Text-book of ophthalmology . ore frequentthan is supposed (sec Note to <; ). — D.] DISEASES OF THE LENS 553 the other eye, we might perhaps be obliged to operate upon a very hypermature cata-ract under unfavorable conditions. For erythropsia following cataract extraction, see page 22. II. Changes of Position of the Lens 493. Anatomical Cause.—Changes of position of the lens always havetheir anatomical cause in changes of the zonula of Zinn. This in the normaleye is tightly stretched, and holds the lens so firmly that the latter remainsperfectly immovable even with the most violent motion
Text-book of ophthalmology . ore frequentthan is supposed (sec Note to <; ). — D.] DISEASES OF THE LENS 553 the other eye, we might perhaps be obliged to operate upon a very hypermature cata-ract under unfavorable conditions. For erythropsia following cataract extraction, see page 22. II. Changes of Position of the Lens 493. Anatomical Cause.—Changes of position of the lens always havetheir anatomical cause in changes of the zonula of Zinn. This in the normaleye is tightly stretched, and holds the lens so firmly that the latter remainsperfectly immovable even with the most violent motions of the , any tremor of the lens, and still more any displacement of it fromits natural position, presuppose a relaxation of the firmness of this attach-ment. Such a relaxation can take place either from a simple elongation andloosening of the fibers of the zonula, or else from their rupture or completedestruction. Changes of this sort may affect either single portions or theentire circumference of the -f Fig. 239.—Subluxation of the Lens. lens has sunk so far downward that its upper edge is visible in the pupil. In consequenceof the relaxation of the zonula, the lens bulges strongly, and is in contact by its lower border with theciliary processes; moreover, the lower half of the iris is pressed forward by it. Above, on the contrary,the anterior chamber, owing to recession of the iris, is abnormally deep. Of the beam of rays emittedby the luminous point O, a portion goes through the aphakic part, o, of the pupil; these rays, on ac-count of the absence of the lens, are insufficiently refracted, so that they come to a focus behind theretina at /, and form upon the retina a diffusion circle, b. That portion of the beam passing throughthe section, I, of the pupil, which contains the lens, undergoes excessive refraction on account of theincreased convexity of the lens, so that the rays intersect in front of the retina at/i, and form upon there
Size: 2016px × 1239px
Photo credit: © The Reading Room / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, bookdecade1910, booksubjecteye, booksubjectophth
