What Should I Do for a Patient Who Presents With 6-D Astigmatism After Undergoing Penetrating Keratoplasty 4 Months ago?
Roger F.
Steinert,
MD
Consider a contact lens first. A rigid gas-permeable contact lens is always the safest manner to correct both regular and irregular (high-order aberration) astigmatism, whether early or late postoperatively. The following responses assume that an adequate contact lens fitting has been attempted with unacceptable results.
Suture Removal: When and Where?
Because the sutures are in place and the patient is only 4 months after surgery, initial management consists of selective suture removal of any interrupted sutures, followed by adjustment of the tension in the running suture if a running suture is present. The fundamental concept is that the steep hemi-meridian, as evidenced by higher power or steepness on corneal topography, will be improved by reduction in tight sutures in that hemi-meridian (Figure 49-1).
Figure 49-1. More than 4 D of astigmatism in a postoperative PK patient (A). Reduction to 1.1 D astigmatism by adjusting the tension on the running suture, tightening the lower power areas at lower right and upper left, and moving the lax suture to the steeper, higher power areas at upper right and lower left (B).
My personal preference is to perform a single running 24 bite 10-0 nylon suture closure on all penetrating keratoplasty (PK) patients where there is no contraindication. Contraindications include vascularization, prior problems with wound healing, or a risk of trauma or pressure on the transplant incision. When a running suture is present, suture-in astigmatism is improved with adjustment of suture tension at the slit lamp with topical anesthesia and a jeweler’s forceps. Lax suture tension in the flatter, lower power hemi-meridian is the starting point. The forceps is used to pull on the suture and generate some lax suture material. This excess suture is then moved into the area of the tight/steep cornea. If the suture material in this area is tight, then reducing the tension will improve the astigmatism. A running suture closure for PK has been shown to result in less suture-in astigmatism and more rapid recovery of good visual acuity than a combined interrupted and running suture technique.1
Other interventions for reduction of astigmatism usually should wait until full removal of all sutures. Otherwise, the distortion of remaining sutures may result in shifts in any astigmatic correction. The timing of safe full suture removal is a subjective judgment. In general, the appearance of some degree of gray haze at the incision is necessary before one can have any degree of confidence that wound healing has occurred. The older the patient and the more peripheral edema in the cornea, the slower the establishment of wound integrity independent of the sutures. Corneal surgeons have experienced wound separation that requires repair after suture removal 4 or more years after initial surgery in elderly patients who had pseudophakic edema. Conversely, most keratoconus patients younger than 30 years will have good wound integrity 6 to 12 months postoperatively. None of these guidelines are concrete, however.
If a patient has had maximal suture removal and/or release of tension of a running suture in the steep/high power area, yet the hemi-meridian continues to show steepness/excess optical power, there is one intermediate intervention to consider when sutures remain. Under topical anesthesia at the slit lamp, a jeweler’s forceps can be used to pry open the anterior aspect of the incision in the steep area. This release of the anterior healed area may allow the tissues to shift so that the donor cornea elevates relative to the recipient rim, reducing the optical power in that zone.
After full suture removal, astigmatism tends to regress toward the mean.2 Patients with low astigmatism will, on average, have an increase in astigmatism, and patients with high astigmatism will, on average, have improvement. No investigation has conclusively proven a permanent improvement in suture-out astigmatism because of suture manipulations in the earlier postoperative period. This does not mean that suture manipulations are a waste of time. Many PK patients will retain sutures for many years after surgery, and the astigmatism with sutures in place is important for a number of years.
Astigmatic Keratotomy
The easiest and least expensive surgical intervention is astigmatic keratotomy. Because the source of the astigmatism is the graft-host junction, I place these incisions slightly inside the g-h junction. Use of a peripheral incision (limbal relaxing incision) is much less powerful and has the additional disadvantage of creating a shift in the normal part of the cornea. If there is a later re-graft, this distortion will still be present.
Astigmatic keratotomy inside the graft-host junction can be quite powerful because the tissue is under abnormal levels of stress compared to virgin corneas. Therefore, I reduce the amount of the correction by 50% compared to the amount predicted by the formulas for virgin cornea astigmatic keratotomy at that diameter. Even then, overcorrections may occur. An overcorrection should be treated by cleaning the epithelial plug out of the AK incision and suturing the incision closed for several months. Undercorrection is treated by lengthening the original incision or, if the incision is already long, adding a second incision 0.5 mm inside the original AK.
AK incisions are best when the astigmatism is regular (geometrically symmetrical). Conversely, the more asymmetric, the less reliable AK will be (Figure 49-2).
Figure 49-2. Partially asymmetric astigmatism. The hemimeridian at lower right has more power than the upper left, but the bow-tie shape is orthogonal. This could be treated with a larger AK in the lower right than the length of the AK in the upper left or, alternatively, with wavefrontguided corneal ablation. A more symmetrical and lower power residual astigmatism could then be resolved with a toric intraocular lens (IOL) implant.
Laser Refractive Surgery
In theory, less symmetrical astigmatism, which means higher-order aberration, should be treated with wavefront-guided (NOT “wavefront-optimized”) laser correction. The surgeon must first determine whether the diagnostic wavefront unit can capture the highly aberrated optics and create a treatment plan that has parameters that match the clinical determinations. If so, the patient must understand that the treatment is “off-label” in the United States because the FDA approval of wavefront-guided corrections is for primary treatments, where low-order aberrations (sphere and cylinder) are high and high-order aberrations are low. This is usually not the case for PK optics.
If laser corneal surgery is undertaken, the primary options are either PRK with mitomycin C to reduce haze or LASIK with the femtosecond laser. A microkeratome will usually cut across the PK incision and create astigmatic shifts, as well as risk buttonholes. A femtosecond laser can be programmed to create a flap entirely inside the PK incision.
Any corneal surgery after prior PK increases the potential for immune rejection. We cover this with increased topical steroids for at least 1 month, as well as antibiotics.
Toric Intraocular Lens
A very attractive option is the use of a toric intraocular lens (IOL), either alone or in combination with corneal surgery. Current astigmatic correction with IOLs is limited to 2 D at the corneal plane, but this limit is expected to increase. IOL-based toric correction is inherently geometrically symmetrical. However, if corneal surgery such as AK or laser vision correction can reduce the patient to moderate amounts of reasonably regular astigmatism, then the toric IOL can provide a highly accurate residual correction and result in excellent uncorrected and spectacle-corrected visual acuity.
References
1. Filatov V, Steinert RF, Talamo JH. Postkeratoplasty astigmatism with single running suture or interrupted sutures. Am J Ophthalmol. 1993;115(6):715-721.
2. Filatov V, Alexandrakis GF, Talamo JH, Steinert RF. Comparison of suture-in and suture-out postkeratoplasty astigmatism with single running suture or combined running and interrupted sutures. Am J Ophthalmol. 1996;122(5):696-700.