INTRODUCTION

With increased life expectancy and technological developments, cataract surgery has become one of the most frequent surgeries in developed countries. The development of accommodative, toric and multifocal intraocular lens (IOL) technology has made cataract surgery a refractive procedure and, in many cases, a solution for presbyopia. In parallel, expectations and demands of patients have also grown.

Macular disease is a relative contraindication for multifocal IOL implantation. On one hand, multifocal IOLs are known to reduce contrast sensitivity, and if this is added to a decrease in retinal sensitivity due to occult macular disease, it can result in a significant reduction in patients' visual function, especially under scotopic conditions. On the other hand, choosing a premium lens can entail increased economic cost and increased patient expectation.

Thus, macula evaluation is an essential part of the preoperative study of patients who are candidates for cataract surgery, especially when considering multifocal IOLs.

PRE-CATARACT SURGERY MACULAR EVALUATION

One of the key points before cataract surgery is the detection and documentation of pre-existing macular disease. Ocular fundus evaluation by slit-lamp indirect binocular biomicroscopy under pharmacological mydriasis is the essential clinical examination that should be performed in all cataract surgery patients and may be complemented by retinography. However, subtle macular pathology may go unnoticed in this examination of the ocular fundus, especially when opacity of media exists. In this context, and when there are doubts or impossibility to analyze the ocular fundus, angiography, ultrasound and optical coherence tomography are complementary means to the objective examination.

OPTICAL COHERENCE TOMOGRAPHY

Optical coherence tomography (OCT) is a well-tolerated, non-invasive, and widely available technology today that has been used over the past two decades to assess macular structure prior to cataract surgery in patients with suspected retinal disease.

The evolution of OCT technology in recent years, first with the appearance of the first spectral domain devices (OCT-SD) and later with swept source technology (OCT-SS), has enabled a faster acquisition of images with better axial resolution (up to 5 μm). The longer wavelength of swept-source devices offers even better penetration in less transparent optical media, such as cataract or hemovitreous.

Several studies published in recent years have evaluated the potential of routine posterior segment OCT in the preoperative evaluation of cataract surgery for the detection of occult macular pathology.

In the study by Enright et al in 140 cataract surgery patients, the OCT detected 10% clinically non-evident maculopathy1. Moreira et al2 found that in 98 patients the OCT, performed 5 hours before cataract surgery, detected in 10 eyes (9.8%) maculopathy not documented by indirect binocular ophthalmoscopy. Also, Creese et al3 in an Australian case series with 218 eyes, reported that the OCT allowed to detect macular anomalies in 10 eyes (4.6%). In this series, it was decided to cancel or postpone cataract surgery based on OCT results in 5 eyes of 4 patients with diabetic macular edema, exudative macular degeneration, epiretinal membrane and macular hole.

Klein et al4 recently performed preoperative OCT-SD evaluation in patients with cataract surgery with advanced technology IOL implantation (toric and multifocal). They included 149 patients in whom anamnesis and objective fundus examination had excluded macular pathology. OCT detected occult macular pathology in 13.2% of cases. The most frequently diagnosed pathologies were age-related macular degeneration (AMD) in 5.66% of cases and epiretinal membranes (4.15%). Subgroup analysis also showed that those patients who were most likely to have occult macular disease were male smokers or former smokers and those with a history of heart disease.

In summary, recent studies show that routine use of posterior segment OCT can reveal in 4.6-13.2% of cases clinically undetectable macular pathology. In order to recommend OCT in all cataract surgery patients, additional studies are also needed to assess the cost-effectiveness of the measure and the financial burden on health systems. In any case, it will be prudent to perform this test on all patients who are applying for premium lens surgery to ensure the best and most effective procedure and to better manage patient expectations.

HOW TO ANALYZE PREOPERATIVE POSTERIOR SEGMENT OCT

The latest posterior segment OCT appliances with spectral-domain and swept-source technology enable volumetric data acquisition that can generate several dozen tomograms. Thorough data analysis often requires the use of software that is not always available to the ophthalmologist when observing the patient.

In clinical practice, often only a few tomograms are printed, and analysis is restricted to the available images. It is therefore important to create image selection protocols that allow a thorough analysis of the examined area and prevent macular pathology from being overlooked.

Systematic examination of macular OCT should result in:

• Map analysis of macular thickness;
• At least one pair of perpendicular tomograms centered in the fovea;
• One or more linear tomograms of detected areas of interest;
• Analysis en face.

The macular thickness map (Figure 1) allows a simple and rapid identification of focal areas of thickness change that may indicate the presence of pathology and direct subsequent analysis with high resolution tomograms.

En face analysis, available on most spectral-domain and swept-source OCT devices, allows for fundus images that respect the retinal anatomy according to the selected segmentation. While analysis of only one or two tomograms may cause a more subtle pathology such as the epiretinal membranes to go unnoticed, en face analysis ensures analysis of a wider area and minimizes this risk (Figure 2).

MICROPERIMETRY

The current assessment of the ocular fundus in patients who are candidates for cataract surgery, either through fundus, retinography or OCT, is only structural. From these images one has to infer whether or not there is retinal dysfunction that may compromise the surgical outcome. On the other hand, these methods can detect lesions that are not significantly functional, and in these cases, patients are ruled out of the choice of a premium intraocular lens, which in fact they could have taken advantage of for many years.

It is therefore interesting to have evaluation methods that allow a functional characterization of the retina. Classically, the potential function of the retina could be assessed by inaccurate tests such as the study of color vision, retinometry by interferometry or by electrophysiology.

Microperimetry is a noninvasive diagnostic technique that also allows functional retinal characterization through spatial mapping of retinal sensitivity in the macular area. It enables direct observation of the ocular fundus, with retinal capability as well, and makes real-time compensation of eye movements. It measures the spatial variation of retinal sensitivity and objectively assesses the stability of the retina.

In a recent study, Klyce et al evaluated 10 candidate cataract surgery eyes with the MAIA microperimeter (Centervue)5. Two patients showed macular abnormalities in the microperimetry study before and after surgery: one patient had decreased mean retinal sensitivity, and one patient showed changes in the metric of fixation and demonstrated eccentric fixation. Both eyes had worse postoperative visual performance after uncomplicated cataract surgeries. These authors consider that the potential benefit of this technique is that functional impairment can be excluded in patients with known mild structural changes.

At the Department of Ophthalmology, Hospital da Luz Lisboa, the MP-3 (Nidek) microperimeter has already been used in the preoperative and postoperative evaluation of cataract surgery. In a case analyzed with this technology, a 51-year-old woman with bilateral cataract, and considering a multifocal IOL, the en face OCT study showed a macular epiretinal membrane in the RE (Figure 3).