CORNEAL (OR RIGID) CONTACT LENS
• Initially, they are made of PMMA only. They
are now made of combination of PMMA,
silicon, fluorocarbon, methacrylic acid (MA)
and PVP (polyvinyl pyrrolidone in various
percentage to offer different oxygen
permeability and surface wetting property.
• The lens diameter varies from 8.5 to 9.5mm
and allows oxygen permeability due to
coverage of smaller area of corneal surface.
• Excellent visual acuity.
• few deposits.
• Modification is possible.
• Easy to insert, remove and maintenance.
• Cost less.
• Oxygen permeability is more than other types.
• Correct corneal astigmatism.
• Easy to check.
• They are easy to fit.
• Rigid contact lens can correct corneal
astigmatism of larger diopter.
• RGP lenses do not cover the entire cornea.
• Variety of complex designs available.
• RGP lenses available in a range of tints.
• Period of adaption is longer and
approximately three weeks.
• Less comfortable than soft contact lens.
• Foreign bodies.
• Risk of loss.
• Initial discomfort.
• Precise fitting required.
Terminology, abbreviations and
• BOZR = back optic zone radius.
• BOZD = back optic zone diameter.
• OZ = optic zone.
• PC = peripheral curve.
• BVP = back vertex power.
• TD = total diameter.
• OS = overall size.
Hydrogel contact lens
• Hydrogel (also called hydrophilic or soft)
contact lenses are made of polymers(plastics)
that absorb water. These lenses may absorb
up to 90% water. This makes the lenses
relatively soft and flexible, so they must be
handled and fitted somewhat differently from
• These most popular contact lenses are
designed to cover the cornea, limbus and 1.5
to 2 mm. of the adjacent sclera.
• The are very comfortable and the fitting
procedure is very simple.
• Their diameter varies from 13.5 to 14.5mm.
• Made of hydrophilic material HEMA
• Are available commercially as daily disposable,
monthly disposable, extended wear (EW) and
daily wear schedules.
• Correct astigmatism up to 1.00D.
• Are used for optical purposes and as
therapeutic soft bandage contact lens.
• Good initial comfort.
• Ease of adaption.
• Natural facial expression and head posture.
• Long wearing time.
• Low incidence of oedema.
• Low occurrence of over wear syndrome.
• Absence of spectacle blur.
• Maintenance of corneal sensitivity.
• Good for intermittent wear.
• Low incidence of photophobia and
• Low incidence of flare, even with large pupils.
• Few problems with foreign bodies.
• Low risk of loss
• Good for sports.
• Can not correct astigmatism of more than 1.00D.
• Requires complex care procedure.
• Solutions allergies.
• Ease contaminated.
• Difficult to check.
• Limited life span.
• Expensive to maintain.
• Difficult to clean. Etc...
Methods of manufacturing
• There are 3 basic methods of manufacturing
1. Lathe cutting
2. Spin casting.
3. Cast molding.