Biomedical Engineering Reference
In-Depth Information
A
12-year-old
0.00 D
F
A
= +3.00 D
FP
+33.33 cm
+3.00D
B
70-year-old
0.00 D
F
A
= 0.00 D
FP
0.00 D
Figure 8-7.
A.
When viewing a distant object, a 12-year-old uncorrected 3.00 hyper-
opic child can accommodate the 3.00 D required to focus the image on the retina.
The patient may, however, manifest symptoms of asthenopia and/or intermittent blur.
B.
A 75-year-old uncorrected hyperope does not have the ability to accommodate.
Therefore the retinal image is out of focus.
As the patient ages and the amplitude of accommodation progressively decreases,
the symptoms will become more pronounced, with the uncorrected patient initially
not able to see clearly at near and ultimately not able to see clearly at distance
(Fig. 8-7B).
NEAR POINT OF ACCOMMODATION
The advantage of uncorrected myopia for viewing near objects can be nicely illus-
trated by determining how near an object can be to the eye and still be imaged
clearly on the retina—the so-called
near point of accommodation
(NPA)
.
