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Acta Neurochir (Wien) (1993) 120:187-189

N urochlrurgica
9 Springer-Verlag 1993
Printed in Austria

Serial Regional Blood Flow and Visual Evoked Responses in Transient
Cortical Blindness
Ch.-W. Wong, T.-Y. Chen, J.-J. Liao, and D.-L. You t
Division of Neurosurgery, Department of Surgery, and 1Department of Nuclear Medicine, Chang Gung Memorial Hospital, Taipei, Taiwan,
Republic of China

Summary

A

May 1,2991
Pl00:i04 mS

Normal regional blood flow was documented by Single Photon
Emission Computed Tomograms 5 and 20 hours before the full
recovery of cortical blindness in two patients, lending itself to the
possibility of being a prognostic factor. Rubbing of the posterior
cerebral arteries against the tentorial edges during trauma instead
of traction was believed to cause blindness in one patient and embolization due to hammering bone grafts home during cervical spinal
fusion, in the other. Pattern reversal visual evoked responses
(PRVERs) were absent during blindness; upon recovery P 100 with
full amplitude and normal latency appeared despite the presence of
tunnel vision. These are consistent with the fact that the central
8 - 10 degrees of visual field represented in the posterior occipital
poles being the main sources of P 100 in association with the x-cells
in the centre of the retina.

Keywords: Blindness; visual evoked potentials; head injury; regional
cerebral blood flow.

Cortical blindness is characterized by the loss of vision
in patients with normal pupillary reflexes and
ophthalmic fundi. Aetiological factors include trauma9'
11, 13, infarction23 embolizationIO, migraine 3, 12, 14, cardiac arrest t7, meningitis s and hydrocephalus with a
malfunctioning shunt 6. Prognoses vary 1.
We report the Single Photon Emission Computed
Tomograms (SPECT) and the Pattern Reversal Visual
Evoked Responses (PRVERs) before and after the recovery of cortical blindness in two patients.

L
May 1,1991

i !/'

Fig. 1. Abnormal PRVERs during blindness and normal PRVERs
after recovery of useful vision despite the constricted visual fields.
A: Patient A. L: left eye. R: right eye. Checkerboard, 2Hz

B

May 21,1991
May 15,1991

PID0:98.2 mS

May 21,1991
L

J

May 21,1991
R

,

Patient Reports
Patient A (CGMH: 3209793)
A 36 year-old motorcyclist with 2 children on board had a brake
failure and bumped her motorcycle into the rear of a ear, throwing
herself over the road. While the children sustained skin abrasions
the patient remained drowsy for 7 hours. As she regained conscious-

Fig. 2. Abnormal PRVERs during blindness and normal PRVERs
after recovery of useful vision despite the constricted visual fields.
B: Patient B. L: left eye. R: fight eye. The hyperopia in the right eye
was not corrected. Checkerboard, 2 Hz

188

Fig. 3. A I, A 2 and B I, B 2: SPECT before recovery of useful vision
in patient A and B respectively. A 3, A 4:3 days and B 3, B 4:6 days
after the first SPECTs respectively, all being normal. Methods: Technetium-99m hexamethyl-propyleneamine oxime 15 mCi Cerebral
Blood Flow Planar (Elscint apex 609 RG), slice thickness: 6mm

Ch.-W. Wong et al.: Cortical Blindness
both eyes were normal. SPECT scans 44 hours after the operation
revealed normal perfusion of the visual cortices and hypoperfusion
in the left re.idle cerebral artery territory (Fig. 3, B l-B2). No
PRVERs was found at 47 hours (Fig. 2, May 15, 1991). At 49 hours
the patient was able to perceive light, read and understand the
Chinese characters on the red ruler, tunnel vision being demonstrated
by confrontation test, nystagmus was absent and CT scans normal.
He identified the key in either of his hands without looking at it.
At 70 hours the patient reported that with his left eye lie saw a girl
in red and a boy in green climbing up and down the intravenous set
in front of him and moving to the left and the right. He also reported
hearing the voice of a man using foul language, threatening to beat
him up. All the hallucinations subsided after the use of Haloperidol
for 1 day. The PRVERs at 188 hours were normal in the left eye
(Fig. 2, May 21, 1991) and remained so 8 weeks later. Although he
had enjoyed rapidly improving visual fields since the recovery of
light perception, the perimetry did not demonstrate normal fields
until 2 months after the operation. The spastic gait remains unchanged.

Ch.-W. Wong et al.: Cortical Blindness

transient occlusion, whereas the oculomotor nerves are
less susceptible to this type of injury, due to their tentorial insertions. This mechanism contrasts with the
traction mechanism12, 14 in which the oculomotor
nerves are more readily exposed to traction injury than
the posterior cerebral arteries. The finding of normal
regional blood flow in the SPECT before the recovery
of useful vision does not weaken the position of
"scratch" or border zone hypoxia iv inducing blindness
in this patient because ischaemia of 1 - 2 minutes could
lead to permanent visual loss. It does strengthen however the position of the traumatic spreading cortical
depression which tends to occur in younger patients
with milder injuriesz~
While visual hallucinations occurring in both patients, the auditory hallucination only affected patient
B whose SPECT showed hypoperfusion in the left middle cerebral artery territory in the presence of normal
CT. These findings suggest that auditory hallucinations
presumably arising from the temporal lobes could be
effected by disturbances of the posterior circulation.
Absence of PRVERs during blindness2' 4, 8, 18 and
rapid recovery of P 100 amplitude with normal latency
accompanying tunnel vision were documented in our
patients. These findings were consistent with the observation that central vision within 8 to 10 degrees
circumference is represented at the posterior limit of
the calcarine fissure5' 22. Collateral blood supply from
the middle cerebral artery ensures its quicker functional
recovery from an ischaemic insult. Furthermore the
posterior occipital poles are the main sources of P 10021
in association with the x-cells in the centre of the
retina 16. The possibility exists of having patients with
central visual fields good enough to produce PRVERs
but not good enough to serve useful functions2' 15. This
contrasts with the unique patient cited by Celesia et aL
of complete cortical blindness whose PRVERs were
normal and whose visual fields documented to be no
more than 2 degrees of the a r c 7.

Acknowledgements
We thank MS P. Y. Wang, Ms Linda Chang, Ms Yun Shu and
MR D. J. Tsai for their kind assistance.

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Correspondence and Reprints: Dr. Cheuk-Wah Wong, Division
of Neurosurgery, Department of Surgery, Chang Gung Memorial
Hospital, 199 Tunhwa North Road, Taipei 105, Taiwan R.O.C.