Optics > Vision > The Eye
 DCS# 6J10.21 v.2
CENCO EYE MODEL

APPARATUS
Cenco Ingersoll eye model with lens set
 101-06-F
light source
 101-06-F
video camera
 202

DESCRIPTION
The eye model is a water-filled tank with a lens/cornea at one end with a slot for the crystalline lens behind it, and a screen/retina at the other end.  There are three positions for the screen, to represent normal, near-sighted, and far-sighted vision.  A set of six lenses and one diaphragm are used to show various defects and corrections.  The power in diopters is stamped on the lens handles.

The model can be used to show nearsightedness, farsightedness, accommodation, astigmatism, the use of a magnifier, the effect of removal of the crystalline lens, and the effect of varying pupil size.

NOTES
Fill the eye tank with water.   Start with the +20 lens in the crystalline lens position and the light source 35 cm from the cornea, which is the near point of the eye model.

lens type
 power (D)
Plano-Convex +7.00
Double Convex +20.00
Spherical Convex +2.00
Spherical Concave -1.75
Cylindrical Concave -5.50
Cylindrical Convex +1.75

demonstration
 retina position
 crystalline lens
 object location
 corrective lens
 notes
accommodation
 normal
 first +7 D, then +20 D
 use window, then light source at 35 cm

near-sightedness
 rear
 +20
 35 cm
 -1.75
 compare object positions with and without corrective lens
far-sightedness forward
 +20
 35 cm
 +2.00
 compare object positions with and without corrective lens
pupil size
 normal
 +20
 35 cm
 diaphragm
astigmatism
 normal
 +20 with -5.5 behind cornea
35 cm
 +1.75
 rotate corrective lens for sharp image
cataract surgery normal remove 35 cm
 +7.00
 note that image is distinct only for near objects
magnifying lens
 normal
 +20
 35 cm/closer
 none/+7.00
 compare image sizes in the two cases

REFERENCES
http://sargentwelch.com/pdf/opinstr/87660.pdf