We must critically evaluate the retina before cataract surgery.
When our cataract patients report a decline in vision it is important to correlate their visual symptoms and current visual acuity to the degree of cataract present. If the patient has only mild cataracts but a large degree of vision loss, we must carefully look for other causes of the decline in acuity. In many cases, a careful examination of the retina can reveal underlying pathology like epi-retinal membranes, retinal wrinkling, and macular pucker with edema.
Epi-retinal membranes are relatively common, with some studies reporting a prevalence of 7% of patients over the age of 60 and as many as 20% of the patients aged 75 or more. This is the prime demographic for cataract surgery patients. Much of the pioneering work with epi-retinal membranes was done by J. Donald Gass MD, considered the father of macular diseases, who created a grading system and method for analysis. While mild epi-retinal membranes may minimally affect the vision, a more extensive lesion can cause macular distortion and can limit the vision after cataract surgery and put the patient at higher risk for post-operative complications.
Clinical examination prior to cataract surgery
In addition to noting a cataract that correlates to the level of visual impairment, the clinical examination should involve a detailed evaluation of the posterior segment. Epi-retinal membranes can be seen during a funduscopic examination of the retina, though in the early stages the changes can be very subtle and easy to miss, particularly when the ophthalmologist’s view is blurred due to the cataract. The surgeon must reinforce to the patient that cataract surgery will only correct the cataract and perhaps the refractive state of the eye, but any other underlying ocular conditions could still limit the patient’s post-operative vision.
A fine cellophane-like sheen over the macula without distortion is Gass Grade 0 (cellophane maculopathy – Figure 1) and these patients can be expected to achieve good vision after cataract surgery especially if post-op inflammation is controlled with topical steroids and NSAIDs.
Once the membrane causes distortion and wrinkling of the underlying retina, the patients may notice visual changes and acuity can drop. This is Gass Grade 1 (crinkled cellophane maculopathy – see Figure 2) and the patients would likely not achieve full recovery of vision after cataract surgery alone.
When the retina becomes very distorted as the epi-retinal membrane expands and thickens, a macular pucker can develop with loss of normal anatomy and leakage of vessels leading to edema. The epi-retinal membrane will likely account for more of the visual deficit than the cataract in Gass Grade 2 (macular pucker) and the patient should be referred for pars plana vitrectomy with membrane peeling before cataract surgery. In some cases, if the cataract is so opaque that it precludes an adequate view of the retina for membrane peeling surgery, the cataract surgery can be done concurrently with the vitrectomy or just prior to it.
Optical Coherence Tomography
Because it provides a more detailed view of the macula, optical coherence tomography (OCT) has improved our ability to detect, measure, and analyze epi-retinal membranes. In cases where an epi-retinal membrane is noted on funduscopy, an OCT scan can show the extent of membrane, the degree of retinal wrinkling and distortion, and the amount of edema present. It can also quantify these changes in order to facilitate comparison with subsequent exams to monitor progression or resolution.
Patients with significant macular pucker, distortion, and edema from the epi-retinal membrane should be encouraged to seek vitreo-retinal consultation prior to being considered for cataract surgery. These patients may not realize that their complaints of poor vision are due to both the epi-retinal membrane and the cataract. Once the epi-retinal membrane is peeled and the macular anatomy is restored, the patients can go on to have successful cataract surgery with excellent recovery of vision.
Recommended further reading:
Agarwal A and Gass JDM: Gass’ Atlas of Macular Diseases, 5th edition. Volume 1. Elsevier Health Sciences, 2011.
Gass JDM. Macular dysfunction caused by epiretinal membrane contraction. Stereoscopic Atlas of Macular Diseases: Diagnosis and Treatment. Vol 2, 4th ed. St Louis, Mo: Mosby; 1997:938-50.