A major factor in optimizing cataract surgery outcomes is obtaining reliable measurements of the cornea. Much of the pathology that compromises this reliability is readily apparent. Being able to identify and address more subtle abnormalities in a timely fashion will allow surgeons to better manage patient expectations and outcomes.
One of the easiest ways to highlight both subtle and overt abnormalities of the ocular surface is with topical fluorescein dye. This should be part of the preoperative evaluation for every cataract patient. Using a lightly moistened fluorescein strip rather than flooding the ocular surface with dye will prevent obscuration of subtle findings.
Two common findings
The two most common findings seen under cobalt blue illumination of fluorescein dye are dry eye and corneal epithelial basement membrane dystrophy. The latter can be seen as areas of “negative staining” with scalloped edges and can be clinically significant when located centrally and associated with fluctuating blurred vision and/or irregular astigmatism on corneal topography. Visually significant dry eye, usually of moderate severity or worse, should be treated using a combination of measures to improve lid margin health and increase and maintain lubrication before surgery. Epithelial basement membrane dystrophy as well as other anterior corneal opacities such as subepithelial fibrosis or Salzmann’s nodules can be treated with either superficial keratectomy with diamond burr polishing or phototherapeutic keratectomy, with corneal biometry deferred for at least 6 weeks after treatment in order to allow for stability of measurements.
Phototherapeutic keratectomy can also be used to address anterior stromal scarring that is contributing to irregular astigmatism as evidenced by corneal topography and inconsistent corneal biometry measurements. There are limits and contraindications to this treatment — in a thin and/or neurotrophic cornea, for example, which would warrant using the other eye to obtain reliable corneal measurements. Postoperatively, a rigid gas permeable, hybrid or scleral contact lens may be a viable option to maximize vision.
In patients with corneal opacities or ectasia who have failed or are not candidates for contact lens therapy, deep anterior lamellar keratoplasty or penetrating keratoplasty can be an option. The timing of cataract surgery in these individuals presents a unique challenge. The cataract and corneal surgeries can be either combined or staged. Combined surgery usually has the benefit of fewer trips to the operating room but requires guessing what the final corneal power will be after suture removal. Furthermore, the cataract surgery can be challenging to perform given a poor view and even if performed via an “open sky” approach. Corneal astigmatism is the most common reason for postoperative suboptimal vision despite a clear graft. In a patient who can wear a rigid contact lens postoperatively, this may not be an issue. In those who cannot, however, it makes sense to stage the procedures. The keratoplasty is performed first. Sutures are removed starting at 6 months for a DALK graft and 12 months for PK, usually staged over 1 to 3 months to prevent graft dehiscence. At least 3 months should be allowed for graft stability after complete suture removal before corneal biometry is obtained. The IOL power is then no longer a product of guesswork, and a toric lens becomes an option to address regular corneal astigmatism. Care should be taken during intraocular surgery after PK to minimize endothelial cell damage.
Combined endothelial keratoplasty and cataract surgery is more commonly performed due to two reasons. First, the refractive outcome of endothelial keratoplasty is more predictable. Descemet’s stripping endothelial keratoplasty results in a hyperopic shift of 1 D to 1.5 D, while Descemet’s membrane endothelial keratoplasty yields a hyperopic shift of about 0.5 D. The IOL power can be increased accordingly to compensate. Second, combined surgery reduces the potential for endothelial cell loss from the transplanted graft. Some of the challenges to combined surgery, however, are unreliable corneal measurements due to edema, poor visibility for cataract surgery, and difficulty in keeping toric IOLs in proper alignment during the keratoplasty portion of the surgery. Osmotic agents such as hypertonic saline or glycerin may be of benefit for the former two problems, and removing the edematous corneal epithelium intraoperatively can prove beneficial. Nonetheless, as with PK, cataract surgery can safely be performed after endothelial keratoplasty.
As with much else in life, output is highly dependent on the quality of input. A systematic approach in the evaluation and management of corneal pathology will yield better cataract surgery outcomes and happier patients and practitioners.
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- Alex Mammen, MD, is a clinical assistant professor of ophthalmology at UPMC and the University of Pittsburgh. He can be reached at University of Pittsburgh, UPMC Eye Center, Eye & Ear Institute, 203 Lothrop St., Floor 6, Pittsburgh, PA 15213; email: firstname.lastname@example.org.
Disclosure: Mammen reports no relevant financial disclosures.