April 2019

IN FOCUS

Innovations in Lenses
IOL options for less-than-normal corneas


by Ellen Stodola EyeWorld Senior Staff Writer/Meetings Editor


A patient with keratoconus and Intacs implantation who underwent cataract surgery with a toric IOL
Source: Karolinne Rocha, MD

 

Addressing astigmatism is an important issue, and surgeons may have to consider certain conditions and previous surgeries when choosing the appropriate IOL option for a patient with a less-than-normal cornea.
The management of astigmatism can be broadly defined by whether it is surgical or medical, said George Waring IV, MD, FACS. When physicians think about the different categories of astigmatism, they should think of two primary categories: regular and irregular.
Regular astigmatism is orthogonal and radially symmetric in nature and should be addressed surgically, Dr. Waring said. For low amounts, femtosecond laser arcuate incisions can be used, and for large amounts, toric IOLs can be used.
Irregular astigmatism is non-orthogonal and/or radially asymmetric in nature and has a number of broad categories. This can be divided into the subcategories of asymmetric bowtie and skewed axes. These variations are often found in disease states such as keratoconus, Dr. Waring said.

Keratoconus patients

The only time you can adequately consider a toric IOL is if you know the true axis of astigmatism, said Jonathan Rubenstein, MD, and often that is very hard to determine in keratoconus because the patient usually has slightly irregular astigmatism. The axis that shows up in glasses, corneal topography, and refraction as well as other modalities is often different. If you can’t figure out the true axis, you can’t put a toric IOL in, he said.
Dr. Rubenstein noted that if the patient is a rigid contact lens wearer and needs those to have adequate vision, he or she will not do well with a toric IOL. “They will usually need the contact lens even after cataract surgery to correct or mask irregular astigmatism,” he said. For these patients, you can put in a non-toric and correct any astigmatism by having them resume contact lens wear postoperatively.
You can get a good sense of whether a patient is a potential toric candidate if they come in and have relatively good spectacle corrected visual acuity, Dr. Rubenstein added.
Dr. Waring said the regular component of the total astigmatism may be managed with toric IOLs in select cases of keratoconus.
When treating irregular astigmatism in keratoconus patients, Dr. Waring recommends evaluating the smallest magnitude of astigmatism 90 degrees away from the steep meridian. A toric IOL is a radially symmetric treatment, but you’re often treating a non-symmetric cornea. Therefore, you want to treat conservatively. Care should be taken not to destabilize a keratoconic cornea with limbal relaxing incisions that are penetrating, Dr. Waring said.
Dr. Waring added that Intacs (Addition Technology) are useful to debulk the irregular astigmatism associated with keratoconus. Crosslinking alone has some regularizing effect to the coma and higher order aberrations and when combined has a synergistic effect with intracorneal ring segments, he said.

Eye with a corneal transplant

Dr. Rubenstein said surgical management of astigmatism can be considered in patients with a prior corneal transplant. In some of these patients, it’s a good solution for residual refractive error, he said. Corneal transplant patients commonly have residual astigmatism and residual myopia or hyperopia. When you have a chance to do cataract surgery and implant a toric IOL, often you can correct them and potentially offer the option to function without glasses for the first time in their life, Dr. Rubenstein said.
However, he noted that you still need to determine the true axis of astigmatism to place the toric IOL. “You’ve got to be sure that the astigmatism is regular enough to determine the true axis,” he said. To know this, Dr. Rubenstein advocated for using corneal maps, optical biometry, elevation maps, manual Ks, and “as much data as you can possibly get.”
Dr. Waring said that in post-penetrating keratoplasty (PK) patients, there may be high levels of astigmatism. This might require a bioptics approach, like a combined toric and femtosecond LRI procedure.
Pseudophakic patients who are not cataractous post-transplant can undergo femtosecond laser-assisted astigmatic keratotomy, he said.

Advanced technology options for post-LASIK or PRK patients

Dr. Rubenstein said that these patients can be tricky, particularly because this is a patient population who paid out of pocket for a procedure to see without glasses, so they want to see without glasses after cataract surgery as well.
It’s important to get a corneal topography, he added, and this has to show both a centered and symmetric ablation on the PRK or LASIK.
If the ablation is decentered or quite asymmetric in the healing pattern, you should avoid any presbyopia-correcting IOL, Dr. Rubenstein said. Meanwhile, if the patients has a well-centered and symmetric ablation, you could consider some of the presbyopia-correcting IOLs.
He added that some LASIK patients may also have dry eye issues, so you have to be sure that they have a good ocular surface.
If the patient has irregular astigmatism, they won’t do well with a premium IOL, Dr. Rubenstein said.

Considerations for patients with dry eye disease

Dr. Waring said that care should be taken with LRIs in severe dry eye patients, but there could be a role for intrastromal LRIs with a femtosecond laser. He added that AKs and presbyopia-correcting IOLs can be an option in patients with moderate dry eye, if preoperatively and postoperatively managed aggressively.
It’s important to watch out for dry eye disease because it can produce an irregular surface and fluctuating vision, Dr. Rubenstein said. If the ocular surface is degrading the quality of vision, there may be an exaggerated negative response to presbyopia-correcting lenses vs. standard lenses.
Dr. Rubenstein said to be sure there is no staining of the cornea, and he emphasized that corneal topography is necessary.
AKs can be used, depending on the level of dryness, but only in mild dry eyes without corneal staining.

IOL options for post-RK patients

The post-RK patient can also be tricky. In general, Dr. Rubenstein said these patients have a higher degree of irregular astigmatism, depending on how many incisions they had, how central they are, and how they were performed. Irregular astigmatism can affect the choice of lens, he said.
Another problem is that these patients can have fluctuating vision. Because the procedure causes weakening of the mid-peripheral cornea, the corneal shape can fluctuate throughout the day.
Dr. Rubenstein said that determining the correct IOL power is tricky because the corneal shape can be hard to assess. Topography and biometry often cannot figure out the correct corneal power, he said, adding that ORA intraoperative aberrometry (Alcon) may be helpful.
The physician should warn these patients that their vision can fluctuate, he said, and that they may not be a candidate for a presbyopia-correcting or toric lens.

At a glance

• Management of astigmatism can be broken down into medical and surgical.
• Astigmatism can either be regular or irregular, with irregular often being found in certain disease states or after surgery.
• When considering a toric IOL, it’s important to know the true axis of astigmatism.
• Using a variety of technologies can help determine astigmatism, but this can often still be tricky following refractive and other surgeries.

About the doctors
Jonathan Rubenstein, MD
Vice chairman and Deutsch Family Professor of Ophthalmology
Rush University Medical Center
Chicago

George Waring IV, MD, FACS
Waring Vision Institute
Mount Pleasant, South Carolina

Financial interests
Rubenstein
: Alcon, Shire
Waring: None

Contact information
Rubenstein
: Jonathan_Rubenstein@rush.edu
Waring: gwaring@waringvision.com

IOL options for less-than-normal corneas IOL options for less-than-normal corneas
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