Understanding Spherical, Toric, Polarized Lenses and Aspheric Lenses

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Describe the physical characteristics of a spherical lens?
Spherical lenses are classified as either concave or convex due to the curving of their spherical
surfaces. Convex lenses are thick at the middle and thin at the edges. When light passes through
the convex lens, it converges thus referred to as a converging lens. Concave lenses are thin at the
middle and thick at the edges. Concave lenses diverge light passing through it thus are diverging
lenses.
Describe the physical characteristics of a toric lens and state the names given to the
principal meridians on the back surface?
Combines a spherical curve and cylindrical curve thus referred to as spherocylindrical
Base curve - a principal meridian on the back surface with a minimum curvature
What is the difference in the focus produced by a spherical and toric lenses?
In a spherical lens, parallel light rays diverge from a singular focal point in concave lenses and
converge in a singular focal point in convex lenses while in toric lenses, focus is at different
focal points from different meridians
How can you improve the field of view for hypermetropic patients?
Patients who have a long sightedness disorder are referred to as hypermetropic patients or rather
suffer from hypermetropia. This means, when parallel light rays pass through their eyes, objects
are focused beyond their eye's retina. First, troubleshoot clinically the level of hypermetropia in
order to give the right prescription. Some stages may require a prescription of spectacles with
convex lenses so that focus of rays is on the retina or contact lenses prescription to eliminate

prismatic effects. Other advanced stages may require surgical procedures but consult with the
patient further if a surgical procedure is the only method that will improve their field of view.
Describe two methods of reducing the finished centre and edge thickness of a pair of
spectacles?
Flattening the lens’s base curve
Using aspheric lens designs that generally use small sizes of spectacle frames, therefore,
reducing the edge thickness of the spectacles
What does minus cylinder form mean how is it used in lens design?
Minus cylinder is a notation used to describe the cylinder power for the few diopters whose
divergence is greater than the sphere component. The plus cylinder and minus cylinder differ by
way of the different shapes produced for the ophthalmic lens used in managing the thickness and
frame fitness during the lens design. Therefore, in lens design, a minus cylinder is used to
manage the thickness of a lens and fitness of a lens into the frame.
Polarization and polarized lenses:
How are polarized lenses manufactured and how does this differ from non-polarized tinted
lenses?
Manufacture of polarized lenses involves stretching a material made of needle-like crystals of
herapathite and a transparent polymer film of nitrocellulose, through the application of magnetic
or electric fields to make the material dichroic. Polarized lenses and non-polarized tinted lenses
differ by way of how they work in protecting an individual if worn as sunglasses. Polarized
lenses for instance protect an individual’s eyes from the sun’s UV rays as well as reflections and