In this presentation slides I will discuss about Ocular tribology. Ocular Tribology is concerned with the mechanisms of contact lens lubrication. There are three major driving forces in contact lens design and development… a. Cost b. Convenience c. Comfort

1. A Presentation by:
Sajeed Mahaboob
2011ME1111
Instructor: Dr. Harpreet Singh
09-10-2014 1

2. 
Introduction
What is Ocular Tribology…
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 Ocular Tribology is concerned with the mechanisms of
contact lens lubrication.
 There are three major driving forces in contact lens design
and development…
a. Cost
b. Convenience
c. Comfort

3. 
Introduction
 It is a lens simply placed in the eye.
 They are considered as medical devices and can be worn to
correct vision, for cosmetic or therapeutic reasons.
 In 2010, worldwide contact lens market was estimated at $6.1
billion.
 The average age of contact lens wearers globally was 31 years old
as of 2010.
09-10-2014 3Source: http://www.daviddarling.info/encyclopedia/C/contact_lenses.html

4. 
Uses of materials in Contact lenses
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 Nowadays generally used soft contacts are made of
pliable hydrophilic (water-loving) plastics called
hydrogels.
 Because of this hydrophilic characteristics, the water
content of various hydrogel contact lenses can range
from approximately 38% to 75%.
 The water content of soft lenses allows oxygen to pass
through the lenses and keep the cornea healthy during
contact lens wear.

5. 
 Availability of hydrogel soft lenses (Based on their water
content)
1. Low water content (Less than 40%)
2. Medium water content (50%)
3. High water content (more than 60%)
 Trending soft contact lenses nowadays called silicone
hydrogel lenses are becoming popular very fast these days.
These lenses include silicone within the hydrogel material to
increase the oxygen transmissibility of the lenses.
Continued…
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6. 
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Tribological Issues
 You will feel itchiness if the friction between eyelid
and eyeball is very high,
 If friction between eyelid and eyeball will be low,
lens might slip out.
 Dynamic friction/static friction ratios plays very
important role to design new lenses.
 Friction changes when the lens starts to dry out.
 Lens property changes when its dipped in contact
lens solution overnight.
 we can’t wear lens and sleep at night

7. 
 Lens will be more comfortable if….
1. The lens has the ability to maintain moisture
(wetting) at the surface.
2. The lens should remains lubricated so that the
mechanical friction and the associated pressures from
the eyelid do not impact the lens and cornea
negatively.
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Wetting and Lubrication of Lenses

8. 
Micro scale:
Micro-tribometry is a technique that uses delicate
flexures to resolve forces to levels approaching 10µN.
Such low force resolution is particularly important in
measuring frictional forces on hydrogels because of
their softness and the low contact pressures(3-5 kPa)
that they experience when being worn.
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Measurement of surface friction

9. 
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Measurement of surface friction
Customized micro-
tribometer instrument, used
for contact lens friction
analysis
Source: http://www.clspectrum.com/articleviewer.aspx?articleid=106075

10. 
 Four commercially available soft contact lenses were tested:
Acuvue Advance, Acuvue Oasys, O2 Optix, and Pure Vision.
 The lenses were prepared by cycling. each lens cycles 6 times
through hydration and dehydration cycles and then
mechanically secured onto a soft probe.
 The lens-coated probes were submerged in either a
HydraGlyde Moisture Matrix solution or in a saline control
solution, and lightly loaded against a highly polished SiO2
surface to average contact pressures below 5 kPa.
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Measurement of surface friction

11. Nano scale:
Atomic force microscopy (AFM) is mainly used in the
topographic analysis of material surfaces on the nanometer scale.
This technique works by detecting the deflection of a weak
cantilever, which supports a probe tip, as function of the
programed motion across a sample surface.
AFM measurements detected frictional differences between each
of the neat lens, as well as additional evidence for the uptake of
the HydraGlyde Moisture Matrix through a reduction in friction
following solution treatment.
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Measurement of surface friction

12. 
 We can measure the lens moisture using Lipophilic
diffusion.
Lenses are placed in a concentrated dye solution (Sudan IV in silicone
oil solution) for either 30 minutes or 16 hours.
The length of time that the lenses are exposed to the hydrophobic dye
environment is meant to simulate an exaggerated hydrophobic lens
wear environment.
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Moisture measurement

13. 
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Moisture and Dye diffusion uptake
Image source: http://www.clspectrum.com/articleviewer.aspx?articleid=106075

14. • Laboratory-based techniques to evaluate contact angles include
the sessile drop and the captive bubble techniques.
• The sessile drop method measures the contact angle between a
drop of water and a contact lens surface exposed to air.
• Dynamic captive bubble technique measures the contact angle
between an air bubble and a contact lens surface in an aqueous
environment.
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Measurement of contact angles

15. 
 Tight lens syndrome
This may be because of the tight fitting of lenses, or it
may be related to increase in dryness of the lens with
the eye.
 Corneal ulcer
Over wear of lenses, improper cleaning of lenses,
extended wear use of lenses, and overly tight lenses
may increase the risk of developing the surface
breakdown.
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Problems with contact lenses

16. 
 Corneal swelling
Essentially, the cornea becomes smothered by the lens.
Sleeping in contact lenses, as with extended wear lenses,
greatly increases the risk of corneal swelling.
 Eye redness
Lens allergy, lens solution allergy, or allergy to protein
build-up on lenses.
Lens over wear with corneal edema, with corneal drying
or a tight contact lens syndrome.
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Continued…

17. 
 Interaction of bacterial toxins trapped beneath the
contact lens leading to corneal irritation.
Corneal ulcer.
Giant papillary conjunctivitis.
Poorly fitting or defective contact lenses
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Continued…

18. 
References
• http://en.wikipedia.org/wiki/Contact_lens
• http://www.daviddarling.info/encyclopedia/C/contact_lenses.html
• http://www.allaboutvision.com/contacts/faq/contact- materials.htm
• http://eprints.aston.ac.uk/10925/
• http://www.tribologyblog.com/2009/04/contact-lens-
• tribology.html
• Biotribology By: Anne Jacobson
• http://www.clspectrum.com/articleviewer.aspx?articleid=106
• 075
• Disscussion and some help with friends and seniors
09-10-2014 18

19. 
27-06-2014 19
So…gentlemen
Thanks for your Patience.