814 SEC. 18. BIOLOGY. 



3976. Simple Fhaenophthalmotrope, small size, for per- 

 sonal use. -P^of. Danders, Utrecht. 



3977. Compound Fhsenophthalmotrope, small size, for 

 personal use. Prof. Danders, Utrecht. 



3978. Snellen's Ophthalmotropometer, for determining 

 the movements to right and left of each eye. . (Handbuch der 

 Augenheilkunde von Saemisch und Graefe, III. p. 236.) 



Dr. Snellen, Utrecht. 



This instrument is intended to determine the movements towards right and 

 left of each eye separately, and of both eyes with regard to each other. 



It consists principally of two bars rotating about an axis ; they form an 

 angle which can be read directly on a graduated arc, attached to one of the 

 bars. 



The instrument is to be placed so that the point of rotation of the bars is- 

 perpendicularly below the point of rotation of one of the eyes. 



For this purpose, the plate upon which the bars lie can slide forward and 

 backward to the right and to the left, independently of the points against 

 which the head rests with the infra-orbital margins. 



The eye under examination is fixed upon the middle of a telescope carried 

 by one of the bars, and by moving to right and left the instrument is ad- 

 justed until the eye is in the middle of the field of view of the telescope. 

 Then the bar with the telescope is turned some degrees, and the eye under 

 examination is fixed again ; if the point of rotation of the eye does not coincide 

 with the point of rotation of the instrument, the eye will now be seen out of 

 the middle of the field of view. By sliding forward and backward until the eye 

 appears again in the centre of the field of view, the instrument is carried into 

 the proper position with regard to the eye. 



Now can be determined 



1. The mobility of each eye outward. 



2. The limits of the lateral binocular vision. 



3. The convergence in straightforward vision, and at any degree of 



lateral fixation. 



4. The degree of deviation in strabismus. 



5. The centre of motion of the eye. 



3979. Ophthalmo-statometer, for the determination of the 

 exorbital protrusion of the eye-ball. Dr. Snellen, Utrecht. 



Two rods, united by a cross rod, are supported on the inner and outer 

 margins of the orbit. Erom the cross rod a small crank can slide down until it 

 presses softly against the eye-ball covered by the eye-lid. The thickness of 

 the eye-lid is to be subtracted from the reading. The position of the top of 

 the naked cornea may be read directly by means of a sight movable on one 

 of the rods. (Ilandbuch der Ophthalmologie, Graefe und Saemisch III., 

 p. 199.) 



Manufactured by P. W. Hiele, Utrecht. 



39 8O. Instrument for the determination of the Movements 



of the Head and Eye, in varying directions of the line of fixation. 

 Bonders and Ritzmann. (Compare Archiv fur Ophthalmologie, 

 XXI., 1, p. 131, 1875.) Prof. Danders, Utrecht. 



