Cataract: Back to basics
September 2022
by Liz Hillman
Editorial Co-Director
Continuing with the “Back to basics” theme of this issue, EyeWorld spoke to Dagny Zhu, MD, and Steve Charles, MD, for a primer on interpreting OCT of the macula and optic nerve in preparation for cataract surgery.
The cataract surgeon is primarily using OCT to detect retinal or glaucoma pathology that could affect whether a patient is a candidate for a premium, presbyopia-correcting IOL. If pathology is detected for the first time that potentially requires treatment, they refer the patient to a retina specialist.
“If you diagnose an issue that you think will be limiting vision, you refer to a retina specialist for their intervention. I think the cataract surgeon should be good at some of those basic diagnoses,” Dr. Zhu said. “With glaucoma, it can be tricky whether the patient truly has glaucoma or not, so I might refer to a glaucoma specialist for clearance on whether they are a glaucoma suspect rather than an actual glaucoma patient.”
Dr. Zhu said she uses the Optovue Avanti OCT device. This device does the basics that she needs—OCT of the macula and optic nerve head—in addition to anterior segment OCT, which can be helpful when there’s a need to look at the angle and/or cornea. Epithelial thickness mapping is another useful feature that can help diagnose subclinical keratoconus or epithelial basement membrane dystrophy, both of which can affect finalvisual outcomes.
Dr. Zhu said she does OCT on all cataract and refractive lens exchange patients. She thinks that because it’s an out-of-pocket expense, not all cataract surgeons do it.
“I treat everyone as a potential premium IOL candidate when they walk through the door, so I get an OCT on everyone even before I see the patient to confirm that a multifocal or trifocal IOL is an option for them. If an abnormality is detected, depending on the extent of posterior pathology, we may limit the options to an extended depth of focus IOL or monofocal IOL instead. Even if we end up using a monofocal IOL, the OCT gives you an idea of the visual potential of the patient. You can counsel them on what their vision might be after cataract surgery because if you find a thick epiretinal membrane or signs of geographic atrophy, their vision might not be as good as you would expect after cataract surgery, and they might be disappointed. An OCT is also helpful in counseling the patient on whether they may need an additional intervention before or after surgery, for example, anti-VEGF injections prior to cataract surgery in an eye with diabetic macular edema or wet age-related macular degeneration to reduce the chances of postop inflammation,” she said.
Dr. Charles emphasized that he thinks OCT should be obtained for all cataract surgery candidates as well and said he also recommends OCT at every office after cataract surgery.
OCT primer
- Familiarize yourself with what a normal OCT of the macula looks like. “Refresh yourself on the different layers of the retina,” Dr. Zhu said. “Oftentimes it’s easy to miss pathology in the inner and outer layers of the retina. If it’s mild atrophy, you might not pick up on the missing retinal layers if you aren’t familiar with what a normal OCT looks like. Sometimes you’ll see a subtle localized RPE defect, and that’s a sign of long-standing atrophy.”
- Consider but don’t necessarily rely on retinal mapping features. “If you’re not good at interpreting each layer, you can use the retinal mapping features on OCT. It will pull up a picture for you and flag areas of atrophy as red. … The healthy areas are green,” Dr. Zhu said, adding that she prefers to scroll through every slice of the OCT herself to better localize defects.
Dr. Charles said he does not advise using thickness maps or pseudo-color. “Review all black and white B-scan slices,” he said. “Do not import a technician-selected single image into EMR; use native imaging software.” - Look at more than one area. Dr. Zhu has her technicians print out the sheet with multiple slices for her review, so she doesn’t miss relevant pathology. “I think it’s important to capture as many slices as possible. Sometimes the surgeon doesn’t have time to sit there and scroll, so you’re relying on the technician to print out the best image for you, and some will print out that one view with the one slice of the fovea and you miss out on the other pathologies. Get the multi-grid view printed, if possible,” she said, adding that anything near the fovea will affect central quality of vision. Dr. Zhu said that patients with parafoveal epiretinal membranes on the outside of the macula or a scar just outside of the fovea could still be candidates for presbyopia-correcting IOLs in some cases.
What to look for
In general, Dr. Charles said cataract surgeons should be looking for macular degeneration, diabetic macular edema, central serous chorioretinopathy, epi-macular membranes, macular holes, and vitreomacular traction syndrome on OCT. He also said it’s important to assess the optic nerve for RNFL loss secondary to glaucoma.
“Many macular disorders are invisible on retinal examination with the slit lamp and 90 diopter lens, Optos wide-angle imaging, [and] indirect ophthalmoscopy,” Dr. Charles said.
Dr. Zhu said OCT can start picking up pathology in the vitreous. OCT can detect vitreous opacities, posterior vitreous detachment, or impending vitreous detachments.
“You can diagnose that on OCT, depending on how the hyaloid face is attached. Sometimes it’s completely separated from the retina. If you see these thick vitreous opacities, that’s a sign that the vitreous might be turbid, and it may not give the best vision with a multifocal IOL,” she said. “The other thing is if you see an impending posterior vitreous detachment where the hyaloid is just detached at one part, but the other part is about to detach, you might want to counsel those patients about floaters postop because cataract surgery may induce them.”
Dr. Zhu said this information is valuable for highly myopic eyes as well. If OCT shows the patient already had a PVD, their risk for retinal tears is lower. If the hyaloid face is still attached, cataract surgery could induce PVD, and they might be at higher risk for a postop retinal tear.
“With highly myopic patients, I almost always send them to a retinal specialist for clearance before cataract surgery, just to make sure that we’re not missing any tears or holes in the periphery. Typically, if they have an axial length of greater than 25–26, I will send them for preop clearance. It’s not uncommon for the retinal specialist to find holes or severe lattice in the periphery that patients never knew about, and they laser them the same day,” Dr. Zhu said.
At the macula, Dr. Zhu said she looks on OCT for epiretinal membranes, especially thick ones on top of the fovea that would be vision limiting, avoiding presbyopia-correcting lenses in these cases. She said she may even refer the patient to retina if she thinks their vision could be improved with treatment. In diabetics, she is looking for hard exudates and macular edema. If the patient has macular edema preop, she sends them to retina for anti-VEGF treatment before cataract surgery. She is also looking for AMD. A single drusen here and there might not impact vision, but confluent drusen throughout would signify the patient would not be a good candidate for a premium IOL and one who should be referred to retina.
[template id=14580]When looking at wet AMD, Dr. Zhu said there will be signs of intraretinal fluid, subretinal fluid, and/or the presence of choroidal neovascularization.
“Those are patients you want to refer to retina right away, before cataract surgery, as they usually need an anti-VEGF injection because they can lose vision quickly. If the retina specialist can stabilize that part of the disease, they can have cataract surgery more safely,” she said.
Other than that, Dr. Zhu said surgeons should be looking for scars from previous infection or trauma. Macular holes are another pathology that’s commonly seen.
“Sometimes the patient will have a partial thickness hole, which doesn’t affect vision much, but sometimes they have a full thickness hole that severely degrades vision and may benefit from surgical repair by a retina colleague, usually after cataract surgery,” she said.
Dr. Zhu said she doesn’t typically get an OCT of the optic nerve as she relies more on biomicroscopy to examine the neuroretinal rim. If the patient has a large cup-to-disc ratio, she will get an OCT of the optic nerve head and a visual field to assess for glaucomatous changes.
“OCT helps you differentiate between a glaucoma suspect and a patient who truly has glaucoma, or at least it helps you decide whether you need to refer to a glaucoma specialist to make that ultimate decision,” she said. “That diagnosis will affect your discussion on IOL selection with the patient.”
About the physicians
Steve Charles, MD
Charles Retina Institute
Germantown, Tennessee
Dagny Zhu, MD
NVISION Eye Centers
Rowland Heights, California
Contact
Charles: scharles@att.net
Zhu: dagny.zhu@gmail.com
