496 Mb. GOODE, ON A PECULIAR DEFECT OF VISION. 



the axis of the convex surface being in the vertical direction. This glass appears to fulfil the 

 required conditions : it enables Mr. Parry to read inscriptions at a few yards distance, and also 

 to have a distinct perception of very distant and minute objects, such as are presented in an exten- 

 sive landscape. 



In order to ascertain if it were possible to detect any error of curvature on the surface of the 

 cornea, I observed the appearance of the reflection of a small luminous square held a few inches 

 from the eye ; but in the central part of this structure the reflected image was perfectly square, 

 while the distortions produced at the circumference were equally produced in the sound eye ; and 

 there was no reason to conclude that the defect of vision arises from any defect in the cornea. 



Mr. Parry finds his sight considerably improved by looking through a small hole in a card, so 

 as to admit pencils only to fall on the central parts of the cornea ; or, still better, by looking 

 through a narrow vertical slit, provided that the illumination of the object be sufficient to 

 compensate for the smallness of the pencils admitted. He finds that a very slight pressure 

 on the eyeball, applied at the outer angle of the eye, improves the vision. I also find the same 

 when gentle pressure is made at the upper and outer part of the ball. It is to be observed, that 

 the application of a narrow slit to a sound eye produces an effect nearly analogous to that produced 

 by a piano-cylindrical lens. 



The second case is that of a student, who stated, that in observing small objects at 20 or 30 yards 

 distance, he saw a second image of the objects, one image, however, being much fainter than the 

 other. He considered that his sight had become impaired by too intense application to books, having 

 only observed that his eyes were defective after several years close study. 



On testing his eyes by a pinhole in a card, he saw the hole as a horizontal line most distinct 

 at about 35 centimetres distance ; beyond this the hole appeared indistinct. Also when he viewed 

 two lines in the form of a cross, when they were held at 35 centimetres distance, he perceived most 

 distinctly the horizontal line, and at some distance beyond this the vertical line. The line seen 

 at the nearer focus was exactly perpendicular to the mesial plane of the body. I ascertained that 

 the distinctness of his vision was considerably improved by applying to the eye a piano-cylindrical 

 concave glass, of about l6 French inches radius. 



Since the above paper was read, I have met with three gentlemen in the University, all of whom 

 have one of their eyes affected with a malformation similar to ray own ; or with " astigmatism," as it 

 has been called. The amount of the " astigmatism " in all of them appears to be corrected 

 by a piano-cylindrical glass, the curvature of which is 12 inches radius. 



In one of these gentlemen it is the more perfect eye that is thus affected. This eye, as observed 

 in some other cases, gives diplopic vision of objects at a certain distance. Another stated that 

 the vision of his eye was perfect until a few years since. 



HENRY GOODE. 



