Spherical GP Problem Solving
BY EDWARD S. BENNETT, OD, MSED
The RGP Lens Management Guide provides troubleshooting tips for spherical, toric, bifocal and irregular cornea patients. Following are managing tips for spherical lens-induced problems are lems derived from this guide.
1 GP lenses that decenter inferiorly can result in variable vision and lens awareness. This could result from a thick lens, thin edge and/or decentered apex. Biomicroscopy will reveal excessive lag. Manage this with plus lenticular for lenses > 5.00D, minus lenticular for lenses < 1.50D and all plus lenses or prescribe an ultrathin or bitoric design if > 2.50D cylinder.
2 When a GP lens decenters laterally and the patient complains of variable vision and/or lens awareness, this could be due to against-the-rule astigmatism and/or a decentered apex. Biomicroscopy will reveal lateral movement with the blink. Increase lens diameter, steepen the base curve or switch to a soft toric lens.
3 Initial reduced acuity and poor vision could result from incorrect power, residual astigmatism and/or flexure. Over-refraction will show toric over-Ks and spherical base curve. It could also result from poor wettability, which appears as haze/rapid tear break-up via biomicroscopy. To resolve poor initial visual acuity, try front or soft toric lenses, flatter base curve, increased thickness and/or reduced Dk material or use lab cleaner or solvent to recondition. If this problem is chronic, talk with your lab.
4 A gradual, acquired reduction in visual acuity could result from poor wettability (muco-protein haze/film on front lens surface) and/or warpage (toricity measured with the radiuscope). Re-educate the patient in lens care and cleaning: tell him to avoid lanolin creams and soap prior to lens handling, use liquid enzyme and clean lenses in his palm. For warpage, try switching to a lower Dk material.
5 Poor initial comfort presents as lens awareness at initial fit, tearing and/or inability to look up. This could result from patient sensitivity or a poor fitting relationship. Try using an anesthetic during fitting and describe the sensation as lens awareness, not discomfort.
6 A patient experiencing dryness, redness and/or lens awareness may have corneal des-iccation. Causes of this include poor tear quality/volume, poor blinking, high Dk material or lid margin disease. It is diagnosed by 3 and 9 o'clock staining, < 10mm phenol red thread test, < six second tear break-up time, possible opacification and/or neovascularization. If it is coalesced, improve centration. Try a low Dk FSA material, decrease the edge clearance, ensure proper blinking and frequency, treat meibomian gland dysfunction and teach the patient lid hygiene and suggest a humidifier or rewetting drops.
7 If vascularized limbal keratitis exists, the patient may experience acute lens awareness, reduc-ed wearing time and/or red eye with visible opaque corneal mass. This problem can result from dryness, extended wear, SA material and/or a steep fit with peripheral seal-off. There will be an elevated, opaque vascularized area in the 3 and 9 o'clock corneal region, and biomicroscopy will reveal coalesced staining. To man age, discontinue lens wear for seven days, instill topical ab-steroid combination (qid for one week, then taper), prescribe an FSA material in daily wear, and/ or flatten the peripheral bevel.
8 With GP lens adherance, the patient may be asymptomatic or have mild lens awareness. Dryness, lens decentration, back surface deposits, peripheral seal-off and extended wear can all contribute to adherence. You may note an absence of lens movement with trapped debris. Biomicroscopy will show SPK and ad herence ring upon lens removal. Improve lens centration, clean posterior surface (and educate patient), flatten peripheral curve, reduce patient to daily wear and/ or prescribe rewetting drops in the morning and at bedtime.
Dr. Bennett is an associate professor of optometry at the University of Missouri-St. Louis and executive director of the RGP Lens Institute.