How to Test an Intraocular Lens

The human eye has a natural crystalline lens that focuses light onto the retina. This natural lens thickens with age. Sometimes the lens becomes clouded because of this thickening and the light entering the eye either is distorted or cannot reach the retina; this is called a cataract. A cataract can be removed by surgery. In this surgery the eye's clouded natural lens is replaced with an artificial intraocular lens (IOL). The main job of the IOL is to focus light onto the retina, similar to the natural, healthy eye lens. According to "The British Journal of Ophthalmology," the star test can be used to evaluate the optical quality of an intraocular lens.

Things You'll Need

• Microscope objective lens
• 0.9 percent NaCl solution
• 2 plano glass plates
• Microscope
• Slide projector
• Digital camera

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Instructions

• 1

  Make a model eye that consists of a diaphragm and a microscopic lens. The lens should be placed behind the diaphragm. The diaphragm will simulate the human pupil and the lens will simulate the human cornea.

• 2

  Place the IOL in 0.9 percent NaCl (saline) solution immersed between two parallel plano glass plates 20 mm apart. A plano plate has two plain surfaces; it can be seen as a lens with infinite curvature. Put the IOL in the model eye with the anterior, or outermost, surface first. This is where the light first enters the lens.

• 3

  Insert this model eye in the condenser stand of a microscope with a rotatable plane mirror reflecting the point source of light coming from the slide projector covered with a pinhole.

• 4

  Capture images of the Airy disc and diffraction rings produced at focus with different diaphragm apertures. An Airy disc is a small disc of light produced by a lens forming an image of a point source of light such as a star. Concentric bright rings around the Airy ring are termed diffraction rings.

• 5

  Examine the clarity and quality of the Airy disc. Also examine the symmetry and uniformity of the expanded diffraction ring patterns.