7.1.4 Understands the techniques of the assessment of infants. Flashcards
History
- Any concerns about their vision?
- Medical history – milestones, significant or recent illness, ongoing conditions, trauma, allergies
- Obstetric history – mothers health during pregnancy, birth complications, neonatal history
- Family history – strabismus, refractive error, severe visual defects
1. History taking in relation to strabismus
1. Direction
1. Age of which it was noticed & who noticed it
1. Onset – sudden or gradual
1. Constant or intermittent
1. When the squint is seen – tired?
1. If the angle is increased or decreased
1. Other features e.g., AHP - Do they sit close to tv or hold books close?
- Do they see themselves in a mirror and at what distance?
- Do they return a silent smile?
*
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
Kay 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
Corneal reflexes
Spotlight @ near, position of the corneal reflection in the fixation eye noted & compared with the reflection of the deviating eye
Displaced temporally in SOT, nasally in XOT
1mm displacement from central cornea = 7 degrees = ~15 prism dioptres
Cover test
- Main method of differentiating manifest and latent strabismus
- Near with pen torch, near with accommodative target, distance with letter
- The information that can be obtained
1. Direction of deviation
1. Difference in angle from N to D
1. Effect of accommodation
1. Effect of patient’s refractive error
1. Other characteristics of manifest: constant vs intermittent, unilateral or alternating
1. Estimation of VA in a constantly squinting eye by studying fixation
1. Speed of recovery if latent
1. Present of latent or manifest nystagmus
1. Concomitance or incomitance - If latent: direction, size, speed of recovery, changes at distances, with/without specs
- If manifest: direction, size, changes at distances, accommodation, with/without specs
- Note other findings: inability to take up fixation, intolerance, latent nystagmus
*
Stereopsis (8 types)
Stereopsis
Generally developed to adult level by 6 months – however compliance can be difficult
All of the below (except Frisby) have a viewing distance of 40cm.
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
Don’t have in practice
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
3. Prism placed in front of eye – eye under prism moves in (adducts) to regain fixation
4. 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
Cyclopentolate hydrochloride
Indicated: 1st eye exam (NHS states all under 16s), children with symptoms, family history of high Rx/strabismus, unequal or reduced VAs, variable refraction, pseudo myopes, latent hyperopes
Antimuscarinic drug acting on the parasympathetic nervous system; causes pupil dilation due to sphincter pupillae relaxation and temporarily paralyses the ciliary muscle
This allows us to relax accommodation and obtain a more accurate refraction
30-40 minutes to work
Ensure full paralysis by ensuring ret reflex is stable
Binocular Vision requires:
- Motor fusion - point in right way to give fixation lock
o Maintained by the vergence mechanism
o Single fused image during vergence movements
o How the EOMs control movements i.e., eyes pointing the right way to give fixation lock
o Interaction between this mechanism and size of deviation determines how well a phoria is compensated
- Sensory fusion
o Appreciate 2 similar images and interpret as one
o How the eyes perceive and how the brain utilises
- Stereopsis
o Need both of these mechanisms to allow for stereopsis
If you are not binocular, then you don’t have any of these
Normal BSV lies on…
Horopter: all images constant size, viewed as single
Panums fusional area: images here as viewed in 3D; images outside space cause large disparities that cannot be fused i.e., physiological diplopia
Retinal rivalry: brain can’t fuse dissimilar images; VA/state of each eye determines dominant eye & the image perceived
Physiological diplopia
Normal retinal correspondence: both foveae have common visual directions, retinal elements nasal to fovea in one eye correspond to temporal elements in the other eye
Emmetropisation & development of binocular vision
- Emmetropisation: expected reduction in neonatal refractive error during normal growth
1. Most active phase 12-18 months
1. Can eradicate 3.00DS / 1.50DC
1. Active element = visual feedback mechanism i.e., time outdoors
1. Passive element = growth of eye; decrease of corneal radius of curvature / increase in axial length - Stereopsis becomes evident at ~ 6 months
- Critical period for binocular vision 0-5 years; most plastic
- Sensitive period 5-8 years; still vulnerable to damage and may respond to treatment
- By age 6; plane of focus should lie on the retina
- 6/6 & 40-60” stereo
What happens with BSV isn’t functioning properly at different ages
- Before age 3 – sensory adaptations & abnormal reflexes
- 3-6 years – symptoms followed by sensory adaptations
- Adults – confusion and diplopia
*
Pathological diplopia
- Can be caused by issue with either motor or sensory fusion:
- (Motor): diplopia occurs in strabismus with minimal suppression caused by the simultaneous appreciation of two separate images by non-corresponding points
1. i.e., acquired squint
1. i.e., decompensating phoria
1. i.e., manifest going out-with its suppression scotoma - (Sensory): diplopia occurs because the disparity between images is too great to fuse
Anisometropia / aniseikonia - EXO = crossed
- ESO = uncrossed
Sensory adaptations
Suppression
- Cortical mechanism; mental inhibition of visual sensations in one eye in favour of the other
- Develops rapidly in childhood; more slowly in older children up to 10years
- Suppression should only be treated if the deviation can be eliminated and strong chance of restoring BSV
- Physiological = normal
- Pathological = used to overcome binocular diplopia in manifest strabismus or incompatible images due to significant degree of anisometropia – central suppression develops in poorer eye
- Investigate using: bagolini glasses, worth’s 4 lights, fixation disparity
- Suppression scotoma is when you map out the area/size of the suppression i.e., when you are straight you are at 0; if you are an ESO + & EXO.
- i.e., if scotoma +20 and px is 25 they will get double vision
- Global suppression = not a term often used, relates to the whole eye
Abnormal retinal correspondence
- Fovea in one eye has a common visual direction with an extra-foveal point in the other eye
- The originally non-corresponding retinal areas now cooperate to produce a form of anomalous BSV in the presence of a manifest strabismus (stereo will not be better than 60”)
- Can only occur constant tropia, small angle i.e., <10, VA ~ 6/12
- Can result in poor results following surgery if not assessed correctly
- Only occurs binocularly (not the same as eccentric fixation which is monocular)
- Harmonious: present in presence of strabismus at objective angle i.e., the angle of the anomaly = angle of the deviation
- Unharmonious: angle of the anomaly >0, but < angle of the deviation. This will only work if the size of the deviation is reduced surgically or using prisms
Cardiff acuity cards;
- 1-3 years old (Assessor will ask you how these cards work!)
- These have pictures & are often more fun, considering px’s over age of 1 can typically recognise basic pictures. These are vanishing optotypes. When beyond the resolution acuity, the picture will vanish for the px.
*
Difference between Teller & Cardiff cards:
- Teller is preferential looking which just focus on resolution acuity
- Cardiff uses vanishing optotypes which focus on resolution & recognition due to the pictures, giving more precise endpoint
- Cardiff is in snellen notation but Teller is cycles per degree
- Teller has peephole, Cardiff doesn’t
Keeler or Teller acuity cards;
- striped grating presented on one side of a large board in black & white. Keeler version has a white bordered outline. Another identical white outline is present at the other side of the card, with no grating.
- The amount of black & white used to make the black & white stripes is the same luminance as the grey background. This means that infant with poor resolution acuity won’t be able to resolve the stripes & hence won’t be visually curious towards either target presented.
- The examiner doesn’t know where the grating is on the other side. They are only focussed on the eye movements of the patient. There is a peephole halfway between the two patches through which the optometrist watches the infant.
- Working distance = 55cm. Same width of the card so the card can be a good estimate of WD.
- The examiner has to present each grating 4 times and must judge the px’s eye movements correctly 3 of those times. As in, if the px’s eyes move right everytime you present the same card, then you’re pretty certain they’ve resolved it correctly.
