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BLOG: Refractive glaucoma surgery? Why?
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The primary concern for both glaucoma patients and the ophthalmologists who care for them is maintaining functional vision throughout life with the least amount of patient risk. A majority of our discussions about patient care and therapy revolve around this goal. The result of this process is to place refractive outcomes from cataract surgery in the back seat with the thought that “glasses will just fix” postoperative refractive error. However, when you step back to evaluate it, glaucoma patients are one of the most important subsets of patients that would benefit most from the best refractive results.
The typical “refractive” cataract patient is one who has otherwise normal anatomy and just needs intervention to return it back to baseline. This can include cataract extraction with placement of a premium IOL along with astigmatism correction as needed. They have a full visual field and can call upon any of this area to help see.
Glaucoma patients are the exact opposite of this “typical” situation. Their visual fields by definition are diminished, ranging from very mild to complete loss. The goal for them must be to maximize the visual potential that is available. This problem would seem to have a simple answer — place premium IOLs into these patients. Unfortunately, these lenses, whether it be multifocal or accommodating, do have limitations when placed in glaucoma patients and are not necessarily the best option. I explain this to my patients by telling them that without a high-definition cable line (optic nerve), the new HD TV (IOL) they want will not give the desired images.
The exclusion of these premium lenses then forces glaucoma patients to have monofocal lens correction. This selection results in the need to use bifocal (or progressive) or multiple monofocal glasses should the desired aim, whether it be for distance or near, is not achieved. Because most patients would prefer to have a single pair of glasses if possible, glaucoma patients would naturally lean toward bifocal glasses. Unfortunately, this ends up not being a simple solution because even bifocals require good functional vision in different areas of the visual field. In glaucoma patients, full fields are not the case, and as such, fitting glasses becomes difficult. For example, imagine a patient with moderate glaucoma with deficiencies in the inferior fields in both eyes. The near section of bifocals will not work as well because this patient needs to look through his glaucomatous fields to use that area.
The best way to avoid this and similar difficulties is to successfully reach the targeted aim with use of a monofocal lens. By achieving this goal, glaucoma patients are left with monofocal glasses and can use the entire lens area for a given distance when needed. Traditionally the aim for cataract surgery would be for distance, and monofocal glasses would then be used for near activities. Refractive error needs to be minimized during cataract surgery in order to reach this goal. This requires the selection of the correct power of IOL and also significant elimination of astigmatism either through astigmatic correcting lenses or corneal incisions.
Although our preoperative methods are quite reliable, sometimes measurements are not as perfect as we desire. This uncertainty is further magnified with varying surgical techniques. This leaves us with discovering residual refractive errors when the patient is next seen in clinic and not when we can do something about it while still in surgery. The use of additional measurements like intraoperative aberrometry helps mitigate this issue. Intraoperative aberrometry can be used to confirm the IOL power selected, titrate astigmatic-correcting incisions (AK or LRI), and also guide in the rotation of toric lenses to the optimal axis.
At first it seems that discussing refractive outcomes from cataract surgery does not appear to be critical in glaucoma patients. However, it can have a significant impact in the quality of life for these patients when correction is needed to achieve the best possible vision. By reducing their need for glasses despite using a monofocal lens, glaucoma patients are not placed at a further disadvantage. They already start out with reduced visual fields, which can quite possibly decrease even more during the patient’s life. The best time to intervene is before cataract surgery to talk about the technology available to us during the procedure.