bozr_bvp_cl_info_flashcards
How would you check the BOZR (Back Optic Zone Radius) of a contact lens?
Using a radiuscope, keratometer with conversion charts, wet cell projection system/electronic system, templates (for soft lenses), or focimeter technique.
How would you measure the BVP (Back Vertex Power) of a soft lens?
With a focimeter, measuring the front and back OZR, then calculating the powers and deducting for BVP.
How can you measure the TD (Total Diameter) of a contact lens?
Using a V gauge, projection system, traveling microscope, or hand loop with an engraved scale.
How would you measure the BOZD (Back Optic Zone Diameter) of a contact lens?
Using a projection system or hand loop with an engraved scale.
What is a full specification for a soft contact lens?
Manufacturer, design, BOZR, total diameter, back vertex power, and fixed material/handling tint by the manufacturer.
What is the Dk value of a contact lens?
The Dk value is the physical property of a contact lens material describing its intrinsic ability to transport oxygen. It is defined as the rate of oxygen flow through the material under specific conditions of thickness and pressure, and it increases with temperature.
What are the disadvantages of high Dk RGP (Rigid Gas Permeable) contact lens materials?
Higher hydrophobicity (resistance to water), causing poor wetting, greater susceptibility to deposits, and more brittle and fragile compared to low Dk materials.
What is the difference between oxygen permeability (Dk) and oxygen transmissibility (Dk/t)?
Oxygen permeability (Dk) refers to the material’s permeability at a given thickness and temperature, while transmissibility (Dk/t) accounts for the actual thickness of the lens, giving the oxygen transmission through the entire lens.
How is the wetting angle of a contact lens measured?
By the Sessile Drop Method or Captive Bubble Method, which measure the contact angle of liquid or air on the surface.
What is the six-part classification for contact lens materials?
- Prefix, 2. Stem, 3. Series Suffix, 4. Group Suffix, 5. Dk Range, 6. Surface Modification Code.
Who is authorized to fit contact lenses in the UK?
Registered medical practitioners, dispensing opticians with a contact lens qualification, optometrists registered after December 31, 1960, optometrists with additional qualifications (e.g., DCLP), and supervised students.
What changes were caused by the GOC’s Section 60 order regarding contact lens practice?
Non-medical professionals can now supply contact lenses, create lists of practitioners for specialist optical services, and regulate plano (non-prescription) lens sales.
What is the difference between hypoxia and hypercapnia in contact lens wear?
Hypoxia is reduced oxygen availability, while hypercapnia is the accumulation of carbon dioxide under the contact lens.
What is ‘3 & 9 o’clock staining’ in rigid lens wearers? What causes it and how is it managed?
Caused by poor blinking, reduced tear flow, excessive edge lift, or tight lenses, drying the cornea at the 3 & 9 o’clock positions. Managed with blinking exercises, adjusting lens design, and using more wettable materials.
What is dimple veil staining, its cause, and management?
Air bubbles trapped under steep-fitting lenses causing indentations in the cornea. Managed by refitting with a flatter lens or different peripheral fitting lens.
What is deep stromal opacification and how should it be managed?
Caused by long-term central corneal hypoxia, managed by stopping lens wear, monitoring long-term, and avoiding lens wear in the future.
What are microcysts in contact lens wear and how are they managed?
Caused by hypoxia or solution toxicity, appearing as small fluid-filled vesicles. Managed by reducing lens wear time and switching to a higher Dk/L material.
What are corneal infiltrates, their causes, and treatment?
Caused by prolonged hypoxia, immune response, or chemical toxicity. Managed by discontinuing lens wear until resolved, using antibiotics, and switching to disposable lenses.
What is the mechanism behind CLAPC (Contact Lens Associated Papillary Conjunctivitis)?
Allergic response to lens proteins, preservatives, mechanical abrasion, and corneal hypoxia.
How is CLAPC graded and managed at each level?
Grades 0-1 require cleaning and solution adjustments. Grades 2-3 require lens refit and use of mast cell stabilizers. Grade 4 requires lens removal until resolved.
What is vCJD (Variant Creutzfeldt-Jakob Disease) and its relevance to contact lens practitioners?
vCJD is a prion disease that may potentially be transmitted through re-use of contaminated contact lenses.
What does the General Optical Council’s policy state about the reuse of diagnostic contact lenses?
Contact lenses should not generally be reused, but special diagnostic lenses can be reused if properly cleaned and disinfected.
What are the consequences for practitioners who do not follow the GOC’s policy on contact lens reuse?
Practitioners who do not follow the GOC policy may be charged with serious professional misconduct.
