CORNEAL GP LENSES

Corneal GP Lens Grand Rounds

These cases show that, when fit properly, corneal GP lenses provide excellent vision, health, and comfort.

By Ronald K. Watanabe, OD, FAAO

Corneal GP lenses are a great option for many patients. Aside from the obstacles of initial lens awareness and required adaptation, they offer many benefits including sharp visual acuity, excellent tear exchange for corneal health, ease of application and removal, and the lowest complication rate of all lens types (Stapleton et al, 2008).

However, fitting corneal GP lenses can be a challenge when they do not position or move as intended. The following cases demonstrate how informed fitting decisions and knowing how to troubleshoot are keys to successful fitting.

Case #1: Fixing the GP Fit

A 35-year-old Asian male presented with complaints that his spherical GP contact lenses were uncomfortable. He had been refit with GPs a few months prior because he was unhappy with the comfort and vision of his spherical soft contact lenses. His previous practitioner told him that he had astigmatism and borderline dry eye, and that GP lenses would improve his vision and decrease his dryness symptoms.

Initial Examination Findings The patient’s entering visual acuity (VA) with contact lenses was OD 20/20, OS 20/20. Keratometry (K) readings were OD 42.00/43.00 @ 90, OS 42.00/43.25 @ 100. Refraction was OD –3.25 –1.00 x 180, 20/20 and OS –3.50 –1.50 x 010, 20/20. Horizontal visible iris diameter (HVID) was 12.0mm.

The patient’s GP lenses were manufactured in Boston ES (Bausch + Lomb [B+L]) material. Lens parameters were OD 8.00mm base curve radius (BCR), 9.5mm overall diameter (OAD), –3.25D power and OS 8.0mm BCR, 9.5mm OAD, –3.50D power.

Biomicroscopy showed that the lenses were dropping inferiorly after being picked up on the blink; there was minimal apical clearance, midperipheral touch, and minimal peripheral clearance OD and OS (Figure 1, left). Biomicroscopy with the lenses off was unremarkable OD and OS.

Figure 1. Inferiorly positioning spherical GP lens with minimal peripheral clearance (left). Lid-attached GP lens with increased peripheral clearance (right).

Discussion Discomfort is one of the most challenging obstacles when fitting corneal GP lenses. The discomfort can result because the upper eyelid cannot adapt to blinking over the lens edge throughout the day, or because the lens is interacting too much with the corneal surface due to a less-than-ideal fitting relationship. In this case, the lens fit was steep in the periphery, as illustrated by the minimal peripheral clearance. The lens peripheries rub along the cornea with every excursion, and the lenses drop to the inferior limbus after each blink movement. The lenses tend to position inferiorly because of the steep fitting relationship, which does not allow them to move upward and be held in place by the upper eyelid.

Steep fitting relationships that result in inferiorly positioning lenses can often be remedied by flattening the BCR and/or peripheral curve radii. By flattening the fit, the lens is able to move up to the flatter superior cornea more easily, and the upper eyelid is better able to grasp and hold on to the lens. In this case, the peripheral curve radii were flattened by 1.00mm, resulting in an increase in axial edge lift of about 0.06mm. Peripheral clearance increased, and lid attachment was achieved (Figure 1, right).

Flattening the BCR by 0.10mm would also have decreased apical clearance and increased peripheral clearance. This is a good choice when there is distinct apical clearance, which this case lacked.

Flat fitting relationships can also result in inferiorly positioning lenses. Flat-fitting lenses exhibit apical touch with greater peripheral clearance, and they may position laterally as well. Between blinks, flat lenses tend to move along the corneal periphery where the cornea is flatter. Steepening their BCR and/or peripheral curve radius would be a better choice.

In either case, if a base curve/peripheral curve radius change alone does not improve the fit, a diameter change may help. Increasing the diameter often helps to achieve lid attachment, but the BCR should simultaneously be slightly flattened to prevent the fit from becoming too steep. Alternatively, a smaller diameter with a steeper BCR can help center a lens in an interpalpebral position if lid attachment is not possible. Finally, adding a minus carrier lenticular can improve the fit when the lens has an ideal fluorescein pattern but is not lid attaching.

Case #2: Superior Vision and Optics

A 22-year-old female presented for her annual examination with complaints of fluctuating vision with her soft contact lenses. She wanted sharper acuity because she was in medical school and had greater visual demands. In addition, although her wearing time was 14 to 16 hours per day, her soft lenses felt very dry.

Initial Examination Findings The patient’s entering VA with soft lenses was OD 20/20^–, OS 20/40^–. Her K readings were OD 42.9/44.1 @ 94, OS 41.8/45.4 @ 85. Refraction was OD –2.25 –0.75 x 180, 20/20 and OS +1.75 –6.00 x 003, 20/25⁺. The HVID measured 11.6mm.

The patient was wearing Acuvue Advance (Johnson & Johnson Vision Care, Inc.) OD with parameters of 8.7mm BCR, 14.0mm OAD, −2.50D power. Her lens OS was a Proclear Toric XR (CooperVision) with parameters of 8.8mm BCR, 14.4mm OAD, +1.75 −4.25 x 005 power.

Biomicroscopy was unremarkable OD and OS.

Discussion I recommended GP lenses due to their superior optics, ability to better correct astigmatism, and because they may decrease dryness symptoms that result from surface dehydration of soft lenses.

The right eye had low with-the-rule (WTR) corneal astigmatism (Figure 2a, left), which was ideal for a spherical GP lens because tear exchange, lateral stability, and lid attachment are easiest to attain on such a cornea. For this patient, I selected a 9.6mm lens diameter because she had an average corneal diameter and her lid position was appropriate for lid-attachment fitting. An “on-flat-K” BCR (7.85mm) was selected because the cornea had 1.20D of WTR toricity. I ordered a power of −2.25D because the lacrimal lens in the flat meridian was plano. Boston EO (B+L) material provided a balance of moderate oxygen permeability and good surface characteristics. The final fit exhibited central positioning with lid attachment, mild apical clearance, midperipheral alignment, and moderate peripheral clearance (Figure 2b, left).

Figure 2a. Corneal topography showing low WTR astigmatism OD (left) and moderate WTR astigmatism OS (right).

Figure 2b. Final GP lens fits: spherical lens OD (left) and back-surface toric lens OS (right).

The left eye had 3.60D of WTR astigmatism (Figure 2a, right), which required a back-surface toric design. I ordered the flat BCR meridian “on flat K” and the steeper meridian 0.75D flatter than steep K to simulate a low WTR fitting relationship. The resulting base curve radii were 8.08mm (41.75D) and 7.54mm (44.75D). The power in the flat meridian was +1.75D. Only the flat meridian needs to be specified for a back-surface toric. Although the base curve toricity is 3.00D, the optics of the back-surface design will correct almost 1.5 times that amount of refractive astigmatism, or approximately 4.50D. Also, another 0.75D of cylinder would be corrected by the lacrimal lens, resulting more than 5.00D of cylinder correction. Although this is less than the 6.00D in the patient’s refraction, it is very close to full correction of the cylinder. Lens diameter was kept at 9.6mm for lid attachment. The final lens provided 20/20– VA and exhibited superior-central positioning with good lid attachment, mild apical clearance with a mildly toric pattern, and moderate peripheral clearance (Figure 2b, right).

These lenses provided good visual acuity and comfort without dryness throughout the day.

Case #3: 3 o’clock & 9 o’clock Staining

A 42-year-old Caucasian office assistant presented with complaints of redness, dryness, and reduced wear time with her GP lenses. She had good vision, but was unable to wear her lenses for more than a few hours. She worked on a computer for most of the day.

Initial Examination Findings The patient’s entering VA with contact lenses was OD 20/20^–, OS 20/20. K readings were OD 43.00DS, OS 42.50/43.50 @ 115. Refraction was OD –4.75DS, 20/20 and OS –3.50DS, 20/20. HVID measured 11.4mm.

She was wearing GP lenses in an unknown material with parameters of OD 7.9mm BCR, 9.6mm OAD, +1.75D power and OS 7.9mm BCR, 9.6mm OAD, –3.00D power.

Biomicroscopy showed that the lenses positioned inferiorly with poor movement; the fluorescein patterns showed apical alignment, midperipheral touch, and minimal peripheral clearance. Biomicroscopy with the lenses removed revealed grade 2 bulbar injection interpalpebrally and moderate punctate epithelial staining at the 4 o’clock and 8 o’clock areas of the peripheral cornea OD, and grade 2 bulbar injection interpalpebrally, mild central corneal staining, an opacified area at the 8 o’clock area of the peripheral cornea with patchy staining overlying, and moderate punctate staining at 4 o’clock OS (Figure 3a).

Figure 3a. Patchy area of peripheral corneal desiccation due to low-riding GP lens.

Discussion Based on the patient’s symptoms and clinical signs, I diagnosed peripheral corneal desiccation (PCD) OD and OS, with vascularized limbal keratitis (VLK) OS. This condition results in areas of corneal surface dryness caused by tear film instability due to the presence of the contact lens. The thickness of the lens edge prevents the upper lid from rewetting the corneal surface adequately on the blink, and over time the area becomes dry. Low-riding lenses tend to exacerbate the condition because they move less, resulting in tear stagnation and blink inhibition. Other contributing factors include incomplete or insufficient blinking, poor tear film quality or quantity, and poor lens material and design selection. The patient’s work habits also contributed; extended computer work tends to reduce blink rate, making the eyes progressively drier as the day goes on.

PCD is one of the most common problems associated with corneal GP lenses. Usually referred to as 3 o’clock & 9 o’clock staining due to its location, it can occur in as many as 80% of corneal GP wearers (Solomon, 1986). In most cases, the desiccation is minimal, and patients are asymptomatic. However, more severe cases can result in significant discomfort and complaints of redness. In extreme cases, patients can develop VLK, which consists of an elevated inflammatory opacity with overlying staining and neovascularization (Grohe and Lebow, 1989). Depending on the level of severity, management can range from artificial tears or lubricants to topical steroids.

Once the staining and VLK have resolved, dry eye management with warm compresses, lid massage, and lubricants can help minimize tear film instability issues that may exacerbate PCD. Then, lens design changes should aim to improve lens centration and movement, perhaps with lid attachment to ensure that the lens does not settle inferiorly. This may include flattening the BCR and/or peripheral curve radii, increasing diameter, and adding a minus carrier lenticular. Alternatively, the lens can be made to center and move more easily by decreasing lens diameter and steepening the BCR, thereby decreasing lens mass and allowing the lens to more easily stay in a central position.

This patient was discontinued from lens wear until the VLK resolved. I reordered the lenses with a larger diameter of 10.4mm, flatter BCR of 8.10mm, –3.00D power in the Hydro2 (InnoVision) material for good surface wettability. The patient noted good comfort and vision, and she felt that the lenses no longer dropped inferiorly (Figure 3b). Her comfortable wearing time increased to 10 hours.

Figure 3b. Large GP lens with lid attachment in a superior-central position.

However, over the next several months, the patient’s dry eye complaints returned. She admitted that she had not really performed the lid therapy. Her lenses had moderate lipid and mucous deposition. The lenses now positioned superiorly with lid attachment; they exhibited apical alignment and moderate-to-high peripheral clearance. Her PCD had decreased to grade 1 OD and OS, and there was mild scarring in the area of her previous VLK. I instructed her to start performing nightly lid therapy and to add Progent (Menicon) to her lens care regimen on a monthly basis to keep her lenses as clean as possible. She was also educated to take frequent breaks while on the computer to blink and rewet her lenses.

Case #4: Lens Adhesion

A 66-year-old Asian female long-time GP wearer presented with complaints of blurry vision and difficulty removing her corneal GP lenses at the end of the day. She had lost her most current right lens and was wearing lenses from two different pairs, both of which were several years old. She was a high myope and felt dizzy when wearing her glasses, so she wore her GP lenses for all waking hours.

Initial Examination Findings The patient’s entering VA with contact lenses was OD 20/50^–, OS 20/40^–. The parameters of her old GP lenses were OD 7.83mm BCR, 8.0mm OAD, –5.75D power and OS 7.88mm BCR, 9.0mm OAD, –6.75D power.

Biomicroscopy showed that the OD lens positioned superiorly and the OS lens positioned nasally, both crossing the limbus; both lenses demonstrated no movement, apical touch, midperipheral clearance, and moderate peripheral clearance (Figure 4a). K readings were OD 43.50/43.75 @ 180, OS 43.00/43.50 @ 90. Refraction was OD –7.25 –1.75 x 090, 20/50 and OS –7.50 –1.00 x 010, 20/30+. HVID measured 11.1mm.

Figure 4a. Decentered and adherent GP lenses.

Biomicroscopy without the lenses revealed mild corneal staining in the areas of lens adhesion OD and OS. Corneal topography showed distortion with inferior-temporal steepening and superior-nasal flattening OD>OS (Figure 4b).

Figure 4b. Corneal topography showing corneal distortion due to decentered and adherent GP lenses.

Discussion Corneal GP lens adhesion usually results from decentering lenses that traverse the limbus. Over the course of the day, the lenses can become progressively more immobile in the decentered position as eyelid pressure slowly squeezes the tear fluid out from under them. Mucin can accumulate under the lenses, causing them to stick. The cornea becomes molded to the shape of the lenses, causing an imprint and surface distortion. The eyelids often play a role in holding the lenses in a very superior position, so it can be difficult to keep such lenses mobile on the eye.

In cases such as this, make lens changes to improve centration. In most cases, steepening the GP fit helps to improve centration and keep the lenses from becoming stuck in an off-center location. Decreasing lens diameter can reduce lid adherence, allowing the lens to stay in a more centered corneal position; however, smaller lenses can also be more unstable. Increasing diameter can steepen the fitting relationship, but it can also result in more lid attachment and decentration. Either way, new GP lenses will tend to position where the previous lenses did, so small-diameter lenses may not provide adequate acuity due to excessive decentration.

In this case, I increased the diameter modestly to 9.2mm. I also significantly steepened the BCR to 7.60mm OD and 7.65mm OS, based on diagnostic fitting and fluorescein pattern assessment. These changes resulted in less decentration and improved movement with the blink throughout the day. The lenses still decentered in the same direction as the old lenses, but the slightly improved centration prevented them from crossing the limbus and adhering.

Summary

Corneal GP lenses can be a great option for patients desiring excellent visual acuity. In some cases, they can improve comfort when soft lenses seem to dehydrate excessively. Suboptimal fitting can cause complications; if you know how to solve these problems, you can help your patients remain successful. CLS

For references, please visit www.clspectrum.com/references and click on document #223.

Dr. Watanabe is an associate professor of optometry at the New England College of Optometry. He is a Diplomate in the American Academy of Optometry’s Section on Cornea and Contact Lenses and Refractive Technologies, and is in private practice in Andover, Mass. You can reach him at watanaber@neco.edu.