Biomedical Engineering Reference
In-Depth Information
Equivalent mirror
surface
Cornea
Equivalent center of
curvature
C
F
-15.0 mm
-7.5 mm
-3.1 mm
-10.6 mm
-18.1 mm
Figure B-3.
The corneal surface and equivalent mirror's surface, center of curvature,
and focal point are shown. The focal length of the equivalent mirror (7.5 mm) is equal
to half of its radius of curvature (15.0 mm). Since the equivalent mirror surface is
located 3.1 mm behind the cornea, Purkinje image III is 10.6 mm behind the cornea.
but the distance from the cornea to the anterior lens surface center of curvature is
−
13.6 mm. Therefore, the object vergence is
n
l
L
=
1.333
=
L
−
0.0136 m
= −
L
98.01 D
To locate the image, we use the vergence relationship
L
′
=
L
+
F
L
′
=
−
98.01
+
42.69 D
55.32 D
This negative image vergence tells us that the image is virtual and located on the
same side of the cornea as the object. The refracted rays that form the image are
located in air:
n
L
′
=
−
L
l
′
=
′
(1000)(1.00)
−
′
=
l
55.32 D
′
= −
18.08 mm
The center of curvature of the equivalent lens is located about 18.1 mm to the
left of the corneal surface.
l
