Dispensing bifocal 3

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Dispensing bifocal 3

  1. 1. Dispensing Bifocal
  2. 2. Three things to remember <ul><li>Make sure the optic axis passes through the center of rotation of the eye. </li></ul><ul><li>Decenter the segment optical centers inwards from the distance fitting point </li></ul><ul><li>Consider optical performance of the lenses </li></ul>
  3. 3. The points to be considered <ul><li>The frame size and shape </li></ul><ul><li>Type of bifocal and lens material </li></ul><ul><li>Distance and near power </li></ul><ul><li>Optical center and segment inset </li></ul><ul><li>Pantascopic tilt and facial wrap </li></ul><ul><li>Ordering and dispensing </li></ul>
  4. 4. The frame size and shape <ul><li>avoid in selecting big frames and aviator shape frames </li></ul><ul><ul><li>the reading portion will be lowered and the reading area will be cut by the shape of the frame </li></ul></ul><ul><ul><li>consider segment width </li></ul></ul><ul><ul><li>the shape, frame color, style, and the length of the temple also be specified </li></ul></ul>
  5. 5. <ul><li>The correct amount of segment inset depends </li></ul><ul><ul><li>The distance PD </li></ul></ul><ul><ul><li>The distance from the back pole of the lens to the center of rotation of the eye </li></ul></ul><ul><ul><li>The fixation distance </li></ul></ul><ul><ul><li>The power of the distance correction in the horizontal meridian </li></ul></ul>
  6. 6. <ul><li>Selection of a proper lens( type of bifocal) </li></ul><ul><li>image jump is eliminated </li></ul><ul><li>Minimize differential displacement at reading level </li></ul><ul><li>the total displacement at the reading level is zero </li></ul>
  7. 7. <ul><li>Marking Seg. height </li></ul>
  8. 8. Pantascopic Tilt and Facial Wrap <ul><li>The pantascopic tilt is known as the inward tilting of the spectacle with consideration of the facial plane </li></ul><ul><li>Pantascopic tilt is usually considered as 6 degrees as cosmetically appealing </li></ul><ul><li>The main aim in giving pantascopic tilt and facial wrap is increasing the field of view </li></ul>
  9. 9. <ul><li>Amount of face form required </li></ul><ul><ul><li>PD= eye size+bridge size= no face form </li></ul></ul><ul><ul><li>PD< eye size+bridge size= positive face form </li></ul></ul><ul><li>Amount of pantoscopic tilt required </li></ul><ul><ul><li>Eyes at OC= no pantoscopic tilt </li></ul></ul><ul><ul><li>Eye above OC= pantoscopic tilt </li></ul></ul><ul><ul><li>Eye below OC= retroscopic tilt </li></ul></ul>
  10. 10. Ordering and Dispensing <ul><li>A laboratory order for a pair of bifocal lenses must include </li></ul><ul><ul><li>Distance and near powers </li></ul></ul><ul><ul><li>Type of bifocal </li></ul></ul><ul><ul><li>Segment size </li></ul></ul><ul><ul><li>Segment height </li></ul></ul><ul><ul><li>Segment inset and total inset </li></ul></ul><ul><ul><li>Frame specification </li></ul></ul><ul><ul><li>Lens material and any process </li></ul></ul><ul><ul><li>tint </li></ul></ul>
  11. 11. Measuring bifocal height <ul><li>using lower lid or limbal method </li></ul><ul><li>Using transparent tape </li></ul><ul><li>Using fresnel press on segments </li></ul>
  12. 12. Measuring for trifocal <ul><li>Lower edge of pupil methods </li></ul><ul><li>Subjective determination </li></ul><ul><li>Comparison with old lenses </li></ul>
  13. 13. Measuring for double segments 13-14mm
  14. 14. Unequal segment height <ul><li>Transparent tape or Drawn line methods used subjectively </li></ul><ul><li>Transparent tape or Drawn line methods used objectively </li></ul>
  15. 15. Some useful tips <ul><li>Height: tall person lower segment than usual </li></ul><ul><li>Posture: walk tall </li></ul><ul><li>Occupation: more desk work= raise segment </li></ul><ul><li>Round segment: 1mm higher than D-segment </li></ul><ul><li>Invisible bifocal: 1mm higher than usual bifocal </li></ul><ul><li>High plus lens: D segment + raised segment </li></ul><ul><li>Children: D segment/ raised </li></ul>

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