Association of Technical Opticians

*data from System for Ophthalmic Dispensing, Brooks and Borish 3rd edition

Just like the RGP fiting nomgram their are rules of thumb that are used for the fitting of Soft Lenses. Here is a common fitting philosophy to help you fit patients more easily and accurately in soft lenses. Since most lenses come in three base curves:

The HVID (Horizontal Visible Iris Diameter) is going to play a role in the fit as well. The average HVID is anywhere from 11.6mm to 12.0mm in size. To get the diameter of the soft lens just add 3mm or 1.5mm to each side of the lens to allow for good coverage. Now if the patient has a smaller or even larger diameter HVID that would mean that the diameter of the lens is going to be smaller or larger respectively. Also the lenses sagittal height is going to mean that the fit is going to change. Bellow is a compensation table to apply to the flattest base before chosing the Base Curve.

Now take the adjusted K’s and convert it to mm with the following equation:

These compensations are performed due to the elliptical nature of the cornea. A good way to remember these compensations is with the following rules.

For every o.2mm difference from the average HVID (11.6mm to 12.0mm) compensate by adding or subtracting 1.00D respectvely to the flattest K’s, then convert the K’s over to mm radius and add 0.3mm to that measure. Also add 3.0mm to the HVID to come up with the final soft lens diameter.

For power Vertex the spectacle Rx to the corneal plane.

This is just a breakdown of an average eye:

*data from CLSAs Contact Lens Manual Vol.1

It is still in the process of being completed, but it is functional and in BETA. This is every soft contact lens and all available parameters listed for search by type of lens. More functionality will be added soon so check back often. Also if you notice any discrepencies like always contact the ATO by using the contact form. Thank you and enjoy.

Contact Lens Database (opens in new window)

This article details insertion and removal techniques of soft lenses. The article also covers cleaning and care. It has been used as brochures for some of the practices in the Baltimore, MD area and I would like to make it available to all the members of this association to use as they see fit. Please modify the text or take from it what you need.

Contact Lens Wear and Care (word document)