Clinics, Refraction Flashcards
What are the 3 levels that make up binocular vision?
-simultaneous perception
-fusion
-stereopsis
what are the advantages of binocular vision?
-increases FOV
-compensates for physiological blind spot
-binocular summation
-stereopsis
where is the physiological blindspot?
the optic disk
when does BV start developing in babies
not present at birth, starts developing mainly during first 2/3 years and stops after 8/9 years
what is the definition of binocular vision?
Condition in which both eyes contribute
towards producing a percept which may or
may not be fused into a single impression
what makes up the near vision triad?
-conversion
-accommodation
-miosis = pupil constriction
what is near point of accommodation?
the distance at which the eyes see when fully accommodated
how does near point of accommodation change with age?
it increases (i.e. the point the object becomes clear)
name 5 causes of accommodative dysfunction
- Systemic and ocular medication
- Ocular trauma
- Inflammatory disease
- Metabolic disorders e.g. diabetes
- Down’s syndrome and Cerebral palsy (reduced amplitude)
- Idiopathic
name 5 symptoms of accommodative dysfunction
- Headache
- Asthenopia (eyestrain)
- Near vision blur
- Difficulty in reading
- Difficulty in changing focus
why is it important to know dynamic ret?
it may be the only way to assess accommodation in children
what are the two methods of dynamic ret?
-(monocular estimation method) MEM
-Nott
what shows lag and what shows lead in dynamic ret?
-lag = with movement so add positive lens
-lead= against movement so negative lens
when reading, why is it normal for us to use less than required AoA? What does this mean?
as we dont focus exactly on the target but instead somewhere behind it due to depth of focus. this means the accommodative response is less than the accommodative stimulus meaning there is accommodative lag
what is normal accommodative lag?
between +0.25DS- +0.75DS
where do eyes focus in relation to the near target in accommodative lag and lead?
-in lag they focus behind the target as response is smaller than the stimulus
-in lead they focus in front of the target as the response is greater than the stimulus
what could it mean if dynamic ret results are >+1.00DS? (accommodative lag)
- near esophoria because convergence system tries to compensate for the insufficient accommodation
- accommodative dysfunction (paresis, fatigue)
- under-corrected hyperope or over-corrected myope
- Higher + diopters (e.g., +2.00DS) shows presbyopia signs
what could it mean if dynamic ret results are < +0.25DS? (accommodative lead)
- Near exophoria
- Spasm of accommodation
- Under-corrected myope
- Latent hyperopia
how can you modify how you do dynamic ret for children?
to maintain appropriate fixation and accommodation, you can ask children to read some of the letters out aloud or to name/describe details in the picture
what are the most common errors when assessing accommodation with dynamic ret?
- Not realising that a small lag of accommodation is normal.
- Taking too long to make a judgement as to whether the reflex is moving ‘with’ or ‘against.’
- Nott method: inaccurate measurement of the distance of the target to the patient and the retinoscope distance from the patient that gives reversal.
- MEM method: leaving the lens in place for too long. The lens can alter the accommodation of the eye.
when might you do Nott dynamic ret instead of MEM?
if you dont have trial lenses to hand
when does presbyopia start becoming clinically significant? what can cause it to occur earlier?
-clinically significant in the fifth decade of life
-occurs earlier in people living in hot climates, people with short arms, short working distances & hyperopes
what happens to the comfortable near point with age?
it increases because accommodation reduces but the percentage of accommodation stays the same as before aging
when determining working distance, what do reading and computer screen distances range from?
-reading : 33-40cm
-computer screens: 50-60cm
what are the common errors when assessing reading addition?
- Assessing the near ADD without the distance correction in place
- Not insisting on the patient to read the lower line they can identify clearly
- Presenting the positive slide of the flippers when refining final add instead of the negative
- Not considering the hobbies of the patient i.e., knitting, sewing, crafting , modelling
- Not considering the occupation of the patient i.e. a contrabass player may benefit from an intermediate add alone for the distance he reads his music
when determining the range of vision:
-how do you find the closest point of near vision?
-how do you find the furthest point of near vision?
-closest point = 1/(near add + AoA)
-furthest point = 1/(near add)
what are the closest and furthest points of near vision in the range of clear vision
-closest point is where px uses total accommodative amplitude through near add
-farthest point is where px relaxes their accom through near add
give 3 tips when assessing near reading addition
-stimulate the workstation environment
-keep referring back to h+s checking the needs of your patient
-check the range of your near add
in general between what ages do people become presbyopic?
between ages 40-45 years old
what factors make the age of becoming presbyopic differ?
-ethnic group
-length of arms
-different working distances
-wether they are hyperopic or myopic to begin with
(those with long arms/working distances and myopes will see prebyopic change later, hyperopes, short arms and working distances later)
how does aoa change with age?
it reduces
why does average reading addition continue to increase after age 6o even though between 55-60 years objective tests indicate accommodation is 0?
due to the increases in add needed by some older subjects with reduced VA who use a reduced working distance to provide some magnification to offset the VA loss.
