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Contact lens
1. CONTACT LENSES (1)
DR. EL-BASHIR EL-SAEED EL-BASHIR
FACULTY OF OPTOMETRY-MAKKA
MARCH 2022
2.
3. Introduction
• Contact lenses are medical devices, which are
primarily used to correct various refractive errors of
the eye. They are the smallest, least visible, the fine
of all devices designed to cover the cornea.
• Contact lens provides a safe and effective way to
correct vision when used with care and proper
supervision.
• They can offer a good alternative to eyeglasses,
depending on the eyes and the individual life style.
4. Introduction (cont.)
• Contact lens is an optical device designed to
stay in contact with the cornea.
• Leoardo da Vinci was the pioneer in
describing, optical principle of contact lens in
Codex of the Eye, Manual D, published in
1508.
• Contact lens is an optical device worn in
apposition with cornea has several advantages
over spectacles.
5. Advantages of contact lenses over
spectacles
• wider field of view: is not restricted and the
distortions which occur through the periphery
of a spectacle lens are eliminated.
• Better for refractive anismetropia.
• Retinal image size almost normal with
refractive ametropia (e.g. with aphakia, high
minus).
6. Image magnification:
• Contact lens causes image magnification in
myopes and image minification in
hypermetropes and aphakics (gives more
physiological retinal image).
7. Advantages of contact lenses
compared with spectacles (cont.)
• No unwanted prismatic effects with eye
movements.
• Less convergence required by hypermetropes
for near vision.
• Avoid surface reflections.
• Contact lens reduces optical aberrations
arising from oblique, i.e. off-axis rays.
8. Diplopia and binocular vision
• Contact lens eliminates diplopia and ensures
binocular vision in high anisometropia and
uniocular aphakia by reducing anisekonia
compared to spectacles.
• In other words, contact lens facilitating
binocularity in anisometropia and uniocular
aphakia.
9. Advantages (cont.)
• Prismatic effect of spectacles is eliminated by
the contact lens.
• Cosmetically superior.
• The stigma of wearing spectacles is avoided.
• More practically for sports.
• Avoid weather problems (rain, snow, fogging
up)
10. Advantages (cont.)
• Provide good acuity for irregular corneas
(keratoconus, trauma, and subsequent to
refractive surgery).
• Therapeutic uses.
• Vocational uses.
11.
12. Disadvantages
• Time required for fitting and adaption.
• Handling skills required by patients.
• Hygienic procedures and lens disinfection
necessary.
• Wearing time may be limited.
• Range of useful tints limited.
• For binocular problems, only limited vertical
prism possible.
13. Disadvantages
• Greater convergence required by myopes for
near vision.
• Lenses can be lost or broken.
• Problems with foreign bodies.
• Peripheral flare (especially at night).
• Deteriorate with use and age.
• Maintenance costs.
• Greater overall expense.
14.
15.
16. Contact Lens materials
• The history of contact lens clearly shows the
development of newer and newer materials that
satisfied the needs of the patients, practitioner
and manufacturers.
• All present day sophisticated researches
approach towards improving the lens materials
that can be ideal for the eye and can be worn for
continuously.
• We still look forward to that ideal lens material.
17. Ideal contact lens material
• Provides sufficient oxygen to the cornea.
• Optically transparent.
• Has stable dimensions.
• Has good wettability when on the eye.
• It require minimum patient care and
maintenance.
• It resists spoliation.
• Easily machinable or easy manufacture.
18. Physical properties of the lens:
• Wettability: it is the ability of the tears to
form a complete film over the lens surface.
• Flexibility: the, more the lens is rigid the less it
will bend when place over the cornea. A
highly flexible material will contour to the
cornea.
• Optical quality: the lens should be optically
homogenous and transparent with minimum
transmission loss.
19. Physical properties of the lens:
• Biocompatibility: the lens should not induce any
inflammatory or immunological responses and
should be inert.
• Manufacturing ease: the process of lens
manufacturing should be easy and coast
effective.
• Stable parameters: lens material should be
dimensionally stable and be easily polished.
• Contact lenses are made of plastic, which are
synthetic or semisynthetic macromolecular
materials called polymers.
