90 Diopter Lens

I.    Purpose:  To view posterior pole as a highly magnified stereo image

II.   Procedure
  A.    Uses a high power plus lens to focus image of retina
  B.    Image is projected in space and viewed with a biomicroscope

III.  Miscellaneous
  A.    Field of view is 30-40 degrees
  B.    Maximum dilation is required
  C.    Yellow filters are available for patient comfort but distort 
        color for clinician

IV.   Set-up
  A.    Position patient comfortably in slit-lamp
  B.    Biomicroscope adjustment:  can be modified for patient comfort 
    i.    2-3 mm beam width
    ii.   height set at size of dilated pupil
    iii.  moderate illumination
    iv.   beam directed straight into pupil 
          (max of 10 degrees off alignment)
    v.    16x magnification

V.    Techniques
  A.    Method #1
    i.    Pull slit-lamp back
    ii.   Localize red reflex thru pupil
    iii.  Place 90D lens in line with slit-lamp and pupil
    iv.   Move forward, following red reflex until retina seen
      a.    Modify height and lateral position as needed
      b.    If 90D lens surface seen, have moved too close

  B.    Method #2
    i.    Focus on cornea
    ii.   Localize red reflex thru pupil
    iii.  Place 90D lens in line with slit-lamp and pupil
    iv.   Pull back, following red reflex until retina seen
      a.    Modify height and lateral position as needed
      b.    If 90D lens surface seen, have not move far enough back

  C.    With either method used
    i.    Must have stable base
      a.    Rest elbow on table or book on table
      b.    Stabilize hand on slit-lamp side or patient cheek
    ii.   Can hold lid with middle finger if necessary
    iii.  Widen beam gradually to see more fundus
    iv.   Keep fundus in focus

  D.    Localizing
    i.    Adjust patient gaze to visualize disc
    ii.   Can move patient gaze to view fundus, but better to move lens 
          slightly
    iii.  Follow arcades in pattern to view all of posterior pole
    iv.   View macula as final activity as it tends to add to patient 
          discomfort