Biomedical Engineering Reference
In-Depth Information
n
′
= 1.333
n
= 1.000
FP
+23.22 mm
-38.61 cm
Figure 7-4.
An object located farther from the myopic eye than the far point will be
imaged in front of the retina.
Next, we use the paraxial relationship to determine the object vergence required
to produce this image vergence.
L
′
=
L
+
F
+ 57.41
D
=
L
+
60.00 D
L
= −
2.59 D
Object light rays with a vergence of
-2.59
D are focused on the retina.
This
is referred to as the
far-point vergence,
and the eye is said to be
2.59
D myopic.
To produce this vergence, the object must be located in front of the anterior
surface of the reduced eye. The distance from the surface to the object is
6
n
l
L
=
(100)(1.00)
l
=
−
2.59 D
l
= −
38.61 cm
As can be seen in Figure 7-3B, an object located 38.61 cm anterior to the reduced
eye's front surface—at what is defined as the
far point of the eye (FP)
—is
focused on the retina.
That is, the far point is conjugate with the retina.
In
myopia, it is always located anterior to the eye's surface. Figure 7-4 shows that an
object located farther from the eye than the far point is focused anterior to the retina.
What power contact lens is required to image an infinitely distant object on
the retina of this myopic eye?
6. Because we have placed a factor of 100 in the numerator, the calculated distance is in centimeters.
