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Toric IOLs in abnormal corneas: How the two can work together
Premium IOLs can be used successfully in patients with corneal pathologies.
Take-Home Message: Premium IOLs can be used successfully in patients with corneal pathologies.
By Lynda Charters; Reviewed by Christopher E. Starr, MD
New York-Careful patient selection is the foundation for successful outcomes when implanting premium toric IOLs in some cases with corneal pathologies. To obtain the best visual results, other procedures may be required before or after cataract surgery.
“When implanting premium IOLs in patients with abnormal corneas, there is really no right or wrong,” said Christopher E. Starr, MD, associate professor of ophthalmology and director, refractive surgery service, Weill Corneal Medical College, New York Presbyterian Hospital, New York.
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Having said that, Dr. Starr’s personal style when dealing with higher-risk eyes tends toward the more conservative in an area in which the patients have unusually high expectations regarding visual outcomes.
“No cornea is static-all corneas change over time,” he said. “Normal corneas tend to change very slowly and predictably over time-normal corneas have regular astigmatism.”
Dr. Starr cited a study by Koch et al. which noted that normal corneas drift from with-the-rule to against-the-rule astigmatism over time-which required adjusting the toric IOL power accordingly. These eyes do well with premium IOLs.
“On the other hand, abnormal corneas tend to change rapidly and unpredictably and can have substantial irregular astigmatism,” he said. “In these eyes, IOL selection is like shooting at a moving target. IOL selection is less precise and managing expectations in these cases is paramount.”
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In Dr. Starr’s practice, dry eye is the most common etiology of abnormal corneas.
“Corneal staining, hyperosmolarity, and rapid tear film break-up time can significantly affect topography and keratometry calculations, creating IOL errors,” he said.
“The pearl in patients with dry eye is to treat aggressively preoperatively (and) delay biometry and surgery until the ocular surface has normalized,” Dr. Starr said. “This can sometimes take a long time.”
However, some patients with advanced cataracts may not want to wait for the cornea to reach its optimal status and demand cataract surgery despite significant dry eye disease. In one such patient in his practice, implantation of toric IOLs after cataract surgery resulted in a plano refraction but substantial visual fluctuations during the day.
‘Lump-and-bump’ pathologies
Epithelial basement membrane, Salzmann nodules, subepithelial fibrosis, and pterygia can cause substantial irregular astigmatism, fluctuate, and recur after removal. However, the big clinical decision associated with these is “to scrape or not to scrape.”
“For patients with high expectations and who want to reduce spectacle dependence, the rule of thumb is to scrape but well before surgery,” Dr. Starr said. “Allow at least 6 to 8 weeks after superficial keratectomy or phototherapeutic keratectomy, repeat keratometry and topography. After another 2 to 4 weeks, repeat these measurements again. When the cornea is stable and regular, a toric IOL can be implanted.”
In certain scenarios, the best approach may be not to scrape.
“In patients with stable mild peripheral lesions, regular astigmatism in the central cornea, normal-sized scotopic pupils, and good spectacle-corrected vision preoperatively, cataract surgery with implantation of a toric IOL can be performed successfully without a superficial keratectomy,” he said.
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Many patients who have undergone LASIK, PRK, RK, or conductive keratoplasty are now developing cataracts and are interested in premium IOL implantation. The catch-22 is this is arguably the most-motivated patient population for spectacle-independence, and yet, their IOL calculations are the most unpredictable, according to Dr. Starr.
“The ASCRS [American Society of Cataract and Refractive Surgery] Post-Refractive IOL Calculator is a godsend for these patients,” he said. “Over time, it has become more and more accurate, and the range of IOL suggestions are much tighter now. I am much more comfortable now targeting plano than previously when I would target some myopia.”
Other tools-such as intraoperative aberrometry and light-adjustable IOLs-have helped to improve refractive outcomes in these patients.
Dr. Starr advised ruling out post-LASIK ectasia before implanting a toric IOL, with the presumption that a high degree of corneal astigmatism is present. He also recommended preoperatively assessing candidacy for a possible laser vision correction touch-up in the event of a refractive IOL “surprise.”
Corneal ectasias
When facing patients with keratoconus, pellucid marginal corneal degeneration, post-LASIK ectasia, post- keratoplasty (PK), and post-deep anterior lamellar keratoplasty, the rule of thumb is if patients can successful wear a rigid gas permeable or scleral lens postoperatively, a toric IOL should not be implanted.
However, a toric IOL is a consideration if patients are contact lens-intolerant, have acceptable spectacle-corrected vision, and have a fairly regular central cornea over the long term as in older patients or after a crosslinking procedure.
A toric IOL is also a reasonable choice in post-PK eyes in which there is a low risk of graft failure and the need for another PK, Dr. Starr explained.
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In patients with mild guttata but no morning blur or Descemet’s folds and a central corneal thickness of 630 µm or less, cataract surgery can be performed with or without implantation of a toric IOL, Dr. Starr advised.
The rule of thumb in these patients is that all posterior lamellar grafts cause hyperopic shifts. In Descemet’s stripping automated endothelial keratoplasty (DSAEK), –1 to –1.5 D is typically targeted. In Descemet membrane endothelial keratoplasty, –0.25 to –0.5 D should be targeted, according to Dr. Starr.
“My preference in DSAEK is a 90-µm thick graft, and my IOL target is about –1 D,” he said.
“Premium IOLs can be used successfully in patients with abnormal corneas,” Dr. Starr said. “For the best refractive outcomes, adjunctive procedures are often needed before, during, and sometimes after cataract surgery, which can delay surgery and/or the time needed to achieve a satisfactory uncorrected visual acuity.”
Christopher E. Starr, MD
This article was adapted from Dr. Starr’s presentation during Cornea Subspecialty Day at the 2014 meeting of the American Academy of Ophthalmology. Dr. Starr has no financial interest in any aspect of this report.
