338 



PHYSIOLOGY 



CHAT. 



By its means a small white or coloured <>ljiv.t fan l>e presented to 

 the subject in any meridian of the field and at any distance from 

 tin- tixation point. 



Fb'rater'a perimeter > .'l-'ig. 1G2), mi which all other.- have been modelled, 

 consists of a half-circle T, of metal, marked with a scale. A runner t<> which 

 small white or colour-'; n lie 1',-istrncil move- along its blackened 



concavi- Mirtaee. Tin- middle nl' tlic arc, which is lixc.l in a hoi i/niilal a\i- 

 a round which it can rotate, I'orius tin- point of fixation. A.I imlicator G 

 Allows the position of the meridian examined on the opposite side of tlie axk 



20 



,60 



180 



Fi'-. U'i3. Normal visual liclrl of liu'ht i-y.- of an individual ai;rd 40. with a n-lnti wjnaiv Ol 



JO si[. iniii. (I.uriani.) 



The subject rests his chin on a support H. The perimeter is graded so that 

 the zero point is in the centre. 



The subject is so placed that the eye to be examined is at the level of the 

 centre of the perimeter, and he is asked to look at the fixation point, the other 

 eye being blindfolded to avoid confusion. The runner with the disc, is then 

 moved slowly from the periphery to the centre, and the subject is asked to 

 indicate the moment at which he first sees it, while his eye remains fixed on 

 the centre of the arc. The corresponding degree is then read on the convex 

 surface of the arc, and the position of the meridian is also noted. When this 

 operation is repeated in different meridians the field of vision can be repre- 

 sented graphically on a chart (Fig. 163). The zero corresponding to the 



