NEAR AND DISTANT SIGHT. 
285 
quence of a morbid accumulation of adept at the bottom of 
the orbit without either of them being more near-sighted than 
those who are free from this imperfection, 
I have seen many instances in which old persons who have instances of 
been lone accustomed to use convex glasses of considerable adjintmcnt 
° . for perfect vt- 
power, have recovered tlteir former sight at the advanced age sion havinp 
of eighty or ninety years, and have then had no further need of 
them. Dr. Porterfield was of opinion, that in such cases 
the amendment is occasioned by a decay of adeps at the bottom 
tof the orbit ; in consequence of which the eye, from a want 
• of the usual support behind, is brought, by the pressure of the 
muscles on its suWs, into a kind of oval figure, in which state 
the retina is removed to its due focal distance from the flat- 
tened cornea. But if a morbid absorption of adeps at the bot- 
I tom of the orbit were sufficient to restore the presbyopic to a 
j good sight, it might be expected that a morbid accumulation 
I of adeps in this part w'ould produce a presbyopic or distant 
( sight. This, how’ever, has not happened in any of the cases 
I that have come under my notice. On the contrary, in some 
■ such persons a degree of near-sightedness has bt*en induced 
by the accumulation : and in others the sight, with regard to 
I distance, has not been afl'ected by it. It appears to me more 
probable, that this remarkable revolution in the sight of old 
I persons is occasioned by an absorption of part of the vitreous 
humour ; in consequence of which the sides of the sclerotica 
are pressed inward, and the axis of the eye, by this lateral pres- 
sure, is proportionably lengthened. An alteration of this 
kind is also sufficient to explain the reason why such aged per- 
sons retain the power of distinguishing objects at a distance, at 
the same time that they recover the faculty of seeing those 
that are near, since the lengthened axis of the eye leaves the 
power by which it is adjusted to see at different distances 
precisely in the same state in which it was before the lengthen- 
ing of the axis took place*. 
Although 
• Dr. Yomig, in the paper to which I alluded in page 38, ha« de* 
•cribed a great number of ingenious experimeuts devised by him to 
