Relative afferent pupillary defect (RAPD)

[voicesinmyhead]

RAPD- when light shone to affected eye from unaffected eye, there is a apparent dilation instead of constriction. (as prev constricted eye (nl consensual reflex) constricts less (defective direct reflex))

If there is a lesion to optic nerve - RAPD in same eye.

If lesion in optic tract - RAPD in contralateral eye.

Could someone explain the cause to me if it is correct?

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[Transposony]

That's correct since RAPD is due to relative defect in the afferent pathway.

There are two explanations for this:
(1) the temporal visual field is larger than the nasal field, and
(2) nasal retina has more sensitivity than temporal retina.

 

[voicesinmyhead]

Thanks.

Just trying to work this out.

Lets say the patient has a lesion in right optic tract (which carries fibres from Rt temporal field and Lt Nasal field)

So if temporal field is larger than the nasal field, then shouldnt we get a RAPD in the right eye, rather than contralateral/left one?

The second explanation works.

Maybe im wrong in my thinking?

 

[Transposony]

Thanks.

Just trying to work this out.

Lets say the patient has a lesion in right optic tract (which carries fibres from Rt temporal field and Lt Nasal field)

So if temporal field is larger than the nasal field, then shouldnt we get a RAPD in the right eye, rather than contralateral/left one?

The second explanation works.

Maybe im wrong in my thinking?

1) and 2) means same thing.
Nasal retina=Temporal visual field.
HTH

 

[voicesinmyhead]

thanks!