Unit 7 Visual Function/ BV Flashcards
what type of drop is cyclopentolate
antimuscarinic drop relaxing the iris sphincter muscle (creating a light resistant dilated pupil) and cycloplegia by relaxing the ciliary body
indications for cyclo
o U16’s with symptoms; headaches
o 1st eye tests
o Presenting strabismus in children
o Family history of squints
o Unequal or reduced VA in children
o Variable refraction
o Suspect latent hyperopes
therapeutic uses of cyclo
o To break synechiae – used when dilating anterior uveitis px Anterior/Posterior Uveitis and Posterior Synechiae breakdown: 1-2 drops of 1%
every 6-8 hours
o To reduce ciliary spasm – reduces pain if px has had trauma to the eye e.g., corneal abrasion
* Alleviation of ciliary spasm: 1 drop of 1% 2-3 times a dayc
dosage for cyclo in relation to age
3 months – 12 years; 1 drop of 1%
12 years – adult; 1 drop of 0.5%
contraindications of cyclo
Hypersensitivity to cyclo or any component of preparation
Px with confirmed or suspected angle closure ( not contraindicated in downs syndrome, but greater risk of angle closure)
Baby < 3 months (due to high systemic absorption)
History of neurological disorder e.g., organic brain syndrome
Cyclopentolate should only be used during pregnancy when clearly needed, and it’s unknown if it passes into breast milk
side effects of cyclo
Transient stringing, blurring
Photophobia
Raised IOP
Conjunctival hyperaemia, oedema
Hypersensitivity may occur – facial & upper body rash 4-6 hours post instillation
Transient stinging may also occur due to pH5 (acidic)
Symptoms of adverse reaction:
o Pain/redness in or around eyes
o Disorientated (CNS reaction) 5-10mins after instillation
o Incoherent speech
o Visual disturbances
o Racing pulse or palpitations
If any of the above, advise px’s parent to contact you or seek medical advice ASAP
unwanted side effect of atropine
ventricular tachycardia.
what prism corrects exo
base in
what prism corrects eso
base out
does plus rx make XOT worse?
yes
what rx makes an esotropia worse
minus
Cardiff cards
Useful for very young, non-verbal children
Vanishing optotype’s which measure resolution acuity – the ability of the eye to detect/resolve target (can’t resolve = whole target looks grey)
Cards are held at 50cm or 1m
Examiner uses child’s eye movements to determine if they see the target
Not very sensitive to amblyopic deficits
There are three cards at each acuity level, an endpoint is reached when 2 out of 3 are correct. Range is 6/60 to 6/6 at 1m, 6/120 to 6/12 at 50cm
Kays Pictures
Patient names or matches pictures
Available as crowded or single
Range 6/60 to 6/6
3-meter version used in practice
Before beginning, to practice run at close distance to check understanding
1mm displacement from central cornea - what does it mean
Displaced temporally in SOT, nasally in XOT
1mm displacement from central cornea = 7 degrees = ~15 prism dioptres
Lea symbols
o Tested at 3m.
o 3 symbols used: house, apple and square
o VAs range from 6/4.8 to 6/24
o Can say outloud what they see or point to the same shape on the near card
o Flipperbook
Lang 2
Easy to use, screening test
No dissociating glasses used to it is useful in young children
Dissociation is provided by the vertical cylinders on the front of the card
Each card shows three objects which assess three different levels of stereo
Lang 2 contains a elephant, car and moon – as well as a star which can be seen monocularly
It measures 600 to 200 seconds of arc.
Randot
Random dots & polarised vectographs to present different images to each to allow for stereoscopic testing
Generally used in adults, but animal portion can be used for paediatric patients
Quantitative = 800 – 40 seconds of arc using shapes, animals and circles
titmus
Cross polaroid’s partially dissociate the eyes
Qualitative assessment = gross stereo = fly (3000 sec of arc)
Quantitative assessment = animals = 500 – 100 sec arc, circles = 500 – 40 sec arc of stereopsis.
Some monocular cues
TNO
Most challenging
Random dot stereogram – random dots are viewed with the aid of stereopsis; the disparity between eyes produces a sensation of depth
Red/green filters partially dissociated the eyes
3 screening plates (1980 sec arc) and 3 quantitative plates (480 – 15 sec arc)
Frisby
Only test which uses real depth, with the image printed on the other side of the plastic to the other print
Used at any age
Child has to indicate which of the 4 has the circle sticking out
3 plates at 9 distances allows for 27 disparities between 600 – 5 seconds of arc
However, if the child moves motion parallax cues can reveal the correct answer
OKN drum
OKN response - physiological reflex nystagmus caused by the attempt to maintain fixation on a moving set of black and white bars
Combination of saccade as smooth pursuit eye movements, which develops around 6 months
Crude assessment to show the visual system is intact
Optokinetic drum is spun in front of the px at about 30cm and their eye movements are observed (head is still, eyes track movement of object)
4^ prism test (or prism reflex with 20^)
Access presence of bifoveal fusion, and prove the presence of absence of BSV
Principle the same as prism reflex, but 4^ prism is used
Base out used initially
- Prism placed in front of eye – eye under prism moves in (adducts) to regain fixation
- Other eye makes conjugate movement out, Herring’s law, and then moves back in to take up fixation
- Size of prism keeps image within the central retinal area, elicits the smallest movement reliably detected by experienced observers
- All 3 movements = bifoveal fusion
amount of accommodation expected for 4y/o
14D
amount of accommodation expected for 12 y/o
12D
amount of accommodation expected for 20 y/0
10D
Optokinetic Nystagmus (OKN)
– Combination of a saccade and smooth pursuit eye movement which develops around 6 months.
Crude assessment to show that the visual system is intact.
Using an optokinetic drum, spin it in front of the Px and watch their eye movements. - f asymmetrical movements then neurological cause
normal response is symmetrical and conjugate, with no abnormalities:
Slow phase: The eye moves smoothly in the direction of the stimulus.
Fast phase: The eye moves quickly in the opposite direction of the stimulus.
* Drum is rotate 12-18 inches in front of the px’s eyes and the response is observed
preferential looking (keeler/teller cards)
way of estimating VA in infants and non-verbal Px.
Child is shown two circles. Principle is that the child will look towards the patterned circle
instead of the blank stimulus.
Pattern is a square wave grating (alternate black and white lines of equal thickness).
* Present the grating and record the looking response
* highest SF that gives correct looking response used to estimate VA.
what is a heterophoria
Latent strabismus in which the visual axes are normally directed to the fixation of the object but deviate when the eyes are dissociated
The fusion reflex maintains correct alignment of the 2 eyes - if this fusion reflex is suspended; the eyes will adopt the ‘fusion free’ position & a measurable deviation of the visual axes will occur
During cover-uncover: the covered eye deviates (under the cover) if heterophoria is present
In compensated heterophoria, motor fusion is maintained - therefore sensory fusion and stereopsis should occur
sheards criterion
Sheards - if more than half the fusional reserves need to be used to control the phoria, the visual system will be under stress & the phoria decompensates
Increasing degrees of decompensation = increase in symptoms
Phoria becomes decompensated when it is too large / fusional reserves too small
o Poor + in EXO
o Poor – in ESO
convergence excess esophoria
Convergence excess (deviation greatest at near) – frontal HA, ocular fatigue, distance focus reduced after prolonged near work – more common
divergence weakness esophoria
Divergence weakness (deviation greater at distance) – worse @ end of day, distance difficulties
o Generally due to high myopia because eye is too big, relaxed state eyes naturally diverge
o Possibly due to 6th
o only option is prism or surgery
stereogram - 3 cats
o Demonstrate physiological dip with 2 pens
o Make the 3rd cat through physiological diplopia
o Distance stereogram (SOP) - card held @30cm – px fixates on distance target just over the top of the card
o Near stereogram (XOP) – card @ 40cm problems at near: look at near object in front of stereogram, appreciated 3rd image
o Flat fusion = eyes ability to produce a composite picture from two images which you are looking at
normal fusional reserves
near: positive 26 break, recovery 16
negative 16 break 8 rec
Distance: positive 20 break, 10 recovery
negative 10 break 8 rec
what does myogenic mean
when there is a weakness in the muscle itself
Herrings law of equal innervation
when increased innervation is sent to a muscle to cause it to contract, a simultaneous and equal impulse is sent to the contralateral synergist
Sherrington’s law of reciprocal innervation
increased innervation is sent to a muscle to contract, decrease innervation goes to the direct antagonist which is therefore caused to relax
BHHT
Allows differentiation of SO palsy from one affecting the contralateral SRo
Theres a Positive result = 5^ difference from tilted R to L
muscle sequelae
- Under action of the primary affected muscle
- Overaction of the contralateral synergist – Hering’s Law
- Overaction of the ipsilateral antagonist – Sherrington’s Law
- Inhibition palsy of the contralateral antagonist
Recent onset = only 1st & 2nd
Longstanding = full sequelae established
