CATARACT/ IOL |
Better detection of macular edema by Matt Young EyeWorld Contributing Editor |
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Study uses OCT and baseline central point thickness to analyze edema  This coronal OCT scan depicts the corneal graft and placement of a glaucoma
implant tube; OCT may also be useful for detecting macular edema Source: Julian P. S. Garcia Jr., M.D.
Although optical coherence tomography (OCT) has become an important modality
in detecting macular edema (ME), until now there has been no standardized
method for detection. That is changing. A study published in the June 2008 issue of Retina,
suggests that a 40% or greater increase in baseline center point thickness
(CPT) as determined by OCT is a reliable and valid means of reporting
clinically relevant post-cataract ME. “Currently in the literature, there is no validated or universally
accepted method for reporting postcataract ME,” according to lead
study investigator Stephen J. Kim, M.D., Department of Ophthalmology,
Emory University School of Medicine, Atlanta. “Standardized reporting
of post-cataract ME would allow for uniform accounting of disease incidence
and objective assessment of treatment outcomes. More importantly, such
a definition would enable direct comparison of results among different
studies.”
Dr. Kim’s study provides a compelling argument for why the percent
increase in baseline CPT method is more reliable than others as a standardized
testing method.
Impressive data
Dr. Kim analyzed 130 eyes from two cataract surgery cohorts—one
group of diabetes patients and one group of uveitis patients and healthy
controls. Fifty eyes (38.5%) had a history of diabetes, 30 eyes (23%)
had a history of uveitis, and 50 eyes (38.5%) were healthy controls.
Eyes underwent OCT analysis within four weeks before surgery and at one
month and three months after surgery.
At one month, 18 eyes developed cystoid abnormalities (and ME) as determined
by OCT. No non-cystoid or diffuse ME surfaced, and no new ME cases appeared
at three months. “The development of post-cataract ME in this study appeared to
be an all or none event,” Dr. Kim reported. “The lowest baseline
increase in CPT for eyes with ME was 81 microns, with several eyes having
increases of more than 300 microns. In contrast, the highest baseline
increase in CPT for eyes without ME was 72 microns (one eye only), with
the remaining eyes tightly clustering around the mean baseline increase
of 8 microns. Therefore, a baseline increase of greater than 80 microns
might appear to be a valid cutoff for defining ME, but such a definition
would underestimate ME in patients at the lower end of normal baseline
CPT and conversely overestimate ME in patients at the higher end.”
Dr. Kim gave the example of one eye having a baseline CPT of 120 microns
(low normal) and a post-op CPT of 192 microns at one month.
“This 62-micron increase would not meet the greater than 80 micron
cutoff mentioned above yet was associated with a two-line loss of vision.,” Dr.
Kim noted. Percent increase in baseline CPT, in Dr. Kim’s view, has more advantages
as a standardized method to define ME. “The average percent increase in baseline CPT for eyes with and
without ME was 115 ± 67% and 6 ± 11%, respectively,” Dr.
Kim wrote. “Therefore, 3 SDs above the 6% mean for eyes without
ME is roughly 40%. Using a greater than 40% increase in baseline CPT
as a cutoff for ME accurately categorized all 18 eyes with ME (100%)
and 111 (99%) of 112 eyes without ME.”
There was one eye mistakenly thought to have ME. This eye had a 46% increase
in baseline CPT, but 20/20 vision at one month with now cystoid changes
observed by OCT. “Because the coefficient of variation of OCT is as high as 10%,
it seems plausible that an underestimation of baseline CPT in combination
with an overestimation of post-operative CPT could result in rare false-positive
results for sufficiently large sample sizes,” Dr. Kim noted. Dr. Kim suggested percent increase in baseline CPT has the following
advantages: 1) It calculates the percent change using the patient’s
own baseline and post-op CPT readings and therefore helps eliminate interpatient
and interinstitution variability. 2) It automatically adjusts for extreme
normal ranges of baseline CPT. 3) It can be adaptable for future OCT
generations. and 4) It’s simple. “Our conclusions may not be valid for instruments other than OCT
3 [OCT 3, Carl Zeiss Meditec, Dublin, Calif.],” Dr. Kim cautioned. “Nevertheless,
we are confident that our methodology can be readily validated for future
OCT versions and offers the best overall means of defining ME.”
OCT is also a better method of finding ME than other methods, said Mark
Packer, M.D., clinical associate professor of ophthalmology, Casey Eye
Institute, Oregon Health & Science University, Portland, Ore. “There’s
no question OCT is very sensitive to finding macular thickening,” Dr.
Packer said. “It’s probably better than florescein angiography.
It’s much less invasive than that.”
Still, for most patients that have normal vision after cataract surgery,
ophthalmologists can assume they have a normal macula, Dr. Packer said. The OCT is particularly useful before cataract surgery to see if someone
who is scheduled for surgery has a normal macula, Dr. Packer said. That
helps to set expectations, because even when the cataract is removed,
some patients could still experience decreased vision resulting from
ME, he said. In a world where patients are asking for multifocal IOLs
for optimal vision, setting realistic expectations is as important as
ever. Editors’ note:
Dr. Kim has no financial interests related to this study. Dr. Packer
has no financial interests related to his comments. Contact information |
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