Clinical Optics Flashcards
what is eye refractive index?
manifestation of the refractory components of the eye (cornea, aqueous humour, lens and vitreous humour), their refractive indices and length of the eye
what is a refractive error?
occur when eye is unable to focus light
what are the clinical features of refractive errors?
Double vision, haziness, flare or halo around bright lights, squinting, headaches, eye strain
what is myopia?
short sightedness
what is hypermetropia?
long-sightedness
what are the causes of myopia?
Unclear
Hereditary component
Link between myopia, academia and occupation
Environmental?
what are the causes of hypermetropia?
Physiological – variation of normal, hereditary
Pathological – developmental abnormality, trauma
Functional – presbyopia, age
what are the causes of astigmatism?
Hereditary
Trauma or surgery
Keratoconus
what is the pathophysiology of myopia?
Parallel rays of light entering the cell focus at a point short of retina
Due to length – too long or
Refractive – too curved or lens too thick, corneal flattening
what is the pathophysiology of hypermetropia?
Rays of light entering eye focus at a point beyond retina
Eyeball is too short, or the lens/cornea become thinner + flatter
what is the pathophysiology of astigmatism?
Cornea has irregular curvature
Light enters at different points and are focused differently
how is myopia denoted?
(-) meaning negative lens is required to correct?
how is hypermetropia denoted?
(+) meaning positive lens are required to correct
what are the clinical features of myopia?
Blurry vision when looking at things far away
Increased risk of retinal detachment (retinal stretching)
what are the clinical features of hypermetropia?
Blurry vision when looking at shirt distances
Headaches, squinting
what are the clinical features of astigmatism?
Blurred vision at all distances
Headaches
Difficulty driving at night
how is myopia treated?
Glasses (divergent/negative lens/concave)
Not required if asymptomatic
how is hypermetropia treated?
If asymptomatic no treatment
Positive dioptric powered lens (converging)
how is astigmatism treated?
Cylindered lens
what is presbyopia?
Reduction of accommodation
what is the cause of presbyopia?
ageing
what is the underlying mechanism of presbyopia?
Lens become less elastic, ciliary body loses ability to contract
what are the clinical features of presbyopia?
Difficulty with near vision
what is the management of presbyopia?
o Convergent (+) lens o Simple reading glasses o Bifocal or varifocal lens
what are the causes of squints?
refractive, non-refractive, mixed, nerve palsies, myogenic, cataract, paralytic, non-paralytic, retinoblastoma
what is a exotropia squint?
Divergent squint (affected eye looks outwards) – divergent angle between eyes
what is a esotropia squint?
Convergent squint (affected eye looks inwards) – convergent angle between eyes
what is a hypertropia squint?
Upwards vertical squint (affected eye looks up) – one eye is lower to the other
what is a hypotropia squint?
Downwards vertical squint (affected eye looks down) – one eye is superior
what is a manifest squint?
Present all the time and is referred to as a “tropia”
what is a latent squint?
On present on dissociation of the eyes and is referred to as a “phoria”
what are the clinical features of squints?
- Misalignment of the eye
- Double vision
- Eye strain
how are squints diagnosed?
- Visual Acuity
- Alignment of the visual axes
- Cover/Uncover test
- Alternate Cover Test
- Assess ocular movements
- Fundoscopy
what is the cover/uncover test?
o Cover the squinting eye. The unaffected eye will not deviate
o Cover the unaffected eye. The squinting eye will move to take up fixation
o Since eye movements are equal and opposite then as the squint moves to take up fixation, the unaffected eye also moves.
o Remove the cover from the unaffected eye. The unaffected eye will resume fixation and the squint will return to it’s original position.
what is the alternate cover test?
Move the cover rapidly between the two eyes. This dissociates the eyes and will show if there is a latent squint.
what is the management of squints?
3Os
o Optical – assess refractive state – spectacles for correction
o Orthoptic – patching good eye encourages use of the one which squint
o Operation - resection and recession of rectus muscles
