RGP insights

RGP Problem-Solving Made Easy

BY ED BENNETT, OD, MSED
February 2000

One of the true benefits of rigid gas permeable (RGP) lenses is the fact that when a problem occurs, it is typically not serious and often quite easy to manage. In fact, most RGP-induced problems are associated with only two basic symptoms:
(1) reduced vision and (2) discomfort. This guide reviews how to manage these problems.

REDUCED VISION   

( A) Initial 

CAUSE # 1:
Poor Initial Wettability

MANAGE: Pre-soak lenses overnight prior to dispensing; If present, use lab cleaner to remove residue and then condition with wetting solution; if condition occurs frequently, talk to laboratory.

CAUSE # 2:
Flexure

MANAGE: If Over-K values are toric but lens is spherical with the radiuscope, lens is flexing; use flatter base curve and/or greater center thickness.

CAUSE # 3:
Decentration

MANAGE: If lens decenters inferiorally, use lenticular (+ if > 5.00D minus power); if a plus or low minus power, use one of available ultrathin designs; if lens is decentering laterally, rule out a decentered corneal apex or ATR astigmatism. An aspheric lens design, steeper BCR or larger OAD may solve the problem, although in ATR astigmatism, a soft toric contact lens may be indicated.

(B) Gradual

CAUSE # 1:
Surface Deposits

MANAGE: Review compliance with cleaning & soaking (i.e., clean upon removal); avoid lanolin creams prior to handling; regularly use a liquid enzyme; A more wettable lens material, typically a low Dk F-S/A lens, may also be beneficial, especially if the patient is a borderline dry eye patient.

CAUSE # 2:
Warpage

MANAGE: Often the result of forceful digital cleaning (i.e., between the fingers); clean carefully in palm of hand with noncircular motion; consider using a "cleaning/ disinfection" combination solution.

CAUSE # 3:
Power Change

MANAGE: Occasional problem caused by digital cleaning with an abrasive cleaner; occurs less often today due to less abrasiveness of cleaners; results in an increase in minus power; managed similar to warpage, but it's important to change to a nonabrasive
cleaner.

DISCOMFORT

( A) Initial 

CAUSE # 1:
Poor Edge Quality

MANAGE: Always inspect RGP edges; quality has improved in recent years due to improved manufacturing; however, an abraded or chipped edge can result in the patient discontinuing lens wear; A projection comparator is useful for this purpose.

CAUSE # 2:
Patient Sensitivity

MANAGE: Often diagnosed via patient reaction to drops, lid eversion, tonometry, etc. Explain that adaptation may take several weeks, but that they should become very comfortable; use terms such as "lid senses movement of lens on eye" or "lens awareness" as opposed to discomfort or pain; use a topical anesthetic at the fitting visit, and then allow patient to gradually experience awareness. This is especially important with patients who are naturally sensitive as well as keratoconic patients and soft lens refits.

(B) Gradual

CAUSE # 1:
Dryness

MANAGE: Often results in 3 & 9 o'clock staining, injection, and reduced wearing time. Determine cause; if due to inferior decentration, treat accordingly. Rule out lid margin disease (i.e., Meibomian Gland Dysfunction) and/or blepharitis. If lid margin disease is present, it must be under control prior to fitting contact lenses. A low (25-50) Dk fluoro-silicone/acrylate lens material would be recommended; patient should also be advised to use rewetting drops as much as every hour; also, ensure that patient is blinking properly; Rule out dry eye via tear volume testing and TBUT (< 6 second TBUT is a poor contact lens candidate).

CAUSE # 2:
Surface Deposits

MANAGE: As recommended under reduced vision.

Dr. Bennett is an associate professor of optometry at the University of Missouri-St. Louis and executive director of the RGP Lens Institute.