extraocular muslces
- recti (dorsal, ventral, lateral, medial rectus)
- obliques (dorsal with trochlear pulley mechanism, ventral oblique)
- retractor bulbi
Iris
Constricrot and dilator muscles
- dilator stronger, and in disease may contract -> miosis
- pupillary zone, iris collateral and ciliary zone
What are PPMs?
Persistant pupillary membranes
- fetal vasculature remnants arise from the iris collateral
- may stay in iris or cornea/lens -> opacity
What are synechiae?
- adhesions of the iris to other structures d/t uveitis
- anterior = cornea
- posterior = lens
Ciliary body
- has own musculature
- focusing
- can cause pain if contracted d/t disease
- produces aqueous humour via carbonic anhydrase enzyme
Anterior uvea consists of..
Iris and ciliary body
Posterior uvea consists of ..
Choroid and tapetum lucidum
- feeds the retina
- carnivores much more reflective tapetum
- horses have “stars of Winslow” all over tappet fund (end on choroidal capillaries that give tappet fundus a subtle, pin prick spotted appearance
Where is aqueous humour resorbed/outflow?
- iridocorneal angle “conventional”
- “unconventional” = uveoscleral outflow as absorbed. Esp important in the horse.
Zonules
Arise in ciliary body, attach to lens and lens equator
Layers of the lens
- front and back bellies
- lens capsule
- epithelial cells that produce lens fibres
- suture lines: at the confluence of the lens fibres, Y shaped in anterior lens and upside down Y shape in posterior part of the lens
- cortex: youngest part of the lens, produced by lens epithelial cells - cells will lose nuclei and become part of the nucleus, becoming more compacted with age (nuclear sclerosis)
- lens nucleus (ambreyonic, fetal, juvenile and adult layers)
components of the retina
- 1 epithelial layer (outermost, RPE retinal pigment epithelium) nurses the photoreceptors
- 9 neural layers: outermost contain photoreceptors (rods and cones) innermost contain ganglion cells and neural fibre layer -> optic nerve
- retinal vasculature: containes paired arterioles and venules (venues larger) dorsal, lateral and medial ones. Branching.
> Horses have more subtle retinal vasculature (few short BVs emanating from optic disk few mms into periphery)
Optic nerve head/disk/papilla
- dog contains fluffy myelin -> square/diamond shaped not round. Plus anastomosing vasculature on top (cats none.)
- very round in the cat d/t lack of myelin
- horses optic disk is oval in the horizontal axis, salmon coloured, larger.
Optic nerve
- arises from optic disk
- fibres from nasal (medial) and lateral retina
- right and left fibres decussate at the optic chiasm and post chasmal nerves = the optic tract
What is the anterior segment comprised of?
Anterior and posterior chamber, divided by IRIS
What does the posterior segment contain?
- Vitreous body
- Fundus (retina/choroid/sclera)
> depedning on level of pigmentation of the choroid, may be able to see choroidal BVs and sclera behind.
> some animals may be atapetal (have no tappetum lucidum) so tappet reflex will be red like humans
What is the fund reflex?
- tapetal/fundic reflex = reflection of light coming through the pupil in response to an external light
- usually yellow/green/orange, may be red in atepetal animals
what nerve innervates orbicularis oculi?
CN7 (facial)
what nerve innervation Mullers muscle?
Sympathetic Innervation (-> ptosis in horners)
Outline the basic visual signal once light has reached the photoreceptor layer
- rods and cones
- inner retina
- ganglion cells
- nerve fibre layer
- optic disk (axons go through lamina cribrosa of the sclera and are bunched together into a nerve)
- optic nerve
- optic chiasm
- optic tract
- lateral geniculate nucleus (before this, branches for PLR)
- Optic radiaton
- VIsual cortex
Outline the pathway of the PLR response
…optic tract
- pretectal nucleus
- E-W and amteriomedian nucleus
- PS fibres of oculamotor nerve (CN3) with ciliary ganglion to pupillary musculature
Which cranial nerves are of importance in ophthalmology?
2: optic (vision)
3: oculomotor (dorsal, medial and ventral recti, ventral oblique, PS innervation of the pupil)
4: trochlear (dorsal oblique)
5: trigem, ophthalmic branch (sensation)
6: abducens (lateral rectus -> abduction of the globe and lateral movement. In animals can also pull globe into orbit though abductor muscles -> retrobulbar fat displacement -> protrusion of the TE)
7: facial (blink)
8: vestibulocochlear (conjugated eye movement, ocular movement in response to sound)
What controls the secretion of the lacrimal glands?
- PS innervation mostle
- first PS fibres travel with CN7 facial and then int he pterygopalatine fossa they travel with and are distributed by CN5 trigem.
See booklet 5/5/15 for list of terms and definitions
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