Introduction to Contact Lenses - 1.pptx

A detailed introduction to different types of contact lenses, materials, classification, modality, etc.,

1. Introduction to Contact Lenses By Lavanya Kalikivayi, M.Opt., FLVPEI., FIACLE., (Pursuing PhD) Associate Professor Ahalia School of Optometry & Research Centre

2. Artificial device whose front surface substitutes the anterior. surface of the cornea Used for correction of: Refractive error Irregularities on front surface of cornea What is a Contact Lens?

3. Diameter Nomenclature Used in Contact Lenses

4. Curves 43.25 41.62 40.25

5. Edge Edge shapes of lenses: (a) posterior; (b) central; (c) anterior; (d) blunt; (e) sharp Union of the Peri.Postr.C & Peri.Antr.C of the lens

6. Power: Central anterior curve determines the power of the lens Measured in terms of posterior vertex power in diopters Thickness: Measured in the centre of the lens Varies depending upon the postr . vertex power of the lens Power & Thickness

7. Tint Color of the lens

8. S. No Characteristic Nomenclature Type British American 1 Optic zone Back optic zone(BOZ) Optic zone(OZ) 2 Radius Back optic zone radius (BOZR) Optic zone radius (OZR) 3 Back central optic radius (BCOR) Base curve radius (BCR) 4 Diameter Back optic zone diameter (BOZD) or back central optic diameter Optic zone diameter (OZD) 5 Central optic portion Back central optic portion (BCOP) Base curve (BC) or central posterior curve (CPC) 6 Peripheral radius Back peripheral radius (BPR) Peripheral curve radius (PCR) 7 Frontal optic portion Frontal central optic portion (FCOP) Optic Cap 8 Central thickness Geometrical central thickness (GCT) Thickness 9 Width Peripheral curve width (PCW) Peripheral curve diameter (PCD) 10 Overall diameter Total diameter (TD) Overall diameter (OD)

9. Terminologies Related to Contact Lens Material Oxygen Permeability Oxygen transmissibility Flexural Stability Heat Resistance Refractive Index Transmission of Light Water content Wettability

10. Contact lenses transmit gases like oxygen. This is denoted by the coefficient of variable DK , where D is the diffusion coefficient, and K is the solubility coefficient. This property doesn't mean the actual permeability of oxygen through the contact lenses. This is a unit by which oxygen passage for a specific lens is obtained. OXYGEN PERMEABILITY

11. Low Dk material Below 20 Mid Dk material 20 to 40 High Dk material 40 to 60 Hyper Dk material Above 60 DK - Continued

12. This is the oxygen passage of a contact lens of a particular thickness. This is denoted by DK/L or DK/t where L/t indicates the thickness. Depends on: Permeability of lens material Thickness of lens Temperature at which test is performed The central thickness is taken as the average thickness for all practical considerations, and -3D is taken as the standard thickness of the lens by the manufacturers. OXYGEN TRANSMISSIBILITY

13. Daily wear , the recommended Dk /t of a contact lens is around 30  Holden and Mertz (1984) suggested a Dk /t of at least 24 for daily wear. Harvitt and Bonanno (1999) thought at least 35 Fatt Dk /t units were necessary . For extended wear , Holden and Mertz suggested a Dk /t of at least 87 . Harvitt and Bonanno (1999) thought at least 125 Fatt Dk /t units were necessary. DK - Continued

14. The percentage of water constituting the contact lens is called the water content. The contact lens has cross-linked monomers, which lead to the formation of pores. The pores absorb the water increasing the water content of the lens. Water content increases the lens's oxygen transmission, permeability, and thickness and increases the lens's mechanical strength. Water content

15. Contact Lens Materials FDA classification Group I: Low water content <50, non-ionic <1% mole Group II: High water content >50, non-ionic <1% mole Group III: Low water content <50, ionic >1% mole Group IV: High water content >50, ionic >1% mole Ionic materials demonstrate considerable higher levels of lysozyme uptake compared to non-ionic. Not only water uptake plays significant role in protein uptake but also the polarity of the materials. Hydrogels/ Hydrophilic

16. Group I: Without Silicon & Fluorine Group II : With Silicon but no Fluorine Group III: With Silicon & Fluorine Group IV : Without Silicon but with Fluorine Contd…. 03-04-2023 Alvarez-Lorenzo C, Hiratani H, Concheiro A. Contact lenses for drug delivery: achieving sustained release with novel systems. American Journal of Drug Delivery. 2006 Sep;4:131-51. 17 Silicon Hydrogels/Hydrophobic

17. It is the property by which liquid binds to the surface of a solid despite cohesive force between the water molecules. Wettability is inversely proportional to the wetting angle. The lower the angle, the better is the wettability and vice versa . The angle that the edge of a bead of water makes with the surface of a contact lens called a wetting angle. Wettability No wetting - Angle 150 degree Partial wetting - Angle 70 degree Complete wetting - Angle 0 degree

18. Biocompatibility Should not be harmful to the eye and should not contain any harmful material potentially dangerous to the eye. Stability The curvature and thickness of the contact lens should be stable to provide an excellent visual function. Molding The contact lens material should be amenable to reshaping and duplication to be manufactured easily. Gas Permeability The contact lens material should have good gas permeability so that it doesn't interfere with corneal oxygen transmission. IDEAL MATERIAL

19. Sterility The contact lens material should be sterilizable or should be resistant to contamination . Tolerance The tolerance of contact lenses depends on the design and oxygen permeability . Surface Chemistry The contact lens material should be wettable so that tear film can cover it and stay over it. Optical Property The contact lens material should be transparent, and its refractive index should be near the tear film. Requires minimal patient care Cost effective Contd…

20. Monocurve / single-cut lens Bicurve Tricurve Multicurve Toric lens - FST, BST, Bi-toric CONTACT LENS DESIGN Tricurve Multicurve

21. Contd… Lenticular lenses Bifocal lenses

22. Optical High myopia Unilateral aphakia Corneal scar Anisometropia Keratoconus Irregular astigmatism Refractive error ( cosmesis ) INDICATIONS

23. COSMETIC INDICATON Aniridia Albinism Coloboma / Large iredectomy Heterochromia Microcornea / Microphthalmos Corneal scars Inoperable cataract Pthisis bulbi INDICATIONS Contd…

24. OCCUPATIONAL INDICATION Actors / public speakers People using telescope / microscope Sportsman Protection from steam, spray, mist etc. INDICATIONS Contd…

25. THERAPEUTIC [ BANDAGE SOFT C.L .] Corneal Pathologies Pseudophakic bullous keratopathy Non-resolving corneal ulcer Recurrent corneal erosion syndrome Dry eyes Epithelial defect Post keratoplasty Perforation Post superficial keratectomy Post corneal tear repair- micro leak INDICATIONS Contd… Glaucoma Drug delivery system Pediatric Amblyopia-Opaque contact lens for occlusion  

26. Diagnostic Gonioscopy Electroretinography Fundus examination in patients with astigmatism Photography of fundus Goldman 3 mirror examination INDICATIONS Contd…

27. Preventive Trichiasis Exposure keratitis Prevention of symblepharon INDICATIONS Contd…

28. OCULAR PATHOLOGIES Blepharitis Chalazion / stye Conjunctivitis Large pterygium /pinguecula Chronic hyperemia CONTRAINDICATIONS Pannus Corneal anesthesia Tear film abnormalities Epithelial dystrophies Scleritis , Episcleratis Iritis

29. SYSTEMIC DISORDERS Diabetes Oral contraceptive use Pregnancy Perimenopausal ALLERGIES Contact dermatitis Asthma Atrophic rhinitis CONTRAINDICATIONS

30. OCCUPATIONAL HAZARD Smoky , dusty hot environment Chemical fumes & irritants High altitude flyers Construction worker / automobile mechanics . OTHER Poor general health Clumsy patient Low hygienic standards Old patient with low motivation Arthritis CONTRAINDICATIONS

31. No peripheral aberration No chromatic aberration Prism distortion can be controlled Less minification / magnification Astigmatism can controlled No fogging Increases field of vision Cosmetically more pleasant ADVANTAGE

32. Problem for old / very young patient Require a lot care Supervision required Costly DISADVANTAGE

33. CLASSIFICATION Based on purpose of use Anatomical location Nature of lens Based on wearing schedule Based on water content/DK Optical Therapeutic Cosmetic Scleral Semi-scleral Corneal PMMA RGP Soft Hydrogel Soft Silicon Hydrogel Daily Wear Extended/Continuous Wear Frequent Replacement Disposable Low DK RGP High DK RGP-Fluorine Low H2O Non-ionic High H2O Non-ionic Low H2O Ionic High H2O I onic Low H2O High DK - Silicon

34. ADVANTAGE Light in weigh High optical quality Non toxic Easy to manufacture HARD CONTACT LENS (RIGID NON-GAS PERMEABLE LENS) DISADVANTAGE Low wettability Low O2 permeability (DK value = 0) Hard Now obsolete Made of PMMA. Confirm to the cornea.

35. Initially made of Cellulose Acetate Butyrate. Silicon Acrylate Copolymer of PMMA & Silicon containing vinyl monomer Fluropolymers -for extended wear. Size- usually 9-10mm. Best in high myopes, astigmatism >2d, keratoconus . RIGID GAS PERMIABLE LENS (RGP) / SEMI SOFT LENS ADVANTAGES Better quality of vision More durable Correction of astigmatism Deposit resistance Less of chance of infection Cost of lens Less comfortable, tough

36. HIGH WATER CONTENT >50% to 85 % of H2O Made of hydrogel HEMA HEMA-VP LENSES MMA-PVD LENSES Glycidyl methacrylate SOFT CONTACT LENS LOW WATER CONTENT 38 – 45 % of H2O HEMA HEMA-VP LENSES HEMA - silicone hydrogel.

37. Very comfortable and easy to adapt Larger & adhere more tightly to the cornea Doesn’t correct astigmatism ADVANTAGES OF SOFT CONTACT LENS HIGH WATER CONTENT Advantages: Higher DK More flexible Faster restoration of shape following deformation. Disadvantages: More fragile More deposit prone Difficult to manufacture Lower tensile strength LOW WATER CONTENT Advantages: Less susceptible to environment changes Low protein deposition Ease of manufacture More wettable Compatible with all lens care product Disadvantages : Low DK Less flexible

38. Central optical zone, formed by Rigid GP ,surrounded by peripheral soft contact lens material . Second generation silicone hydrogel CL, called Duette , having highly oxygen permeable GP centre , surrounded by a soft silicone hydrogel “skirt” for comfort. HYBRID RGPs

39. What to check in a CL? - Hydrogel/Silicon Hydrogel - Rigid Gas Permeable (RGP)