beginners guide to ophthalmology Flashcards
what is the most common cause for being registered blind or partially sighted under 65
diabetes mellitus
what is the visual system comprised of?
- a coordinated pair of eyes
- appropriate protective mechanisms around the eyes
- neural apparatus to interpret visual infomation
what is the function of the eyes?
- formation of a focused image on the retina
- transduction of the image into an electrical signal
look in notes to learn the anatomy of the eye
when looking at an otoscopy image how can you tell whether it is the right or left eye
the optic disk is always nasal to the fovea
the fovea is always temporal to the optic disk
what is the function of the iris, lens and the pupil?
pupil - allows light in
iris - smooth muscle which alters diameter of the pupil to allow more or less light in
lens - involved in focusing
what is the macula and the foeva?
macula - the central vision area of the retina which lies lateral to the optic disk and is slightly darker than the rest of the retina due to yellow luteal pigment. it has the highest desity of cones
foeva - centre of macula where all light is focused to. It is rod free and has the highest visual accuity
what is the function of the cornea?
it is transparent as it is the first structure that light must pass through
major refractive component of the eye
provides barrier to infection and trauma
what does transparency of the cornea depend on?
relative dehydration of the stroma - maintained by impermeable epithelial barrier and active pumping mechanisms of the corneal endothelium
regular spacing of individual stromal collagen fibrils
what are the 5 layers of the cornea?
epithelial cells bowman's membrane stroma descendants membrane endothelial cells
what is the sclera and what is its function?
this is the outer coat of the eye which maintains the eye shape, maintains intraocular pressure and provides a barrier to infection and trauma. It is opaque and mechanically tough and consists of irregularly arranged collagen fibres which form the posterior 5/6 of the outer coat of the eye.
what is aqueous humour and what is its function?
This fills the front part of the eye (in front of the lens) and is involved in maintaining intraocular pressure between 10-21mmHg through a dynamic balance between secretion and drainage. It is formed by active secretion from the epithelium of the ciliary body and drained out through 2 routes
- - Conventional route - 85% drains through the trabecular meshwork into the canal of schlemm in the anterior chamber angle
Uveoscleral route - 15% drains through the ciliary body and into ciliary circulation.
what is viterous humour and what is its function?
This fills the back part of the eye (behind the lens) which is made from collagen type II arranged in fibrils and a few cells called hyalocytes which secrete glycosaminoglycan. This is responsible for protecting the ocular structures and for passive transport and removal of metabolites. It is not as essential as aqueous humour.
what is the crystalline lens?
This a transparent structure made from an orderly arrangement of the lens fibres with a small difference in the refractive index between the various components. It contains no blood vessels. It is responsible for fine focusing and is often subject to age related, metabolic or congenital changes which cause opacification (cataract)
what is the function of the retina?
this is transparent and is responsible for transducing the light energy into nervous impulses. It is made of at least 11 layers containing photoreceptors (rods and cones)
what is the optic nerve and the optic disk?
optic nerve - contains over 1 million nerve fibres which are myelinated only after leaving the eye and the nasal fibres cross at the optic chiasm but the temporal fibres do not giving us our 3d vision
optic disk - the exit point of the optic nerve from the eye which corresponds to the blind spot of visual field as it does not contain any overlying photoreceptors
look in notes for overview of the optic pathways
when taking an occular history, what do you need to ask about in HPC?
general symptoms
- bilateral/ unilateral
- onset
- duration
- any pain
- any photophobia
- any redness
- any discharge
visual symptoms
- visual loss - sudden/ gradual distortion
- field defect - unilateral, bilateral, central, peripheral
- flashers or floaters
- diplopia - horizontal, vertical, binocular, monocular
when taking an occular history, what do you need to ask about past occular history?
do you wear glasses or contacts?
refractive history
- emmetropia - no refractive error and light rays from infinity are brought to focus on the retina
- ametropia (x3)
1. myopia (short sighted) - light rays from infinity are brought to a focus in front of the retina. This happens if the eye is too long of the lens is too strong
2. hypermetropia (long sighted) - light rays from infinity are brought to focus behind the retina. This happens because the eye is too short or the lens is too weak.
3. astigmatism - the cornea is not spherical (rugby ball shaped) which results in reduced visual acuity.
what else do you need to ask about in an occular history?
PMH - in children it is important to ask about obstetric history, pregnancy and birth details and neonatal history
FH - specifically occular disease, other related diseases eg. diabetes mellitus
DH - occular side effects, allergies, immunisations especially in children
SH - ability to undertake daily activities/ work/ hobbies. if child include development history and milestones
what do you need to test in an opthalmic examination?
vision - accuity, fields, colour perception
pupils - size, reaction to light
eye movements - 6 directions
look at the front of eye with pen torch
