Introduction to Ophthalmology Flashcards
How is transparency of the cornea maintained?
relative dehydration of the stroma is maintained by impermeable epithelial barrier and active pumping mechanisms of corneal endothelium. regular spacing of individual stromal collagen fibrils
What is the sclera? Describe it.
Outer coat of the eye; opaque, mechanically tough. forms posterior 5/6 of the outer coat of the eye. consists of irregularly arranged collagen fibres
How can you visually differentiate between the retinal arterioles and retinal veins?
retinal arterioles are thinner and lighter in colour than the veins
What forms the aqueous humour and where is it located?
Active secretion by epithelium of the ciliary body in the anterior and posterior chambers; anterior is between the cornea and iris and posterior is between the iris and lens
What are three functions of the sclera?
- maintains the eye shape
- maintains intraocular pressure
- barrier to infection and trauma
What are the two routes of drainage of the eye? What are the relative proportions of each?
- Conventional route 85%: drains through the trabecular meshwork into the canal of Schlemm in the anterior chamber angle
- Uvoscleral route 15%: drains through ciliary body and into ciliary circulation
Where is the ciliary body located?
Behind the iris (continuous with it anteriorly, posteriorly continuous with choroid) and encircling the lens, forms part of the uveal tract; divides the posterior chamber from the vitreous
Where is the trabecular meshwork located?
Anterior chamber drainage angle; in front of the iris, in angle between iris and cornea
What is the range of normal intraocular pressure?
10-21mmHg
What maintains the intraocular pressure?
dynamic balance between secretion and drainage of aqueous humour
What is the general name of the condition in which there is high intraocular pressure?
Glaucoma
What can glaucoma lead to if untreated?
Loss of visual field and eventual blindness
What are 3 things that help ensure the lens is transparent?
- orderly arrangement of the lens fibres
- small difference in refractive index between the various components
- absence of blood vessels
What are 3 important roles of the vitreous humour?
- transparent
- protects the ocular structures
- passive “transport and removal” of metabolites
where is the vitreous humour located?
between lens and retina
What are the two key structures present in the retina?
- Rods/ photoreceptors: 120 million (monochromatic)
2. Cones: 6 million (colour and fine vision)
What are the two key structures present in the retina?
- Rods: 120 million (monochromatic)
- Cones: 6 million (colour and fine vision)
(both types of photoreceptors)
What are 3 structures present in between the photoreceptors (rods and cones) and optic nerve fibres?
bipolar cells, synapse, ganglion cells
What is the macula?
Central vision area of the retina
Where is the macula located?
Lies lateral (temporal) to the optic disc: 3-3.5 mm temporal to temporal edge
How can the macula be identified/ what does it look like?
Slightly darker than the rest of the retina due to yellow luteal pigment
What is the centre of the macula and how is it different?
Fovea; rod free, highest visual acuity
What part of the optic nerve fibres are demyelinated?
Nerve fibres are only demyelinated after leaving the eye
What is the course of the optic nerve fibres? Include the 6 components
nasal fibres decussate at the optic chiasm (but not temporal fibres). optic nerves –> optic chiasm –> optic tracts –> lateral geniculate nuclei (thalamus)–> optic radiations –> visual cortex (occipital lobe)
What is the optic disc?
entry of the optic nerve into the eye, approximately 1.5x1.5mm
What are 7 general symptoms and 4 visual symptoms to ask about in an ophthalmological history?
General: 1. unilateral/ bilateral 2. onset 3. duration 4. pain 5. photophobia 6. redness 7. discharge Visual: 1. visual loss or distortion 2. field defect, where 3. flashers/floaters 4. diplopia - horizontal/vertical/binocular/monocular
What is key (in addition to general and visual symptoms) that should be included in an ophthalmological history?
Past ocular history, including refractive (spectacles, contact lenses)
Which part of the eye will a red eye be associated with?
Front of eye
Which part of the eye will painless loss of vision be associated with?
Back of eye
Which part of the eye will distortion of vision/central scotoma be associated with?
Macula
Which part of the eye will flashes and floaters be associated with?
Vitreous or retina
What are two classes of refractive error?
Emmetropia (no refractive error) and ametropia
What are the 3 types of ametropia?
myopia, hypermetropia, astigmatism
What is myopia?
Short sightedness; light rays brought to focus in front of the retina as the eye is too long OR the lens is too strong
What is an example of when the lens is too strong, causing myopia, and what is this called?
Nuclear sclerotic cataract; index myopia
What is hypermetropia?
Long-sightedness; light rays brought to a focus behind the retina as the eye is too short OR converging power of the cornea or lens is too weak
What is astigmatism
the cornea is not spherical, i.e. is rugby ball shaped rather than football shaped
What is accommodation?
Physiological mechanism that allows close objects to be focused on the retina
What changes occur in the ciliary muscle to bring about accommodation?
in the non-accomodative state it is relaxed, allowing the suspensory ligaments to remain taught. in accommodation, the ciliary muscle contracts and suspensory ligaments become lax, causing the naturally elastic lens to assume a more globular (convex) shape
What is presbyopia?
with age (usually over 45 years) the lens gradually hardens and is unable to accommodate (as in hypermetropia)
How can presbyopia be corrected?
By a weak converging (plus) convex lens
What are 5 things to examine in an eye exam
- Visual acuity
- visual fields
- colour vision
- pupil reflexes (light and accommodation),
- Ophthalmoscopy
(AFRO+ colour vision)
Why shouldn’t you ask a patient to look into the ophthalmoscope light?
They will accommodate so will constrict, and pupil will also constrict due to light
How can you determine whether a patient is hypermetropic or myopic? 2 stages
- ask them - do you struggle with seeing things up close e.g. reading, or far away e.g. television
- look through their glasses; if things appear smaller–> myopic, if larger –> hypermetropic
How should the ophthalmoscope be adjusted for hypermetropia and myopia?
- Hypermetropia –> positive i.e. black numbers
- Myopia –> negative i.e. red numbers
(if thicker glasses, dial to a higher number)
How should you decide which diaphragm level (Size of light beam) to use in ophthalmoscopy?
use small white beam for undilated pupil, large white beam for dilated pupil
What are 4 things to look for/ comment on in opthalmoscopy?
colour of disc, cup:disc ratio, contour of disc, new vessels
What is the difference between retinopathy and maculopathy?
haemorrhages and hard exudates etc. don’t affect macula in retinopathy but do in maculopathy, which is sight threatening
How can pre-proliferative retinopathy be identified?
more than five cotton wool spots
What 3 venous changes can occur in pre-proliferative retinopathy?
thickening, tortuosity or beading
How can proliferative retinopathy be classified?
NVE - new vessels everywhere
NVD - new vessels of disc
