GP Lens Case Grand Rounds Troubleshooting Guide – 46

Post-Refractive Surgery – RK & LASIK: Robert Maynard, OD

Background

This 36-year-old male computer sales executive presented in January 2003. He had radial keratotomy performed OU in 1995 and post-LASIK in 1998 OU.

Test Procedures, Fitting/Refitting, Design & Ordering

Visual Acuities (with Spectacles):

OD: 20/80-1
OS: 20/100

Manifest Refraction:

OD: -2.00 -0.75 x 013 20/25-1 ghosting & doubling
OS: +3.00 -5.00 x 098 20/25-1 ghosting & doubling

Keratometry:

OD: 41.37 @ 018; 45.37 @ 108
OS: 34.50 @ 109; 43.12 @ 019

On this initial visit, three pair of lenses were diagnostically fit from our trial fitting cases, including two pair of Comfort Kone (Metro Optics) lenses and a standard keratoconic lens.

Initial Fit

Lens Parameters:

Power(D)BCR(mm)OAD/OZD(mm)SCR/W(mm)PCR/W(mm)

OD: -6.50 7.67 11.2/8.8 9.00/.5 11.75/.5
OS: -7.25 7.50 11.2/8.8 9.00/.5 11.75/.5

Over-Refraction:

OD: +0.75DS 20/30
OS: +0.75DS 20/25

Slit Lamp Examination:

OD: The lens is well centered and moved well with the blink. Good fluorescein pooling centrally as well as superior and inferior.
OS: The lens is well centered and moved well with the blink. There was central pooling with slight touch superior-temporal, slight touch nasally, and slight touch inferior/temporal existed.

Two Week Follow-Up Visit:

Visual Acuities (with Lenses):

OD: 20/100 (foggy vision)
OS: 20/200 (foggy vision)

Slit Lamp Examination:

OD: The lens is centered over the superior limbus with dimple veiling present over the papillary zone; the lens appears to be tilting backwards over the superior limbus.
OS: Identical fitting relationship as present OD

Second Fit:

Lens Parameters:

Power(D)BCR(mm)OAD/OZD(mm)Cap Size(mm)SCR/W(mm)PCR/W(mm)

OD: -5.75 7.80 11.2/8.4 8.40 8.80/.7 10.00/.5
OS: -6.75 7.58 11.2/8.4 8.40 8.60/.7 10.00/.5

Over-Refraction:

OD: +1.50DS 20/30
OS: +1.75DS 20/25-2

Slit Lamp Examination:

OD: The lens is well centered and exhibits good movement with the blink. A bubble is present at 12:00 superior to the pupil.
OS: Similar fitting relationship as present OD with the additional presence of mild dimple veiling.

Visual Acuities:

OD: 20/30+2
OS: 20/40-1

Over-Refraction:

OD: +0.50DS 20/30+2
OS: +1.75DS 20/25-2

Slit Lamp Examination:

OD: The lens is well centered with apical clearance and good peripheral edge clearance
OS: Identical fitting relationship as present OD with the exception of mild dimple veiling superiorly

Third Fit (New Lens OS Only):

Lens Parameters:

Power(D)BCR(mm)OAD/OZD(mm)SCR/W(mm)PCR/W(mm)

OD: -6.75 7.58 11.2/8.4×9.0(oval) 8.60/.7 10.00/.5

Over Refraction:

OS: Plano 20/25-2 (fluctuates)

Slit Lamp Examination:

OS: Good centration and movement although dimple veiling was still present in various regions underneath the lens.

Follow-Up Care/Final Outcome

Final Fit:

Essentially, the right contact lens was not changed, and continued to provide excellent vision, as well as comfort. The left lens was modified several more times, including fenestrations to reduce the dimple veil problem. The final lens parameters were:

Power(D)BCR(mm)OAD/OZD(mm)Cap Size(mm)SCR/W(mm)PCR/W(mm)

OD: -5.75 7.80 11.2/8.4 8.20 8.80/.7 10.00/.5
OS: -6.00 7.50 10.6/6.8×7.8(oval) 6.80 8.50/.85 10.50/.85

5 fenestrations (OS only)

Over-Refraction:

OD: +0.50DS 20/25-2
OS: -0.75DS 20/20-2

Slit Lamp Examination:

OD: The lens is decentered slightly superiorly with mild dimple veiling paracentrally at 4:00 and just inside the superior limbus from 11:30 to 12:30.
OS: Similar fitting relationship as present OD with good lid attachment. Fenestrations appear to be successful. There is a minor punctate stain at 4:00, very minor scattered dimple veiling and some inferior edge standoff. The fluorescein patterns of the lens-to-cornea fitting relationship of both lenses are provided in Figures 1 and 2.


Figure 1


Figure 2

Overall, he was “delighted” with his vision and comfort. We decided not to correct the prescription on the left eye, since he would not gain that much improvement. We sent him away to return for another complete primary care examination in three months. It took 10 months for him to be successfully fit with a lens for his left eye but it was well worth the effort. At the next eye examination visit his vision was holding steady, the fitting relationship was still good, and he had no complaints; therefore, he was scheduled to return for a routine 6 month contact lens evaluation.

To date, he has retained this same pair of lenses, with only one modification to both, and that pertained to a minor power change. He has maintained good visual acuity, as well as excellent corneal health.

Discussion/Alternative Management Options

This represents a good example of the importance and benefits represented by exhibiting patience in the fitting process. Whereas the use of an oval optical zone — as well as fenestrations — represent the exception to the rule in such fits, their importance should not be discounted. This is an example of how important your CLMA laboratory consultant can be as well. The experience in such cases can be invaluable when troubleshooting lens design parameter changes in irregular corneas. Likewise, the www.gpli.info website has a comprehensive database which includes the lens designs from all of the CLMA member laboratories and the ability to access a particular design (i.e. reverse geometry, keratoconus, etc.) is present. However, the importance of being able to perform corneal topography is invaluable in the management of these cases and is valuable to share with your laboratory in determining the final lens design parameters.

This case also illustrates the importance of the “risk-benefit” ratio. It is almost impossible to achieve a perfect alignment fitting relationship; therefore, one should strive to obtain the best possible fit, knowing there may be slight compromise as the visual benefits to the patient can be life-changing. In this case, the patient was extremely pleased and experienced a better quality of life as his corrected visual acuity improved from an initial 20/80 – 20/100 to 20/25. The presence of dimple veiling, which consists of bubbles underneath the lens or an indentation in the epithelium (but not staining) should not be alarming if it does not impact visual acuity (i.e., excessive dimpling located centrally). It is often caused by excessive pooling, a not uncommon clinical finding when a GP lens is fit to an irregular cornea.

It is evident that a GP lens was certainly indicated in this case as it is in almost every irregular cornea patient due to the improvement in visual acuity being achieved by providing a more spherical corneal contour. The type of GP lens design can be determined via corneal topography. In most post refractive surgery patients, a reverse geometry lens design is indicated due to the flatter central topography (versus paracentral/midperipheral). Reviewing a recent corneal topography taken of this patient (see Figure 3), it is evident that this option could have been considered as well.


Figure 3

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