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Klaus Ehrmann, Darrin Falk, Indrani Perera, Percy Lazon de la Jara, Brien Holden
To determine and generate oxygen transmissibility
(Dk/t) profile maps across various contact lenses in
different powers.
Oxygen transmissibility is defined as the oxygen
permeability (Dk) of a certain material divided by the
lens thickness (t) at a given location. Traditionally, trans-
missibility was quoted as a single value only, referring
to the center thickness of a 3.00D lens of a given
lens type. While providing some relative comparison
between lens types, this value does not reflect the
clinically more relevant differences across the power
range and averaged Dk/t measures for central and
peripheral areas.
Although, there are still different opinions on what
minimum transmissibility is required to maintain
a healthy eye, the two benchmark values set by
Holden & Merz1 (87units) and Papas2 (125 units) to
avoid overnight corneal oedema and limbal redness
respectively, are now widely accepted.
Lenses: 4 different silicone hydrogel lens types and
materials were investigated for this study:
PureVision balafilcon A
Acuvue Advance galyfilcon A
Focus Night & Day lotrafilcon A
O2Optix lotrafilcon B
Of each lens type, two lens powers, -3.00D and
+3.00D were measured. All lenses were stored in
ISO standard PBS for at least 24 hours prior to
any measurements.
Thickness Measurements: A custom built thickness
profiler was used to obtain thickness profiles of all
lens types and powers. Five lenses in each group
were measured in four meridians and all the thickness
profiles averaged. In addition, the center thickness
of all lenses was measured in accordance with ISO
9339-23 and thickness profiles adjusted to comply with
those results
Oxygen Permeability Measurements: As there is
no valid international standard for measuring oxygen
permeability of high Dk silicone hydrogel lens materials,
the method described in ISO 9913-24 was adapted in
conjunction with a modified DK1000 coulometric oxygen
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