DISORDERS IN RELATION TO THE EYE 7G7 



tion, on the one hand a constant more or less automatic action for local pur- 

 poses of protecting the retina from the effect of bright light and the 

 conjunctiva and exposed portions of the globe, particularly the cornea 

 from drying and from the irritating action of dust and small foreign 

 bodies, in which the tear secretion acts as a miniature irrigation and the 

 wink (Lid-schlag) or sweep of the lid as a mechanical cleansing or mop. 



There is reason to believe that this manifestation of the function is 

 under vagus control, as it responds to local sensory impressions via the 

 trigeminus and is increased by local irritation, as in conjunctivitis or the 

 presence of a foreign body within the lids or by irritation of the mucous 

 membrane of the nose. Lachrymation and clonic blepharospasm are 

 common symptoms in all superficial ocular inflammations and injuries. 

 Both lachrymation and the reflex lid sweep are diminished or abolished 

 when the sensibility of the surface of the eye is diminished or abolished 

 either by disease or drugs (glaucoma, cocain), and conversely, the cornea 

 becomes hyp-or anesthetic in affections attended by paralysis of the lid 

 (paralytic lagophthalmos, neuroparalytic keratitis). The physiologic 

 rate of winking and of tear secretion under like conditions and varying 

 vagus or sympathetic tone or with varying endocrin dominance would 

 be an important and possibly instructive subject for clinical and experi- 

 mental study. The sympathetic control of winking and tear secretion 

 is shown most strikingly in crying under the influence of emotion. The 

 biological mechanism and the purposive, phylogenetic development of this 

 reaction are not known. 



Tonic contraction of the orbicularis, causing a partial closure of the 

 lid-fissure, is part of the mechanism of a defensive intensification or ac- 

 centuation of fixation, as is noted in peering or screwing up the lids in 

 the attempt to hold the eye on an object of interest and to get the sharp- 

 est possible vision by concentration of the gaze. There is no question 

 here of an optical effect by the production of a stenopeic slit, as might be 

 assumed, for the reason that the lids do not encroach on the visually 

 concerned central area of the pupil. Quite the same reflex is noted as a 

 protection of the globe against sudden strain on the ocular vessels and 

 against mechanical protrusion in sudden rise of intra-abdominal pressure 

 as in straining at stool, lifting a heavy weight, vomiting, or the expulsion 

 of the fetus ; in obstructed expiration, as in sneezing, coughing, laughing. 1 



Rider has shown that there is a uniform tendency to wink with the 

 functionally, visually weaker eye. 



Alteration of tear secretion has been noted in various dyscrinisms 

 as mentioned above (v. hyperthyroidism). Infrequent winking is noted 

 in extreme fatigue, in terminal stages of wasting disease, and after in- 

 stillation of cocain, adrenalin, and atropin. In the case of the two latter 



1 With tonic contraction of the brows, the pupil, and the jaws, this narrowing of 

 the lids is seen in all offensive-defensive reactions of the organism, and is the char- 



