Article

Seeing the Unseen with Swept-Source OCT

Identify unusual ocular structures before cataract surgery

After undergoing modern cataract surgery, patients expect good quality distance and near vision. Over the last few years, we’ve realized that achieving those visual outcomes depends, in large part, on how we plan cataract surgery. The more testing, imaging, and planning done in advance, the better prepared we are to produce optimal visual outcomes.

But the steps we’re taking — patient history, clinical exam, biometry, topography, refraction, acuity, slit lamp, and on and on — are only feasible if we balance them efficiently. How do we do that? I’ve found that integrating swept-source OCT (IOLM700, Zeiss) into my practice has helped me become more efficient in my approach to cataract evaluation and has enhanced my ability to identify unusual structures prior to surgery.

ADVANTAGES OF SWEPT-SOURCE OCT

Swept-source OCT technology uses a laser with variable wavelengths to generate optical B-scans (cross-sections) to determine biometric data of the eye. Swept-source OCT has several advantages over other biometry techniques. It is both high speed and non-invasive, and it allows collection of two- and three-dimensional data in hundreds of milliseconds, with high lateral resolution and axial resolution.

Those imaging strengths translate into clinical advantages for patients. Swept-source OCT measurements are more accurate, with both fixation checks and high-speed image acquisition to ensure precision. A fixation check sounds simple, but we often don’t know if patients are fixating in the line where the light is passing through the eye. The IOLM 700 visual display shows OCT visualization of the anterior structures in addition to a 1-mm foveal snapshot, all of which allow us to see whether the patient was correctly fixated (Figure 1).

Figure 1. The swept-source OCT imaging system easily shows whether an eye was fixated during measurement and imaging.

In addition to biometric data, swept-source OCT also lets us image the retina to identify pathology with an integrated OCT foveal image capture (1-mm section). Retinal evaluation is an important part of cataract evaluation today. Many times, patients come to us reporting blurry vision. We can see they have a cataract, but because the cataract obstructs our view to the back of the eye, it can be difficult to assess the eyes for macular pathology or other retinal pathology that could be contributing to the blurred vision. Patients could have diabetic macular edema, macular degeneration, epiretinal membrane, or other common problems that we need to identify and consider before surgery. You might choose to do a macular OCT on all cataract patients, premium cataract patients, or only those whose 1-mm foveal image suggests a problem.

Another major advantage that has helped with clinical efficiency and patient testing fatigue is that swept-source OCT can penetrate into dense lenses better than some other technologies. It improves workflow. More importantly, it allows us to perform fewer A-scans, which is great because patients don’t like them, and they are highly variable in precision depending upon the training level of the technician who is performing the test.

CASE STUDY: SEEING THE FULL ETIOLOGY

To illustrate how swept-source technology helps in our clinic, I want to share a case example of a patient I saw earlier this year. A 69-year-old woman was referred to us by her optometrist with blurred vision. She said the vision in her left eye was blurrier than the right, and we measured her visual acuity at 20/60 left and 20/40 right. She had significant cataract, and I could see she had a little more cataract in the left eye.

The swept-source OCT system showed that she wasn’t totally fixating at her fovea. It also showed why: she had significant subretinal fluid there (Figure 2). During a clinical examination, with a fairly dense cataract, I may have seen a loss of the foveal light reflex, but I wouldn’t see in enough detail to make that diagnosis. However, when the technician acquired the 1-mm foveal image during biometry, she detected the abnormality and performed a full macular OCT that clearly showed wet macular degeneration. Cataract surgery was not the patient’s only etiology of blurred vision, so I referred her to a retina colleague.

Figure 2. This patient’s poor fixation was attributed to subretinal fluid. Macular OCT revealed wet macular degeneration.

I’ve found that cases like this one don’t just happen every few months. They are routine. My technicians have taken ownership of ordering a full macular OCT driven by their interpretation of the 1-mm foveal OCT, and they enjoy showing physicians that they’ve found something unusual. They find it easy to acquire accurate results, and they like playing a role in patient care.

Swept-source OCT has enabled us to find appropriate candidates for premium technology in advance of cataract surgery. For example, when a patient wants a multifocal IOL and the 1-mm foveal image shows some irregularity, we get a full macular OCT. If the patient has vitreomacular traction or an epiretinal membrane, we might not want to implant a multifocal lens or, at least, we would need to have a significant conversation beforehand so if something happens post-operatively, the patient knows the problem existed before cataract surgery.

Figure 3. The swept-source OCT 1-mm foveal image capture reveals: A) macular hole, B) macular pucker, C) AMD, RPE detachment.

BETTER SURGICAL RESULTS

Swept-source OCT is a screening tool and source of biometric data. It allows us to rule out retinal pathology prior to surgery, and having OCT within the biometer has helped my efficiency in deciding who needs a comprehensive OCT image.

Clearly, the swept-source OCT’s high-resolution 1-mm foveal image reveals a great deal. I think that, in a time when we’re ordering so many tests on our patients, this is exactly the kind of insight we need to decide who needs further testing and who does not. All the data this system supplies isn’t just good for practice flow, patient experience, and exam efficiency, it’s also making me a better clinician. The ability to see and address abnormal structures before cataract surgery means that surgery is more accurate and, as such, more successful. ■