Cataract Surgery Following Cornea Transplant
Cataract surgery after corneal transplantation necessitates specific attention to stability and optimization of the corneal graft to enable good IOL selection, and preservation of the corneal graft since lens removal insults the corneal endothelium. The type of corneal graft will dictate planning; treatment of cataracts after full thickness penetrating keratoplasty (PKP) and treatment after Descemet's membrane endothelial keratoplasty (DMEK) differ on many levels. The rate of endothelial cell loss is higher after penetrating keratoplasty and endothelial keratoplasty. While surgery after EK has a higher risk of graft dislodgement and graft failure
Fig 1. DMEK graft with detached peripheral edge
Patient counseling is of paramount importance. Patients should understand the known risks to their current graft as well as refractive goals, predictability and likely outcomes.
Offering cataract surgical treatment should take into account numerous factors including but not limited to: vision, fellow eye status, patient needs, graft status, type and duration, lens density and medical necessity
Optimizing the ocular surface
Optimizing the ocular surface is important before cataract surgery. This is even more pronounced in the context of prior corneal surgery. Categorical rejuvenation in the form of increased lubrication or other dry eye topical treatments are likely warranted to blunt the expected increase in ocular surface inflammation and secondary surface disease which happens even in the most quiet of cataract surgeries.
Preop-Biometry and Topography/ Tomography
The corneal graft must be clear to allow for optical biometry with good signal strength. If the corneal graft is not clear, A-scan biometry could bypass the non-clear cornea. This would likely be in setting of a combined procedure (cornea graft, lens extraction, intraocular lens implantation), which has its own challenges and is a topic of separate discussion.
Compared to combined procedures, performing cataract surgery after corneal transplants has the advantage of better refractive outcomes (Hayashi and Hayashi, 2006). Care should be taken to confirm stability of the keratometry. In these patients, all corneal sutures should be removed before final keratometry readings are obtained. Topography/ Tomography will be especially helpful in cases of PKP/Therapeutic Keratoplasty (TKP)/Lamellar Keratoplasty (LK)/Deep Anterior Lamellar Keratoplasty (DALK) as these grafts are known to have high rates of significant astigmatism (regular and irregular) at times confounding easy IOL planning. IOL calculations are more reliable for EK compared to PKP/DALK.
Significant level of consistency and confidence in analyses (and counseling) are needed if considering IOL models other than standard monofocal styles (e.g. toric, see astigmatism management below). Caution must be taken on use of any IOL model that induces aberrations significantly or lowers contrast sensitivity as corneal grafts present a range of compromised optics whether it is in the form of interface haze for lamellar based procedures or significant aberrations from different forms of astigmatism. It is often challenging to characterize higher order aberrations for PKP/DALK. Therefore focus should be maximizing treatment of lower order optics including 2nd order Zernike optics (myopia/hyperopia/astigmatism). Future IOL choices for irregular and aberrated corneas will include pinhole IOL optics and adjustable optics.
Anesthesia considerations should follow what would be best suited for the patient ranging from topical anesthesia to general anesthesia based on patient ability to cooperate with the surgery. If anticipating maneuvers that include scleral tunnel, manual ECCE, SICS, retrobulbar block +/- without facial nerve block can be utilized. Positioning for these larger incision treatments should aim to minimize posterior pressure.
Incision Locations and types
Standard clear corneal incisions are a viable option as long as care is taken not to extend near the edges of graft endothelium peripherally causing detachments of dissections. Shorter uniplanar wounds that are sutured at the end may offer a compromise approach to achieve this.
Scleral tunnel utilization in preparation for standard Phaco/IOL, ECCE, SICS offers advantages of decreasing direct trauma via keratome incisions to endothelium.
Soft-shell techniques and viscoelastic choices
Use of a dispersive viscoelastic that coats the endothelium is likely to be universally employed as intraocular surgery, particularly cataract extraction by phacoemulsification (and to some degree manual ECCE) leads to endothelial loss along with the effects of irrigating and fluid flow.
Phacoemulsification, FLACS, Manual ECCE, Manual SICS
The choice of method for cataract extraction should factor in the graft's endothelial cell count, surgeon comfort and confidence with the technique. Endothelial cell loss rate is higher in phacoemulsification compared to ECCE (ref). Femtosecond laser-assisted cataract surgery also leads to reduced endothelial cell loss compared to phacoemulsification (ref). When using phacoemulsification greater distance from the corneal endothelium should be maintained to avoid close energy and aggressive fluid flow near the graft. Methods of nuclear disassembly such as phaco-flip or pop and chop should be chosen with caution.
Particularly for PKP/DALK grafts, attention must be paid toward the presence of astigmatism, both irregular and regular as this can significantly affect operative planning and refractive goals. For clinically significant levels of regular astigmatism management can include a variety of adjunct techniques in isolation or in combination such as the use of corneal relaxing incisions (in the graft-host junction, internal to the wound interface) and toric IOLs. Limbal relaxing incisions in the context of PKP/DALK likely have limited role as the biomechanical effects likely have little translation to the central optical zones. Bioptic treatments afterward may be used but with caution on the effects of ocular surface health. If utilized, the newer platforms using topography guided ablation algorithms may offer some tactical advantage of optical rehabilitation for cases with some component of irregularity.
Intraoperative techniques to gauge the astigmatic treatment effect range from simple techniques like a Vicryl wheel or safety needle pinhead to built in keratoscopy or aberrometry guide the achieved effect at the moment, though wound healing and time will dictate the longer term lasting effects. Preoperative regional pachymetry, OCT of confocal microscopy may adjunct decision making on wound depth, amount of existing fibrosis (versus epithelial plug). Incisions can be made with various instruments ranging from dedicated keratotomy knives to LASERs.
Preoperative treatment with additional immune modulating therapies
There maybe extra considerations for adjunct increase in topical steroids or other ways to decrease immune mediated response against the graft peri-operatively for the cataract surgery. Likely there will be corneal edema and increased pachymetry after surgery as part of the post operative findings, particularly for phaco based techniques using higher amounts of energy.
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