Intro to Ophthalmology Flashcards
Where is light mainly refracted in the eye?
the cornea
and a little bit at the lens
What are the 3 layers of the tear film?
upper/outermost
LIPID: sealant to prevent evaporation of tear film
WATER: provides moisture and dissolves O2 to the exterior to the cornea
MUCIN: contains enzymes and electrolytes
How does accommodation by the lens change for a distant object?
ciliary muscle relaxes
suspensory ligaments are tense
lens flattens and elongates
How does accommodation by the lens change for a close object?
ciliary muscle contracts
suspensory ligaments relax
lens become fat and spherical
What is hypermetropia (hyperopia)?
refraction error: far-sightedness
ocular globe is too long
image is focused behind the retina
corrected with convex lens
What is myopia?
refraction error: short-sightedness
ocular globe is too short
image focused in front of the retina
corrected with concave lens
What is presbyopia?
age-related vision loss loss of elasticity in the lens inability to focus weakened accommodation "reading glasses"
What proportion of the refraction does the cornea do?
2/3 of total refraction
What is the function of the sympathetic innervation to the eye?
- dilates pupil
- arousal/fear
What are the sympathetic nerves suppling the eye?
- ophthalmic division of trigeminal nerve (V1)
- long ciliary nerve
What is the function of the parasympathetic innervation to the eye?
- constricts pupil
- focusing of lens (accommodation)
What are the 2 pupil reflexes?
- light reflex
- near reflex
What is the near reflex of the pupil?
"triple reflex" causes: - miosis (constricted pupils) - accommodation of lens (small and fat) - convergence of eyes
PNS controlled
What is the light reflex of pupil?
reflex controlling pupil diameter in response to light intensity
PNS controlled
What is the clinical importance of pupils?
tested as part of neurotransmitters exam
- provides info on pre-chiasmal afferent visual pathways (retinal and optic nerve)
- window into function of CN III (oculomotor)
How does the sympathetic innervation to the eye travel?
travels down via the spinal cord
and then comes back up the neck
to the internal capsule
How does the PNS innervation to the eye travel?
travels from the midbrain with CN III (oculomotor)
What is the main function of the SNS in the eye?
DILATION of pupil
What is the main function of the PNS in the eye?
near pupil reflex
light reflex
What is aqueous humour?
- fluid produced by ciliary body
- fills the anterior chamber and hydrates the vitreous
- supplies O2 an nutrients to the posterior cornea
- maintains into-ocular pressure and so shape of eyeball
- disorders of drainage: glaucoma
What is glaucoma?
disease of optic nerve/retinal ganglion cells
can cause blindness
generally asymptomatic
3 key signs
- raised intra-ocular pressure
- optic disc cupping
- visual field loss
main risk factor: AGE
What is the normal intra-ocular pressure?
10-21 mmHg
What is the Rx for glaucoma?
MEDICATION (eye drops)
1) Beta blockers: reduced aqueous production
2) PG analogues: increase outflow
SURGERY
trabeculectomy
What are the main causes of eye disease worldwide?
- cataract (50%)
- glaucoma
- macular degeneration
- corneal scars
- diabetic retinopathy
- childhood blindness
- trachoma
- onchocerciasis
What are the biggest causes of eye disease in the UK?
- age-related macular degeneration
- glaucoma
- diabetic retinopathy
What are cataracts?
- loss of clarity of the lens
- risk factors: age, smoking, DM, steroids
- congenital (rare)
- Sx: blurring, glare, monocular double vision
- Clinical signs: reduced acuity, normal fields, normal pupils, dim red reflex, hazy view of fundus
What is the Rx for cataracts?
surgery
replace with plastic lens
