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  KNEW VISION Bifocal Fitting Guide



Our objective is to help make your Knew Vision Bifocal contact lens fitting experience as effortless as possible, and most importantly, successful. The following is a direct result of successfully fitting thousands of patients with Knew Vision Bifocal and identifying the commonly asked questions posed to our consultants. We are confident the following "tips" will help you maximize your fitting success, especially when used with diagnostic lenses.



Patient Selection
An important key to a successful fit is knowing which patients will have the highest probability of success with the Knew Vision Bifocal. The following patient characteristics typically increase the probability of a successful fit:

High patient motivation.

Prior PMMA or GP Lens wearer.

Firm lower lids to help support the lens and facilitate translation when the patient looks down through the near portion.

Lower lids that are tangent with or slightly above the lower limbus. Patients with lower lids below the lower limbus require a higher seg height and less truncation in order to allow the pupil to adequately translate through the near portion of the lens.

Base Curve Selection
Select a flatter base curve than you would with conventional single vision lenses. A flatter base curve allows the lens to drop quickly to its primary position (at or close to the lower lid) after a blink. It also helps the lens translate smoothly upward to position the seg line slightly above the pupil center on down gaze (Fig. 1).

 

 

 

Seg Height
If the lower lid is tangent to or above the lower limbus: Have the patient fixate on a penlight held at eye level, 20 inches from the eye. Measure the distance between the light reflection and the lower lid. Subtract 1.3mm from this measurement to determine the seg height (Fig.3). As mentioned, a .4mm truncation is generally recommended when the lower lid is positioned tangent to or above the limbus.

If the lower lid is below the lower limbus: When the lower lid is below the lower limbus, the seg height needs to be high enough to allow the pupil to translate through the lower near portion for reading. In these cases, two measurements are needed:

1.Distance between the light reflection and the lower limbus
2.Distance between the lower lid and the lower limbus (Fig. 4).

IF the second measurement is .5mm or less, subtract 1.1 mm from the first measurement to determine the seg height.

IF the second measurement is greater than .5mm and less than or equal to 1 mm, subtract l.0mm from the first measurement to determine the seg height.

Use a lens with .2mm of truncation and a slightly larger diameter (+.1 to .2mm) when the lower lid is below the limbus. If the lower lid is more than .1mm below the limbus, the seg height and diameter should be increased slightly.

Prism Power and Axis
The prism power is typically dictated by the power of the lens. More prism is required with higher minus lenses and less is required with higher plus powers.

The prism axis will vary depending on the lid action and the power of the lens. It is important to use diagnostic lenses to observe any lens rotation. The prism axis will always be placed in the direction of the lens rotation. For example, if you observe the right lens rotating nasally, the prism axis will be placed 15 nasally (105). If the left lens rotates nasally, the axis will be placed 15 nasally (75).