July 2018

REFRACTIVE

Refractive editor’s corner of the world
Diagnostics in refractive cataract surgery: Corneal topography


by Michelle Stephenson EyeWorld Contributing Writer

To remove someone’s cataract and have his or her vision not improve because of undiagnosed keratoconus should not happen in modern day cataract surgery. The same can be said for macular pathology. A thorough exam is critical before any surgical procedure, but our exam does not rule out all pre-existing issues such as keratoconus and an epiretinal membrane. As Steven Dell, MD, and Douglas Koch, MD, teach us, corneal topography should be a part of every cataract evaluation for setting up pre-cataract surgery expectations, understanding if the ocular surface/tear film is affecting image quality (both can be optimized before any cataract surgery), and improving lens implant calculations. Corneal topography has become mainstream technology in anterior segment surgery and can make us better cataract surgeons and diagnosticians. Corneal topography is also a reminder to us that cataract surgery is indeed refractive surgery. Thank you to Dr. Dell and Dr. Koch for sharing their wisdom in this month’s “Refractive editor’s corner of the world.”

Vance Thompson, MD,
Refractive editor

 


Galilei Placido mires that show irregularity from EBMD

Greatly improved but not perfect mires after healing following epithelial debridement
Source: Douglas Koch, MD, and Ildamaris Montes de Oca, MD

A standard Cassini display that shows anterior, posterior, and total astigmatism

The seven LEDs of the Cassini with the bright reflections off the anterior corneal surface and the faint but measurable images reflecting off the posterior corneal surface
Source: Douglas Koch, MD, and César Vilar, MD

Few surgeons perform cataract surgery without first performing corneal topography, and it is critical for refractive cataract surgery. “Every patient who comes into our clinic receives corneal topography,” said Steven Dell, MD, Austin, Texas. “It surprises me that there are surgeons who perform cataract surgery without the benefit of corneal topography, but I do see that occasionally. I would not be comfortable proceeding with cataract surgery without the benefit of the information that we get from a topographer.”
Douglas Koch, MD, Houston, agreed and said there are at least six reasons for performing corneal topography on every refractive cataract surgery patient:
1. It is imperative for evaluating the health of the cornea. “Placido disc topography is critical because you can look at the regularity or irregularity of the mires, and this is an excellent way to detect the optical impact of surface disorders such as epithelial basement membrane dystrophy,” Dr. Koch said.
2. It is used to evaluate and confirm the meridian and magnitude of the astigmatism that the biometers provide. Ultimately, as devices improve in their ability to measure the posterior cornea, it will also calculate true total corneal astigmatism.
3. Combined with tomography, it is used to determine whether the cornea is sufficiently thick and sufficiently healthy or normal. “In other words, it is used to confirm that the patient doesn’t have keratoconus, that there is no irregular astigmatism or other pathology that would rule out certain IOLs, and that the patient’s cornea would tolerate a postoperative excimer laser adjustment,” Dr. Koch explained.
4. It should be used, especially for patients wearing rigid gas permeable lenses, for at least two sequential measurements to determine that patients’ corneas are stable after discontinuation of the contact lenses.
5. “In patients who have undergone corneal refractive surgery, I can assess corneal asphericity to select an IOL whose asphericity is an optimal match,” Dr. Koch said.
6. Postoperatively, it can be helpful to detect unusual changes. “You can look at the cornea to see if there are unusual topographic features that were ostensibly introduced from the surgery,” Dr. Koch said.

Ocular surface

Dr. Dell explained that one of the main reasons for performing corneal topography is to ascertain the status of the patient’s tear film and anterior corneal surface. “The Placido image from a corneal topographer is valuable in assessing the quality of the anterior refracting surface of the eye. The first thing we’re using topography for is to determine whether the patient has ocular surface disease irregularity-related topographical abnormalities. Then we’re screening for pathology, like keratoconus, forme fruste keratoconus, pellucid marginal degeneration, or other things, that might influence our decision on whether the patient is a candidate for cataract surgery in the first place and if so, what type of implant he or she might eventually receive,” he said.
If a patient is found to have ocular surface disease, topography is used to follow the patient’s progress. “That’s one of the key factors in our determining whether a patient has reached an endpoint of sufficient improvement in their ocular surface disease to proceed with refractive cataract surgery,” Dr. Dell said. He uses topography in conjunction with devices like the LENSTAR (Haag-Streit, Koniz, Switzerland) and the IOLMaster (Carl Zeiss Meditec, Jena, Germany) to verify and confirm that he has achieved good readings on the patient’s overall corneal power and corneal astigmatism.
Dr. Dell screens for posterior corneal astigmatism using devices like the Pentacam (Oculus, Wetzlar, Germany) in patients who are having laser refractive surgery or corneal refractive surgery. “We don’t routinely image the posterior corneal curvature in our cataract patients because we haven’t found it to be consistently helpful, so we use nomogram-based adjustments of our toric power calculations that have been described well, either in some of the modern IOL astigmatic toric calculators or nomogram adjustments like that proposed by Dr. Koch and Li Wang, MD,” he said.

Lens calculations

Dr. Koch is using corneal topography, in combination with other tools, to determine lens calculations. “We look at the anterior corneal astigmatism, and we look at the total corneal astigmatism with the Galilei [Ziemer, Port, Switzerland]. I am also using the Cassini [The Hague, the Netherlands] for my toric IOL calculations. The Cassini works using a completely different principle because it has colored LEDs that are reflected off the anterior corneal surface, and it has seven white LEDs whose reflection off the posterior corneal surface can be detected to measure posterior corneal astigmatism. As they continue to improve their software, I’m finding it to be an increasingly valuable way of measuring total corneal astigmatism,” he said.

Abnormal corneal topography

If the corneal topography is abnormal, Dr. Koch said to look for the cause. “If it appears to be an ocular surface issue, I will look for ocular pathology, such as epithelial basement membrane disease or Salzmann’s nodular dystrophy. I may do a dry eye evaluation and treat the dry eye. If it’s epithelial basement membrane disease or Salzmann’s nodular dystrophy, and I think it will affect either the accuracy of the calculations or the quality of the vision postoperatively, I will treat that first by scraping it and letting the patient’s eye heal for about 3 months. Then I will repeat the calculations,” he said. “At that point topography again is important because subtle irregularities can persist and need to be detected to assist in patient counseling and IOL selection.”

Editors’ note: Dr. Dell has financial interests with Johnson & Johnson Vision (Santa Ana, California), Bausch + Lomb (Bridgewater, New Jersey), Presbyopia Therapies (Coronado, California), Ocular Therapeutix (Bedford, Massachusetts), Optical Express (Glasgow, U.K.), Tracey Technologies (Houston), Advanced Tear Diagnostics (Birmingham, Alabama), and Lumenis (Yokneam, Israel). Dr. Koch has financial interests with Alcon (Fort Worth, Texas), Carl Zeiss Meditec, and Johnson & Johnson Vision.

Contact information

Dell
: steven@dellmd.com
Koch: dkoch@bcm.edu

Diagnostics in refractive cataract surgery: Corneal topography Diagnostics in refractive cataract surgery: Corneal topography
Ophthalmology News - EyeWorld Magazine
283 110
220 153
,
2018-06-25T15:10:57Z
True, 7