Hydrogels and silicone hydrogels

Churwan Lal Sahu M Optom 1

HYDROGELS & SILICONE HYDROGELS

WHEN AND WHY??

Churawan Lal SahuM Optom



Hydrogels-Advantages

Offers good initial comfort

Less Prone to displacement

Offers Good Centration

Stabilize promptly after insertion



Hydrogels-Disadvantages

Poor oxygen transmission

More dryness

Greater care and maintenance

Limited parameters available



Hydrogels-Disadvantages

Lens handling can be difficult

Uptake of preservatives

May discolour with topical medications



Hydrogels-Indications

Who rarely uses CL

Who uses CL only for 6-8hours

Who are concerned about Money



How does the cornea get its O2 if it doesn’t have blood vessels?

Cornea – Avascular Structure

O2 required – Principally from the atmosphere

Reduced oxygen supply can result in changes to the epithelium, stroma and endothelium



What happens if the eyes don’t get enough oxygen?

Red Eye Polymegathism Hypoxia Neovascularisation Corneal Edema



What happens if the eyes don’t get enough oxygen?

More prone to deposits Dehydration Inflammation Infections in Extended Wear



Why isn’t DK/t 24 always enough?

Patients experience increased oxygen need resulting from environment conditions( Altitude, dryness )



Long wearing days More contact lens users nap in their lenses:84% !

http://images.google.com/imgres?imgurl=http://i.cnn.net/cnn/2002/WORLD/europe/11/21/biz.trav.desks/story.office.cnn.jpg&imgrefurl=http://edition.cnn.com/2002/WORLD/europe/11/21/biz.trav.desks/&h=168&w=220&sz=13&tbnid=4avGAvQgyR0J:&tbnh=77&tbnw=102&hl=en&start=4&prev=/images?q=office+work&svnum=10&hl=en&lr=

http://images.google.com/imgres?imgurl=http://www.musicworkshops.ca/images/classpics-bg1/wk1candids/nap%20time.jpg&imgrefurl=http://maroc-chat.de/forum-thread-621--.html&h=960&w=1280&sz=319&tbnid=kTx46UoWmakJ:&tbnh=112&tbnw=150&hl=en&start=2&prev=/images?q=nap&svnum=10&hl=en&lr=



Requirements for healthy wear

Oxygen transmissibility DW – Dk/t > 35 Oxygen transmissibility EW– Dk/t > 125 Low modulus Surface wettability Resistant to dehydration Biocompatibility




Why silicone hydrogels?

SILICONE

High oxygen permeability




Silicone Hydrogels

High DK Hydrophilic

Highly oxygen Permeable , wettable material




Silicone hydrogels: Advantages

More healthier than conventional SCL

Increased oxygen transmission

More resistance to protein deposits

Less dehydration

Lower risk of infection

Lower incidence of complication with EW




Silicone hydrogels: Indications

High prescriptions

Wearers who experience end of day discomfort/dryness/redness

Wearing hours>12-14hrs

Whose eye requires more oxygen

Who work long hours in low humidity/air conditioning




Silicone Hydrogels:Properties 1.Oxygen Transmissibility

O2 is transmitted throught Si Component

Oxygen Permeability

Hypoxic Problems with EW




2.More Comfort

Less Dehydration More Comfort




3.Increased rigidity

Easily handle

Corneal astigmatism is masked




4.Surface wettability

Contact Angle (CA) -Ability of a fluid to spread over a contact lens surface

CA more wettable the surface

Higher Wettability More comfort




Silicone Hydrogels:Disadvantages

More expensive

Attract lipid deposits Blurred vision/Discomfort

Rigid material Adaptation Issues




HYDROGEL

Combination of polymer&water- soft with limited oxygen

Redness around cornea if worn longer than recommended

Limited wearing hours

SILICONE HYDROGEL

Combination of silicone,polymer&water- soft ,5-6 times more o2 than hydrogels

Healthier ,whiter eye even if worn longer

Long wearing hours



More water content,more dryness at the end of the day

More protein deposits-compromised comfort

Difficulty during handling

Less dryness (low water content

Less protein deposits-More comfort

Very good handling due to shape factor

HYDROGEL SILICONE HYDROGEL


THANK YOU

Hydrogels and silicone hydrogels

Presentations & Public Speaking

Transcript of Hydrogels and silicone hydrogels