Modification & Delivery
In-Office Modification

Polishing Compounds: Lenses can be polished using a polishing compound which is a mild abrasive agent. These agents are known as Silvo or Xpal and are mixed with either oil or water. Since Silvo is a coarser abrasive, it tends to scratch the relatively soft gas permeable materials, therefore the finer compound Xpal is generally more desirable. Also, there are several commercially available polishing solutions which are specifically designed for gas permeable lenses such as Alox PG, or Sil O2 care.

Blending Transition or Junction Zones: The junction zone between two curves should be a smooth transition. If not, it can interfere with tear exchange under the lens. If the junction zone is particularly sharp, it may irritate the cornea in a manner similar to a sharp lens edge. A transition zone may be blended by using a tool in which the radius of curvature is half way between that of the two curves being blended. The junction may occur either between the CPC and IPC or the IPC and PPC.

Reducing the Optic Zone Diameter: Doing this will loosen the fit of the lens since the size and curvature of this zone will help determine how tight or loose the fit will be. This may be accomplished either by increasing the width of the PPC or IPC, or by adding a blend or increasing the width of the blended area.

Reducing the Overall Lens Diameter: This modification most noticeably effects the lens-cornea relationship. This adjustment will also have the effect of loosening the fit of the lens. As illustrated below, it may be accomplished either through the use of a razor blade, an emery board, or by employing a cone shaped stone.

Flattening the Intermediate or Preipheral Curves: This is accomplished by resurfacing the existing intermediate curve with a felt-covered tool of a flatter radius of curvature. Flattening the peripheral curves or adding a posterior intermediate curve to a rigid contact lens effectively flattens the lens thereby losening the fit.

Adding Minus Power: Up to one diopter of minus power may be added to a lens. It is accomplished with a tool covered either with a piece of velveteen or sponge and is the modification most easily performed.

Adding Plus Power: Up to one diopter of plus power may be added to a rigid contact lens. The technique is similar to that used for adding minus power.

Removing Scratches: It is possible to remove scratches from both the front and back surfaces of a rigid gas permeable or PMMA contact lens. However care must be taken not to alter the power of the lens in the process.

Polishing and Refinishing the Lens Edges: Several techniques may be used for this purpose. The most widely used method utilizes a felt disc.

Adjusting Peripheral Curves: Peripheral curves may be flattened , blended, or made wider. This is generally achieved through the use of a diamond impregnated tool of the correct radius of curvature.

Flattening the Base Curve: The base curve of a lens may be flattened by about 0.50 D. This in not a frequently performed in-office lens modification.

Identifying the Lens: In order to more easily distinguish the right lens from the left, the right lens often contains an identification marking such as a red dot. The marking can be applied through the use of one of several available in-office techniques.

Fenstrating the Lens: The drilling of one or more holes through a rigid lens is known as fenstrating and there are modification units designed specifically for this purpose. Fenstration has the effect of loosening the fit of a lens. It does not significantly increase the flow of oxygen through the lens as is sometimes believed.

Modifications Most Frequently Performed: Although all of the above-mentioned modifications are possible, those most frequently performed include blending the transition zones, removing surface scratches, adding minus power, and dotting the lens for identification.