Modification of gas-permeable lenses is essential for long-term patient satisfaction. The procedures are easy to perform, require little time or expense, and result in both patient satisfaction and a lower dropout rate.

In-office modification of rigid lenses enables any contact lens practice to increase its efficiency and provides a valuable service to the patient. Every student, assistant, and practitioner should be proficient at performing the modifications discussed in this chapter. Almost any material can be modified, including the superpermeables, if the modifier exercises care in the procedures. These valuable skills are acquired easily through practice and the benefits derived easily will justify the effort.¹

If a patient’s lenses need modification, the inconvenience of sending the lenses to the laboratory and interrupting the patient’s wearing schedule can result in a very dissatisfied patient. Patients place a high value on their time and appreciate receiving personalized custom services. It also reduces practice expenditures incurred by purchasing additional lenses. The returned lenses may not be satisfactory to the practitioner or the patient, which leads to further delays and the need for readaptation. In-office modification not only provides for uninterrupted lens wear, but also allows the practitioner to correlate the applied lens modifications with the desired fitting results and, therefore, to develop techniques that allow the best lens-to-cornea fitting relationship. This gives the practitioner optimum control over the fit of the lenses, and saves time for patient and practitioner by reducing the number of patient visits.

The ability to modify GP lenses is a powerful in-office problem-solver. GP quality is improving because of technological advancements in manufacturing. Nevertheless, there will be that occasional defective edge, or poorly wettable lens. For example, a patient experiencing symptoms of lens awareness can often be managed by a simple edge polish.² Dryness and/or fluctuating vision can be managed by surface polishing. A lens that feels dry and exhibits very little movement with the blink can be managed by blending and/or flattening the peripheral curves. If the addition of a slight amount of power will provide the patient with better vision and eliminate the need for reordering the lens, this can be performed in the office as well. Solving these problems in the office will not only result in a much more satisfied patient, but will also minimize the resulting negative effects of a dissatisfied patient who may communicate his or her feelings to other people and, as a result of frustration, give up on contact lens wear in general.

Modifying rigid lenses is simple and requires little time. The procedures discussed in this chapter all take no more than a few minutes to perform. As will be discussed, there are several ways for practitioners to gain proficiency in performing common modification procedures. In addition, technicians in the office can easily be trained to perform these procedures. The expense for equipment is, at most, a few hundred dollars; this is not much to ask to keep patients satisfied while enhancing the lens performance. Some modifications, such as a clean and polish, can be provided as an annual service to patients who have a service agreement.

Modification of gas-permeable contact lenses begins with the modification unit. Cost is not a factor since most units are very reasonably priced and pay for themselves over a short period. The basic modification unit consists of a small, electric, motor-driven spindle mounted below a steel or plastic bowl. Some units also have multiple spindles and a variable spindle speed. The latter option has become a very desirable feature with the introduction of newer, softer materials. Many units have fixed spindle speeds in the range of 1,200 to 1,600 rpm, whereas the new materials require speeds of only 1,000 rpm or less.³ High spindle speed causes polish to be removed very quickly, which results in a dry tool. As the tool dries, excess heat is built up, resulting in lens surface defects that will affect surface wettability.⁴,⁵ A variable speed modification unit would be preferable, although the spindle speed of a unit can be monitored with a rheostat system purchased at a local hardware store. Caution is needed when using variable speed units. These units are easily inadvertently set to the fastest speed, greatly increasing the risk of lens damage.

The spindle base may be encased in a wood, plastic, or metal protective covering or may be built directly into a table (Fig. 9.1). The splash bowl prevents water and polish from splashing onto the operator and gives the operator room to place his or her hands and tools near the spindle. A plastic bowl is less likely to scratch or chip a lens that may be thrown from the spindle and is therefore a safer option.⁶ A table-mounted bowl is a desirable feature because it provides a place for the operator to rest his or her elbows and steady his or her hand during modification procedures.

Holding the contact lens firmly with good centration without altering the lens parameters is crucial for all modification procedures. The most common types of lens holders include the suction cup, concave and convex tools incorporating double-sided tape, and spinners.

Most modification procedures involve the use of a suction cup as a lens holder. It is very helpful to use a suction cup that has interchangeable ends, such as the R & F Stronghold suction cup (DMV Corporation), so that both the concave and convex surfaces of the lens may be attached. It is suggested that though the concave and convex ends can be reversed, two separate holders are used to allow easy conversion from one to another. DMV now offers largerheaded suction cup tips for both convex and concave surfaces, providing more stability of holding increasingly more common larger GP lenses. The suction cup should be wet when the lens is attached, and special care should be taken to ensure lens centration (Fig. 9.2). Failure to center the lens will result in an oval optical zone diameter and uneven edge or surface polishing and will possibly compromise the lens optics.⁴ Minimum pressure should be used during application to prevent lens warpage. The suction cup should be held by the operator as close to the lens as possible to impart maximum control during the modification process.

Spinner tools are very beneficial for certain procedures requiring care in maintaining optical quality, such as front surface polishing and power changes. The exact style of spinner may vary, but all types work similarly. Most utilize a suction cup for lens attachment, which is preferable over one requiring double-sided tape. Double-sided tape often leaves a residue on the surface of the lens that must be removed by a compatible solvent. Once the lens is attached to the spinner, it is free to spin along with the spindle while the handle is held stationary. This allows power changes or polishing to be performed slowly and evenly, resulting in little or no optical distortion.

Several accessories are required in addition to the modification unit and lens attachment devices, including radius tools, polishing sponges, and polish (Table 9.1). The radius tools used for polishing and grinding are often included with the unit and commonly attach to the spindle by a form fit. The tool contains a tapered hole drilled along its axis that matches the tapering of the spindle. Friction then holds the tool in place as it is spinning. Although some tools are interchangeable with other units, taper size may vary for both units and tools. It is important to keep in mind that the tapers must match exactly. Incorrect taper size can result in tool wobble and improper modification. Some Contact Lens Manufacturers Association (CLMA) Laboratories where you can obtain modification equipment are listed in Table 9.2.⁷

The amount of cost for modification equipment varies depending on the number of procedures that are performed. For basic edge and surface polish procedures, many laboratories have economical packages ranging from $225 to $350.⁸ This typically includes a single-speed modification unit in addition to sponge and/or velveteen tools for polishing procedures. Suction cups and polish are also typically provided. A deluxe package (often $300-$500) allows the practitioner and/or staff to perform peripheral curve procedures such as blending and flattening, in addition to changing the power of the lens. This package typically includes a suction cup spinner for polishing and repowering, radius tools for peripheral curve procedures, a 90-degree anterior bevel cone tool for thinning the edge, and possibly a 7× magnifying loupe and/or a diameter gauge. As most CLMA laboratories either manufacture or distribute modification equipment, it is recommended to contact a local laboratory to determine if it provides modification equipment and, if so, what types of packages are available.

The importance of polishing compounds used for modification should not be overlooked. Liberal use of polish specifically designed for GP lenses is necessary for all modification procedures. These solutions contain a mild abrasive—typically a grit aluminum base—that erodes lens material along with surfactants and detergents to lubricate and cool the lens during modification. They all appear to be successful in modifying GP lens materials. One study evaluated the effectiveness of seven commonly used polishes in repowering GP lenses.⁹ The polishes used included the following premixed liquid solutions: Boston White Finishing Polish (Polymer Technology Corporation, Wilmington, MA), Evergreen (R & F Products, Denver, CO), Mirapolish (ABBA Optical, Stone Mountain, GA), Nu-Care 2000 (Polychem, Gaithersburg, MD), and Sil-O2-Care (Polychem, Gaithersburg, MD). Two dry powder polishes were used (which can be mixed with water or saline): Al-Ox 721 (Transelco Ferro, Cleveland, OH) and X-Pal (Davison Chemical, Chattanooga, TN). It was found that all seven polishes were effective in adding 0.50 D of power to a 92-oxygen permeable (Dk) GP lens material. The powder forms were faster, taking 35 to 40 seconds, whereas the premixed solutions took up to 2½ minutes to add the desired amount of power. Therefore, it is advisable to practice with a particular polishing compound to ensure predictable results with future modifications. Products containing ammonia are not suitable for use with GP lenses since they can adversely affect surface wettability. Silvo was a popular polish with polymethylmethacrylate (PMMA) lenses, but it contains ammonia and therefore is not recommended for GP lenses.