Sbisa bar
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.
Neutral density filter bar
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
- Patients wears refractive error.
- VA is recorded in either eye and with both eyes open.
- Occlude abnormal eye. Place bar in front of eye and record filter when VA drops by 2 lines.
- 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
PAT
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
- Visual axis straight and BSV confirmed
- Residual microtropia
- Visual axis reconverge to original angle- prism “eaten up”
- 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.
