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Ocular tribology

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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

Veröffentlicht in: Ingenieurwesen
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Ocular tribology

  1. 1. A Presentation by: Sajeed Mahaboob 2011ME1111 Instructor: Dr. Harpreet Singh 09-10-2014 1
  2. 2.  Introduction What is Ocular Tribology… 09-10-2014 2  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. 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. 4.  Uses of materials in Contact lenses 09-10-2014 4  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. 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… 09-10-2014 5
  6. 6.  09-10-2014 6 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. 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. 09-10-2014 7 Wetting and Lubrication of Lenses
  8. 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. 09-10-2014 8 Measurement of surface friction
  9. 9.  09-10-2014 9 Measurement of surface friction Customized micro- tribometer instrument, used for contact lens friction analysis Source: http://www.clspectrum.com/articleviewer.aspx?articleid=106075
  10. 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. 09-10-2014 10 Measurement of surface friction
  11. 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. 09-10-2014 11 Measurement of surface friction
  12. 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. 09-10-2014 12 Moisture measurement
  13. 13.  09-10-2014 13 Moisture and Dye diffusion uptake Image source: http://www.clspectrum.com/articleviewer.aspx?articleid=106075
  14. 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. 09-10-2014 14 Measurement of contact angles
  15. 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. 09-10-2014 15 Problems with contact lenses
  16. 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. 09-10-2014 16 Continued…
  17. 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 09-10-2014 17 Continued…
  18. 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. 19.  27-06-2014 19 So…gentlemen Thanks for your Patience.