The Early Bird Catches the Complexity
The importance of preoperative corneal and retinal disease diagnosis
When you’re seeing your patients for preoperative cataract evaluation, there are a number of conditions that can lead to erroneous measurements or variability in biometry measurements. Put simply, we must identify any retinal or corneal disease that is present at the time of the cataract evaluation. In the cornea, dry eye and ocular surface disease may not only lead to erroneous keratometry measurements, but they can also lead to patient dissatisfaction after surgery because of discomfort and visual complaints.
Cataract is only one cause of blurry vision, and in patients presenting for cataract evaluation it’s important to also judge the health of the whole eye; therefore, assessing retinal health is another important consideration. When it comes to the retina, we know that the incidence of age-related macular degeneration (AMD) increases with patient age, but there can also be underlying comorbid conditions, such as epiretinal membrane (ERM) and diabetic macular edema (DME) that can also lead to blurred vision. If those conditions are not diagnosed preoperatively, two things can happen: i) we might not be identifying the correct cause of the patient’s blurred vision or ii) we might make a different intraocular lens recommendation based on certain retinal pathology.
Here, I outline my approach to identifying retinal and corneal diseases preoperatively and share valuable clinical resources that drive my surgical and clinical decision making.
My protocol
In my postoperative clinical evaluation of cataract patients, I assess tear osmolarity and use a patient questionnaire to screen for dry eye. I routinely perform topography (Atlas, Carl Zeiss) as well as biometry using two different biometers — a swept-source (SS) OCT biometer (IOLMaster 700, Carl Zeiss) and an optical low-coherence reflectometry biometer (LENSTAR LS9000, Haag-Streit). Obtaining two sets of biometry readings allows me to confirm that there’s repeatability within the actual measurements. SS-OCT presents several advantages over other techniques to perform biometry; it’s noninvasive, high speed, and allows collection of two- or three-dimensional data in hundreds of milliseconds with high lateral and axial resolution. Given its broader functionality, I heavily lean on SS-OCT technology. It uses a laser with variable wavelengths to generate optical B-scans (cross-sections) to determine biometric data of the eye. It provides a direct measurement of total corneal power (not assumptive), also known as total keratometry (TK). This measurement combines the direct anterior and posterior corneal power measurement, allowing for more accurate corneal power measure. This value has been incorporated into intraocular lens calculation formulas, aiming to help reduce outliers in astigmatism correction and improve refractive outcomes. Another major clinical advantage of SS-OCT is that it allows me to identify retinal pathology with integrated OCT foveal image capture, which provides a 1-mm foveal snapshot. And that offers time savings in clinic as full macular OCT scans can be ordered only for those patients that show alterations in the snapshot image, rather than as a screening tool in all patients.
First case study
A 69-year-old woman presented for cataract evaluation with blurred vision in her right eye. She had 2-3+NS/2+ PSC in the right eye and PCIOL in the left eye. Her BCVA was 20/60 in the right eye and 20/25 in the left eye. Biometry using SS-OCT and A-Scan showed steep keratometry readings. The technician doing the work-up noted abnormality in the fovea on the snapshot OCT on the biometry printout and performed a full macular OCT. A diagnosis of wet AMD was made.
My clinical pearl: Integrated OCT can screen for retinal pathology and eliminate unnecessary alterations in patient work up flow to obtain OCT imaging. Macular OCT has become an important part of the premium cataract work-up, and SS-OCT biometry has made it easier to streamline OCT testing.
Second case study
A 55-year-old male presented for cataract evaluation with blurred vision and was mostly bothered by his left eye. He was 1-2+NS in the right eye and 3+NS in the left eye. He underwent myopic LASIK in 2000. His BCVA was 20/20 in his right eye and 20/50 in his left eye. His left-eye MRX was -0.75 + 1.25 X 120. Notably, it is more difficult to determine the anterior corneal power in post-refractive eyes. SS-OCT allows for integration of multi-point anterior measurements with direct posterior corneal measurements. Haigis TK in post-refractive eyes and Barrett Universal TK in non-refractive eyes has been shown to result in greater accuracy and lower mean absolute error (1). The surgical options included: i) femtosecond laser LRI or ii) toric IOL implantation to manage astigmatism. TK measurements suggested a toric IOL and anterior measurements suggested femtosecond LRI. Femtosecond LRI was performed with a 35-degree arc that was made intraoperatively. Postoperatively, the patient had 1 D of residual astigmatism, so he would have benefited instead from the toric IOL.
My clinical pearl: TK gives a more accurate assessment of true corneal astigmatism due to measurement of both the anterior and posterior cornea – this can be especially helpful to increase accuracy in post-refractive eyes.
In modern practices, we’re trying to constantly find ways to conduct a more efficient preoperative cataract evaluation. Identifying retinal and corneal pathologies preoperatively is critical, and it can inform lens selection and treatment plan. Modern devices that integrate SS-OCT help us improve our clinical flow and refractive outcomes due to their broad applications.
- E Fabian, W Wehner, “Prediction accuracy of total keratometry compared to standard keratometry using different intraocular lens power formulas,” J Refract Surg, 35, 362 (2019). PMID: 31185101.
Associate Professor of Ophthalmology at Duke University School of Medicine, Cornea and Refractive Surgery Division, and Clinical Director at the Duke Eye Center of Page Road in Durham, NC, USA.
