![Based on the mode of wear-
• Daily wear contact lenses, worn during the day, removed at night.
• Extended wear contact lenses, worn overnight(up to 30 days depending on the type).
• Disposable contact lenses, replaced daily, biweekly or monthly.
Based on the water content(hydrogel lenses)-
• Low water content [0-40%]
• Medium water content [40-55%]
• High water content [>55%]](https://image.slidesharecdn.com/contactlensanoverview-250501071458-b03eee02/85/Contact-Lens-An-Overview-pptx-Optometry-6-320.jpg)
![Vertex distance-
Distance between back surface of the lens and front surface of the cornea.
Vertex distance formula-
Dc=SPH/[1-(d*SPH)]
Where-
Dc- contact lens power
SPH- spectacle power
d- vertex distance](https://image.slidesharecdn.com/contactlensanoverview-250501071458-b03eee02/85/Contact-Lens-An-Overview-pptx-Optometry-12-320.jpg)
![Indications and contra-indications of CL
INDICATIONS CONTRA-INDICATIONS
• Optical indication - refractive error correction(myopia,
hyperopia, astigmatism and presbyopia).
• Therapeutic indications – corneal diseases, disease of
iris, in glaucoma, in amblyopia, bandage soft contact lens.
• preventive indications – as chemical burn, exposure
keratitis, trichiasis.
• Diagnostic indications-
• Operative indications-
• Cosmetic indications- coloured contact lens
• Occupational indications- sportsman, pilots, actors
• Keratoconus and corneal irregularities
• Aphakia
• Anisometropia
• Mental incompetence and poor motivation
• Disease of lacrimal [DCR]
• Disease of eyelids such as stye & blepharitis
• Conjunctivitis
• Disease of cornea like cornea dystrophy, corneal
degeneration
• Episcleritis and scleritis
• Dry eye
• Inability to use hands
• Occupational hazard
• Poor personal hygiene
• Allergic patients](https://image.slidesharecdn.com/contactlensanoverview-250501071458-b03eee02/85/Contact-Lens-An-Overview-pptx-Optometry-13-320.jpg)
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Contact Lens:::: An Overview.pptx.: Optometry
- 1. CONTACT LENS:AN OVERVIEW MUSHAHID RAZA M.OPTOM JAMIA HAMDARD UNIVERSITY, NEW DELHI
- 2. Introduction • Contact lens is a medical device, which are primarily used to correct various refractive errors of the eye. They are smallest, least visible, the fine of all device designed to cover the cornea. • Contact lens provides a safe and effective way to correct vision when used with care and proper supervision. • They can offer a good alternative to eyeglasses, depending on the eyes and the individual life style. • Contact lens is a device designed to stay in contact with the cornea. • Contact lenses are medical devices worn directly on the cornea to correct the refractive error for therapeutic, cosmetic or diagnostic purposes.
- 3. History • In 1508, the concept for the development of contact lens came from Leonardo Da Vinci. • In 1946, corneal contact lens, made of polymethyl methacrylate (PMMA) were popularized. • In 1961, introduction of soft contact lenses were made by Wichterle.
- 4. Contact lens terminology Contact lens classified as- • Based on the Anatomical position • Based on the material • Based on mode of wear • Based on the water content(hydrogel lenses)
- 5. Based on the anatomical position- • Scleral contact lenses , cover the cornea and conjunctiva overlaying the sclera. • Semi-scleral contact lenses, cover the limbus to lie partially on the conjunctiva. • Corneal contact lenses, which confirm the cornea. Based on the material- • rigid non gas permeable contact lenses, these lenses made of PMMA • Rigid gas permeable contact lenses, these made of cellulose acetate butyrate(CAB) and silicone lenses. • Soft contact lenses, these made of HEMA(hydroxyethyl methacrylate). • Hydrogel lenses-
- 6. Based on the mode of wear- • Daily wear contact lenses, worn during the day, removed at night. • Extended wear contact lenses, worn overnight(up to 30 days depending on the type). • Disposable contact lenses, replaced daily, biweekly or monthly. Based on the water content(hydrogel lenses)- • Low water content [0-40%] • Medium water content [40-55%] • High water content [>55%]
- 7. Terms use in relation to lens material properties Wettability It is the adherence of a liquid to the surface of a solid despite the cohesive forces holding the liquid together, lower wetting angle better the wettability- o Complete wetting- wetting angle 0 degree o Partial wetting- wetting angle- 70 degree o Non-wetting – wetting angle 150 degree Water content Contact lens has pores that are formed by cross-linking of monomers. These pores absorb water, forming the water, content the water Water content high- oxygen transmissibility high If water content increased by 20%, oxygen permeability is doubled.
- 8. Oxygen permeability - • Property of the polymeric material to transmit gaseous substance. • It is express as a co-efficient of variable DK. • D- diffusion coefficient • K- solubility coefficient Oxygen transmissibility- • It refers to oxygen permeability for a contact lens of given thickness. • Expressed as DK/T, where T is denote by thickness of the lens.
- 9. Properties of CL material Physiological properties Physical properties Optical properties • Oxygen permeability • Ionicity • Water content • Biocompatibility • Wettability- necessary for long term lens tolerance • Durability- lens should withstand normal handling and wearing • Deposit resistance- for comfort, good vision lens must resist deposits • Scratch resistance- maintenance of good optical surface properties • Elasticity • Tensile strength • Rigidity • Surface smoothness • Thickness • Transmission • Refractive index • Scattering • Dispersion • Aberration control
- 10. Manufacturing technique of CL Technique Description Lens type Advantage Disadvantage • Lathe cutting Lenses are cut from a solid button using a precision lathe then polished. RGP, custom soft, scleral lenses High precision, customization, ideal for irregular corneas . Time consuming, higher cost, more manual process. • Spin casting Liquid monomer is placed in a spinning mould and polymerized. soft hydrogel Low cast, high- volume production. Mass production of soft contact lens. • Cast moulding Liquid monomer is injected into a mould, then cured. Hydrogel, silicone hydrogel. Accurate reproducible, economical for disposable lenses Most common method for soft lenses. • 3D printing (emerging) Layer by layer additive manufacturing of lenses Various photopolymers Customization potential, rapid prototyping Research custom, design development.
- 11. Terms of contact lens Base curve(BC)- The primary curvature of central posterior surface of the contact lens, adjacent to the cornea • It measured by its radius of curvature(mm) or is sometimes converted in dioptres(D) by taking of reciprocal of its radius t Peripheral curve(PC)- Secondary curve just outside of the BC at the edge of a contact lens. • They are typically flatter than BC to approximate normal peripheral flat cornea. Optic zone(OZ)- The area of the front surface of contact lens that has the refractive power of the lens. Diameter(D)- The total width of the contact lens from edge to edge, measured in mm. Typically range-soft contact lens- 13mm to 14.5mm, RGP lens 8.5mm to 9.5mm, scleral lens 14.5mm to 24mm.
- 12. Vertex distance- Distance between back surface of the lens and front surface of the cornea. Vertex distance formula- Dc=SPH/[1-(d*SPH)] Where- Dc- contact lens power SPH- spectacle power d- vertex distance
- 13. Indications and contra-indications of CL INDICATIONS CONTRA-INDICATIONS • Optical indication - refractive error correction(myopia, hyperopia, astigmatism and presbyopia). • Therapeutic indications – corneal diseases, disease of iris, in glaucoma, in amblyopia, bandage soft contact lens. • preventive indications – as chemical burn, exposure keratitis, trichiasis. • Diagnostic indications- • Operative indications- • Cosmetic indications- coloured contact lens • Occupational indications- sportsman, pilots, actors • Keratoconus and corneal irregularities • Aphakia • Anisometropia • Mental incompetence and poor motivation • Disease of lacrimal [DCR] • Disease of eyelids such as stye & blepharitis • Conjunctivitis • Disease of cornea like cornea dystrophy, corneal degeneration • Episcleritis and scleritis • Dry eye • Inability to use hands • Occupational hazard • Poor personal hygiene • Allergic patients
- 14. Complications of contact lens Cornea complications- conjunctiva complications - Epithelial oedema Allergic conjunctivitis Epithelial microcysts Giant pupillary conjunctivitis Corneal abrasion Superficial punctate keratitis Lens related issues Corneal neovascularization Lens deposit Microbial keratitis Discomfort & dry eye Corneal warping Lens intolerance Corneal endothelial change solution sensitivity
- 15. Fitting assessment of contact lens The main steps of contact lens fitting are describe below- Initial patient work-up- • History • General ocular examination- eyeball, eyelids, cornea, tear film adequacy, conjunctiva. • Refraction • Keratometry • Corneal diameter
- 16. Trial lens fitting technique Selecting the initial trial lens: the trial lens with following parameters should be selected initially- • Overall diameter • Base curve • Power of the lens Evaluation of the trial lens fit: Evaluation of the base curve of the lens- • Movements of the lens over the cornea • A flat or loose fit lens moves • a steep or tight fit • Centring of the lens over the cornea • Effects of blinking on the clarity of visual acuity Evaluation of the diameter
- 17. Guidelines for a change in trial lens- If the trial lens selected initially is not found to be ideal one, the new trial lens selected and again evaluated, based on the above evaluation following guidelines- • Centration • Edge compression • Steep fitting • Flat fitting
- 18. Post-fitting patient management • Ordered contact lens • Examination of the ordered lens & evaluation the fit • Handling and care of contact lens General instruction: 1-hand must be washed 2-cosmetic,lotions, soaps and cream mot come in contact with the lenses. 3-lenses must be stored in normal saline solution. • Insertion and removal
- 19. Insertion and removal Insertion of the contact lens- Wash and dry hands: o Use handwash liquid/soap and water, then dry with a lint-free towel. Inspect the lens: o Place the lens on your fingertip( should form a bowl-shape). o Check the tears and debris o Ensure its not inside out( edges should curve up, not flare out). Open your eye: o Use your non-dominant hand to hold your upper eyelid. o Use the middle finger of your dominant hand to pull down the lower eyelid. Insert the lens: o Look straight ahead or up. o Gently place the lens on the centre of the eye o Slowly release your eyelids and blink a few times. Check comfort and vision: o Lens should feel comfortable and your vision should be clear.
- 20. Removal of contact lenses- Wash and dry hands: o Again, always begin with clean hands. Look up: o Pull down your lower lid with your middle finger. Pinch and remove- o Use your thumb and index finger to gently pinch the lens and remove it. o Avoid using nails to prevent damage. Clean or dispose- o If reusable, clean with recommended solution. o If disposable, discard properly.
- 21. Thank you