Early diagnosis, treatment of glaucoma using advanced technology is an ethical obligation
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Before the introduction of OCT, the standard of care for identifying initial glaucomatous damage was based on the physical examination.
Ophthalmologists gauged progression by an increase in the cup-to-disc ratio. Identifying and tracking these changes over time, however, were hampered by their subjective nature. Physicians often had to wait until visual field testing showed a scotoma consistent with glaucoma in order to quantify disease effect and stratify treatment.
We now know that by the time ganglion cell loss manifests as a scotoma on visual field testing, anywhere from 30% to 45% of ganglion cells have been lost. By today’s criteria, this would indicate moderate glaucoma at the very least. Before laser treatment and microinvasive glaucoma surgery were available and their value established in evidence-based clinical trials, this strategy was acceptable. Treatment with IOP-lowering drops was the early option for most, and specialists monitored patients and adjusted their medications as they saw fit. Ultimately, patients progressed to invasive surgeries.
Today, with the help of advanced OCT modalities, we can do much more than prevent patients from losing vision. We have the ability to identify disease sooner and intervene earlier — well before 30% or more ganglion cell loss. The paradigm shifts from a goal of ensuring patients lose as little vision as possible to helping patients keep as much vision as possible.
The fact that we have the ability, with the aid of modern technology, to detect disease earlier and protect vision for longer also makes it an ethical obligation to our patients that we employ these tools. In the best interest of our patients, we must find and track disease, identifying changes before noticeable vision loss occurs. We can preserve the vision of patients with glaucoma and, therefore, their quality of life for longer.
Staging glaucoma
Mild glaucoma is indicated by optic nerve abnormalities consistent with a glaucomatous pattern but no visual field defects on any visual field test. Once a patient begins to have visual field defects that are in either hemifield but not within the central 5° of fixation, that becomes moderate glaucoma. If defects progress into the central 5° or begin to involve both hemifields, severe glaucoma is present.
When it comes to mild glaucoma, the goal is to separate the normal patients from those with identifiable disease. OCT allows us to compare retinal nerve fiber layer and neuroretinal rim parameters to adjusted reference parameters. The results are displayed in color-coded graphs that indicate if the measurements are within normal limits (green), borderline (yellow) or outside of normal limits (red). With mild glaucoma, OCT shows around 1% thinning of the ganglion cell layer thickness per year (more than the 0.5% change in normal patients) in a glaucomatous pattern — a proxy for ganglion cell loss.
Capturing high-quality images
In order to get the most accurate stage, we must capture high-quality images. Improving patients’ tear film is one way that we can enhance our ability to capture high-quality images and further ensure we are making the correct diagnosis. Most of our patients when dilated, especially those who are older, have some level of dry eye. By adding artificial tears before OCT imaging, we can dramatically increase the scan quality (Figure 1).
Some OCT platforms offer other tools for ensuring accurate images. For example, Spectralis (Heidelberg Engineering) corrects the effects of ocular magnification by entering the C-curve, thus improving measurements for individual patients. For patients with abnormal axial lengths, such as high myopes or high hyperopes, we can mirror the patient’s prescription using the proper focus that will obtain clearer images. Patients with cataracts or posterior capsular opacification have less light penetrating to the retina. For them, we can increase the brightness to improve image quality.
Many patients have a hard time fixating properly. One possible solution to this can be true eye tracking that follows them as their eye moves, pauses when they blink, and consistently captures the image slice we want. This is more comfortable for the patient and more productive for the clinic. Equally critical is the ability to have this same image at every visit in order to track the smallest level of change over time.
Correct segmentation
Once we have obtained high-quality images, we also must ensure that there is correct segmentation. The platform provides tools that allow for adjusting the layers to optimize our measurements. We have the flexibility to choose the specific structures of the eye we wish to study and edit the segments. By adjusting each line, we can polish abnormalities to make a clean layer for a crystal-clear view. I use these tools when a patient has an epiretinal membrane or even the beginning of a posterior vitreous detachment. These structures can confound layer segmentation, so adjusting segmentation is a quick and easy fix.
Efficiency is crucial in our clinics. We have implemented centrally located pods with floating licenses in our clinic that let us open, view and segment patients’ images immediately, and remotely, after their OCT exam. Having verified the segmentation myself, I can be confident that any progression I see is valid, and the process does not interrupt our flow. No matter what the situation is, I have that data before I even walk into the patient room. I can start to brainstorm various management strategies and apply them on the spot with the patient, improving efficiency and streamlining the workflow (Figure 2).
Patient experience, satisfaction
Because I have analyzed the image and determined the treatment plan based on whether there are changes or not, when I see my patients, I can immediately educate them on their condition and status. If they need pressure reduction with drops, surgery or laser, treatment can begin that much faster. In today’s age of glaucoma management, we have many tools that we can employ to avoid patients losing vision needlessly. When a patient is properly educated about all the aspects of glaucoma and how we plan to manage it, they are happier, trust that they are in good hands and satisfied that they are receiving proper care.
OCT improves our clinical management of glaucoma with invaluable data, and the platform’s tools help create a more efficient workflow with easy adaptation into the clinic. We know how much of an impact glaucoma has on our patients’ quality of life. Our ethical obligation is to use technology to benefit our patients. We owe it to them.
- References:
- Hood DC. J Glaucoma. 2019;doi:10.1097/IJG.0000000000001380.
- ICD-10 glaucoma reference guide. https://www.aao.org/Assets/5adb14a6-7e5d-42ea-af51-3db772c4b0c2/636713219263270000/bc-2568-update-icd-10-quick-reference-guides-glaucoma-final-v2-color-pdf?inline=1. Updated June 2018. Accessed Dec. 14, 2023.
- For more information:
- Sanket S. Shah, MD, a comprehensive ophthalmologist in practice at InSight Vision Center, Fresno, California, can be reached at sanketsshah23@gmail.com.
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