Ophthalmic inserts -Phm 2206

• Ophthalmic inserts


  Sterile solids or semi-solids preparation for insertion into the conjunctival sac, containing a reservoir of active material which is slowly released from a matrix or through a rate-controlling membrane over a known period
• Ophthalmic inserts


  • Each have their own sterile container
  • Labelled to state the total quantity of active substance per each insert and /or its rate of release
  • In their manufacturing the EP requires an appropriate product dissolution behaviour
• Cornea, lens, and humour compartments

  Vascular, facilitates the transmission of light and vision
• Exchange of nutrients and waste

  Takes place entirely by diffusion process through the Aqueous humour, through the lens and cornea and through the lachrymal fluid
• Corneal metabolism


  Affected with contact lenses which reduce diffusion of oxygen to the cornea
• Tears


  Perform the function of lubricating, hydrating, cleaning and disinfecting the anterior surface of the eye
• Lysozyme


  Enzyme in tears that catalyses the hydrolysis of 1,4-glycoside linkages between N-acetyl muramic acid and N-acetyl-glucosamine in the peptidoglycan layer of the bacterial cell wall, disinfecting
• Layers of the precorneal film

  • Mucus (Henle and Manz glands)
  • Water (Krause and Wolfring glands)
  • Oil (Meibomian, Moll and Zeis glands)
• Tear electrolyte content


  Similar to serum except that the potassium ion is approx. 4-6 times greater (24mEq/l compared with 4-6 mEq/l), with albumin and globulin as the main protein content (0.7% compared with 7% in serum)
• Stimuli for tear production

  • Emotional via psychological factors
  • Sensory via external irrants
  • Continuous via automatic nervous control
  • Systemic via chemicals in the blood stream affecting the nerves innervating the lachrymal glands
• Tear pH


  Slightly alkaline, 7.2 pH, with buffering capacity to adjust rapidly the pH of small volumes of weakly buffered solutions to pH 7.2
• Eyelids


  Protect and clean the eye, with the outer margin closing slightly before the inner margin and sweeping fluids across the eye towards the lachrymal duct at the inner angle of the eye
• Lachrymal fluid


  Can pass via the lachrymal sac into the GIT, where systemic absorption of excess eye medication can take place
• Bacterial flora


  Lachrymal fluid is not sterile, with Staphylococci and diphtheroids found in normal conjunctiva, and Gram-negative enteric bacilli found in the conjunctiva and lids of 5% of people
• Sir John Herschel used a refractive glass shell to protect the cornea from a diseased lid


  1823
• Dr. Eugen Fick introduced the term "contact lens" and produced blown glass lens to correct defective vision


  1887
• Tuohy introduced hydrophobic hard plastic corneal lens


  1984
• Prague University introduced soft pliable lens


  1962
• Extended-wear lenses introduced


  1981
• Requirements of contact lens production

  • Correct vision
  • Maintain their position on the eye
  • Allow respiration of the cornea
  • Permit free flow of tears round or through the lens
  • Not release toxic substances not introduce microbial contamination
  • Be wearable throughout the day
  • Be easy to handle and economical
• Hard lens


  Made from perspex (poly-methylmethacrylate, PMMA), with similar properties to spectacle crown glass, and lachrymal fluid does not readily wet this hydrophobic material
• Solutions required for hard lenses

  • Wetting - facilitates wearing
  • Storage, hydrating, decontaminating - facilitate care of lenses when not in use
• Disadvantages of original hard lens

  No free passage of oxygen and carbon dioxide to and fro from the corneal epithelium, leading to common corneal oedema and distortion
• Modern hard lenses


  Designed to be gas-permeable, physiologically user-friendly and with greater wearer acceptance
• Types of gas-permeable lenses

  • Cellulose acetate butyrate (CAB) - readily wetted and quite acceptable
  • Silicon and Fluorine lens - greater gas-permeability
  • Silicone methacrylate copolymers - silicone composition controls permeability properties and the PMMA controls the degree of rigidity
  • Fluorosilicone metacrylate copolymers - high oxygen permeability, good wetting properties
• Advantages of hard lenses

  Easy to care for, better optical qualities, less subject than soft lens to deposits of lipids, protein and other substances from the lachrymal fluid
• Soft lens


  Made of hydroxymethyl ester of polymethacrylic acid (HEMA), with a large number of hydroxyl groups conferring hydrophilic properties, flexible, and absorbing approximately 47% of its own weight of water
• Soft lens


  More comfortable and easy to wear than hard lenses, but more difficult to care for
• Another type of soft lens

  Copolymers of poly-HEMA with vinyl pyrrolidine (VP), absorbing approximately 80% by weight of water depending on the ratio, with higher water content lenses having greater gas-permeability and comfort
• Disadvantages of soft lenses

  • More fragile
  • Difficulty to care, greater tendency to attract deposits
  • More solution problems, less precise optical properties
• Concurrent use of cosmetics with soft lenses


  Insert soft lens before applying eye makeup, nail polish, hand cream, perfumes, powder; use aerosols with caution
• Disposable lenses


  Can overcome life span and manufacturer problems, discarded after one month, one week or a day (no solution), offering an advantage to those who wear lens on an irregular basis
• Hard lens solutions - Wetting solution


  Purpose: achieve rapid wetting by lachrymal fluid and promote comfort, facilitate insertion, provide cushioning and lubrication, enable cleaning after removal, must be non-irritant during daily use
• Hard lens solutions - Wetting solution formulation

  Contains wetting and viscolizing agents like polyvinyl alcohol and Hypromellose, with a viscosity of 15-20 mPas, pH 6.8, tonicity 0.9 - 1.1%, and antimicrobials like benzalkonium chloride 0.004% plus disodium edetate 0.1%
• Hard lens solutions - Storage/soaking solution


  Purpose: cleaning, microbial inactivation, and hydration
• Soft lens solutions - Cleaning solution

  Purpose: remove deposits such as lipoproteins adhering to the lens, formulation contains viscolizing surfacing acting agent like Hypromellose and fast-acting antimicrobial benzalkonium chloride 0.004% with a contact time of 20-30 seconds
• Soft lens solutions - Storage solution

  Purpose: hydrating, cleaning, inactivation of microbial contamination, formulation is isotonic 0.9% w/v sodium chloride with a powerful oxidizer antimicrobial like 3% hydrogen peroxide at acid pH used for disinfection over 6 hours
• Contact lens solution containers

  Usually packed in plastic, where antimicrobial concentration should not be reduced to ineffective levels due to sorption effects, containers must be kept in hygienic condition and changed periodically