EDUCATION

Mark Andre, FAAO
Matthew Lampa, OD, FAAO

What is a Custom Soft Contact Lens?

With the progression in modern contact lens material sciences and manufacturing
capabilities, the eye care practitioner has a vast array of potential soft lens options for
achieving optimum success in the contact lens patient. In this column we aim to share our
insights, successes and failures as we try to manage the custom soft contact lens patient.

Throughout this column we intend to take a stepwise process to designing and
prescribing custom soft contact lenses. There has been some debate and confusion
about what constitutes a custom soft contact lens. Is a lens with a wide range of
parameter options a custom soft contact lens? Is it a lens that you have to order beyond
the standard parameters in your diagnostic fitting set?  

Though there may be many definitions, we will share ours with you. We feel that at its core,
a custom soft contact lens is one in which the practitioner has full control of the
parameters: base curve, power, and overall diameter. This means you could potentially
order a lens in 0.1 D power steps versus the traditional 0.25 D steps, or an overall
diameter could be specified in 0.1mm steps versus the traditional one or two fixed overall
diameter options. Also within that same definition are other potential parameters including
but not limited to: optic zone size, central thickness, spherical versus aspherical optics,
cylinder axes as precise as 1 degree increments and several material options.

We feel soft contact lenses can be separated into three different categories based on the
parameter availability:

  1. Inventory or “off the rack”: these are the lenses found in traditional diagnostic sets.
  2. Expanded parameters: these are lenses that go beyond the traditional standard
    diagnostic set, but are generally limited by the same base curves and diameters
    and the practitioner then needs to order powers that are outside of their diagnostic
    set.
  3. Custom: these lenses are made to order.

Through the next several editions we will explain the usefulness of varying specific soft
lens parameters, the type of patient that would benefit from such a lens, and case
examples illustrating these ideas.
We will start with the one we feel is the most important to success in soft lens fitting:
carefully measuring and matching the shape of the eye with the proper lens shape.

The corneal measurement most commonly linked to initial trial lens selection is central
keratometric readings (K value). While there are several reliable ways today in clinical
practice to measure central Ks, this measurement alone does not adequately describe
the overall corneal contour and sagittal height of the anterior eye. That is best
accomplished through measuring the visible iris diameter and corneal asphericity, as
these two measures play the most significant role in the overall sagittal height of the
anterior eye.

The effect of horizontal visible iris diameter and K value is best demonstrated visually
through cross-sectional images of the anterior eye. The patients have identical K values
but their visible iris diameters are very different.

Image

The effect of the horizontal visible iris diameter and K value relationship is most magnified
at the extremes (e.g. large, steep cornea or small, flat cornea), as a large, steep cornea
will have sagittal height that is much deeper than a more average eye and will require a
much larger and deeper soft contact lens. The patients at the extremes make ideal
candidates for custom soft contact lenses, as the inventory or “off the rack” lens is
intended and designed for the more normal or average eye.


Mark Andre
Mark Andre is presently an associate professor of Optometry at Pacific University College
of Optometry in Forest Grove, Oregon. He is also a consultant to CooperVision and a
specialty contact lenses and instructing both Ophthalmology and Optometry Residents
on this subject since 1979. He lectures primarily on the subject of contact lens design on
this subject since 1979. He lectures primarily on the subject of contact lens design and
fitting. Mark is a Fellow member of the Cornea and Contact Lens Section of the American
Academy of Optometry. He is also a Fellow member of the Contact Lens Society of
America and a past board member of the society. In the past, he served as chairman of
the board for the National Contact Lens Examiners.

Matthew Lampa received his Doctor of Optometry degree from Pacific University College
of Optometry in Forest Grove, OR, where following graduation he also completed a
residency in Cornea and Contact Lenses. He is currently an assistant professor at Pacific
University College of Optometry where he is involved with specialty contact lens fitting,
contact lens instruction of optometry students, and clinical research.  He is also an
associate in a private practice in Oregon and a consultant to SpecialEyes.
Matthew Lampa