ADDITIONAL TESTS

Question 1

Sbisa bar

Answer 1

Purpose:
Measures density of suppression
Strength of normal or abnormal BSV
Indications:
Density of suppression: assess the risk of intractable diplopia e.g. In an older child starting occlusion.
To determine how well abnormal correspondence is established.

Method:
Performed at near.
Patient looks at a pen torch.
Bar is held over fixing eye and filters increased light-dark.
Filters increased until diplopia, a swap of fixation or a manifest deviation is observed.

Question 2

Neutral density filter bar

Answer 2

When a graded density filter is placed in front of a…

• Normal eye
• An eye with uncorrected refractive error
• An eye with an organic lesion eg. Optic neuritis
  The vision is reduced sooner and to a great extent than if placed in front of an amblyopic eye.
  Most reliable in strabismic amblyopia than anisometropic! Anisometropic will have similar results to a normal eye.
  Indications:
• Differentiate the cause of reduced vision between organic lesion and amblyopia: For example, a patient with suspected optic neuritis comes in who reports a
  history of amblyopia in the same eye.
• Can help to differentiate different types of amblyopia
  Method

1. Patients wears refractive error.
2. VA is recorded in either eye and with both eyes open.
3. Occlude abnormal eye. Place bar in front of eye and record filter when VA drops by 2 lines.
4. Occlude normal eye and place this same filter in front of the eye.
   Results:
   If VA in abnormal eye is the same with and without the filter= strabismic amblyopia.
   IF VA in abnormal eye significantly decreases with the filter the following can be suspected..

• Organic Lesion
• Anisometropic amblyopia
  Deprivational Amblyopia

Question 3

PAT

Answer 3

Use:
Usually pre surgery
Assess for potential for BSV
Decide on an appropriate target angle
Method:
Completely correct or overcorrect angle of deviation with Fresnel prisms.
Observe patients motor response over a period of time. One week later
Prisms divided between the two lenses.
Assessment of eyes prior to patient leaving, if angle has increased 8^ or more before leaving clinic, strength ^.
Requirements:
Equal/near equal VA 6/12 or better
Deviation must not exceed 40^

Results
4 Possible Responses

5. Visual axis straight and BSV confirmed
6. Residual microtropia
7. Visual axis reconverge to original angle- prism “eaten up”
8. Visual axis remain convergent

• If there is demonstrable BSV, Bifoveal or microtropia= prism responder.
  Prism can be increases to assess max angle. Patient seen at weekly intervals until stable angle less than 8^ is seen. Surgery performed at max angle found.
• If binocular potential cannot be shown= non responder. Surgery based on PCT.