Glaucoma, cataract combination poses special challenges

September 15, 2013

Patients with glaucoma undergoing cataract surgery require consideration of a number of factors to ensure optimal outcomes postoperatively.

Take-Home

Patients with glaucoma undergoing cataract surgery require consideration of a number of factors to ensure optimal outcomes postoperatively.

 

Dr. Hill

By Lynda Charters; Reviewed by Warren E. Hill, MD

Mesa, AZ-With increasing patient age, the prevalence of glaucoma increases markedly. This-combined with the fact that in excess of 3 million people are estimated to undergo cataract surgery in 2013 in the United States-means that surgeons must anticipate the requirements of this patient population.

Warren E. Hill, MD, recommended how to approach these patients.

Dr. Hill, who is in private practice in Mesa, AZ, pointed out that in patients older than 80 years, the prevalence of glaucoma is 6.3% in Caucasian patients, 8.9% in Hispanics, and 10.7% in Blacks compared with 2.2%, 3.2%, and 7.8%, respectively, in patients under 74 years of age.

Axial length

Changes in axial length (AL) related to glaucoma surgery, he noted, is an important factor. With mild transient IOP lowering after glaucoma surgery, there can be a 0.25-mm decrease in AL that often returns to the preoperative value; with a moderately low IOP, a greater decrease in axial length might occur.

In patients with transient hypotony, there can be a 0.35-mm or greater decrease that can gradually increase as the IOP increases. In prolonged hypotony, the AL can sometimes decrease by more than 2 mm and this usually stays lower than the preoperative value.

These AL changes, of course, affect the IOL power calculations; for example, a decrease in AL of 0.33 mm translates into a 1 D hyperopic shift, Dr. Hill said, depending on the original axial length.

He recommended that if a combined procedure is planned and the IOP will be very low, the surgeon should target myopia rather than plano.

“Hitting the refractive target may not be possible and the refractive error can change over time,” he said.

In patients with high to extreme myopia (AL, > 25 mm), Dr. Hill recommended adjusting the optical axial length. He uses the Wang-Koch axial length adjustment algorithm with the Holladay 1 formula: Adjusted AL = 0.8814 X ALoptical + 2.8701.

By entering an adjusted AL into an optical biometer (IOLMaster, Carl Zeiss Meditec; or Lenstar, Haag-Streit), using the Holladay 1 formula, and selecting an IOL that provides the least minus, the number of eyes with a hyperopic outcome can be minimized.

In eyes with high to extreme hyperopia, he recommended using modern formulas and pointed out that theoretical formulas can only use an estimated effective lens power (ELP). The higher the power of the IOL, the more sensitive the ELP is.

While myopic errors for high axial hyperopes are common, it becomes less of an issue when using the advanced Haigis, Holladay 2, and Olsen formulas.

IOLs

When patients with glaucoma opt for implantation of a diffractive multifocal IOL, there is often a decrease in contrast sensitivity associated with glaucoma that can be problematic over the long term. In their own right, diffractive optics multifocal IOLs represent a compromise with a decrease in contrast sensitivity. Decreased contrast sensitivity is associated with increased disability in patients with glaucoma.

Dr. Hill cited the results of a 2006 study by Batiste et al. who reported that “decreased contrast sensitivity is an important determinant of why patients with glaucoma have difficulty performing the tasks of daily living.  Measuring contrast sensitivity may be more important than more standard methods of assessing the well-being of patients with glaucoma.”

Toric IOLs may work well in patients with glaucoma if post-trabeculectomy refraction and IOP are stable. With these IOLs, there is no IOL-induced contrast sensitivity compromise.

However, a combined trabeculectomy and toric IOL implantation can provide varying outcomes. Toric IOLs provide the best outcomes in eyes with regular symmetrical astigmatism.

Dr. Hill advised surgeons to calculate the surgically induced astigmatism and consider including the posterior corneal astigmatism.

Preoperative corneal astigmatism

When measuring the preoperative corneal astigmatism, he uses a two-step approach: determine the orientation of the steep and the flat meridians and measure the power difference between the two meridians. The corneal measurements for calculating the spherical IOL power and the measurements for the toric IOL may be obtained differently.

“Multiple methods may be useful for confirmatory purposes, but resist the temptation to average multiple measurement methods,” he said. “Multiple measurements do not always correspond.”

Myopic LASIK and PRK

A key factor in patients who have undergone myopic refractive procedures is that glaucoma may be detected late.

In addition, glaucoma plus increased higher order aberrations and cataract result in decreased contrast sensitivity.

Another consideration is that IOL power calculations are not uniformly accurate. Importantly Dr. Hill advised using the ASCRS post-keratorefractive surgery calculator available on the ASCRS website (www.ascrs.org).

He also advised using IOLs that add negative spherical aberration for patients that have previously undergone myopic refractive procedures. Diffractive multifocal IOL implantation results in loss of contrast sensitivity.

Warren E. Hill, MD

E: hill@doctor-hill.com

Dr. Hill has no financial interest in any aspect of the subject matter.

 

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