The supranuclear arc of the corneal reflex

Tactile corneal reflex development in full-term babies

OBJECTIVE

To evaluate the development of the tactile corneal reflex in healthy full-term babies.

DESIGN

Prospective longitudinal comparative case series.

PARTICIPANTS

One hundred and ninety-one babies aged 1 to 3 days examined in the nursery, and 200 babies aged 1 to 12 weeks examined in an orthopedic outpatient clinic.

METHODS

The tactile corneal reflex was evaluated by three ophthalmologists using the Cochet-Bonnet esthesiometer.

MAIN OUTCOME MEASURES

The probability of the presence of the tactile corneal reflex was calculated in relation to gestational age, postpartum age, postconceptional age, and birth weight.

RESULTS

The proportion of children with tactile corneal reflex was expressed in a linear logistic model. We found that 10% of the babies had tactile corneal reflex in at least one eye at 2 days of age, 25% at 1 week, 50% at 3.5 weeks, 75% at 6 weeks, and 100% at 12 weeks. The postpartum age had a greater impact on the development of the tactile corneal reflex than the gestational age. The birth weight also had a statistically significant influence (P = 0.005, Wald's test).

CONCLUSIONS

The tactile corneal reflex is present in only a minority of newborns and develops during the first 3 months of life. These results demonstrate that the tactile corneal reflex has a longitudinal neurologic development and is part of the normal neurologic maturation process.

Analysis of the corneal reflex with air puff: normal controls and patient groups

Though there are several reports published about the corneal reflex elicited by different methods, a standardized electrophysiologic study with air puff in man has not been published. The aim of this study is to standardize the corneal reflex elicited by air puff to cornea. The authors studied the corneal reflex with air puff and direct touch by using a standardized method in patients with thalamic hemorrhage (n = 15), hemispheric infarction (n = 9), brainstem infarction (n = 9), multiple sclerosis (n = 12), and Bell's palsy (n = 12) and in normal control subjects (n = 21). The conventional blink reflex (BR) was also studied. The reflex responses were recorded from both orbicularis oculi muscles by air puff and direct touch to cornea in addition to the electrical stimulation of the supraorbital nerve. No statistical difference could be detected between the responses elicited by air puff or direct touch to cornea (P > 0.05). Corneal reflex responses were statistically different from the R2 response of the BR (P < 0.005). Because the responses elicited by direct touch and air puff to cornea are identical, air puff to cornea can be used confidently to study the corneal reflex.

[Spontaneous tegmental-mesencephalic hematoma: neurobehavioral aspects of the rostral third of the human brainstem]

The tegmentum of the midbrain is a complex area traversed by a number of anatomical and functional systems, including local circuits, ascending activating systems and descending fibers from the cerebral hemispheres. In the present paper we report on the case of a 67-year-old man who suffered a spontaneous central tegmental hemorrhage and was initially supposed to be in coma due to bilateral ptosis and lack of speech and initiative. By the second hospital week, however, he was shown to be able to respond to verbal commands, sit, stand and walk. He died in sepsis one month later. This case shows that the clinical diagnosis of coma may be misleading in certain patients in whom wakefulness is preserved, though concealed from a casual bedside examination due to abulia and ophthalmoplegia.

Blink reflex in patients with hemispheric cerebrovascular accident (CVA). Blink reflex in CVA

A blink reflex consists of an early unilateral component, R1, and a late bilateral component, R2. During an acute phase of hemispheric cerebrovascular accident, R1 and R2 were abnormal in 30 and 50 of 66 patients, respectively. Paired stimuli usually corrected R1 but not R2, which was profoundly suppressed. The discrepancy between polysynaptic R2 and oligosynaptic R1 indicates a greater disfacilitation at the level of interneurons than at the motoneuron, which serves as the final common path. Abnormality of R2 occurred bilaterally with stimulation on the affected side of face and contralaterally after stimulation on the normal side in 31 patients. This finding suggests a diffuse loss of internuncial excitability, contralateral to the hemispheric lesion. Changes of R2 implicated the brainstem pathways forming the afferent and efferent arc of the reflex in 7 and 8 patients, respectively. The remaining 4 comatose patients had no R2 irrespective of stimulus sites. Clinical localization of the hemispheric lesion showed no consistent correlation with the type of blink reflex abnormalities. The CT scans revealed widely scattered changes in 29 patients with abnormal blink reflex but with a tendency to overlap in the inferior Rolandic area. This contrasted with conspicuous sparing of the inferior post-central region in 10 patients with normal blink reflex. These findings suggest the presence of crossed facilitation to this reflex from wide areas of the cortex but most prominently from the sensory representation of the face.

The orbicularis oculi response after hemispheral damage

The corneal and blink reflexes were evaluated in 20 normal subjects and in 30 patients with motor deficits secondary to unilateral hemispheral lesions of vascular origin. In the normal population there were no differences between subjects below and subjects above 50 years of age. In the patients the reflex evoked by electrical stimulation of the cornea of the clinically affected side was depressed in 24 out of 30 cases. The depression mainly affected the afferent branch of the circuit, which triggers both homolateral and contralateral orbicularis oculi discharge (afferent abnormality). In three cases the depression was exerted concomitantly on the efferent branch (afferent and efferent abnormality) and only in one case was it limited to the efferent branch (efferent abnormality). The late R2 component of the blink reflex was depressed in 15 out of 30 patients. The early R1 component was slightly facilitated on the affected side. The changes of the corneal reflex and of the R2 component of blink reflex were similar, but the blink reflex had a greater safety factor. The patients with an abnormal corneal reflex had more extensive damage than had the patients with normal corneal response, as shown by computer tomography, but the site of the lesion was comparable in the two groups. Conduction through the brain stem circuits mediating the orbicularis oculi response is normally under pyramidal facilitatory influences while facial motoneurons are subjected to pyramidal inhibition. After pyramidal damage the transmission of impulses in the brain stem was slowed down, ultimately to a degree that abolished the reflex. Removal of pyramidal inhibition on facial motoneurons is probably the basis of the slight facilitation of the R1 component of the blink reflex.

Corneal reflex in hemisphere disease II

In man, contralateral cerebral decortication or removal of a hemisphere does not permanently abolish the corneal reflex. Destruction of the contralateral thalamus or contralateral mesencephalic trigeminal tract does abolish the corneal reflex.

In the cat however, the corneal reflex remains intact after contralateral decortication, he mi sphere ctomy and total ablation of the thalamus. Some of these procedures diminished the corneal reflex or increased the threshold, but neither of these changes were seen for more than a few days post-operativ ely. In this animal however, the second reflex response, evoked by supra orbital nerve stimulation, is abolished by certain thalamic lesions and by contralateral hemi-transection of the brain stem at various levels.

Corneal reflex in hemisphere disease

The contralateral corneal reflex may be absent in patients with a deep lesion of the parietal lobe. Frontal and temporal lobe lesions apparently do not interfere with this reflex.