This is an age-old question in ophthalmology that still leaves cataract surgeons, retina specialists, and patients who are considering cataract surgery without a satisfactory answer. Although rigorous clinical trials have not proven an unequivocal link, a commonly-held belief by retina specialists is that cataract surgery catalyzes the transformation of dry age-related macular degeneration (AMD) to wet AMD.
This evidence/belief disconnect reminds me of the old adage that “to every rumor, lies a bit of truth.” To be sure, the highest level evidence supporting a link between the neovascular transformation of AMD and cataract surgery is conflicting. The Blue Mountains Eye Study and the Beaver Dam Eye Study both suggested that undergoing cataract surgery increases one’s risk for subsequent diagnosis of wet AMD, but as many have pointed out, the methodology of these studies makes it difficult to glean useful prognostic data for our AMD patients considering cataract surgery. Indeed, the data from these analyses suggest widely varying degrees of relative risk, while other more rigorously carried out studies (e.g., AREDS) show an absence of increased relative risk. What are we to make of these conflicting reports?
The first step is to be aware that dry AMD is present to some degree in your preoperative patient. When the appearance of the cataract is not commensurate with the degree of visual deterioration, additional testing is necessary. The easiest tests to obtain are Amsler grid testing, pinhole visual acuity, or a Potential Acuity Meter (PAM). Diagnostic evaluation of the macula with optical coherence tomography (OCT) is a simple and non-invasive method of determining the presence of macular pathology. If signs of wet AMD are detected on the OCT scan (subretinal fluid, cystoid macular edema, or a pigment epithelial detachment), it is prudent to obtain a fluorescein angiogram (FA) to refine the diagnosis. Certainly a new diagnosis of wet AMD will result in a postponement of the patient’s cataract surgery until the wet AMD has stabilized, vision has been optimized, and the residual visual decline is felt to be due to cataract.
Studies like AREDS have given us useful prognostic indicators to evaluate the extent to which a patient is at risk to progress from dry AMD in one or both eyes to advanced AMD in one eye over the next 5 to 10 years. In addition to the published evidence, I like to assess the degree of irregularity of the outer retinal contour on OCT. In my experience, a perfectly linear RPE-Bruch’s membrane complex on OCT generally confers a low likelihood of conversion of dry AMD to wet AMD in the short-term. By contrast, an OCT scan that demonstrates an RPE-Bruch’s membrane contour with a sawtooth-like configuration is a poor prognostic indicator for neovascular transformation (anecdotal clinical experience).
Does this mean that we would advocate cataract surgery for the first patient (linear OCT appearance), but no cataract surgery for the second patient (sawtooth-like OCT appearance)? Not necessarily. Because good prognostic evidence is lacking for patients of varying dry AMD severity undergoing cataract surgery via contemporary small incisional phacoemulsification techniques, the physician needs to simply inform the patients that neovascular transformation is a possibility and what that means for the patient. What that means for the patient is well known. The natural history of neovascular AMD is associated with continually declining vision over several years and eventual irreversible damage via disciform scar formation.
With early diagnosis and early treatment intervention with intravitreal vascular endothelial growth factor (VEGF) inhibitors like ranibizumab (Lucentis, Genentech) or off-label bevacizumab (Avastin, Genentech), excellent visual outcomes can be achieved. Managing patient expectations in the presence of preexisting AMD will help the patient cope with eventual worsening of the patient’s central vision or to help the patient decide whether cataract surgery is right for them.
What I tell my patients is to first gauge their visual disability (ability to read, drive, or do their favorite hobbies). I then try to help them determine how much of this visual disability is due to AMD and how much is due to cataract. For the patients who I believe are more at risk for neovascular transformation, I inform them of this possibility and stress the importance of retinal re-evaluation within the early post-operative period. The reason for this early postoperative retinal evaluation is that patients may have poor visual acuity in the first few weeks following cataract surgery due to new wet AMD appearance that may be erroneously attributed to other causes and therefore result in a delayed wet AMD diagnosis and poorer prognosis.
So, while the exact risk that cataract surgery confers upon the dry AMD patient remains unknown, what is important is that the patient’s expectations be carefully managed and that the specter of neovascular transformation be constantly suspected in the early postoperative period.
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