ID:  63-year-old retired male.

CC:   Vision loss OU following his left occipital haemorrhage.

HPI:

• 1993  - Right occipital haemorrhage.
• 1997 March 10 - Severe intermittent headache associated with nausea, vomiting, and dimming of vision. CT of head revealed a left occipital haemorrhage
• 1997 May 12 ­ Suffered another stroke and right occipital haemorrhage leaving him mostly blind to color and shapes.
• He has trouble discerning colours and shape.

PMHx:
No known history of cardiac disease, no diabetes, no neck manipulations, mild HTN only.
Long history of migraine headaches relieved by fiorinal.

SHx: non-smoker, no alcohol.
FHxX: non-contributory
ROSX: no constitutional symptoms
Allergies: none
MEDS: fiorinal prn.

EXAM:

SYSTEMIC
Vitals: BP:180/100 HR:72 reg. T: afebrile
CV:  normal heart sounds with S3 present, no murmurs or bruits
RESP:  clear breath sounds
CNS: Mental status examination normal.
  Cranial Nerves: normal except for vision.
  Motor: strength 5/5 bilaterally, reflexes 2+ and symmetric,
normal tone, toes downgoing.
  Sensory: normal bilaterally.
  Cerebellar: unremarkable.

OPHTHALMIC
Vision: OD: Hand Motion  OS: Hand Motion
The patient states he can perceive motion in either field, but he has trouble discerning shape or contrast.
Pupils: Equal, briskly reactive to light.
Ishihara Colour Plates: 0/10 OU
EOM: Normal OU.
OKN: Normal OU.
SLE: Normal OU.
IOP: 16 OU.
Fundus: Normal OU.
Visual Fields: Right and Left presented.

INVESTIGATIONS:
Angiogram (March 97): no abnormalities noted.

CT Head (May 97):

• Intra-axial hyper-intense lesion of the left occipital lobe with mass effect diagnosed as a new left occipital hematoma.
• There is also a large irregular old appearing lesion of right occipital lobe with atrophy of tissue from the prior hematoma.

DIAGNOSIS:
Bilateral haemorrhagic strokes, etiology: presumed congophilic angiopathy.
 
 
  Riddoch Phenomenon

Historical Background:

Prior to Riddoch’s work (1917), ophthalmologists believed that area V1 (calcerine cortex) was the "sole" visual perceptive cortex:

"… the only entering place of the visual radiation into the organ of psyche." (Flechsig, 1905)

In 1910 the notion of a perceptive centre for colour outside V1 was absurd.

"…with the calcerine cortex destroyed and the (extra-striate cortex) intact, the patient would have to be absolutely blind and yet be able to see colours, which makes no sense." (Henschen 1910)

This scenario, which seemed so improbable to Henschen, is the very one that Riddoch described in his 1917 paper.

Riddoch examined WWI soldiers with gunshot wounds that affected the calcerine cortex (V1) who demonstrated a dissociation of visual perception, such that motion is perceived in a portion of the visual field otherwise blind due to occipital lobe injury.

This is called the Riddoch phenomenon.

Visual Information Pathways:

There are two streams of visual information from the retina - parvocellular (P) stream and magnocellular (M) stream:
- M stream (or dorsal stream) is unconscious, and is more involved with "where" - motion and location perception.
- P stream (or ventral stream) is conscious, is more involved with "what" - colour and shape perception.

Milner lists several projections from the retina to areas outside of V1, which are thought to project to the dorsal stream only.

There are connections from the dorsal stream to the ventral stream.

Consequently damage to V1, while not directly invading either of the 2 streams, would effectively denervate the ventral stream but would leave part of the dorsal stream intact.

Thus damage to V1 would give a loss of visual shape and colour perception but may retain part of motion perception, either conscious or unconscious.
 
Definitions and Theories of Etiology:

Riddoch -  The conscious perception of moving stimuli in a blind field, but unable to attribute shape or colour to the movement.  An example is this patient.
  ie: Activates dorsal stream (V5), projects to ventral stream (V4) for conscious perception.

Blindsight ­   The unconscious perception of light stimuli and of objects in a blind field.  An example is a cortically blind subject who can negotiate a room of obstacles.
  ie: Activates dorsal stream (V5), but not projected to ventral stream (V4), thus unconscious perception.
 
Akinetopsia -  Being unable to perceive motion, thus seeing the world as a series of stills. An example is the person who needs a line on her coffee cup to avoid spilling.
  ie: Activates V1 and ventral stream (V4), but not V5.

                     V1*         Ventral(V4)*         Dorsal(V5)*
Riddoch         NO            YES                     YES
Blindsight      NO             NO                      YES
Akinetopsia     YES         YES                     NO
*from Milner et al, 1997

Summary:

Conscious perception of motion is possible without the striate cortex, a finding called the Riddoch phenomenon.  Patients with this ability should be investigated for occipital lesions.

References:
1. Lessell S, Lessell IM, and Glaser JS. "Topical Diagnosis: Retrochiasmal Visual Pathways and Higher Cortical Function" in Duane’s Clinical Ophthalmology.  (Lippincott-Raven: Philadelphia, 1996) (2) 7: 1-11.
2. Zeki S, and ffytch, DH. The Riddoch Syndrome: insights into the neurobiology of conscious vision. Brain 1998; 121: 25-45.
3. Nepple EW et al. Bilateral Homonymous Hemianopia. Am. J. Ophth. 1978 Oct; 86: 536-43.
4. Milner, AD and MA Goodale The Visual Brain in Action (Oxford University Press:1997) 67-86

June 1998

Maintained by Frank Hassard, MD, UWO Ophthalmology Mail me your comments by clicking here