BLOG: Surgeons must weigh perioperative considerations for complex corneas
In the previous installment, we reviewed our diagnostic approach for complex corneas stemming from dry eye, “lumps and bumps” and ectasia. Here we move into preparing these patients for surgery and intraoperative considerations.
Preparation for surgery
To achieve the best refractive outcomes in patients with complex corneas, pretreatment is essential. Lumps and bumps need to be removed, ocular surface disease must be treated, and ectasia must at least be identified and potentially cross-linked.
A Salzmann’s nodule or pterygium can be removed in the clinic at the slit lamp or as a surgery preoperatively. Once the pathology is removed, the ophthalmologist must wait for the cornea to heal and for topography to stabilize and then reassess the patient to determine IOL choice.
This remains true for ocular surface disease; we take an aggressive treatment approach choosing a range of therapies appropriate for the etiology of patients’ conditions. When topography has normalized, the tear film has improved and the ocular surface staining has decreased, patients will then have more options for IOLs. For patients who have achieved a clean ocular surface, they will likely be motivated to continue their ocular surface management to ensure good quality vision postoperatively.
Some patients will have recalcitrant dry eye to the extent that the residual amount of irregularity will affect the lens choice. In some situations, the best option may be to choose a monofocal lens and continue treating the dry eye disease.
There may be a role for cross-linking in some patients with ectasia. For example, if a patient’s cornea is showing instability with progressive changes to their keratometry after the age of 40 years — something we see particularly in post-refractive ectasia — we consider stabilizing with a cross-linking procedure. We would wait for some degree of stability in their corneal keratometry measurement prior to cataract surgery.
It is important to understand that IOL calculation formulas are based on “virgin” corneas. Previous refractive surgery, whether it is LASIK, PRK or RK, changes the anterior cornea but not the posterior cornea, which alters the ratio between the two. If a formula for a normal cornea is used, there will be errors in the IOL calculation. Additionally, surgeons should be aware that the effective lens position can also change in post-refractive surgery eyes.
The ASCRS calculator available online and put together by Hill, Wang and Koch, is a great resource (https://iolcalc.ascrs.org/) that provides many different formulas, including the Barrett True-K and Haigis-L for post-refractive patients. Intraoperative aberrometry can also help decrease the window of error for eyes having had previous refractive procedures. It is necessary for surgeons to inform these patients that the power calculation is more challenging for them. We let them know that, although we still have a target that we will aim for, they may need a follow-up procedure to correct any residual refractive error.
RK eyes are the most difficult eyes in which to achieve an accurate refractive outcome, and our lens choices in these patients are limited. Another aspect of previous RK is that vision will fluctuate preoperatively, intraoperatively and postoperatively. We tell patients that their vision on postoperative day 1 is not necessarily the same as what it will be at month 1. Corneal RK incisions can sometimes swell open and then relax over time.
We reserve intraoperative aberrometry for patients with challenging IOL power calculations. For those with keratoconus, any kind of ectasia or previous RK, and even in patients with a LASIK flap, we are less likely to do any relaxing incisions, whether it is with a femtosecond laser or manually. These eyes already have a tendency toward corneal instability.
It may be reasonable, however, to implant a toric IOL in post-refractive patients with regular central 3-mm corneal astigmatism. Two recent publications show good outcomes in toric IOLs in patients who have had previous RK and LASIK but with regular astigmatism.
For patients with irregular astigmatism, although not yet FDA approved, we believe pinhole technology such as the IC-8 IOL (AcuFocus) is a good choice. The small aperture offers an extended depth of focus and an increased tolerance of spherocylindrical residual refractive errors compared with multifocal implants, tolerating up to 1.5 D of corneal astigmatism. The IC-8 IOL has been shown to provide up to 3 D of extended depth of focus and also tolerate up to 1 D deviation from the target manifest refraction spherical equivalent. With multifocal technology, more than 0.75 D of residual sphere will compromise visual acuity and spectacle independence. The IC-8 IOL has also been found to enhance vision at all distances, with improved visual acuities and a broad range of continuous functional vision.
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