Chapter VI 

 OPHTHALMOSCOPY OF THE FUNDUS IN LIVING BIRDS 



The method employed by the writer in ex- 

 amining the background of the eye in living 

 Birds does not much differ from that of the 

 physician in his examination of human eyes 

 as described in the previous chapter. 



For a proper exploration of the vertebrate 

 fundus it is, as previously stated, highly de- 

 sirable that the pupil be widely dilated. 

 This is accomplished in Man and other Mam- 

 mals by such mydriatics as atropin, hom- 

 atropin, euphthalmin, etc., which bring about 

 an enlarged pupil mainly by inhibiting the 

 action of the non-striated sphincter muscle 

 fibres of the iris. In Birds, however, these 

 agents have little direct effect on the striated, 

 voluntary, sphincter musculature of the iris; 

 hence they are of little value in an ophthal- 

 moscopic examination of most Birds. One is 

 obliged, therefore, to resort to such agents as 

 galvanism, nicotine, strophanthin, curare, 

 stipticin, etc., and to such drugs (eserin, 

 atropia) as render the bird unconscious with- 

 out actually killing it. 



In collecting the heads of birds for niacro- 

 scopical and histological studies the writer 

 found that satisfactory ophthalmoscopic 

 views of the fundi can be had a few minutes 

 before and after the death of the specimen, 

 during which period the pupil not only dilates 

 ad maximum but the bird does not use his 

 third eyelid. Many of the appended reports 

 were gathered in this way. 



Owing to the peculiar arrangement of their 

 lacrimal apparatus (see the writer's work on 

 this subject) fluids instilled into the eye (con- 

 junctival sac) of Birds run immediately into 

 the throat and gullet, there to be absorbed 

 and to produce precisely the same systemic 

 effects as if they were poured directly down 



the throat of the animal. Great care should 

 be used, therefore, in using eye drops for their 

 expected effect upon the visual apparatus; 

 if poisonous for the bird they may cause his 

 death in short order, and rare and valuable 

 specimens may be sacrificed to the ignorance 

 of the observer. The writer has not the least 

 doubt but that some of the so-called mydri- 

 atics or pupil-dilating drugs recommended for 

 an examination of the ocular interior of the 

 Bird act as systemic intoxicants and not 

 specifically upon the iris muscles, as is the 

 case with the mammalian eye. 



As an example of this action of the so- 

 called mydriatics on the eyes of birds the 

 writer once fell into the same error as other 

 still earlier observers in attempting to dilate 

 by atropia the pupils of a Yellow Parakeet 

 {Melopsittacus undulatus). This bird was an 

 adult individual, sex unknown, in captivity 

 for six months. In dull light the pupils 

 were 2.5 mm. wide, contracting irregularly 

 to 1.5 mm. A single drop of a 1% solution 

 of atropia sulphate put into the eyes appar- 

 ently dilated the pupils ad max (3 mm.) in 

 12 hours, but as the bird was taken ill a few 

 hours following the instillation (stupor, ver- 

 tigo, quick, weak heart and final unconscious- 

 ness) and died 30 hours after the use of the 

 drops, it is quite likely that its death was due 

 to the poison that ran into its throat from the 

 conjunctival sac. The writer had a similar 

 experience with a number of other birds. 



The following notes were made of experi- 

 mentation intended to determine the best 

 mydriatic for the Bird's eye, especially for 

 field work. 



Laboratory Notes of Experiments on the 

 Pupils of Passer domesticus. One drop of 



[33 



