article in this series described development of the O2Optix
Custom lens (CIBA Vision), including its material and manufacture.
Here we will look at how to fit the lens.
The Fitting Process
fitting process for this custom lens is different from most modern
lenses. Due to safety concerns surrounding the re-use of diagnostic
lenses on different patients, trial fitting sets won't be available.
Instead, you fit the initial lens empirically. This may seem
daunting if you've spent decades using diagnostic lenses before
making a final order, but a fitting guide (Table
1) is available to help the decision process.
initial lens diameter at least 2mm larger than the horizontal
visible iris diameter. Order the back vertex power as the vertexed
spectacle lens power and select the base curve from the fitting
guide. The rigidity of the lens allows reasonable masking of corneal
cylinders, and we've found surprisingly good visual acuity with
corneal cylinders up to 1.25D.
decide on the base curve, diameter and power, order diagnostic
fitting lenses to use for an extended fitting trial. After the
patient returns for the diagnostic lens fitting evaluation, you can
feel confident that the fitting characteristics observed within 20
minutes of application will remain constant throughout the lens'
should fit just as any other soft lens, providing suitable
centration, movement and optimal visual acuity. If the diagnostic
lenses fit appropriately, then you can dispense that pair of lenses.
It may be prudent for this extended trial to last two to three
weeks, because as in many instances where patients are refit into
silicone hydrogel lenses, there may be a short period of adaptation
before they report equivalent or superior comfort to their previous,
low-Dk lenses. This may result from the increased lens rigidity,
change in surface properties from their habitual lens or the rapid
oxygenation of the cornea, resulting in hypoxic rehabilitation.
trial period, carefully evaluate the visual acuity and
over-refraction to determine any prescription changes and to perform
a mandatory slit lamp examination. Look particularly for the
presence of any microcysts, regression of neovascularization and
epithelial staining due to solution incompatibility.
this visit, decide on any minor alterations to the lens parameters.
If a large alteration is required, then choose another pair of
diagnostic lenses and repeat the fitting process. If there's no
change or only a small change (as occurs in most instances), then
you can order a four-pack of lenses for each eye (with modifications
incorporated), which will provide the patient with lenses for one
A Look Ahead
article in this series on the O2Optix
Custom lens will describe some case examples.