Major properties of hydrogel lenses

1. Contact lens Properties
Arooba Naeem
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2. • What is Contact Lens.
• What is Soft Contact Lens.
• Properties of Hydrogel Material.
• Physical Properties
• Optical Transparency.
• Mechanical Properties.
• Surface Properties.
• Wettability.
• Water Content.
• Oxygen permeability.
• Oxygen transmissibility.
• Refractive Index
• Dimensional stability.

3. What is contact lens?
Contact lens as the name indicate is an
optical device ,in contact to the eye.
USED FOR CORRECTION OF:
• Refractive Error.
• Irregularities on front surface of cornea.
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4. Soft Contact Lens:
• A contact lens made of soft water-
absorbing plastic that adheres
closely and with minimal
discomfort to the eye.
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5. Properties of Hydrogel Material:
The ocular environment places significant demands on
the performance of hydrogels as biomaterials.These
must be:
• Maintain a stable, continuous tear film.
• Be permeable to oxygen.
• Be permeable to ions.
• Be comfortable.
• Provide clear, stable vision.
• Be durable for the lifetime of the lens.
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6. Physical Properties:
• pH.
• Temperature.
• Tonicity.
• Elasticity.
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7. Optical Transparency:
• A hydrogel to be used as a contact lens
material need to be transparent in order to
achieve maximal visual performance.
• The light transmittance of polymers
includes the description of materials as
being transparent, translucent or opaque.
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8. Mechanical Properties:
• The mechanical properties of hydrogel
contact lenses are fundamentally
important because they are directly related
to factors such as the comfort, visual
performance, fitting characteristics,
physiological impacts, durability and
handleability of the lenses.
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9. Surface Properties:
• The surface characteristics of the hydrogel
lens will directly affect its interactions
with the tear film and consequently its
biocompatibility in the ocular
environment.
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10. Wettability:
• Wettability in a contact lens is the ability
of the tear film to spread and maintain
itself over a contact lens surface.
• Wettability depends upon:
1. Low contact angle.
2. High surface energy.
3. High interfacial tension.
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11. • Comfort. • Discomfort.
• Decrease in friction. • Increase in friction.
• Debris resistance. • Low debris resistance.
• Visual
performances.
• Giant pupillary
conjunctivitis.
• LWP.
Advantages Disadvantages
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12. Methods:
• In vitro:
- Sessile drop.
- Captive bubble.
• In vivo:
- Tear break up time.
- Interferometer.
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13. Water Content:
• Oxygen permeability.
• Refractive index
• Rigidity (handling)
• Durability.
• Minimum thickness.
• Environmental susceptibility.
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14. Disadvantages
• Less susceptible to
environment influences.
• Low Dk.
• More rigid, easier to
handle.
• Less flexible.
• Higher refractive index. • Thin lenses are difficult to
handle.
• Pervaporation staining is
less.
14Low water content:

15. Advantages Disadvantages
• Higher Dk. • Fragile.
• More flexible. • More deposit prone.
• Faster restoration of
shape.
• More susceptible to the
environment.
• Lower refractive
index.
• Pervaporation
staining, is more.

16. Measurement of Water Content:
• Water content of contact lens can be
measured by using Refractometer.

17. Oxygen Permeability:
• Oxygen permeability is a property of the
material itself and is described as Dk.
• Where D is diffusivity of the material, and k is
the solubility of the material.
• Measured in unit Fatt.
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21. Thank you!
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