Paediatric ophthalmology Flashcards
what is amblyopia?
decrease in vision due to dysfunctional processing of visual information due to retinal image degradation during sensitive period of visual development.
if problem is corrected during visual development period, can restore vision by allowing development to continue.
how does strabismus (a squint) cause amblyopia?
with a squint, the visual axes of the 2 eyes are not aligned, so the image in the squinting eye is suppressed by the brain, so when vision in the 2 eyes is tested together, only 1 object is seen and there is no diplopia.
if prolonged and constant during sensitive period of visual development, it causes a reduced visual acuity in squinting eye as the image being produced by that eye is ignored.
how can strabismus be detected in babies?
shine pentorch into their eyes and look for the corneal light reflex being centered over the pupil in both eyes=absence of strabismus.
what is pseudostrabismus?
illusion of crossed eyes due to nasal epicanthic folds-skin folds of upper eyelid covering inner corner of the eyes.
but patient has normal corneal light reflexes and no refixation on cover testing.
what is the difference between a tropia and a phoria?
a tropia is a misalignment of the eyes which is always present, e.g. exotropia-eye turned outwards, esotropia-inwards, hypertropia-upwards, hypotropia-downwards
a phoria is an eye misalignment that isn’t always present, may occur when patient is fatigued or acutely unwell.
a patient has a L exotropia which is only apparent on cover uncover testing, what would this test show?
when the R eye (good eye) is covered and you look at the L eye, you would see the L eye move inwards in order to correct vision when the good eye is covered.
when would the abnormal eye be unable to take appropriate fixation when the normal eye is covered?
if a nerve palsy causing muscle paralysis, or the eye can’t see.
what is alternate cover testing used to determine?
here cover is moved quickly from eye to eye without allowing binocular vision, observing movement of the uncovered eye means that a phoria (or latent squint) is present, which occurs only when the 2 eyes are not simultaneously stimulated.
most common causes of amblyopia?
refractive error-myopia, hypermetropia, presbyopia or astigmatism, asymmetric most commonly
strabismus-abnormal eye alignment
early onset cataract
what is a non-paralytic/concomitant squint?
this is the common squint seen in childhood
there are full movements of both eyes, BUT only 1 eye is directed towards the fixated target
angle of deviation is constant and unrelated to the direction of gaze
what is a paralytic/incomitant squint?
the visual axes don’t always have to be malaligned, the size of the squint depends on the direction of gaze, and so if a nerve palsy, is greatest in field of action affected by that muscle-e.g. when patient asked to look R and there R lateral rectus muscle is paralysed by an abducens nerve palsy.
there is underaction of 1 or more eye muscles due to nerve palsy, EO muscle disease or globe tethering.
where might there be a problem to cause nystagmus?
vestibular system-central-vertical nystagmus, peripheral-horizontal nystagmus
brainstem nuclei
what happens if a child alternates their squinting (strabismic) eye?
they DON’T develop amblyopia as a focused image always falls on 1 or other retina
however, they don’t develop stereopsis-the ability to see a 3D image (as eye movements and visual alignment not coordinated?)
most common factor in development of a nonparalytic/concomitant squint?
this is where only 1 eye is directed towards the fixated target but movement of both eyes are full
most commonly related to a refractive error which prevents clear image formation on the retina, if this error is dissimilar in the 2 eyes (anisometropia) then 1 retinal image will be blurred.
what do we want to know about a squint in a child?
who was it detected by? at home or at school?
how old was the child? how long has it been there?
which eye?
when is it present? intermittent or constant?
FH of a squint or refractive error-do people in your family where glasses at a young age?
past medical and birth hx of the child?
how does it impact on the child and their family?
investigations: visual acuity any abnormality of eye movement detection and measurement of squint measurement of stereopsis determination of any refractive error careful eye examination, including dilated fundus view.