GP Lens Case Grand Rounds Troubleshooting Guide – 41

Penetrating Keratoplasty: Kenneth A. Lebow, OD, FAAO

Background

This patient presented with bilateral keratoconus. He had a penetrating keratoplasty on the left eye two years prior to this visit. He had a previous history of graft rejection with associated graft/host junction scarring with a clear central cornea. He had an 8 mm round penetrating transplant with five embedded ruptured interrupted sutures (photo below).

Test Procedures, Fitting/Refitting, Design & Ordering

Corneal Topography and Refraction:

Keratometry Reading:

OS: 42.25 @ 034; 46.72 @ 124
Shape Factor: Oblate shape (-2.02)
Irregular astigmatism — corneal irregularity measure (CIM) = 5.40
Reference sphere = 44.9 diopters

Axial Map:

Elevation Map:

Manifest Refraction:

OS: -1.75 -1.00 x 20 20/25 (ghost images and shadows)

Contact Lens Diagnostic Fitting (OS):

Spherical Power Effect (SPE) Bitoric Lens Fitting:

Lens #1:
Base Curve Radii(BCR): 7.94/7.41 mm
Overall/Optical Zone Diameter(OAD/OZD): 9.2/7.8mm
Slit Lamp Evaluation: Excessive apical bearing with excessive inferior edge standoff

Lens #2:
BCR: 7.76/7.25 mm
OAD/OZD: 9.2/7.8mm
Slit Lamp Evaluation: Improvement in centration; however, definite central apical touch, excessive blink-induced lens movement and an oblique astigmatic fluorescein pattern was evident

Lens #3:
BCR: 7.50/7.03 mm
OAD/OZD: 9.2/7.8mm
Slit Lamp Evaluation: Excessive lens movement with the blink and excessive inferior edge standoff was present

Lens #4:
BCR: 7.33/6.88 mm
OAD/OZD: 9.2/7.8mm
Slit Lamp Evaluation: Overall good geometric lens centration with some temporal decentration, alignment-to-moderate touch superior-temporally and nasally, slight inferior pooling with minimum inferior edge standoff. (fluorescein pattern below)

Over-refraction: -3.00 diopter sphere over contact lens to 20/20

Patient Consultation and Education

The Following Topics Were Discussed with This Patient:

  1. Irregular astigmatism and the effect on vision
  2. Problems with transplant rejection and the distortion associated with transplantation procedures
  3. Difficulty in achieving uniform bearing pressures across the cornea and over the host/graft junction
  4. The need to adapt to the presence of a contact lens as nothing has been worn on that eye for over two years after the transplant surgery

Follow-Up Care/Final Outcome

At the dispensing and the one week follow-up visit, the patient had the following clinical findings:

Visual Acuity:

OS: 20/20 (Plano over-refraction)

Fluorescein Evaluation:

No change in fluorescein pattern comparing the fitting visit to one week of contact lens wear. Overall, a geometrically centered contact lens with the optical zone over the transplant and slight temporal decentration. There was also moderate superior temporal and nasal touch areas. Mild edge standoff inferior-nasal in the steep axis was present and was exacerbated with the blink.

Subjective complaints of edge awareness and difficulty adapting to the presence of the lens which feels as if it wants to pop off the eye was evident during the adaptation process.

Discussion/Alternative Management Options

Fitting post-operative refractive surgery patients is entirely dependent upon corneal topography analysis and whether the corneal shape is primarily prolate (steeper centrally than peripherally) or oblate (steeper peripherally than centrally). Usually, oblate corneal shapes require reverse geometry lens designs, but when the corneal toricity is relatively low, conventional lens geometries may be used. In this situation a SPE bitoric design was attempted because of the relatively low amount (-4.50 D) of corneal astigmatism.

The area of central pooling evident in the fluorescein pattern is a result of the oblate shape of the corneal surface and is responsible for the unusual fluorescein pattern. It is not atypical for post-transplant eyes to demonstrate odd fluorescein patterns. While all attempts should be made to achieve as close to an alignment fitting pattern as possible, it is critical to realize that this may not always be possible. Close monitoring of these patients is extremely important. Certainly, the use of bitoric lenses will not be successful in most irregular corneas in which the axis differential does not approximate 90˚.

In the event visual acuity was not corrected to 20/20 with this lens design a spherical reverse geometry lens would be the next alternative. Other lens designs which could be attempted in this situation are:

  1. Reverse geometry spherical lenses
  2. Reverse geometry toric lenses (either SPE or Cylinder Power Effect or CPE design)
  3. Larger overall diameter lenses
  4. Semi-scleral lens designs
  5. Aspheric base curve lenses

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