Contact Lens Doc - Gelai PDF

CONTACT LENS Introduction to contact lenses Definition: it is a thin lens considered to be a medical device placed directly on the surface of the eye to: o correct vision o cosmetic o therapeutic reasons History Leonardo da Vinci (1508) - fi...

CONTACT LENS Introduction to contact lenses Definition: it is a thin lens considered to be a medical device placed directly on the surface of the eye to: o correct vision o cosmetic o therapeutic reasons History Leonardo da Vinci (1508) - first describe the concept of a lens that comes into contact with the eye. Yohn Herschel (1827) - describe a glass contact lens designed to match the shape of the eye EE. Moller (1887) - fitted a blown glass lens to the eye of a patient whose eye had been surgically removed. A.E. Fick (1888) - describe the first contact lens intended to correct vision Muller and Obrig (1938) - constructed the first plastic scleral contact lens E. Kalt (1940's) - designed and fitted glass corneal contact lenses - All contact lenses available were scleral types Kevin Touhy (1947) - first plastic corneal lens made from PMMA Otto Wichterle - Developed FEMA Classification of Contact Lens: According to Material According to Mode of Use Hard Daily Wear Non – gas permeable Disposable Gas permeable Planned replacement Soft Extended Hydrogel Continuous wear Silicon Hydrogel Flexible wear According to Design According to Size Monocurve Corneal Bicurve Semi-Corneal Tricurve Scleral  Aspheric According to purpose or Use Optical o Spherical o Toric o Presbyopic Therapeutic Cosmetic Spherical Contact Lens - Used to correct myopia hyperopia, aphakia and small amount of astigmatism - Available in wide range of correction (-20.00D to +20.00D) Toric Contact Lens - For the correction of significant amount of astigmatism Presbyopic Correction ▪ Monovision or monofit ▪ Bifocal soft contact lens o Alternating vision o simultaneous vision ▪ Multifocal o Center near design o Center distance design o Modified monovision (balanced design) Tinted contact lenses ▪ visibility tints ▪ Opaque colored lenses ▪ Combination of transparent and opaque tint Therapeutic (Bandage) Lenses Modern Contact Lenses ▪ Ortho-K contact lens gas permeable contact lenses that temporarily reshape the cornea to reduce refractive errors such as myopia, hyperopia and astigmatism ▪ Hybrid contact lenses large-diameter lenses that have a cigid gas permeable central zone, surrounded by a peripheral zone made of soft or silicone hydrogel material ▪ Google contact lens  contact lens prototype that monitors glucose levels in tears Contact Lens Terminologies ▪ Base Curve (BC) Radius of curvature of the posterior Zone ▪ Optic Zone (OZ) Posterior central optic portion of the lens It indicates the size visually usable portion of the lens ▪ Lens Diameter (LD) A measure of the maximum external dimension of a lens ▪ Posterior Peripheral Curve Radius (PPCR) Radius of the peripheral curve. ▪ Peripheral Curve Width (PCW) Width of the posterior peripheral curve portion of the lens, ▪ Sagittal value (sag) Distance from the line drawn between the the back surface outer edges of the lens to the center of the back surface. ▪ Optic cap (OC) Central anterior optic portion of a lens ▪ Optic cap radius (OCR) Radius of central anterior optic portion of a lens ▪ Anterior Peripheral Curve Zone (APCZ) Anterior peripheral or lenticular portion of the lens Properties of Contact Lens Materials Oxygen Performance - Lens acts as a barrier to atmospheric oxygen - When eye is deprived of oxygen, corneal physiological processes become compromised dk (Oxygen Permeability) - Quality or state of the material that allows the oxygen to move through it. ❖ Higher oxygen content = higher the dk Low dk = less than 30 Medium dk = 30 – 60 High dk = higher than 60 / Dk/t (Oxygen transmissibility) - States how much oxygen goes through the lens ❖ Thinner the lens = higher amount of oxygen can pass through the lens.  o (25) for daily wear o 87 and above for overnight wear EOP - Equivalent Oxygen Performance - This is a measurement of the cornea's oxygen thirst following lens wear o The minimum EOP for daily wear is ______ o Minimum EOP for EW is _________ Corneal Swelling - Most valid indicator of real-life clinical performance - It is the measure of the percent increase in the corneal thickness with great precision Tensile Properties - Four measurement used to evaluate physical tensile properties: o Tensile strength o Modulus elasticity o Coefficient of elongation o Tear strength Water Content - High water content materials become dehydrated while on the eye - High water content tends to lose more water than low water content lenses Refractive Index - A physical property of which defines how light rays are affected as they pass through the material. - It is important to the lens designer to achieve the proper optical effect on the eye. - As water content increases the refractive index decreases - Materials with lower index of refraction will require thicker lens design to achieve the desired optical effect on power Biocompatibility - Contact lens interact with the corneal tissue, therefore it is important to evaluate the physiological balance of the material with the ocular environment. - There are number of different tests that are used to evaluate biocompatibility o 21-day Rabbit test o Resistance to microbial growth - confirmed by assessing the compatibility of the lens material with lens care systems Dimensional Stability - It is assessed in the laboratory periodically by measuring water content, sagittal value, power, thickness, and base curve to make sure that the lens parameters are not changing. - This ensures that the material can maintain consistent lens performance Hydrolytic stability - Since contact lenses are placed in the tear film, which is primarily made up of water, the hydrolytic stability of the material is always assessed prior to placement on the eye. - Only materials that are stable in water can be used for contact lenses Lens Handling - Case of handling is primarily a function of the tensile properties of the lens and the lens design. - The more rigid the lens materials, the easier they are to handle Wettability - Wettability is the characteristic of lens performance that is important to (RGP materials. - Since soft contact lens materials are inherently hydrophilic, there is no problem with water adhering to the surface of the lens. - However, some RGP materials with silicone act as water repellant, thus causing problems with comfort, vision, and deposit formation - With RGP lenses, wettability is tested in the laboratory by measuring the wetting angle. The higher the wetting angle, the less wettable the surface is. - The wetting angle of hydrophilic material is considered zero. Contact lens material IDEAL CONTACT LENS MATERIAL a. Meets cornea's oxygen requirements f. Durable b. Physiologically inert g. Optically transparent c. Excellent in vivo wetting h. Requires minimal patient care d. Resists spoilation k. Easily machineable e. Dimensionally stable IMPORTANT MATERIAL PROPERTIES a. Oxygen permeability e. Flexibility (SCLs) b. Wettability f. Durability c. Scratch resistance g. Deposit resistance d. Rigidity (RGPs) OPTICAL PROPERTIES a. Refractive index c. Dispersion b. Spectral transmission d. Scatter Rigid contact lens - Material used is PMMA  - Backbone of all rigid lens materials Gas permeable lenses - rigid lenses - Material used are: a. Cellulose acetate butyrate c. Fluoropolymers (teflon) b. Silicone acrylate d. styrene SOFT CONTACT LENS MATERIALS PHEMA Other variants to improve PHEMA are: o PVP Poly Vinyl Pyrrolidone o MA Methacrylic Acid o MMA Methyl Meth Acrylate o GMA Glyceryl Meth Acrylate o DAA Di Acetone Acrylamide o PVA Poly Vinyl Alcohol Synthetic elastomers Not only flexible but show rubber like behaviour Intermediate characteristics b/w thermoplastic and hydrogel materials. Oxygen permeabilities 100x-1000x more than PMMA Hydrophobic - surface treatment Ethylene propylene terpolymer (EPT) Silicone rubber or poly (dimethyl siloxane) Contact lens Nomenclature. Contact lens materials are divided into hydrophilic and hydrophobic groups - Materials with water content greater than or equal to 10% by weight at ambient temperature are assigned "-filcon” names. - The "-focon" stem is assigned to hydrophobic lens materials with water content less than 10% Contact lens Groups Contact Lens Material can be Categorized as Ionic and Non-lonic ❖ Group 1: Low water / non-ionic polymers ❖ Group 2: High water / non-ionic polymers ❖ Group 3: Low water / ionic polymers ❖ Group 4: High water / ionic polymers Ionic vs. non ionic contact lens - Based on lens hydration (primarily related to the ionic nature of the material) ▪ non-ionic polymer: o can interact with Solar molecules, such as water, without resulting in a formal charge. ▪ ionic material o Charged molecule, which increases lens hydration. o Ionic materials are sensitive to changes in pH and osmolality o more sensitive to the components in a lens care system o greater interaction with the ocular environment, such as increased uptake of proteins Low Water Content Lenses - Provide excellent physiological response for patients with refractive errors in the - 1.00 to minus - Compatible with (all Jens care systems including thermal, hydrogen peroxide, and chemical disinfecting systems - Has Lower protein uptake tendencies which contributes to longer lens life - Higher tensile strength - Exhibits good material stability - Since low water content materials don't absorb preservatives, they don't have problems with discoloration. High Water Content Lenses - High oxygen permeability, therefore, an excellent choice for the high plus and minus lenses - Lower tensile strength - Not compatible with all disinfecting systems - Higher incidence of acute red eye and lens discoloration - Usually produced with either lathe cut or cast molding process Mid Water Contact Lens - Typically, ionic or non-ionic materials - These lenses are an attempt to combine the best of both high and low water materials - Provide good physiology and are produced in thin/ comfortable designs - Exhibits Increased in protein uptake usually are nor compatible with thermal disinfection techniques Manufacturing Process ▪ Spincasting ▪ Lathe Cutting  ▪ Cast Molding Optics of Contact Lenses - Optically, contact lenses are considered THICK lenses - Their thickness, compared to their short radii of curvature, is optically significant o Surface Power o Index of refraction. o Thickness Surface Power: D= n - 1 /r Nominal Power: Dn = (n - 1 / r1) + (n - 1 / r2) or Dn = D1 + D2 Equivalent Power: Deq = D1+D2-t/n (D1D2) Effective Power - The position of the second principal focus from the back vertex of the lens - Dv = Dn + t/n (D1)2 Neutralizing Power: Dfv = Dn + t/n (D1)2 Correction for Vertex Distance. DCL. = DSpec/ 1 - d(Dspec) DCL= Power of the Contact Lens to be Prescribed Dspec = Spectacle Refraction d = vertex distance in meters Spherical Equivalent - 4:1 Rule - If amount of astigmatism is less than 1.00 D - Dc.= Sph + ½ cyl Spectacle Magnification ▪ SM = corrected image size/uncorrected image size CL Magnification - CLM = 1 – d (DSpec) CORNEAL TOPOGRAPHY: MEASUREMENT AND SIGNIFICANCE ▪ Corneal diameter  o HVID: 10 - 14 mm o Ave:11.7 mm o VVID: Ave: 10.6 mm o smaller than HVID of about 0.5 - 1.0 mm ▪ CORNEAL THICKNESS Clinical Studies: o 0.50 - 0.65 mm o Gullstrand's Eye No. 1: 0.50 mm o CORNEAL THICKNESS MEASUREMENT: PACHYMETERS INSTRUMENTATION FOR CORNEAL TOPOGRAPHY MEASUREMENT Optical Photokeratoscopy and placido disc keratometer y Computer assisted tomography Contact methods casting and molding ultrasound trial contact lenses KERATOMETERS Measure radius of curvature of the optic cap 3-4 mm. Total power of the cornea Calibration index: 1.3375 Converting radius to power: D = 337.5 / r r = 337.5 / D Where: r= radius D = power of the cornea Computing for CL Base Curve: ▪ Rigid Lenses = 337.5 /D ▪ SCL = (337.5 / D) + 0.7 Assessment of Tears ▪ Non-invasive o NIBUT  o Tear prism assessment ▪ Invasive o Schirmer's test o TBUT o Phenol red thread test Spherical Soft contact lens fitting SCLs are larger than the cornea BOZR flatter than the cornea, Lens movement, generated by blinking action of the lids, should be such that the lens edge does not cross the limbus. SOFT LENSES FITTING REQUIREMENTS Soft lenses must: a. Centre on the eye b. Conform to the anterior eye c. Cover the cornea in all eye positions d. Move adequately SOFT LENSES PERFORMANCE REQUIREMENTS: Soft lenses must: a. Produce good and stable vision b. Provide minimal physiological disturbance c. Be wearable for practical periods d. Be comfortable DESCRIBING CENTRATION a. Cartesian system b. Binasal c. Literal description FITTING DESCRIPTIONS a. Good, optimum, ideal b. Steep, tight, bound c. Flat, loose, mobile d. Centred, decentred e. Low riding, high riding f. Superior, inferior, nasal, temporal and combinations of the above SOFT LENS FITTING BOZR SELECTION Measure Ks (mm) then add either: o 0.3 - 0.9 mm to flattest K.  o 1 mm to average of Ks o 4D flatter than average K SOFT LENS FITTING EFFECT OF A BLINK ❖ Too steep vision is clear immediately after a blink ❖ Too flat vision is blurred immediately after a blink SOFT LENS FITTING WHY IS MOVEMENT REQUIRED? o Removes and disperses ocular debris o Promotes tear exchange o Possibly aids epithelial wetting. FITTING SPHERICAL RIGID GAS PERMEABLE CONTACT LENSES Trial Lens Selection: Corneal Topography o The BOZR is +/- 0.10 mm usually of the flattest corneal radius of curvature o Factors that dictate the suitability of the chosen BOZR, Corneal toricity Dynamic fitting characteristics. o The evaluation of the fitting characteristics determines the final BOZR to be ordered for the patient. o The corneal topography also plays a role in the choice of the BOZD for the lens. A smaller BOZD Is used for steeper corneas A larger BOZD is use for flatter corneas. Trial Lens Selection: Corneal Size Usually, an RGP lens diameter is 2 mm smaller than the HVID is chosen for the initial trial. When choosing lens diameter, the positions of the lids are more important selection criteria than HVID alone. When the corneal diameter is small (0.50 D annually) careers require unaided acuity better than they currently have patients who want to be less dependent on glasses and contact lenses PATIENT SELECTION patient is in good health (both general and ocular) Myopia (-6.00) astigmatism (-2.00) Those With large pupils should be discouraged because they will very likely suffer from ghost images at night. well-motivated patients (20/20 might not be achieved) ❖ Contact lens material: High Dk ❖ Design: Reverse geometric design ❖ Fitting: Empirical fitting and Diagnostic fitting (trial fitting) Empirical fitting – Provide: ✔ K result (topography result) ✔ Corneal diameter ✔ Pupil diameter Contact Lenses for Presbyopia ▪ Spectacles ▪ Monovision ▪ Bifocals Alternating bifocals Simultaneous vision bifocals ▪ Multifocal (Progressive) Centre-distance  centre-near. ▪ Modified monovision Lens Care Regimen Classification of ingredients Contained in Lens Care Products: ▪ Active Ingredients Directly contribute to product efficacy ▪ Non-Active Ingredients (excipients) - Additional ingredients to produce a usable produce Example: Water, Salts, Viscosity enhancing agents, Buffer systems, etc. Solution Characteristics: ▪ pH ▪ Osmolality ▪ viscosity pH - Measure of the relative amounts of hydrogen ions - Method of expressing the strength of acids and bases (acids bases) Acids - Is a molecule that Included a positively charged hydrogen ton (H+) as part of Its chemical structure and can transfer this ion to another molecule Base - Is a molecule that has a negatively charged hydroxide group (OH-) within Its chemical structure and can accept hydrogen ion from an acid Importance: ▪ Average pH of tear film: 7.4 ▪ pH range of contact lens solutions: 6,5 - 8.0) ▪ Lens Reaction to pH extremes: ✔ Brittleness ✔ Discoloration ✔ Breakdown of material polymer Buffer System - One or more chemical compounds that when dissolved resist drastic changes in pH ▪ Borate: Boric acid (B&L products) and Sodium Borate  ▪ Citrate: Sodium Citrate and Citric acid ▪ Phosphate: Sodium phosphate and phosphoric acid Osmolality - A chemical term which describes a solution's total salt concentration - Usually expressed in milli-osmoles per kilogram (mOsm/ kg) - 302 mOsm/kg (average tearfilm osmolality) Tonicity - Describes a solution's effect on the tone or shape of a cell ▪ Hypotonic solution ▪ Hypertonic solution ▪ Isotonic solution - Effect of Osmolality on Contact Lenses ▪ SCL retain their original shape in an isotonic solution. ▪ A hypotonic solution causes SCL to lose water and shrink ▪ A hypertonic solution causes the SCIto gain water and expand Viscosity - Describes the thickness of a solution - Importance ▪ Daily cleaner: cleaner remains in contact with the lens during the rubbing step ▪ Lubricant drops and RGP wetting solutions: Increase contact time on the ocular or contact lens surface Microbiology - Microorganisms ▪ Small individual forms of life commonly referred to as germs. ▪ Includes viruses, bacteria, fungi and protozoa - Antimicrobial agents ▪ Chemical harmful to microorganisms Preservatives (bacteriostatic) a. Thimerosal b. BAK (benzalkonium chloride) c. Chlorhexidine Disinfectant (bactericidal) a. Sorbic acid & EDTA b. Dymed c. Polyquad CONTACT LENS CLEANING SYSTEM Consequences if contact lens deposits are not removed: 1. Giant papillary conjunctivitis 2. eye infections Types of contact lens deposits: I. Physiologic deposits or Organic contaminants - tears constituents due to tears evaporation A. Organic contaminants 1. proteins - most common contaminants, troublesome esp. in soft contact lens - carry electropositive (+) while the soft contact lens carries electro- negative (- thus appears "filmy" deposits - characteristics "doughnut" pattern around the edges of crystalline lens 2. lipid and mucin - troublesome esp. in rigid gas permeable (RPG) contact lens and also in soft contact lens - are secretions from Meibomian or tarsal glands - characteristic "slick & greasy" deposits B. Inorganic contaminant 1. crystalline - inorganic (electrolytes) contaminants such as Nat, K+, Catt, Mg salts that intertwined with proteins, lipid and mucin II. Non-physiologic deposits a. finger soils - "always wash and rinse your hands thoroughly" before handling the contact lens b. cosmetics - mascara, eyeliner, powder eye shadow c. environmental & occupational factors - smog, nitrosamine (smoke), fumes, dusts Type of contact lens contaminants: A. Organic 1. proteins 2. lipids 3. mucins B. Inorganic 1. calcium phosphate 2. rust 3. mercurial deposits C. Microbial 1. bacteria a. Pseudomonas aeruginosa (common in hydrogel extended contact lens) b. Staphylococcus aureus c. Staphylococcus epidermidis d. Streptococcus pneumonia e. Streptococcus viridans f. Moraxella or Branhamella lacunata g. Corynebacterium diphtheriae h. Mycobacterium i. Enterobacter aerogenes j. Klebsiella pneumonia  k. Escherichia coli 2. Fungus or mycosis 3. Virus D. Pigments Methods of Contact Lens Cleaning 1. Cleaning Agents A. Surfactant - surface active agent, synthetic that possess 2 centers in one molecule: 1. polar - hydrophilic 2. non-polar – lipophilic has affinity for surface and reduce surface tension called "film pressure" increases solubility of hydrophilic drug by altering permeability of epithelial membranes acts by softening or loosening action that helps remove the deposits along with the surfactant during rinsing process Uses: 1. wetting agent 2. detergent 3. emulsifying agent 4. germicidal agent *total surface tension of tears = 40 dynes/cm. surface tension of mucin = 35 dynes/cm. B. Enzymes - protein biochemical catalyst causing chemical reactions to remove deposits enzymes Ex. Proteins- -> amino acids which are remove by rubbing and rinsing the lens Frequency of use: daily wear contact lens -> lx a week Soaking time: extended wear contact lens - 6-12hrs. and 15mins. S/E: allergy 1. Papain - papaya extract 2. Pancreatin - pork pancreas extract 3. Subtilisin - from Bacillus lichenformis C. Oxidizing agents - act by forming free radicals that affect and dispense debris rapidly 1. hydrogen peroxide 2. Na+ peroxide 3. Na+ hypochlorite 4. Na+ perborate II. Mechanical method III. Ultrasonic method - uses 1:5,000 BAK sterilizing 75% contaminated (Pseudomonas) tonometer for 1 min. and 100% kills Pseudomonas for 3 mins. Disinfection - process by which rendering contact lens "free of pathogenic microorganisms" or "render them inert" Types of Disinfectants: A. Thermal Disinfection - used for hydrogel contact lens disinfection 1. Heat - 80° C for 10 mins. but can NOT destroy spore-former Bacillus but can be destroy by autoclave (121°C at 15 lbs/inch pressure for 15 mins) Disadvantages: a. surface soilage - seen esp. in nightly thermal disinfection - causes Giant papillary conjunctivitis b. hydrogel contact lens discoloration due to interaction between tear protein by products (amino acids) and preservative by-products (aldehydes from sorbic acid & K+ sorbate) 2. Cold - more promising method B. Chemical Disinfection - more convenient to travelers - commonly used today because of greater varieties of material in contact lens with less polymer degradation - resistant to Acanthamoeba Uses: 1. preservative 2. Disinfectant 1.) 0.001% Thimerosal - binds with surface proteins but does not bind with Hydroxyl- EthylMethAcrylate (HEMA) MOA: inhibit sulfhydryl enzyme causing bacterial cell lysis Uses: a. bacteriostatic b. fungistatic S/E: a. allergy b. band keratopathy - calcium deposited at Bowman's membrane of cornea 2.) 0.005% Chlorhexidine - good for Gm (+) & Gm (-) bacteria - binds with surface proteins and HEMA MOA: adhere with microbe cell surface causing cell lysis Uses: a. fungistatic b. fungicidal c. bacteriostatic d. bactericidal e. mouthwash f. skin cleansing g. disinfectant - for instruments S/E: cytotoxic - prevented by using low concentration 3.) 0.5% Chlorobutanol - bacteriostatic to Pseudomonas and Staph. Aureus S/E: diffuses corneal epithelium - damage the epithelium by inhibiting 02 utilization and loosening of epithelial adhesion 4.) Benzalkonium chloride (BAK) - quaternary ammonium compound  - most commonly used cationic detergents - adsorbed to hydrogel contact lens Uses: a. preservative & disinfectant (1:5,000 for ophthalmic solution and 1:750 for sterilizing instruments for 30 mins) *for Pseudomonas sterilization: i. 1:5,000 BAK for 3 days ii. 0.5% chlorobutanol for 1 day iii. polymixin B 1,000 units/ml. b. wetting agent - for easy transcorneal penetration of water soluble drugs e.g. carbachol, done by damaging epithelial cells c. sterilizing skin & mucous membrane - using 1:750 BAK to remove dirt, desquamated epithelium, skin fats and bacteria d. rust inhibitor - using 0.5% Nat nitrate e. lubricating eye drops 5.) 0.013% Triethyl ammonium chloride (TEAC) - alkyl, quaternary ammonium compound Contents: a. quaternaryary ammonium chloride b. thimerosal c. polysorbate 80 - acts as surfactant Uses: a. preservative b. disinfectant c. Cleaner 6.) 0.001% Polyquaternium (Polyquad) - has molecular weight of 5,000 Limitation of use a. prevented borate buffer - instead used citrate buffer to polyquad b. incompatible with Crofilcon A low water hydrogel contact lens and FDA group 4 high water ionic hydrogel contact lens 7.) 0.00005% Polyaminopropyl biguanide (Dymed) - newer, cationic - facilitate microbial attachment 8.) Povidone iodine - water soluble, non-toxic and wash out easily unlike for tincture of iodine Uses: a. antiseptic - use as ophthalmic preoperative preparation *Anti-bacterial property on skin remains for 1 hour and diluted preparation can clean conjunctiva before surgery. Kills bacteria for 1 min. and spore- formers slowly b. disinfectant 9.) Hexachlorophene (Physohex) - germicidal cleaning agent Contents:  1. 80% NA+ octylphenoxy-ethoxyethyl ether sulfonate 2. hexachlorophene c lanolin esters Uses: pre-operation skin preparation around the eye C. Oxidative (hydrogen peroxide) disinfection - quick, effective, non-toxic - has cleaning activity MOA: interaction between metallic ions by bacterial cell wall and H202 causing 02 release and cell wall lysis S/E: due to residual peroxides a. keratitis b. endothelial cell damage c. cataract *Natural occurring metabolites/enzymes which neutralized H2O2: 1. catalase 2. glutathione peroxidase 3. superoxide bismutate *Types of Neutralizers: 1. catalytic 2. reactive 3. serial dilution - uses saline rinse D. Chlorine - faded tinted hydrogel contact lens E. Irradiation 1. microwave disinfection 2. ultraviolet disinfection Two types of contact lens care systems: 1. Multipurpose contact lens (MPL) solutions 2. Hydrogen peroxide-based (HPB) care systems