Introduction to ophthalmology Flashcards
What is included in ophthalmology?
concerns the eyeball and the visual tract, right back to the visual cortex
What systemic diseases is the visual system commonly involved in?
RA, diabetes, IBD and many cancers
What is the purpose of the eye and how does it do it?
form a focussed image on the retina
- dependent on ocular shape, transparency of the ocular media, and the ability of the transparent structures to refract light
Once image formed on the retina it will be traduced into an electrical signal
What is the cornea?
transparent outer later of the anterior eye - transparent due to the regular spacing of individual collagen fibrils within it
transparency also maintained through relative dehydration
What are the main functions of the cornea?
main refractive component of the eye and serves as a barrier to infection and trauma
What is the sclera?
opaque, mechanically tough outer coating of the eye- opacity is due to the irregular arrangement of collagen fibrils within it
What are the main functions of the sclera?
maintains the shape of the eye, IOP and serves as a barrier to infection and trauma
What is the aqueous humor formed of and where is it found?
formed from an active secretion by the epithelium of the ciliary body, lies in the anterior compartment between the cornea and lens
What are the 2 routes of drainage for the aqueous humor?
1) conventional route = through the trabecular meshwork into the canal of schlemm - travels forward from the ciliary body through the pupil it is reabsorbed at the angle between the iris and cornea
2) Uveoscleral route - through the ciliary body and ciliary circulation (15%)
What is the normal value for IOP what is it dependent upon?
maintained at 10-21mmHg
dependent on dynamic balance between secretion and drainage of aqueous humor
IOP>21mmHg = glaucoma
What is the crystalline lens formed of?
transparent due to regular fibre arrangement - avascular structure gaining nutrients and oxygen from aqueous humor and air
What is the function of the lens?
fine focussing - structural irregularities can be caused by age-related, metabolic or congenital changes in the lens fibre - lead to opacification and cataract formation
What is the vitreous humor?
transparent medium formed from collagen, secreting hyalocytes and glycosaminoglycan
What is the function of the vitreous humor?
serves to protect the ocular structures making up 80% of the globe volume
What is the most important layer of the retina?
transparent and formed of several layers - most important is the photoreceptors which transduce light energy into nerve impulses
What is the macula?
central vision are of the retina - lies lateral to the optic disc within the vascular arcade - contains majority of cone photoreceptors giving it highest visual acuity
What is the fovea?
part of the macula which contains all cones and no rod photoreceptors
What is the optic disc?
optic disc of the retina always lies nasally - corresponds to the blind spot of the visual field as it does not contain photoreceptors- due to its location = where the non-myelinated optic nerve fibers exit the eye as the optic nerve
How does the visual pathway progress from the retina?
from the retina s the optic nerve, there is a hemidecussation at the optic chasm, leading back to the optic tract which terminates by synapsing in the lateral geniculate nucleus giving rise to the optic radiation
Optic radiation terminates in the visual cortex where the image is processed
What are some of the key characteristics that need to be established in an ophthalmic history?
unilateral or bilateral
- with unilateral it is more likely to be a problem with the eye itself
onset and duration of the symptoms and any associated factors
e.g. pain, photophobia, redness, discharge
What are some visual symptoms the patient might have?
visual loss, visual field defect, flashes/floaters and diplopia
What are the common symptoms seen with damage to the front of the eye?
red eye, pain, photophobia, discharge
What are the common symptoms seen with damage to the back of the eye?
painless visual loss
What are the common symptoms seen with damage to the macula ?
distortion of visions/central scotoma
What are the common symptoms seen with damage to the vitreous or retina?
flashes / floaters
What can amiodarone do to the eye?
cause deposits in the eye
What can some TB antibiotics cause?
optic nerve damage
What should the social history of an ophthalmic history focus on?
focus on ability of person to carry out their general activities of daily living - also important to see if they are still driving as it may be illegal
What additional aspects need to be added to an ophthalmic history for a child?
obstetric history, pregnancy, birth details and neonatal problems - premature infants are more likely to have retinopathy, and eyes can be damaged in forceps delivery
developmental history and milestones
immunization history
What is emmetropia?
vision that does not require any lens correction as there is no refractive error and light rays are brought to focus on the retina
What is ametropia?
requires lens correction and comes in 3 main forms
- myopia
- hypermetropia
- astigmatism
What is myopia?
short sightedness
- due to either the eye being too long (axial myopia) or the lens being too strong (index myopia) so light rays are brought to focus in front of the retina
What is hypermetropia?
long sightedness
eye is too short or the converging power of the lens is too weak so light rays brought to focus behind the retina
What is astigmatism?
occurs where the cornea is not spherical meaning that the curvature differs at different angles
What is the accommodation reflex?
physiological mechanism that allows close objects to be focused on the retina
What happens in the non-accomadative state?
circular ciliary muscles are relaxed allowing the suspensory ligaments of the lens to remain taught
What happens during accommodation?
ciliary muscles contract and the suspensory ligaments become more lax, causing the lens to assume a more convex shape
What happens to the lens with age?
usually >45 the lens gradually hardens and is unable to accommodate - this is presbyopia and is corrected by using weak converging reading glasses when focussing on nearby objects
What is the first test ophthalmic examination?
visual acuity using a snellen chart - if the pt can’t do that then they can count fingers, moving hands and light perception can be used
What is tested after visual acuity?
pupillary reaction to light
How is the front and back of the eye checked?
Front of the eye - use a pen torch, ophthalmoscope or slit-lamp biomicroscope
Back of the eye - check using a direct or indirect ophthalmoscope
What is an ophthalmoscope?
instrument used to look at the retina - it is formed of a lens, light and diaphragm
What does the ophthalmoscope need to be corrected for in terms of each individual patient?
corrected to the patient’s refractive error
If patients have concave lenses to correct for myopia what should you do to the ophthalmoscope?
Everything will look smaller through the glasses so you should dial to the red numbers on the ophthalmoscope
If patients have convex lenses to correct for hypermetropia what should you do to the ophthalmoscope?
Everything will be magnified through the glasses so you should dial to the black numbers on the ophthalmoscope
What does a thicker lens mean?
the stronger the glasses are - therefore higher number of correction on the ophthalmoscope
How is direct ophthalmoscopy carried out?
should be carried out in a dark room
- start by using your dominant eye on the patient’s same eye
- general approach should be from an angle about 15 degrees temporal from the patient at their level, by aiming 15 degrees nasal you should hit the optic disc
- red reflex is assessed at first
- optic disc should be assessed in terms of color (pink if there is no atrophy), cup:disc ratio, contour, and the formation of any new vessels
- calibre of the retinal vessels should be checked, arterioles are thinner and lighter than veins - if you cannot see the disc follow along blood vessels
What is the first stage of diabetic retinopathy?
background retinopathy - not sight threatening
- there will be scattered hemorrhages and hard exudates present, not affecting the macula
What happens in diabetic maculopathy?
hemorrhages and hard exudates spread and involve the macula - may be a leakage of fluid from the vasculature causing macula edema
How should diabetic maculopathy be treated?
focal laser
After background retinopathy, what happens in diabetic retinopathy?
pre-proliferative retinopathy - defined as >5 cotton wool spots indicating retinal ischemia - this is sight threatening
- venous changes include thickening, tortuosity and beading
What is the final stage of diabetic retinopathy?
proliferative retinopathy - involves the formation of new blood vessels
- NVD is new vessels in the disc and NVE is everywhere else
These new vessels can bleed causing vitreous hemorrhage - requires extensive laser treatment and pan-retinal photocoagulation
