Pre-operative optical coherence tomography macula: An indispensable investigation to predict post-operative outcomes

INTRODUCTION

Cataract is the leading cause of blindness in the world with the World Health Organization estimating that nearly 17.7 million suffer from cataract and the number only keeps increasing as the world population grows.^[1]

Cataract surgery has been revolutionised with the introduction of phacoemulsification, femtosecond laser-assisted cataract surgery,^[2] correction of corneal astigmatism and the use of premium intraocular lenses^[3] to get the best post-operative visual outcomes.

Often due to media opacities and inadequate pupil dilatation for detailed evaluation, subtle macular changes cannot be identified on routine fundoscopy. These undiagnosed macular pathologies may result in erroneous treatment decisions, leading to suboptimal visual outcomes. Hence, identifying these subtle changes become of prime importance to the operating surgeon and aid in managing the modern-day cataract patient’s expectations.

Optical coherence tomography (OCT) is a non-invasive imaging technique which utilises Michelson’s interferometry principle. It is an optical analogue of ultrasound imaging that uses low coherence interferometry to produce cross-sectional images of the retina^[4] and is a critical tool in the diagnosis and monitoring of ocular disease involving the retina, choroid and optic nerve.^[5] OCT permits evaluation of tissue pathology at the cellular level, achieving a resolution of 2–3 μm and can image through most media opacities including vitreous haemorrhage, cataract and silicone oil.^[6]

In spectral domain (SD) OCT, the light composing the interference spectrum of echo time delays is measured simultaneously by a spectrometer and a high-speed charge-coupled device, thereby the information of the full depth scan can be acquired within a single exposure. SD OCT’s higher acquisition speeds allow for a shift from two-dimensional to three-dimensional (3D) images of ocular anatomy.^[5]

MATERIALS AND METHODS

The required permissions to conduct a hospital-based cross-sectional study were obtained from the Institute’s Human Research Ethics Committee before the commencement of the study.

Patients visiting the ophthalmology OPD to undergo pre-operative evaluation for cataract surgery in a tertiary care government hospital in South Gujarat, India, and consenting to be subjects of the study were enrolled. They were evaluated during a period from July 2019 to September 2020 and were examined thoroughly as per the protocol.

Patients included in the study were individuals aged above 40 years of age with immature cataracts, a normal appearing macula on fundoscopy and giving informed written consent to be a part of the study.

Patients with mature and dense posterior subcapsular cataracts which preclude capturing of OCT images, preexisting retinal or macular pathologies and patients who have already undergone treatment for retinal disorders (intravitreal injections/vitreoretinal surgeries/LASER treatment) were excluded from the study.

The participating patients underwent establishment of best-corrected visual acuity by an illuminated Snellen’s chart at 6 m distance and near vision measured with Roman’s near vision chart, anterior segment examination and cataract grading using slit lamp, dilated (with 0.5% tropicamide) posterior segment examination using direct and indirect ophthalmoscope (Heine Omega 500 LED, Munich, Germany), slit-lamp biomicroscopy of the fundus using + 78D lens (Volk double aspheric lens, USA). Fundoscopy in the OPD was carried out by consultant general ophthalmologists.

Patients with a normal fundoscopic appearance on biomicroscopy underwent OCT Macula by SD OCT using Topcon 3D OCT-1 Maestro (Topcon Europe, Netherlands).

The 3D macula protocol was used on OCT for macular thickness measurements. It consists of a raster scan composed of 256 × 256 (vertical × horizontal) axial scans covering an area of 6×6 mm² in the macular region. It identifies the layers of the retina and determines macular thickness by measuring the distance between the inner limiting membrane and the inner boundary of retinal pigment epithelium (RPE) in each of the nine regions.^[7]

RESULTS

Three hundred and ten eyes of the 200 study participants were included in the study. The mean age of the 200 study participants was found to be 60.6 ± 9 years of age, with the minimum age being 40 years and maximum being 85 years of age. The maximum number of patients was in the age group of 60–69 years and the least number of patients were in the age group of ≥80 years. Among them, 107 (53.5%) were male and 93 (46.5%) were female [Chart 1].

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Chart 1:

Age-wise distribution of the study participants.

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In the present study, 245 eyes were labelled as normal on clinical examination which was found to be consistent with the OCT findings. Fundoscopy failed to identify subtle macular pathologies in 65 eyes.

Among the identified pathologies, the most common finding was the presence of an epiretinal membrane (ERM) which was found in 22 eyes. Other OCT findings were pigment epithelial detachment [Figure 1] (n = 14), drusen (n = 9), lamellar macular hole (n = 5), vitreomacular traction [Figure 2] (n = 5), IS-OS junction abnormalities (n = 4), RPE alterations (n = 2), juxtafoveal telangiectasia (n = 1), foveal thinning (n = 1), pseudovitelliform lesion (n = 1) and spongy oedema (n = 1) [Chart 2 and Table 1].

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Figure 1:

Optical coherence tomography showing pigment epithelial detachment.

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Figure 2:

Optical coherence tomography showing focal vitreomacular traction due to ERM.

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Chart 2:

Distribution of abnormal optical coherence tomography findings.

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Drusen were identified in 9 (2.90%) eyes. Of these, two eyes had subfoveal drusen and one eye had a juxtafoveal drusen. The previous studies have found that patients with drusen have a higher risk of developing exudative AMD,^[8] thus the diagnosis of drusen identifies such patients at risk.

DISCUSSION

Based on defined inclusion and exclusion criteria, 200 patients undergoing routine pre-operative evaluation for cataract surgery in a tertiary care hospital in South Gujarat between July 2019 and September 2020 were enrolled in our study. Three hundred and ten eyes had normal fundoscopy findings on fundus biomicroscopy.

Sixty-five (20.96%) eyes were diagnosed with abnormalities on OCT macula scans which were undiagnosed on routine fundoscopy.

In Neto et al.^[9] study conducted in 2015, 98 eyes of 98 patients were evaluated and underwent SD-OCT 5 h before surgery. OCT preoperatively diagnosed macular disease in 21 eyes (21.4%). This value was found comparable to our study.

In Weill et al.^[10] study conducted in 2018, 453 eyes of 453 patients were enrolled in the study and underwent SDOCT macula. Among these eyes, 22.8% of them were found to have macular pathologies which were previously missed on fundoscopy.

In Huang et al. study^[11] conducted in 2017, 1176 eyes of 1176 patients underwent a pre-operative OCT macula. One hundred and eighty-four eyes were excluded from the study due to poor scan quality. Among them, 294 (25%) eyes showed macular pathologies.

In Kowallick et al.^[12] study conducted in 2018, 174 eyes of 133 patients were enrolled in the study. Twelve eyes of 10 patients were excluded from the study due to poor OCT scan quality. One hundred and sixty-two eyes underwent successful SD-OCT macula. Among these, 20 eyes (12.35%) had pathologies with potential impact on visual outcome. They also classified 69 eyes (42.59%) as eyes with degenerative vitreous changes without any impact on visual outcome.

In Zafar et al.^[13] study conducted in 2016, 155 eyes of 155 patients were included in the study and underwent SSOCT, of these 17 (10.9%) eyes showed macular pathologies.

In Klein et al.^[14] study conducted in 2016, 265 eyes of 149 patients were evaluated and underwent SD-OCT macula. Among these, 35 (13.2%) eyes showed macular abnormalities.

In Sudhalkar et al.^[15] study conducted in 2018, 1539 eyes were enrolled in the study. Seventy-five eyes (4.87%) precluded OCT scan imaging and were excluded from the study. Out of the 1444 eyes, 133 (9.2%) eyes showed macular abnormalities.

In the present study, out of the 310 eyes evaluated with OCT macula, 22 (7.09%) eyes showed an ERM. One eye showed an ERM with traction resulting in a lamellar macular hole (ERM with LMH). One eye showed an ERM in the presence of subretinal fluid.

In Kowallick et al.^[12] study, out of the 162 eyes studied, 10 (6.17%) eyes showed an ERM, two of these caused foveal elevation due to traction. These findings are comparable to our study.

In Huang et al.^[12] study, out of 1176 eyes studied, 130 (11.05%) showed an ERM on OCT macula. This can be attributed to its larger sample size.^[15]

In Neto et al.^[9] study, out of the 98 eyes included in the study, 3 (3.06%) eyes had an ERM on OCT macula.

In Zafar et al.^[13] study, out of the 155 eyes studied, 4 (2.58%) eyes showed an ERM on SS-OCT Macula.

In Klein et al.^[14] study, 265 eyes were enrolled in the study and 11 (4.15%) eyes showed an ERM which was identified on OCT macula.

In Sudhalkar et al.^[15] study, out of the 1444 eyes that underwent successful OCT scans, 53 (3.67%) eyes showed an ERM.

An ERM is slowly progressive and leads to visual impairment only in some cases.^[16] It has been demonstrated that patients with a pre-operative ERM have higher risk for the development of post-operative pseudophakic cystoid macular oedema, epimacular membrane rip and potentially lead to visual impairment.^[17]

Drusen were identified in 9 (2.90%) eyes. Of these, two eyes had subfoveal drusen [Figure 3] and one eye had a juxtafoveal drusen.

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Figure 3:

Optical coherence tomography showing multiple subfoveal drusen.

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In Kowallick et al.^[12] study, SD-OCT imaging revealed drusen in 4 (2.47%) eyes, of these two eyes had subfoveal drusen. This was found comparable with our study.

In Klein et al.^[14] study, 15 (5.66%) eyes showed AMD, this could be attributed to the higher number of older individuals in their study.

In Huang et al.^[11] study, 10 (0.85%) eyes of the 1176 eyes studied showed age-related macular degeneration.

The previous studies have found that patients with drusen have a higher risk of developing exudative AMD,^[18] thus the diagnosis of drusen identifies such patients at risk.

The limitation of our study is the absence of post-operative follow-up examination. Accordingly, we have not been able to identify the post-operative consequences of the macular pathologies and its correlations with the visual outcome. Therefore, it would be more beneficial to conduct a prospective interventional study comparing the functional outcomes with pre-operative OCT macula.

CONCLUSION

We were able to diagnose subtle macular pathologies which went undiagnosed on routine fundoscopy done during pre-operative evaluation of cataract in a significant (20.96%) number of patients on SD-OCT macula which could have had a potential impact on the post-operative visual outcomes. It might be important to know if these subtle retinal findings would have had any impact on the visual outcome.

These were conveyed to the primary treating surgeon. Accordingly, their surgery was deferred or cataract extraction was done by experienced senior surgeons with explained visual prognosis.

By incorporating SD-OCT macula in routine pre-operative evaluation of patients for cataract surgery, we can also avoid medicolegal implications that might arise from postoperative patient dissatisfaction.

Therefore, these subtle macular pathologies should be diagnosed preoperatively so as to aid us in deciding the therapeutic strategy, to improve patient’s informed consent and to estimate the visual expectancy.

Thus, we conclude that pre-operative OCT macula is of paramount importance to identify occult macular pathologies and should be used as a mandatory screening tool in patients posted for cataract surgery.

The routine use of OCT before cataract surgery will enable ophthalmologists to make relevant therapeutic decisions, appropriate choice of IOLs, modify the informed consent and temper down patient’s post-operative expectations accordingly.

In today’s era, where cataract surgery is a refractive as well as a rehabilitative procedure, it becomes imperative to make OCT a mandatory tool in the pre-operative evaluation of cataract patients to screen for occult macular disease.