Lens Dynamics, Inc.

Penetrating keratoplasties (PKs) are performed for a variety of reasons. The most frequent indications are keratoconus, Fuchs' endothelial dystrophy, pseudophakic bullous keratopathy and central corneal scarring from herpes simplex. Postoperative contact lens fitting may be performed as early as 3 months with sutures intact — if the patient requires early visual rehabilitation — and as late as 18 months with all sutures removed. In these early-fit cases, the lenses will need to be changed as the sutures are cut.

Generally, I like to fit a post-PK eye about 12 months postoperatively with a stable refraction and keratometry and all sutures removed. This way, lens modifications are kept to a minimum.

Correcting irregular astigmatism
Gas permeable lenses are used to correct irregular astigmatism caused by the surgery. Spherical, aspherical and bi-toric designs are used with great success, especially if the astigmatism is regular. Reverse geometry such as plateau lenses are also very successful. SoftPerm (Wesley Jessen, Des Plaines, Ill.) lenses are very comfortable and give good acuity, but should be reserved for a last choice if possible due to the increased risk of newvascularization to the graft.

My inital lens of choice is the large-diameter post-graft design lens by Lens Dynamics. This post-graft design is a 10.4 mm diameter lens with a standard 9.0 mm optic zone and multiple peripheral curves. The large diameter is used to vault the central graft area, and the peripheral curve structure is used to fit the host peripheral cornea. The 9.0 mm optical zone is larger than the usual 7.0 mm to 8.0 mm graft diameter and is standard. This aids in fitting the lens, because it limits the variables of change when adjusting the base curve.

Changing the optic zone diameter affects the base curve-cornea relationship. Changing the diameter can affect centration. If you change one variable independently of the other, you can affect the fitting relationship in a more subtle way. If the standard 9.0 mm optic zone does not obtain an acceptable fluorescein pattern, you can use the floating optic zone. This optic zone varies: as the base curve increases in steepness, the optical zone decreases.

Taking measurements
I begin by performing four measurements:

Manifest refractions: Remember that the refractions can be very difficult, often with high degrees of astigmatism. The astigmatism may be irregular, and the refractive error may be from one end of the spectrum to the other.
Keratometry: I like to use these measurements as a guide, remembering that keratometry measures only the central 3 mm of the cornea. Assess the mires for distortion and irregularity.
Topography: Data from topography is very useful. Topography easily shows astigmatism, irregularity of corneal surface, corneal apex, graft-host interface, size of recipient bed, neovascularization and scarring.
Slit lamp evaluation: I evaluate and note the thickness and irregularity of the graft, the smoothness of the graft-host interface, the size of the recipient bed, neovascularization and scarring.

Next, determine the radius of the curvature 3.5 mm to 4.0 mm from the visual axis along the temporal horizontal meridian from the topography. Select the lens that is closest to that radius and use that lens as your initial diagnostic lens. Use 2% sodium fluorescein to evaluate the fit, and change the base curve steeper or flatter to achieve the desired fit. The, over-refract for power.

Fitting Technique
Fitting guidelines include centration with minimal bearing or clearance and good tear exchange with adequate movement. A successful fit is determined by a lens that does not compromise corneal physiology, gives the patient good acuity and stable vision and is comfortable.

I used this technique on my patient A.G., a 67-year-old Caucasian woman who has a left PK, extracapsular cataract extraction and posterior chamber IOL implant 1 year prior to my fitting.

Manifest refraction: -9.00 + 4.00 x 104 20/40.
Keratometry: 46.87/48.12 @ 077 distorted mires.
Topography: 4 mm temporal to visual axis approximately 46.30 D.
Slit lamp: Graft clear and compact graft override at 7:00 to 8:30, posterior chamber IOL in place, anterior chamber deep and quiet.

I used this technique on my patient A.G., a 67-year-old Caucasian woman who has a left PK, extracapsular cataract extraction and posterior chamber IOL implant 1 year prior to my fitting.

Manifest refraction: -9.00 + 4.00 x 104 20/40.
Keratometry: 46.87/48.12 @ 077 distorted mires.
Topography: 4 mm temporal to visual axis approximately 46.30 D.
Slit lamp: Graft clear and compact graft override at 7:00 to 8:30, posterior chamber IOL in place, anterior chamber deep and quiet.

Lens selection
I selected a 7.34 mm radius, 10.4 mm diameter, 9.0 mm optical zone, standard peripheral curves (proprietary information), -5.62 power post-graft design lens by Lens Dynamics, made with Boston ES material.

With fluorescein, I determined the base curve-cornea relationship to be too flat with excessive movement and excessive edge lift, but it had good centration. My next diagnostic lens was 7.18 mm radius, 10.4 mm diameter, 9.0 mm optical zone, standard peripheral curves and -6.75 power, post-graft design lenses by Lens Dynamics. With fluorescein, I determined the lens to center well and have a fairly even alignment pattern without harsh bearing or too much steepness, even in the area of the graft override. I over-refracted this trial lens with a +1.25 sphere and was able to achieve 20/20-2 visual acuity.

I then inserted a lens with a 7.03 mm radius, 10.44 mm diameter and 9.0 mm optical zone standard peripheral curves to compare fluorescein patterns. This lens centered well but had mid-peripheral bearing and too much apical clearance. I then tried a lens with a 7.18 mm radius, 10.4 mm diameter, 9.0 mm optical zone, 11.5 mm secondary curve and 12.5 mm peripheral curve. The central fluorescein pattern over the graft appeared fairly flat with a very steep area nasally at the graft-host interface. The central graft area actually started to show diffuse punctate staining from mechanical irritation with this lens.

I ordered the lens with a 7.18 mm radius, 10.4 mm diameter, 9.0 mm optical zone, -5.50 sphere post-graft design. The post-graft design lens, with its multiple peripheral curves, large diameter and large optic zone, aided centration of the lens, improved the fluorescein pattern and the base curve-cornea relationship, helped stabilize vision and incread the comfort of the lens.

Topography is helpful, because it is very easy to choose the intial diagnostic lens with the topographical data. Final lens specifications cannot be determined without diagnostic fitting and the use of 2% sodium fluorescein to obtain the best base curve-cornea relationship.

For Your Information:

Mary Jo Stiegemeier, OD, FAAO, is in group multidisciplinary practice at Signature Eye Associates in Beachwood, Ohio. She can be reached there at 2501 Chagrin Blvd., Suite 150, Beachwood, OH 44122; (216)831-0120; fax: (216)292-5544; e-mail: mjstieg@aol.com. Dr. Stiegemeier has no direct financial interest in the products mentioned in this article, nor is she a paid consultant for any companies mentioned. Dr. Stiegemeier would like to acknowledge Mark Newkirk of Helioasis Digital Imaging for his help with the images presented with this article.

Lens Dynamics can be reached at 4090 Youngfield Street, Wheat Ridge, CO 80033; Tel: (800) 228-2691; Fax: (800) 661-6707.

Edited by Rodger T. Kame, OD. He may be contacted at 250 East First Street, Suite 802, Los Angeles, CA 90012-3875; (213) 628-7419. Dr. Kame has no direct financial interest in any of the products mentioned in this article, nor is he a paid consultant for any company mentioned.

Last Updated 7/08/2008