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Multifocal GP Fitting Guide

  • Select a patient with +2.00 add or lower interested in full-time wear and conducting visual tasks at varying levels.
  • Interview patient regarding expected lens use, vocation and hobbies, previous type of lens wear, etc.
  • Measure the cornea, refractive error, lid structure and position. K's and spectacle Rx will be the key measurements for initial lens selection.
  • Place a diagnostic lens on the eye to achieve alignment. Choose this lens from the Initial Base Curve Selection Chart. Determine lens power by over-refraction.
    •  Perform spherical over-refraction over the best-fitting diagnostic lens
    • Adjust over-refracted power for vertex distance if above ± 4.00D
    • Over-refraction is best performed with loose trial lenses or a trial frame (not a phoropter)
  • Look for central to superior-central lens position. This provides for adequate distance vision, while reducing edge glare and flare in dim light or at night. Boston MultiVision lenses provide both simultaneous and alternating vision through unique posterior surface construction. This means that the lens must translate easily across the corneal surface as the patient looks from distance to reading tasks. Proper base curve selection will usually ensure that the lens will move easily along the vertical corneal meridian.
  • Evaluate fluorescein pattern and lens translation. Unlike other posterior surface aspheric GP multifocals, the Boston MultiVision lens is designed to be fit in alignment with the central and superior-central cornea.
  • No modifications should be made to the back surface. Due to the complex posterior surface geometry of the Boston MultiVision back surface, modifications should not be performed. Any induced surface changes will compromise clinical performance by impacting the optical and fitting characteristics of the lens.
initial-base-curve-selection-chart

Intial Base Curve Selection By Keratometry

  1. Measure the central corneal curvature and identify the flat K reading (smallest dioptric value). Example: Flat K = 43.00 @ 180, 44.00 @ 90 (The Flat K is used as the reference point to select the base curve.)
  2. Calculate the amount of corneal astigmatism (difference between the flat and steep K). Corneal astigmatism = + 1.00D
  3. Select the Initial Base Curve based on the amount of corneal astigmatism.
    Recommended base curve is 7.70mm

Evaluation Of Lens Positioning And Fluorescein Pattern

preferred-fit-alignment

Preferred Fit Alignment fit with central to superior/central positioning

flatter-fit

0.1mm Steeper Fit
Increased apical clearance, combined with mid-peripheral bearing

steeper-fit

0.1mm Flatter Fit
Increased central bearing with loss of lens stability

Evaluation Of Lens Position And Movement

  • Ideally, the lens should position in the central to superior/central position, with the lens optics situated over the pupil.
  • Typically, the fluorescein pattern will demonstrate "alignment" along the flattest corneal meridian.
  • During downward gaze the lens should easily translate superiorly providing maximum reading vision.
  • NOTE: If an alignment fitting relationship combined with acceptable vertical translation cannot be achieved with the initial diagnostic lens, simply choose the next steeper or flatter base curve and evaluate.