7.1.3. Assesses children’s visual function using appropriate techniques.

Question 1

Hypermetropia - When to prescribe

Answer 1

• 3-6months; partial rx if VA poorer than 6/100 and astigmatism
• 1yr >3.25 - Partial rx (1.00 less sph, half cyl)
• 4yrs and >2.50D, undercorrect by 1.00D to 1.50D (as child does not need fully hypermetropic rx)
• 1.25D in school years - a full rx may be given as emmetropisation has ended

Question 2

Myopia - When to prescribe

Answer 2

• 0-1yrs old; >5.00D reduce by 2D for emmetropisation
• From one year old or walking >2.00D, reduce by 0.5D or 1.00D until school age (emmetropisation)
• 4yrs-early school age; <1.00D or lower if it improves VA, can give full
• School age children - prescribe full rx

Question 3

Astigmatism - when to prescribe

Answer 3

• > 2.50D at age 15months; undercorrect cyl by 1.00D or give 50%
• 2yrs 1.75D> at 2yrs, partial cyl up to 3 to 4years then give full cyl
• 4years >1.25D at age 4yrs
• 1 year> correct oblique astig >0.75D from 1 year
• School age, > 0.50D correct full

Question 4

Tests to check VA for different ages

Answer 4

• 2.5 or under
  
  • Cardiff Acuity Cards
• 2-3 year olds
  
  • Kay pictures
• 3.5-4 year olds
  
  • Kay pictures
  • Snellen letters/numbers
    
    • Same as with kay pictures, you can get patient to have a matching card of different numbers or letters and then present them on a chart
• Retinoscopy
  
  • Mohindra useful
  • Instead of taking 2.00D for the WD, take -1.00 for child 2 or over, -0.75 if below 2 & 1.25 if adult. This is all due to tonic accommodation.

Question 5

Discuss Kay pictures

Answer 5

• The test comprises of a series of symbols, the component parts of which conform to the Snellen principle of subtending 1 minute of arc, but the overall size of the picture subtends 10 minutes of arc.
• It’s an optotype test (figures or letters of different sizes used in testing the acuity of vision)
• The pictures are of common objects that should be known to a child and the test is based on the child recognising and naming the object, although there are matching cards available for very shy children. It is effective and useful for children aged 2-3 years.
  
  • Test for those that cannot name letters or numbers well enough yet
• The test is available as either single pictures or crowding in LogMAR format for use at 3 metres to measure acuity from 1.0 – 0.1, or a standard Snellen format with single pictures for use at 3 or 6 metres to measure acuity from 3/3 (6/6) – 3/30 (6/60).
• • Parent can occlude other eye of child to make him/her feel more comfortable
    
    • When testing other eye, open pages from back of the book so that different arrangement of pictures can be used to avoid child memorisation
• Child might say “nana” instead of “banana” for example so worth knowing what they child is used to naming objects by asking parents beforehand
• Recognition booklets can also be supplied and add to the usefulness of the test, as they can be loaned to a parent for practice in naming the pictures and having one eye occluded at home.
• Good for those with learning difficulties
• WD of 3m. Near vision tested at 33cm. If not within this range, then compensate findings depending on distance used e.g. 50cm instead of 33cm is quite different.

Question 6

Oculo motor balance tests

Answer 6

Ocular Motor Balance (OMB) Assessment Techniques

1. Cover Test:
   
   • Helps identify the presence of a phoria or tropia.
   • Performed under distance and near fixation.
2. Motility Test:
   
   • Determines whether an eye movement is comitant (equal in all gaze directions) or incomitant (varies depending on gaze direction).
3. 20 Base-Out Prism Test:
   
   • Purpose: Tests fusion ability by challenging binocular vision.
   • Procedure:
     
     • Place a 20 diopter base-out prism in front of one eye.
     • Expected response (if fusion is intact):
       
       • The eye under the prism moves in.
       • The fellow eye moves out (per Hering’s Law).
       • Then, the fellow eye moves back in to fuse the images.
     • Abnormal responses:
       
       • Suppression: The eye under the prism does not move.
       • Impaired fusion: If the fellow eye moves out but fails to return to fuse the images, it implies the fellow eye is suppressing.
4. Bruckner Test:
   
   • Uses a direct ophthalmoscope to observe:
     
     • Corneal reflexes.
     • Pupil reflexes.
     • Fundus reflexes.
   • Interpretations:
     
     • Brightness differences in fundus reflexes suggest anisometropia.
     • Elliptical reflexes indicate significant astigmatism.
     • Asymmetry in corneal reflexes suggests strabismus.
     • Differences in size of reflexes can indicate a pupil abnormality.
5. Hirschberg Test:
   
   • Shine a pen torch at both eyes and assess corneal reflex positioning.
   • Findings:
     
     • Reflex displacement is opposite to the eye’s deviation:
       
       • Esotropia: Reflex displaced temporally.
       • Exotropia: Reflex displaced nasally.
   • Limitations:
     
     • Cannot detect phorias (since both eyes fixate accurately during the test).

Question 7

Stereopsis tests

Answer 7

• Lang - Done at 40cm. The child needs to identify three 3D objects like a cat or a truck
• Frisby - Done at 40cm. In one of the four groups, a circular region is printed on the other side of the plate. This makes the region physically stand out in depth. The child has to indicate which of the four groups has a disk ‘popping out’
• Titmus - Done at 40cm. The optometrist can ask the child to describe the fly or ask whether it stands out. Alternatively, they can encourage the child to touch the wings and see where in space the child grasps (above the page or on the page). Nine diamonds each have four circles inside them. One of the circles appears to float in front of the page. The child has to detect the circle that is coming closer to them
• Randot - Not as used

Question 8

Expected visual acuity and rx norms for different ages

Answer 8

• Visual Acuity:New born VA: 6/120 – 6/360
  1 year VA: 6/15 – 6/90
  2 years VA: 6/9 – 6/24
  3 years VA: 6/5 – 6/12
• Rx:
  • Emmetropisation - the eye trying to match its axial length to its optical power as it develops
  • In addition to spherical refractive error astigmatism of around 1 – 2 dioptres is common. This tends to be predominantly against-the-rule in Caucasian infants, but may be with-the-rule in other ethnic groups, e.g. oriental children. This has largely disappeared by about one year of age.

Question 9

Expected norms for stereopsis:

Answer 9

• Frisby measures between 600-5 secs of arc
• TNO is 480-15
• Lang 1 = 1200-550. Lang 2 (sharper detail) = 600-200
• Titmus measures 3000-40 secs of arc. With Titmus, by age 4 it should be 80-100 or so
• From table & other findings:
  
  • at age 6 months —> 600 secs
  • at age 1 year —> 200 secs
  • at age 2 —> 150
  • at age 3 —> 100
  • at age 4 —> 70
  • at age 5 —> 40
  • at age 6 —>10-20

Question 10

What are the norms for Ocular Motor Balance:

Answer 10

• There is similarity in phoria across age groups which suggests that the demand on the fusional vergence system is similar across age for typical binocular conditions.
• By the age of 5 years, a child should cooperate with the measurement of the prism fusion range using a prism bar. The normal range for near is 35 Δ – 45 Δ base-out to 12 Δ – 8 Δ base-in.
• Normal range is:

Vergence Ranges (Expected Norms)

Vergence ranges are measured to assess a patient’s binocular vision ability to converge (Base-Out) and diverge (Base-In) at both distance and near. Below are the typical break values for each category, with expected norms in parentheses:

Distance
- Base-In: 5-10 Δ (norm: 10 Δ)
- Base-Out: 15-20 Δ (norm: 20 Δ)

Near
- Base-In: 15-20 Δ (norm: 20 Δ)
- Base-Out: 35-40 Δ (norm: 40 Δ)

Question 11

When Prescribing…

Answer 11

 All forms of esotropia = full hypermetropic correction; no requirement to subtract any lens power for cycloplegia, reasonable lower limit for glasses Rx is +1.50DS
 Exotropia = uncorrected hypermetropia may be preferrable, assuming good vision
 Future review is to diagnose and classify strabismus, monitor visual development, maintain, or restore BSV where potential is present
 Period of refractive adaptation is recommended after glasses prescribed – may take up to 18 weeks
 Follow up visits usually occur after 6 weeks
 Annual refraction is required to monitor Rx
 College of ophthalmologist dictates child with strabismus is best managed by the orthoptist in conjunction with ophthalmologist in all children under 5

Question 12

4 dioptre prism test

Answer 12

 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
1. Prism placed in front of eye – eye under prism moves in (adducts) to regain fixation
2. 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