The most common macular diseases in patients with cataract are age-related macular degeneration (AMD), diabetic retinopathy (DR), epiretinal membranes (ERM) and vitreomacular adhesion (VMA) syndromes.
When considering cataract surgery in the presence of such conditions, several factors come into play. Foremost is the visual prognosis; if, for example, there is a large, dense disciform scar and only mild-to-moderate nuclear sclerosis, surgery is unwarranted. In most cases, however, such decisions are more difficult and are informed by an understanding of the risks of surgery worsening the macular disease. The two basic mechanisms by which cataract surgery may adversely affect the macula are inflammation and mechanical.
The inflammation induced by cataract surgery causes worsening of diabetic macular edema (DME), which can result in permanent visual loss. Surgery should be delayed until resolution of the DME is achieved and, even so, an intravitreal injection of steroid or anti-VEGF agent may be given perioperatively to ‘protect’ the macula. The same is probably true for all causes of macular edema, such as retinal vein occlusion.
Similarly, wet macular degeneration is best controlled prior to performing surgery and the operation may be performed with an intravitreal injection of anti-VEGF at the same time or beforehand. Whilst there is currently consensus that cataract surgery does not induce choroidal neovascularization, some uncertainty persists as to whether the surgery causes progression of dry macular degeneration through a phototoxic effect from the operating microscope light.
In all patients, but particularly those at risk of phototoxicity (eg. AMD, Stargardt’s disease, retinitis pigmentosa), every effort is made to minimise light exposure through measures aiming for shorter surgery, using dimmer lighting and switching off the operating light at all possible times during the surgery. The increasing use of blue-filtering intraocular lenses is predicated on concerns regarding the chronic photochemical effects of long-term exposure to blue light after implantation of a clear IOL; most retinal surgeons who perform cataract surgery use blue-filtering IOLs.
There is little high-quality evidence available regarding the effect of cataract surgery on epiretinal membranes. For symptomatic ERMs in the presence of significant cataract, the operation of choice is a combined vitrectomy with ERM peel and cataract extraction. Here, the cataract extraction is necessary primarily to improve the surgeon’s view for the epiretinal membrane peel. Considering the fact that the vitrectomy itself accelerates cataract formation, many perform combined surgery to reduce the number of procedures required. This can sometimes, however, result in variable refractive outcomes for patients due to the unpredictability of the effective lens position within the eye.
Asymptomatic ERMs often require no particular attention and cataract surgery alone may readily be performed with a guarded prognosis- some patients only notice the effects of the ERM after their cataract surgery. Considering the low additional surgical risk of addressing the ERM, it may be worth performing combined surgery for ERMs that distort the fovea markedly.
Most ERMs are associated with a posterior vitreous detachment. In this case, the anterior shift in the vitreous that follows the replacement of the (thick) crystalline lens with a (thin) IOL has no effect on the macula. However, some ERMs are part of a disease spectrum known as vitreomacular adhesion (VMA), in which there is an extramacular posterior vitreous detachment but persistent attachment of the posterior vitreous face to all or part of the macula. In this situation, any anterior shift of the vitreous body following cataract surgery may result in a forward mechanical pull on the point of vitreomacular adhesion. If the VMA is broad, affecting much of the macula, the result may be a thickening of the whole macula, but if there is vitreofoveal traction alone, a macular hole may result. In VMA, therefore, there is a very strong case for either performing the vitrectomy first or concurrently.
A significant part of vitreoretinal surgeons’ practice in the past was spent salvaging disappointed cataract surgery patients. Macular disease can be very subtle and is often difficult or even impossible to detect on fundoscopy alone and even more so in the presence of cataract. Nowadays, though, this aspect of our practice is less common due to a greater understanding of the importance of macular assessment by general ophthalmologists, better treatments for macular diseases and (above all) the use of optical coherence tomography routinely before cataract surgery. Many retinal surgeons would recommend this as a routine part of any cataract assessment.