Spheres
The curved surface is part of the spherical lens and the dioptric power is equal at all axis positions. After passing through the lens, the light beam converges at a point (or at a virtual focus). Spherical lenses include concave (-) and convex (+) lenses, and are used to examine myopia, hyperopia, and presbyopia.
Cylinders
The curved surface is part of the cylindrical lens and the dioptric power is not equal at all axis positions. After passing through the lens, the light beam converges into a straight (or broken) line. Cylindrical lenses include concave and convex versions, used to examine astigmatism.
Prisms
The tangent plane of a prismatic lens is wedge-shaped. When passing through the lens, the light beam deflects toward the base and the object shifts toward the edges. This type of lens is used to assess the ocular musculature, deviation, and latent deviation, as well as to exercise the eye muscles.
Occluder
Opaque lens used to cover the patient’s non-examined eye in a dark room.
Frosted Lens
Semi-transparent covering lens, used mainly for infants or, outside the office, as an occluder.
Slit Lens
At its center it has a slit through which light passes, while the rest of the lens blocks it. By rotating this lens in front of the eye, astigmatism can be examined: if vision improves or worsens at a given axis position, astigmatism is present; if it does not change, its existence is ruled out.
Plano Lens
Transparent, flat lens that does not deflect light passing through it. It is used to examine simulated blindness (false blindness).
Color Lenses
Available in different colors —red, green, blue, yellow, and dark brown—, they are used to examine color sensitivity. In patients whose dioptric image is cloudy (for example, with cataracts), the red or green lenses are suitable. They are also used for re-inspection and color blindness examination.
Cross Cylinder
Lens with opposite dioptric powers at two axis positions, used to determine the degree and axis position of the cylindrical lens when evaluating astigmatism. To use it, place it in front of the cylindrical lens matching one of its axes with that of the lens and rotate it 90° counterclockwise, observing the change in vision. If vision does not change, the degree of the cylindrical lens is adequate; otherwise, adjust according to the result. To correct the axis position, place the two axes of the cross cylinder at 45° on each side of the test axis and rotate counterclockwise, comparing vision in both positions, until the difference is almost imperceptible, which confirms that the cylindrical lens is in the correct position.
Maddox
On its surface it has a series of rods through which a point of light is transformed into a line perpendicular to those rods.
Pinhole (Pin Hole)
At its center it has a small hole through which the light beam passes, forming an artificial pupil. It is used to improve the diopter, especially astigmatism, when placed in front of the eye.
