Restricted Access

You must be logged in to view this content.

CASE REPORT: RGP fitting for teenager with keratoconus

$currentPage/@nodeName

By Heidi Hunter
BOptom GradCertOcularTher 

CASE REPORT

In March 2014 patient JT, a 17-year old Caucasian male, was referred by a general ophthalmologist for contact lens management of the boy’s recently diagnosed keratoconus.

At his initial attendance, JT reported vision difficulties with his university studies and his main complaint was monocular diplopia and ghosting with his spectacles. He was seeking a contact lens correction for both eyes to enhance his overall vision quality.

Habitual vision with current spectacles was RE 6/18, LE 6/12 which further corrected to RE 6/9+1, LE 6/7 with a refraction of RE +1.75/-4.50x15, LE -0.25/-1.75x165. Even though his binocular acuity was 6/7, the haloes and ghosting were visually significant.

Baseline topographic Axial Power maps (Medmont E300 Corneal Topographer) confirmed keratoconic changes, more pronounced in the RE (Figures 1 and 2). The inferior apices were positioned within two millimetres of the visual axis in both eyes (60 D cone RE, 47 D cone LE).

 

CLF04 - Figure 1 - online

Figure 1. Right Axial Power map

 

CLF04 - Figure 2 - online

Figure 2. Left Axial Power map

 

We proceeded to rigid gas permeable (RGP) contact lens trial fitting. Based on the topographic data, the Rose K design was chosen as a starting point. It was estimated that the RE would need a base curve of between 7.2-7.4 and the left eye 7.5-7.6.

Trial lens fitting began with a RE Rose K 7.2/8.7/-3.00 and LE 7.5/8.7/-3.00. Both lenses were too steep and bubbles pooled under both lenses.

We then trialled flatter lenses RE Rose K2 7.3/8.7/-3.25 and LE 7.6/8.7/-2.25. These lenses were a good fit across the central optic zone diameter and were left to settle, with the assistance of anaesthetic.

Thirty minutes later the fit was reassessed. Even though there was adequate clearance over the apex of the cone in both eyes, the lenses had excessive movement and it was deemed the lens diameter was too small.

Looking at the fluorescein pattern (Figures 3 and 4), there is excessive inferior stand-off in the right eye, and to a smaller degree superiorly in the left eye. The slitlamp biomicroscope video of this lens fitting portrayed the lenses moved in a rocking motion on the eye, so it alternated between inferior and superior stand-off.

CLF04 - Figure 3 - online

Figure 3. Right lens Rose K 7.2/8.7/-2.75

 

CLF04 - Figure 4 - online

Figure 4. Left lens Rose K 7.5/8.7/-1.75

 

Over refraction was RE -1.25/-0.50x155 (6/6-4)  LE -0.75/-0.25x50 (6/7)  OU 6/7+3

The patient reported an immediate resolution of all ghosting and haloes when R -1.50 and L -0.75 corrective lenses were held over the eyes wearing the trial lenses.

When deciding the best way to align the lens fitting in the periphery, you have a few options to consider.

Rose K lenses are also available as:

  • Peripheral toric: which has a spherical optic zone but the last 1.0 mm of the lens is toric
  • Back surface toric
  • Bitoric
  • Front surface toric: with spherical base, to correct residual astigmatism.

In this case the diameter was increased and the decision was made to reduce the overall edge lift slightly. To further stabilise the lens, a peripheral toric design was selected to resolve the excessive edge lift at 6 and 12 o’clock.

Another reason to consider a peripheral toric design is to eliminate tightness, which is most commonly seen along the horizontal meridian at 3 and 9 o’clock. Be mindful that often when you add a toric periphery, the lens becomes tighter along the flat meridian and slightly steeper along the steep meridian.

Lenses were ordered with the following parameters:

  • RE Rose K2 7.1/9.5 diam/-6.00 D standard decreased lift (-0.5), 8/10th toric periphery
  • LE Rose K2 7.4/9.5 diam/-4.25 D standard decreased lift (-0.5), 8/10th toric periphery

On delivery the lens fitting was unacceptable even though the patient reported outstanding vision with no ghosting (Figures 5 and 6). There was insufficient edge lift and there was minimal movement. Although the diameter was better, the mid-periphery was tight, and there was excessive clearance centrally in the LE. Both lenses’ toric axis markers were stable with no rotation while blinking.

 

CLF04 - Figure 5 - online

Figure 5. RE Rose K 7.1/9.5/-6.00 D, -0.5 edge, 8/10th TP

 

 

CLF04 - Figure 6 - online

 

Figure 6. LE Rose K 7.4/9.5/-4.25 D, -0.5 edge, 8/10th TP

 

 

The lenses were reordered. This time we removed the request for decreased edge lift, instead opting for standard lift. The decision was also made to flatten the base curve on the left lens slightly to 7.5.

  • RE Rose K2 7.1/9.5 diam/-6.00 D standard edge lift, 8/10th toric periphery
  • LE Rose K2 7.5/9.5 diam/-4.25 D standard edge lift, 8/10th toric periphery

On delivery and at the two week after-care visit, this was the fluorescein pattern with the new lenses (Figures 7 and 8). There was no 3 and 9 o’clock staining, no discomfort concerns, the lenses displayed good centration and movement, and the vision and visual quality were excellent.

 

CLF04 - Figure 7 - online

Figure 7. Delivered right lens

 

CLF04 - Figure 8 - online

Figure 8. Delivered left lens

 

Nine months later, JT returned to the clinic for a routine after-care visit. His right lens had dislodged during wear a few months earlier and he was currently wearing the left lens only.

Repeated topographic maps revealed his keratoconus had progressed with marked progression in the right eye. He was immediately referred to a corneal surgeon for collagen cross-linking consideration. No further rigid lenses were ordered at this stage.

Three months after collagen cross-linking, JT returned for reassessment and further contact lens fitting. The protocols for post- collagen cross-linking contact lens fitting vary for new and established lens wearers. Ultimately, it is at the discretion of the surgeon and the individual patient response to the procedure.

Studies have shown that corneal flattening may occur up to 48 months postoperatively. Initially after surgery, you may see corneal thinning and steepening, followed by relative flattening and thickening of the cornea. Because of these changes and their effects on vision, it is possible existing RGP wearers may require parameter changes to optimise the fitting post-treatment. Because corneal flattening can continue for up to 48 months, it is important to check these patients regularly as refitting may be required.

Two months after the collagen cross-linking procedure, the left lens fitting remained unchanged. There was progression and then subsequent flattening so the net result was not much overall change in corneal curvature, which meant the 2014 lens parameters were still a good fit (Figure 9).

 

CLF04 - Figure 9 - online

Figure 9

 

It was a very different story for the right eye. The original right lens was RE Rose K 7.1/9.5 diam/-6.00 D standard edge lift, 8/10th toric periphery. Based on his topographies and progression, I decided to start with a 6.7/9.5/-8.75 ROSE K, Standard edge lift, 8/10th toric periphery.

Delivery of that lens revealed it was an unacceptable fit with heavy bearing centrally and in the periphery (Figure 10). Steepening the base curve to 6.4 did not resolve the issue as there was still central touch (Figure 11).

 

CLF04 - Figure 10 - online

Figure 10

 

CLF04 - Figure 11 - online

Figure 11

 

From there we moved to a Rose K 6.3/9.5/-11.75 D with standard increased edge (flat lift +1.0) and there was still central touch (Figure 12).

 

CLF04 - Figure 12 - online

Figure 12

 

At this point it became apparent under the slitlamp that the topographic data did not align with the actual lens performance. JT had significant progression of his keratoconus in the RE, but we had gone from a 7.1/9.5 lens to a 6.3/9.5 and there was still no apical clearance. According the lens simulation module in the Medmont topographer, a 6.3 lens on his eye should be far too steep.

Going back to his topographic maps, you can see that there are not only progressive central changes, but also the peripheral corneal toricity has progressed significantly and confuses the lens simulations for his RE.

Figures 13 and 14 show the comparison between the original map of the RE, versus the current RE map. Looking at the tangential power (Figure 13) and axial curvature maps (Figure 14) you can visualise the obvious progression in the right eye centrally and the enlargement of the conical area.

 

CLF04 - Figure 13 - online

Figure 13

 

CLF04 - Figure 14 - online

Figure 14

 

Figure 13: on the left is the original RE tangential power map, on the right is the more recent map. The red colour indicates that the keratoconus has progressed.

Figure 14: on the left is the original RE axial curvature map, on the right is the more recent map. The red colour indicates that the keratoconus has progressed.

Instead of continuing to modify the lens fitting, it was decided it was best to refit him by altering the lens design. The aim was to find a lens design with a looser periphery. We began the fitting process again with two alternative lens designs for keratoconic corneas: ACL Kera design and Rose K Nipple Cone design.

The Rose K Nipple Cone (NC) design is a great choice when you have a small ectasia near the centre of the cornea. The lens design has a small aspheric back optic zone diameter (BOZD) to reduce paracentral pooling just outside the nipple cone. The front optic is the same as on a standard Rose K design so there should not be any difference noticed with night driving difficulties or flare.

Below details the lens fitting for the RE. The left lens remained unchanged.

Refitting RE with a Rose K2 NC 6.3/8.4/-13.00 (Figure 15), then Rose K2 NC 6.1/8.4/-13.00 (Figure 16)

 

CLF04 - Figure 15 - online

Figure 15. Rose K2 NC 6.3/8.4/-13.00

 

CLF04 - Figure 16 - online

Figure 16. Rose K2 NC 6.1/8.4/-13.00

 

After allowing time for the lens to settle the vision was RE 6/7-1. Over refraction was +0.25 (6/7-1). Figure 17 shows the Rose K2 NC 6.1/8.4/-13.00 after settling for five minutes, and Figure 18 after settling for 30 minutes.

 

CLF04 - Figure 17 - online

Figure 17. RE with five minutes settling

 

CLF04 - Figure 18 - online

Figure 18. RE with 30 minutes settling

 

To ensure we had an optimum fit, a decision was made to trial the ACL Kera design as well. The ACL Keratoconus Kera design allows for complete customisation, as all of the peripheral curves are known and able to be modified. The fitting philosophy is similar to most of the keratoconic designs in that you achieve an acceptable central fitting and then evaluate the periphery of the trial lens.

I tried three different base curves from the ACL Kera trial set. They were all 8 mm total diameter with an optic zone diameter of 5.8 mm, and first, second and third peripheral curve widths of 0.5 mm, 0.3 mm, and 0.3 mm, respectively.

The first diagnostic lens was a 6.2 base curve, with peripheral curve radii of 7.1, 8.5 and 12.0, respectively (Figure 19).

 

CLF04 - Figure 19 - online

Figure 19

 

The second diagnostic lens was a 6.0 base curve, with peripheral curve radii of 6.9, 8.5 and 12.0, in other words, steeper than the first lens (Figure 20).

 

CLF04 - Figure 20 - online

Figure 20

 

The third diagnostic lens was a 6.1 base curve, with peripheral curve radii of 7.0, 8.5 and 12.0, in other words, half-way between the first and second diagnostic lenses in terms of base and first peripheral curve radii (Figure 21).

 

CLF04 - Figure 21 - online

Figure 21

 

Using a trial set for this particular cornea, you will see that overall the periphery of the lens is tighter and there is insufficient edge lift compared to the Rose K2 NC trial fitting.

Finally, we proceeded to order a lens for the right eye. The parameters were Rose K2 NC 6.1/8.4/-12.75. The toric periphery was no longer required as moving to a different design and reducing the diameter has improved the overall lens fitting for this patient.

One week after collecting this new lens, JT returned for an after-care visit. His vision is 6/7, his over refraction is plano and he is once again happy with his vision. Figure 22 is the final delivered lens.

 

CLF04 - Figure 22 - online

Figure 22. Rose K2 NC 6.1/8.4/-12.75

 

This case demonstrates the trial and error involved with complex speciality contact lens fitting, especially when there is progression of the corneal disease.

Here was a patient who presented for a routine check-up because it had been nine months since his last review and he simply wanted to reorder a new right contact lens to replace the lens he had lost a few months earlier.

One size does not fit all when it comes to keratoconus patients. Having knowledge of one lens design or one trial set is rarely enough. Even when you think you have the lens fitting finalised, there are no guarantees that the underlying corneal condition will remain stable, and you may be required to start that lens fitting from the beginning.

Often the time spent fitting or refitting patients is considerably more than you initially expected.

1 comment for “CASE REPORT: RGP fitting for teenager with keratoconus”

  1. Gravatar of MkMk
    Posted Saturday, August 5, 2017 at 1:51:03 PM

    Hi,
    Please explained how do you estimate that BC RE 7.2 to 7.4 Le 7.5 to 7.6 ? did yiu base on K reading Of R 60 D L 40D ??
    Regards ,
    MK

Like us on Facebook



Latest Tweets




Recent Comments