RIGID GAS PERMEABLE LENS PROBLEM SOLVING

Progress Evaluation Procedures
  1. Lenses On
    1. Visual Acuity
    2. Retinoscopy (Over-Refraction)
    3. Sphere-Cylinder
    4. Biomicroscopy
    1. Lag
    2. Surface Quality
    3. Edema
  1. Lenses Off
    1. Biomicroscopy
    1. Staining
    2. Limbal Vasculature
    3. Lids
    1. Keratometry
    2. Subjective
    3. Verification

Reduced Visual Acuity

  1. Flexure
    1. The bending of a flexible RGP lens on a toric cornea.
      2.
    2. Diagnosed via over-keratometry; if toric and radiuscope is spherical = flexure
      3.
    3. Managed via flatter BCR, smaller OZD and/or increased center thickness
  1. Warpage
    1. Typically caused by excessive digital pressure, especially with a high Dk material and an abrasive cleaner
  1. Decentration
    1. Inferior
      2.

      Causes:

      •Lens Design

      •Lens Material

      •Corneal Topography

      •Lid Tension/Blink Quality

      Complications:

      •Reduced/Variable Vision & Flare

      •Limbal Irritation/3&9 o’clock staining

      •Lens Awareness

      •Lens Dislocation

      •Poor Corneal Alignment; excessive flattening & steepening with possibility of distortion

      Management:

      •Reduce Center Thickness

      •Proper Edge Design (-lenticular < -1.50D/Plus; +lenticular > -5.00D)

      •Bitoric > 2.50D corneal cylinder

      •Lid Attachment Design
    2. Lateral

Causes:

•ATR astigmatism

•Displaced corneal apex

Management:

•Increase OAD or Steeper BCR

•Aspheric Design
  1. Reduced Surface Wettability
    2.
  2. Power Change

 

 

 

Corneal Desiccation
  1. Definition – dryness or peripheral desiccation staining commonly occurring in the 3 and 9 o’clock regions of the cornea. It occurs in over 50% of rigid lens wearers. It ranges from diffuse punctate staining to corneal opacification and neovascularization.
    2.
  2. Design Parameters
    1. Diameter – larger reduces area; smaller decreases mass
    2. Lens Position – inferior least desirable
      3.

      Henry, Bennett, Forrest (AJO, 1986)

      3 and 9 o’clock Staining to Fitting Relationship

      Position # Eyes 3 & 9 %

      Sup-Central 125 48 38

      Interpalpebral 193 111 57

      Inf-Central 46 34 73
    3. edge Lift – intermediate best

      4. Effects of too small versus too large
    4. Center Thickness – problems of large CT/VERIFY
      5.
    5. Edge Shape – well-polished/thin, tapered

Refitting Contact Lens Wearers into RGPs
  1. PMMA
    1. Complications
    1. Edema (98%)
    2. Corneal Warpage
    3. Corneal Exhaustion
    1. Possible Applications
    1. Keratoconus
    2. High Astigmatism
    3. Presbyopia
    4. RGP Failures (Dryness, Corneal Sensitivity and Poor Care Habits)
    5. Orthokeratology
    1. Liability
      2.
    2. Communication
    1. Explain RGP benefits
      2.

      •Oxygen Permeability

      •Modern Technology

      •Vision in Spectacles

    2. Audiovisuals

•Photographs/slides

•Videotapes – CLMA/RGPLI

(Clinical Pearls – Volume II)
    1. Refitting Procedure
    1. Immediate refit without loss of wearing time or WT for one week with CWS cases
    2. Same Design or New Design???
  1. Low Dk (First Generation)
    1. Some patients have PMMA-like clinical signs after 5-10 years
    2. Case Example
  1. Hydrogel (park-Nicollet Study)
    1. 200 Consecutive Refits

      2. 44% from PMMA

      46% from Hydrogel into RGP

      10% from RGP/PMMA into Hydrogel
    2. Most frequent refits
    1. GPC
    2. Poor Vision