Advancements in cataract surgery techniques and technologies have transformed cataract surgery from a routine visual rehabilitation procedure to more of a refractive procedure, allowing excellent visual outcomes and complete spectacle independence. Despite such advancements, unanticipated suboptimal visual outcome in some patients is a cause of substantial dissatisfaction.1,2 One of the reasons for suboptimal visual outcomes may be the presence of unrecognized retinopathies, particularly the maculopathies sheltered by cataract.3 As such, identifying the presence of a concomitant retinal pathology and estimating patients' visual potential are an important part of the preoperative cataract surgery work-up. It could also help determine whether a patient is not a candidate for a presbyopia-correcting intraocular lens (IOL) implantation.4

Ocular pathologies including macular pathologies are often found to coexist in patients presenting with cataract. Fundus biomicroscopy is a routinely performed procedure to identify clinically visible pathology in the macular region of patients with cataract. However, in some cases, macular pathologies may be confounded by visually significant cataract, other opacities of the ocular media, and associated photophobia, which may impair the detection of subtle macular pathologies using ophthalmoscopic techniques.1,5–8

Spectral-domain optical coherence tomography (SD-OCT) is the gold standard imaging tool to visualize structural changes in the retina.3 With a scanning speed of up to 25 000 A-scans/s, a scanning area of 6 × 6 mm, and a scanning depth of 2 mm, SD-OCT generates 3D scans allowing for sharp, high-resolution imaging of the retina even in the presence of dense media opacity or narrow pupil.1,9–11 Routine use of macular SD-OCT before cataract surgery is believed to potentially improve the accuracy of preoperative diagnostic process and help surgeons avoid misdiagnosis and postoperative retinal pathology surprises.1,5–8 Although all patients with cataract can potentially benefit from preoperative SD-OCT scanning to rule out macular pathologies, it is highly recommended for patients considering advanced technology presbyopia-correcting or toric IOLs to maximize visual performance and predictable outcomes.3,12

A swept-source frequency domain optical coherence tomography (SS-OCT)–based biometer (IOLMaster 700) allows performing a full-eye length tomography, depicting anatomical details on a longitudinal cut through the entire eye and providing keratometry, central corneal thickness, anterior chamber depth, anterior aqueous depth, lens thickness, axial length, corneal curvature, pupil diameter, and white-to-white measurement for cataract surgery planning.13–18 The whole scan image can be visualized allowing assessment of the eye geometry and the axis of the measurement.13 The SS-OCT biometer provides a 1 mm retinal OCT image corresponding to the point of fixation. Visualizing foveal pit on this 1 mm scan allows the surgeon to affirm correct fixation by the patient for optimal biometry measurements.15,19 Although the primary function of the “fixation check” image is to verify the visual axis in an objective way, the device can also reveal retinal anatomy information and may indicate macular abnormalities not seen clinically.13,16,18,20 As such, some surgeons tend to use the information revealed from retinal scans generated by SS-OCT biometer, IOLMaster 700 during fixation check to rule out macular pathology.2,20,21

This study was designed to evaluate the sensitivity and specificity of SS-OCT biometer, IOLMaster 700 in comparison with the gold standard SD-OCT for detecting macular pathology in patients scheduled for cataract surgery.

METHODS

This prospective, cross-sectional, observational, examiner-masked study was conducted at Eye Centers of Tennessee, Crossville, TN. The study protocol adhered to the tenets of the Declaration of Helsinki and was approved by Alpha Independent Review Board, San Clemente, CA. Written informed consent was obtained from all patients using an Institutional Review Board–approved informed consent form.

The study enrolled all consecutive patients aged 50 years and older, who underwent cataract presurgery work-up between August 2019 and March 2020. One eye of each participant was included in the study. If the participant had unilateral cataract (fellow eye clear lens/pseudophakic), the eye with cataract was the study eye, and if a participant had bilateral cataract, the eye to be operated first was considered as the study eye.

Participants with corneal disease or pathology, and advanced cataract that may impede the performance of SS-OCT or SD-OCT scans of the macula and preclude adequate imaging were excluded. In addition, patients with secondary cataract (eg, steroid-induced or trauma-induced cataract) or those participating in any other ophthalmic drug or device clinical trial during the time of this clinical assessment were also excluded.

The sample size calculations were based on the literature-reported values of sensitivity (42%) and specificity (89%) of IOLMaster 700.21 A minimum sample size of 100 participants was required for 80% power, α of 0.05, null hypothesis of area under the curve (AUC) 0.5, and ratio of 1:1 between healthy and pathologic eyes. Considering 14% images may not be clear enough to be analyzed or some others may not get included in the analysis for other reasons, a sample size of 130 participants (65 with macular pathology and 65 without macular pathology) was planned.21 A review of literature revealed a wide range of prevalence (11% to 24%) of macular disease among patients undergoing cataract surgery.2,3,5 The study site estimated the prevalence to be 10%. Accordingly, ∼650 cataract participants were evaluated (OCT imaging) to allow recruitment of 65 consecutive patients with macular pathology. Since a much higher number of participants with normal retina were evaluated, first 65 consecutive normal participants with no retinal pathology were recruited into the study.

All participants underwent a routine ophthalmic examination including dilated fundus examination and biometry scan using a SS-OCT biometer (IOLMaster700, Carl Zeiss Meditec, Inc.). The ZEISS IOLMaster 700 with swept-source biometry provides a full-eye axial length tomography that captures details, such as crystalline lens thickness, anterior chamber depth, and corneal thickness measurements of the eye, and has the latest IOL formulas. In addition, as part of this study, all enrolled patients underwent full macular OCT scans performed with the SD-OCT (Cirrus, Carl Zeiss Meditec, Inc.). Cirrus OCT is a SD-OCT system that allows for a detailed cross-sectional evaluation of the macular region even in the presence of media opacity or narrow pupil.

All SS-OCT biometer scans and SD-OCT scans were exported after deidentification (ie, without patient information, such as name, date of birth, or diagnosis). The scans of all recruited participants were assigned a 3-digit randomized identifier using a randomized number generator starting from 001, before sending the scans to 3 independent masked examiners for evaluation. For scan analysis (SS-OCT and SD-OCT scans), the following questions were asked from the examiners: (1) is the scan clear enough to be analyzed; (2) is the scan pathological (response options: normal/abnormal); and (3) if abnormal, what pathology is suspected. For SS-OCT biometer scan analysis, the examiners were also asked to rate their confidence level using a 3-point scale (low, moderate, high). To avoid the possibility of bias, examiners were also masked to the randomization ratio of healthy and pathologic scans. The analysis of the scans was performed independently, and the results were not exchanged among the examiners.

Statistical Analysis

All study data (collected on case record form) were entered in a spreadsheet for further processing and analysis. Different measures of diagnostic accuracy were calculated. Sensitivity (true positive rate) refers to the ability of a test to correctly identify an individual as “diseased” and was calculated as follows:Sensitivity=true positive/(true positive+false negative)

Specificity (true negative rate) refers to how well a test identifies patients who do not have a disease and was calculated asSpecificity=true negative/(true negative+false positive)

False positive and false negative rates were calculated asFalse positive rate=false positive/false positive+true negativeFalse negative rate=false negative/false negative+true positive

Accuracy was calculated asAccuracy=true positive+true negative/true positive+true negative+false positive+false negative

Positive and negative predicted values were calculated asPositive predicted value=true positive/true positive+false positiveNegative predicted value=true negative/true negative+false negative

The receiver operating characteristic (ROC) curves that plot the true positive rate vs the false positive rate were constructed using the online software tool created by Johns Hopkins University (http://www.rad.jhmi.edu/jeng/javarad/roc/JROCFITi.html). These ROC curves provide the trade-off between the sensitivity and 1-specificity. The AUC was calculated to assess the ability of the SS-OCT biometer device (compared with the gold standard SD-OCT device) to differentiate between eyes with pathological macula and eyes with healthy macula. An AUC of 1.0 represents perfect discrimination, whereas an AUC of 0.5 represents chance discrimination.

RESULTS

A total of 132 patients (132 eyes) were recruited into the study. Of these, 2 patients requested withdrawal from the study. For 5 patients, at least one of the examiners felt that OCT scans (either SD-OCT or SS-OCT biometer) were not clear enough to be evaluated. After excluding 7 scans, a total of 125 patients were available for analysis.

The mean age of 125 patients was 72.5 ± 8.1 (range 31 to 94 years). There were 64 female and 61 male patients. When evaluating the examiners' opinion on SD-OCT scans, in 12 eyes, at least 1 examiner had a different opinion regarding the presence or absence of macular pathology, yielding interobserver reproducibility of 90.4% (113/125). For the remaining 113 eyes, the opinion regarding the presence or absence of macular pathology on SD-OCT was identical for all the examiners. As such, sensitivity and specificity of SS-OCT biometer scans were calculated from these 113 eyes.

Compared with the gold standard SD-OCT, the true positive rate (sensitivity) of SS-OCT biometer ranged from 71.1% (32/45) to 79.2% (42/53) for the 3 examiners and the false negative rate was between 20.8% (11/53) and 28.9% (13/45). The true negative rate (specificity) ranged from 86.8% (59/68) to 94.1% (64/68), and the false positive rate was between 5.9% (4/68) and 13.2% (9/68). Table 1 presents the sensitivity, specificity, accuracy, false positive rate, false negative rate, positive predicted value, and negative predicted value of SS-OCT biometer for the 3 examiners. Figure 1, a–c shows the ROC curves corresponding to the sensitivity and specificity of SS-OCT biometer based on the evaluations by examiners 1, 2, and 3, respectively. The fitted ROC area ranged from 0.83 to 0.95.

Table 1. - Measures of diagnostic accuracy of SS-OCT biometer scans for detecting macular pathologies in 113 eyes of participants who underwent precataract surgery work-up Clinimetric parameters Examiner 1 Examiner 2 Examiner 3 Sensitivity (true positive rate) (%) 71.1 79.2 77.8 Specificity (true negative rate) (%) 86.8 91.7 94.1 False positive rate (%) 13.2 8.3 5.9 False negative rate (%) 28.9 20.8 22.2 Accuracy (%) 80.5 85.8 87.6 Positive predicted value (%) 78.0 89.4 89.7 Negative predicted value (%) 81.9 83.3 86.5

Data of 3 independent examiners are presented

Figure 1.:

The ROC curves of the SS-OCT biometer scans for discriminating eyes with healthy and pathological macula: (a) examiner 1, (b) examiner 2, and (c) examiner 3. ROC = receiver operating characteristic

DISCUSSION

Preoperative macular evaluation before cataract surgery has important prognostic implications.1 Eyes with healthy macula may be suitable for any type of IOL implantation; however, the choice of IOL in eyes with macular diseases or those at risk of macular disease may depend on the specific manifestation of macular pathology, chances of progression of the disease, patients' preferences, etc.

Advanced technology IOLs such as a multifocal IOL may not be recommended for patients with macular pathologies such as macular hole, epiretinal membrane, intraretinal fluid, and macular degeneration.22,23 Owing to their light-splitting optics, with alternating powers for distance and near, multifocal IOLs can potentially compound the visual deficits associated with the macular pathology and increase the risk for dysphotopsia.24 Incorrect treatment decisions or unrealistic expectations for postoperative visual outcome due to missed macular pathology may cause postoperative patient dissatisfaction or even legal consequences.1 This becomes even more important in patients desirous of presbyopia-correcting or toric IOL implantation.

SD-OCT is the gold standard for the diagnosis of macular disease during presurgical assessment of patients undergoing cataract surgery; however, some surgeons choose the SS-OCT biometer as a cost-effective replacement/screening tool to assess macular pathologies.3 In this study, we determined the sensitivity (true positive rate) and specificity (true negative rate) of SS-OCT biometer in comparison with the gold standard SD-OCT. For any test to be used as a screening tool, it must have high sensitivity. This is because a highly sensitive screening test has low chances of yielding false negative outcomes (ie, people who test negative while they have the disease).

Compared with the gold standard SD-OCT, the sensitivity of the SS-OCT biometer in this study ranged from 71.1% to 79.2% for different examiners. Correspondingly, it indicates that the SS-OCT biometer failed to identify the disease in 20.8% to 28.9% patients who actually also had the disease. Although the SS-OCT biometer's 1 mm retinal scan does provide some retinal information about the likelihood of macular abnormality, it is certainly not diagnostic. As such, it may not be prudent to rely only on IOLMaster 700 biometry scans as a replacement of the gold standard SD-OCT to rule out macular pathology.

Even when using the SS-OCT biometer as a screening tool (ie, SS-OCT biometer followed by SD-OCT imaging for diagnostic confirmation), only patients who were recognized as diseased (true or false positives) on the SS-OCT biometer would undergo further evaluation for macular pathologies using SD-OCT. Owing to low sensitivity (∼71% to 78% in this study; ∼42% to 68% and ∼77% to 83% as reported in the literature), patients incorrectly screened as disease-free by the SS-OCT biometer (false negatives; ∼21% to 29% in this study, ∼17% to 23%, ∼32% to 58% reported in the literature) may not undergo further testing and receive standard monofocal or premium (presbyopia-correcting or toric) IOLs.20,21 Owing to retinal issues that were actually present but were not identified while evaluating SS-OCT biometer retinal images, the patients may not show expected visual benefits postoperatively despite an uneventful cataract surgery.

In this study, specificity ranged from 86.8% to 94.1% for different examiners. Correspondingly, SS-OCT biometer images seemed to suggest that macular pathologies were present in 5.9% to 13.2% (false positives) patients who were actually disease-free. When using the SS-OCT biometer as a screening tool, such false positives will likely undergo further diagnostic evaluation and would be correctly diagnosed disease-free after SD-OCT biometer imaging.

By contrast, if surgeons rely only on the SS-OCT biometer scans, those wrongly identified as diseased would not be considered for treatment modalities they were actually eligible for, precluding them from the potential visual benefits and spectacle independence of presbyopia-correcting or toric IOLs. This may also pose a negative financial impact on the practice because the surgeon would not consider these false positive patients for presbyopia-correcting or toric IOLs, which they were eligible for due to the actually healthy macula that was not correctly identified in SS-OCT biometer scans.

The values of sensitivity and specificity showed slight variation among different examiners. This is similar to what has been documented in previous related publications.20,21 This variation from examiner to examiner may be due to the fact that identifying the presence or absence of the disease involves certain level of subjectivity, based on the skill and experience of different examiners.

The findings of this study indicate that evaluation of SS-OCT biometer images may not be as sensitive to allow them to be used for ruling out macular pathologies in patients scheduled for cataract surgery. This difference in the performance of SS-OCT biometer and the dedicated macular SD-OCT scanning devices might be attributed to the lower resolution (22 μm vs 5 μm) and smaller scanning zone (1 × 1 mm vs 6 × 6 mm). Although extrafoveal pathologies such as atrophy and epiretinal membranes are likely to be missed because of limited scan width, the SS-OCT–based biometer could potentially detect some of the centrally located macular holes and intraretinal fluid. However, it may not be totally accurate as even with best patient cooperation, SS-OCT biometer images may have artifacts and other distortions.25 In addition, the fovea appears rather flatter on the SS-OCT biometer retinal images and may be prone to erroneous interpretation.20

In conclusion, the SS-OCT biometer can provide some useful results while assessing macular pathologies during cataract work-up; however, using the SS-OCT biometer as a replacement to the dedicated macular SD-OCT scan for screening or diagnosing macular health would not be appropriate because of low sensitivity. As such, the SS-OCT biometer may potentially fail to identify approximately one-fourth of the patients (20.8% to 28.9%, in this study) who actually have the disease. Therefore, the final decision on the macular health should be based on the gold standard SD-OCT scans. When full macular SD-OCT scans are not accessible, the limited retinal scan information from the SS-OCT biometer may still provide useful insights into the macular health.WHAT WAS KNOWN Routine use of macular SD-OCT before cataract surgery improves the accuracy of preoperative diagnostic process and helps surgeons avoid misdiagnosis and postoperative macular pathology surprises. Some surgeons tend to use the information revealed from fixation-check retinal scans generated by SS-OCT biometer, IOLMaster 700 to rule out macular pathology.

WHAT THIS PAPER ADDS The sensitivity (∼71% to 78%) of SS-OCT biometer to diagnose macular pathology is not high enough to warrant its use for ruling out macular pathologies in patients scheduled for cataract surgery. The final decision on macular health should be based on the gold standard SD-OCT scans. With a false negative rate of ∼21% to 29%, the SS-OCT biometer may incorrectly identify the macula as normal when they actually have a macular pathology. These patients may not show expected visual benefits postoperatively, despite an uneventful cataract surgery with or without presbyopia-correcting or toric IOL implantation. Acknowledgments

Raman Bedi, MD (IrisARC - Analytics, Research & Consulting, Chandigarh, India) provided research, statistical, and editorial assistance in the preparation of this manuscript.

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