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Critical evaluation of retina necessary before cataract surgery
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When cataract patients report a decline in vision, it is important to correlate the visual symptoms and visual acuity to the degree of cataract present. If the patient has a large degree of vision loss but only mild cataracts, we must carefully look for the cause. In many cases, a careful examination of the retina can reveal underlying pathology such as epiretinal membranes, retinal wrinkling or macular pucker with edema.
Some studies report a prevalence of epiretinal membranes in 7% of patients older than 60 years and in 20% of patients aged 75 years or more — the prime demographic for cataract surgery.
Much of the pioneering work with epiretinal membranes was done by Gass, considered the father of macular diseases, who created a grading system and method for analysis. While mild epiretinal membranes may minimally affect vision, a more extensive lesion can cause macular distortion and can limit vision after cataract surgery and put the patient at higher risk for postoperative complications.
Examination prior to 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. Epiretinal membranes can be seen during a funduscopic examination of the retina, but 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 postoperative vision.
Gass classification
A fine cellophane-like sheen over the macula without distortion is Gass grade 0 (cellophane maculopathy), and these patients can be expected to achieve good vision after cataract surgery, especially if postop inflammation is controlled with topical steroids and NSAIDs.
Once the membrane causes distortion and wrinkling of the underlying retina, the patient may notice visual changes and acuity can drop. This is Gass grade 1 (crinkled cellophane maculopathy), and the patient would likely not achieve full recovery of vision after cataract surgery alone.
Figure 1. This patient has a mild epiretinal membrane (green bracket) and a slight amount of wrinkling (blue arrow). The patient’s best corrected vision of 20/60 corresponded well to the degree of cataract present (inset). After cataract surgery, the patient recovered 20/20 vision with no development of cystoid macular edema.
Images: Devgan U
Figure 2. This patient has a more extensive epiretinal membrane formation (green bracket) with extensive surface wrinkling and macular pucker (blue arrow). OCT examination (inset) shows distortion of the macular anatomy with associated edema and thickening. This patient would be at higher risk for further edema and decline in vision after cataract surgery.
Figure 3. This patient presented for cataract surgery with a best corrected vision of 20/200, although the cataract was mild to moderate (inset). Posterior segment examination shows a large epiretinal membrane (green bracket), extensive wrinkling (blue arrow) and macular pucker. The patient was referred for pars plana vitrectomy and membrane peeling prior to cataract surgery and eventually recovered 20/20 vision.
When the retina becomes very distorted as the epiretinal membrane expands and thickens, a macular pucker can develop, with loss of normal anatomy and leakage of vessels leading to edema. The epiretinal 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 has improved our ability to detect, measure and analyze epiretinal membranes. In cases in which an epiretinal 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 epiretinal membrane should be encouraged to seek vitreoretinal consultation prior to being considered for cataract surgery. These patients may not realize that their complaints of poor vision are due to both the epiretinal membrane and the cataract. Once the epiretinal membrane is peeled and the macular anatomy is restored, the patients can go on to have successful cataract surgery with excellent recovery of vision.