Recovery from Cortical Blindness THE possibility of central deafness has been recognised for a long time: a child with bilateral involvement of the auditory tracts to the temporal cortex can be just as deaf as one with both cochleae destroyed’. Some such children begin to respond to sounds as they grow older, although among them will be those whose follow-up examination will show deafness which is both central and peripheral (from brainstem auditory nuclei to the external ear). This is not surprising when the cause is anoxia, for example, which can just as easily damage the auditory tracts and radiation as it can the cochlea.

A similar phenomenon within the sphere of vision has not received the same attention, but undoubtedly occurs. One child who had been registered blind and sent to a school for blind children had a degree of peripheral visual handicap, though this may not have been severe, but equally certainly had a profound disorder of visual perception. One report said that she would make better progress with Braille if she would stop looking at what she was doing’. It is also notoriously hard to predict visual acuity in

conditions such as hydrocephalus, when an infant may show little interest in visual stimuli and the optic discs may be pale, yet when adult life is reached there may not be any particular visual disability.

The definition of blindness itself is difficult unless it is confined to inability to perceive light, for vision has so many aspects necessary for ‘seeing’-perception of movement, colour, separation of images in space and time, estimation of direction and depth-to name but a few, and many of these cannot be assessed in the infant. Moreover, because of the activity of the secondary, or colliculo-pulvinar-parietal, visual system’, the cortically blind individual may be able to reach for what he cannot consciously see, while the individual with bilateral parieto-occipital lesions may see but be unable to follow or aim, and might well appear to be blind.

This raises the problem of delayed visual maturation4. The term has been applied to fullterm infants who, at the age of six weeks or more, show no visual awareness and are unable to fixate or to follow a bright object5. Obviously this can be due to defects of brain development and be associated with general retardation or abnormal neurological findings. ILLING- WORTH^ confirms that the most common cause of delayed visual maturation is mental handicap, and that this, combined

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with the pale disc of the normal young baby, can lead to a wrong diagnosis of blindness. He also says that delayed visual maturation is a rare feature in some normal babies. He had previously described a boy examined at four months because he appeared not to be able to see: otherwise the baby's development was normal and there were no ocular abnormalities. By 10 months he was normal in all respects. ILLINGWORTH also reported a girl who apparently saw nothing for the first six months of life, although there were no abnormalities on examin- ation and she was normal by the age of one year.

However, there are doubts whether such children are 'normal'. COLE and col- leagues4 studied 16 blind babies pro- spectively. They showed no response to visual stimuli and four parents commented that their infant did not blink in response to a flash. At first none of them fixed or followed a light or bright object, and no optokinetic nystagmus was elicited. All had normal pupillary responses to light and normal fundi. Electrodiagnostic tests were done for four of the infants and the electroretinograms were normal, but the visual evoked responses showed ab- normal configurations. The babies became visually responsive between four and six months, and between nine and 12 months all were found to have normal or near- normal visual acuities. On further follow- up, one child was generally retarded, one suffered minor motor seizures, one child with persistent squint and nystagmus began to have generalised epilepsy, two developed convergent squints not due to refractive errors, and two had delayed speech development. Several also had behaviour problems.

MELLOR and FIELDER' described four such children and their electrophysio- logical findings. All the electroretinograms were normal but the waveforms of the visually evoked potentials were immature, with normal latencies. The evoked potentials became normal with increasing age. Similar findings were reported by HAREL and colleaguesg: three infants were said to be blind in the first four months of life but were found to be normal on neurological and ophthalmological ex- amination. After the age of six months

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normal vision gradually developed. For all three, visually evoked responses showed both prolonged latencies and immature waveforms, although they soon became normal. Such findings only confirm defects of visual pathways and not of vision.

HOYT er a1." have reported the clinical and electrodiagnostic features of another eight infants who showed no visual responses when first examined but subsequently developed normal vision, and the visually evoked potentials, previously significantly attenuated, also became normal. Six of them were either small for gestational age at birth or premature. Seven had definite delays in general motor development, and at first six of the eight failed to develop nystagmus with a fast phase in response to perotatory stimulation, indicating that they could not generate saccadic eye-movements.

It seems likely, therefore, that children with delayed visual maturation have suffered some disturbance of cerebral structure, and not just of function. Various investigations favour a combination of delayed myelination and delayed dendritic and synaptic formation7* ', and this could easily result from hypoxic-ischaemic brain damage. The children's progress needs to be carefully checked as they grow older, particularly in terms of their ability to learn.

Obviously, acquired cortical blindness can follow a number of conditions, for example bacterial meningitis"-", head traumaL4, acute cerebral anoxia after cardiac arrest" and respiratory arrest, uraemia and hydrocephalus16. It may result from irreversible brain damage from such causes as trauma, cerebral infarction, cerebral haemorrhage or neoplasia, in which case loss of vision can be permanent. However, cortical blindness may be transient if the cause is diaschisis following acute damage to the brain, or s e i~ures '~ or migraine lasting only a matter of days or less. If significant recovery does occur in the presence of such obvious lesions or after more subtle ones, as in delayed visual maturation, what are the possible mechanisms?

It can be argued that if there is marked improvement in cerebral function after apparent brain damage, the relevant part

of the brain was not destroyed in the first place. But this seems to belittle the brain's ability to adapt to injury, especially in childhood, and for one part to take over the function of another. For example it is well recognised that if there is a large porencephalic cyst on one side of the brain the remaining cerebral hemisphere can control motor function to a considerable extent on both sides of the body.

After meningitis, a putative mechanism could be vasospasm caused by blood vessels being involved as they cross inflamed meninges", and they could be affected in the same way after subarachnoid haemorrhage. Vasospasm may also occur in migraine. Cerebral oedema is another possibility, but seems less likely, especially after meningitis, as the blindness tends to be delayed. In ACKROYD'S report" of a case of cortical blindness following bacterial meningitis, the CT scan favoured a diagnosis of cortical thrombophlebitis with infarction, and did not show evidence of oedema. BARNET er a/.", in discussing children with cortical blindness from a variety of causes, did not think it likely that the common factor for four of them was cerebral oedema or herniation of the medial portions of the temporal lobes into the tentorial opening, compressing the pos- terior cerebral arteries. None of these children had a third-nerve palsy or sparing of macular vision, quite apart from evidence of more widespread cerebral damage. The more probable cause was the 'border zone' hypothesis, in which regions between the distributions of the three major cerebral arteries will suffer most during hypotensive episodes. The results of such lesions certainly would affect those areas responsible for the higher aspects of visual perception. For one child with uraemia the blindness may have been due to focal oedema of the white matter, and for one with meningitis it was possibly due to the same mechanism or to thrombosis of superficial cortical veins. The remarkable thing about ACKROYD'S case'' was that the first scan showed infarction of both occipital regions, without oedema, while the second showed occipital atrophy, which raises the question of how the child (who recovered vision) now sees.

DODGE and SWARTZ'* discussed the complications of meningitis and concluded

that cortical dysfunction can only be explained in part by anatomical findings, and that a 'toxic factor', hypoxia, shock, fever and increased CSF pressure may all contribute to brain damage.

Another mechanism of particular interest is the possible rale of naloxone. This is a specific opiate receptor- antagonist and has been used to infer the activity of endogenous opioids. It is now accepted that endogenous opiate ligands are concerned with CNS function in health and disease, both in the perception of pain and in contributing to other disorders such as seizures and mental i l l n e ~ s ' ~ . BASKIN and HOSOBUCHI'9 showed that intra- venous administration of naloxone briefly reversed certain ischaemic deficits in man. Naloxone temporarily abolished the hemiplegia of two patients with cerebral ischaemia, but had no effect in a patient with cerebral infarction. The mechanisms underlying this improvement are not known, but in some cases it may be related to improved cerebral bloodflow and perfusion2', although the two patients who improved had no changes in blood pressure, pulse rate, respiratory rate or blood gases. Coma was reversed by naloxone in a man with evidence of brainstem ischaemia2', and it was suggested that, as the area is rich in opioids, these might have been released by the ischaemia and their effects reversed temporarily by the naloxone; in other words, since the ischaemic lesion was present whether the patient was in or out of coma, it was not the immediate cause of unconsciousness. Perhaps in some in- stances of cortical blindness recovery can be accelerated by the use of naloxone.

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These problems underline the occasional difficulties in giving a prognosis for eventual visual function, and the younger the child the harder this may be. As with other problems, such as delay in starting to walk, some tests can be done to clarify the situation, but a period of observation almost always will make a firm opinion possible, and most parents will accept the reasons for uncertainty if they can be assured that they will be told as soon as possible. This policy in the case of a developing child is surely better than making dogmatic statements based on 385

inadequate data, which often can turn out to be wrong.

The clinical examination of the cortically blind infant is well reviewed by KNOX22. Apart from the obvious need for a careful history, his scheme for examination includes checking following movements of the eyes and head, fixation of a light, opticokinetic nystagmus, response to a threatening gesture, blink reaction and pupil responses to a bright light, the range of ocular movements, responses to body rotation, and examination for nystagmus. Responses to non-visual sensory stimuli also should be tested. Ophthalmoscopy may show evidence of developmental anomalies, and neurophysiological tests- including visual evoked potentials, electro- retinography ‘and electroencephalo- graphy-can help to resolve the level of a possible lesion, and in predicting recovery23. Often the return of vision to children with cortical blindness who have been studied in detail has been remarkable, but it is probable that many will have perceptual defects because of involvement of the parieto-occipital watershed areas”.

References 1. Gordon, N. (1966) ‘The child who does not talk.

Problems of diagnosis with special reference to children with severe auditory agnosia.’ British Journal of Disorders of Communication, 1.78-84.

2. Gordon, N. (1968) ‘Visual agnosia in childhood.’ Developmental Medicine and Child Neurology, 10,377-379.

3 . Weiskrantz, L., Warrington, E. K., Sanders, M. D., Marshall, J. (1974) ‘Visual capacity in the hernianopic field following a restricted occipital ablation.’ Brain, 97, 709-729.

4. Cole, G. F., Hungerford, J., Jones, R. B. (1984) ‘Delayed visual maturation.’ Archives of Disease in Childhood, 59, 107-1 10.

5. Lancet (1984) ‘Delayed visual maturation.’ Lancet. 1, 1158-1 159.

6. Illingworth, R. S. (1980) The Development of the Infant and Young Child, 7th Edn. Edinburgh Churchill Livingstone.

7. Illingworth, R. S. (1961) ‘Delayed visual maturation.’ Archives of Disease in Childhood, 36,407-409.

8. Mellor, D. H., Fielder, A. R. (198O)’Dissociated visual development: electrodiagnostic studies in infants who are ‘slow to see’.’ Developmental Medicine and Child Neurology, 22,327-355.

9. Harel, S., Holtzman, M., Feinson, M. (1983) ‘Delayed visual maturation.’ Archives of Disease in Childhood, 50,298-309.

10. Hoyt, C. S., Jastrzebski, G., Marg, E. (1983) ‘Delayed visual maturation in infancy.’ British Journal of Ophthalmology, 61, 127-130.

11. Ackroyd, R. S. (1984) ‘Cortical blindness following bacterial meningitis: a case report 386

These may be disorders such as piecemeal vision or object-background difficulties. In the former, details can be seen but not the whole picture, so that a row of dots cannot be counted because while looking at one dot the others do not exist, which is different from sorting objects from the background. Such disorders must be deliberately sought so that appropriate remedial measures can be taken. They can be infinitely varied-for example visual perceptual disabilities may or may not be associated with reading retardation-and they are likely to change with time. There is much more to vision than merely acuity, and special tests are needed to assess the affected child, just as pure-tone audio- metry does not test hearing in the broad sense. Such considerations must be of particular importance in the field of remedial education.

JOHN FOLEY NEIL GORDON

Booth Hall Children’s Hospital, Charlestown Road, Blackley. Manchester M9 2AA.

with reassessment of prognosis and aetiology.’ Developmental Medicine and Child Neurology,

12. Margolis, L. H., Shaywitz, B. A., R0thman.S. G. (1978) ‘Cortical blindness associated with occipital atrophy: a complication of H. influenzae meningitis.’ Developmental Medicine and Child Neurology, 20, 490-493.

13. Teppenberg, J., Nussbaum, E., Feldman, F. (1977) ‘Cortical blindness following meningitis due to H. injluentae type B.’ Journal of Pediatrics, 91,434-436.

14. Griffth, J . F., Dodge, P. P. (1968) ‘Transient blindness following head injuries in children.’ New England Journal of Medicine, 270,648-65 I .

15. Weinberger, H. A., van der Wonde, R., Maier, H. C. ‘Prognosis of cortical blindness following cardiac arrest in children.’ Journal of the American Medical Association. 119,126-129.

16. Lorber, J . (1967) ‘Recovery of vision following prolonged blindness in children with hydro- cephalus or following pyogenic meningitis.’ Clinical Pediatrics, 6 , 699.

17. Barnet, A. B., Manson, J . I . , Wilner, E. (1970) ‘Acute cerebral blindness in children.’ Neurology, 20, 1147-1 156.

18. Dodge, P. R., Swartz, M. N. (1965) ‘Bacterial meningitis-a review of selected aspects. I I . Special neurological problems, post-meningitis complications and clinico-pathological cor- relations.’ New England Journal of Medicine,

19. Baskin, D. S., Hosobuchi, Y. (1981) ‘Naloxone reversal of ischaemic neurological defects in man.’ Lancet. 2, 272-275.

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272, 1003-1010.

20. Gillman, M. A., Lichtigfeld, F. J. (1981) Neurosurgery and Psychiatry. 47, 77-78. ‘Naloxone reversal of ischaemic neurological 22. Knox, D. L. (1964)‘Examination of the cortically deficits.’ Lancet, 2, 643. blind infant.’ American Journal of Ophthal-

21. Goldman, S., Cordonnier, M. J. B., Sztencel, J. mology, 58,617-621. (1984) ‘Brainstem ischaemia presenting as 23. Harden, A., Pampiglione, G . (1970) ‘Neuro- naloxone-reversible coma followed by down- physiological approach to disorders of vision.’ ward-gaze paralysis.’ Journal of Neurology, Lancet. 1 , 805-808.

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Congenital Hypothyroi dis m HETEROGENEITY in the clinical expression of a single disease is perplexing. In the case of heritable metabolic disorders, this has been attributed to variable degrees of a single enzymatic deficiency. With regard to congenital thyroid deficiency, it has long been recognized that the clinical conse- quences may be extremely variable. In North America the disease is most often the result of partial o r complete agenesis of the thyroid gland, and while early treatment avoids the more serious permanent manifestations, such as mental retardation, this relation is not a perfect one. Some late-treated cases do very well and a few early-treated cases are retarded. This may be related to the degree of thyroid dysgenesis: some late-treated patients with good results had evidence of a functioning remnant of thyroid tissue. However, the exact reasons for this variation are not clear. Perhaps the degree of thyroid deficiency during fetal development is critical. There are no precise measurements of the degrees of thyroid impairment during human fetal development. It has been generally accepted that maternal thyroid hormones cross the placenta very poorly and that this maternal source will not protect a hypothyroid fetus. Whether this is strictly and universally the case is questionable. Is it possible that some congenitally thyroid- deficient infants have enjoyed preservation of brain development because of small amounts of thyroid hormone available from the mother?

In some parts of the world congenital hypothyroidism is a consequence of severe

iodide deficiency. The issue of variability of expression in the affected individual is raised because of the severity of the clinical, and especially the neurological, manifestations described in such areas as South-east Asia and India, as opposed to North America’-4. Extreme degrees of neurological deficit and deaf-mutism have been described, which are rarely seen elsewhere. How is this to be explained?

There is no clear-cut explanation. The etiology is different: in one case there is complete or partial absence of the thyroid gland and in the other case, while the thyroid gland is fully developed, there is a lack of an essential ingredient of thyroid hormone, namely iodine. The common denominator is a deficiency of thyroid hormone. While there are many possible explanations for the clinical differences, two in particular suggest themselves. In the mountainous regions of Southeast Asia, with its endemic iodide deficiency, the mother herself is also hypothyroid. It has been suggested that the thyroid deficiency in both mother and fetus produces an even greater deficit, leading to faulty acoustic and neurolo ical development during early fetal life . In North America, usually the mother is not deficient in thyroid hormone. Is it possible that iodides themselves play some important rBle in the development of the central nervous system which is not yet understood? The dysgenetic hypothyroidism in North America is not associated with deficient iodine.

Some of the peculiar features ac- companying endemic cretinism in iodine- deficient regions of the world have also been noted in the upper central highlands of New Guineas-’. Certain features are distinctive and are not commonly seen in the congenital hypothyroidism of North

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