Biomedical Engineering Reference
In-Depth Information
FP
-100.00 cm
Figure 8-5.
When an object is located at the far point of the myopic eye, no accommoda-
tion is required for it to be imaged on the retina. The far point is conjugate with the retina.
from the eye to the object (in meters). Substituting into the vergence relationship
for accommodation, we find
F
FP
=
L
+
F
A
0.00 D
= −
3.00 D
+
F
A
3.00 D
As with the emmetropic eye, the required accommodation is 3.00 D.
When an
eye is corrected in the corneal plane with a contact lens (or refractive sur-
gery), the required accommodation is equal (and opposite) to the stimulus to
accommodation.
F
A
= +
We'll look at one more example for this 1.00 myopic eye.
Suppose an object is
located at a distance of 100 cm. How much accommodation is now required if
the eye is uncorrected?
Since the object is located at the far point of the eye, as indicated in Figure 8-5, it
is by definition imaged on the retina. No accommodation is required. Alternatively,
we could use the vergence relationship for accommodation
F
FP
=
L
+
F
A
−
1.00 D
= −
1.00 D
+
F
A
F
A
= +
0.00 D
Next, let's consider uncorrected hyperopia.
To image an object located at a dis-
tance of 33.33 cm on the retina, how much must an uncorrected 1.00 D hyper-
opic eye, as measured in the plane of the cornea, accommodate?
Figure 8-6 shows that following accommodation, the vergence must equal the
far-point vergence of
+
1.00 D. Using the vergence relationship for accommoda-
tion, we have
