Cataract continues to be the leading cause of preventable blindness worldwide, contributing significantly to the global burden of visual impairment, particularly in low- and middle-income countries. Each year, an estimated 20 million cataract surgeries are performed globally, rendering cataract extraction the most commonly undertaken surgical procedure across all medical

specialties.[1-3] The advent of phacoemulsification, introduced by Dr. Charles D. Kelman in 1967, revolutionized cataract surgery by enabling emulsification of the lens using ultrasonic energy through a small incision. This innovation significantly reduced postoperative inflammation and accelerated visual recovery.[1]

In the current era of refractive cataract surgery, accurate postoperative refractive outcomes are largely contingent upon precise preoperative ocular biometry.[4] Conventionally, A-scan ultrasonography utilizing either contact or immersion techniques has been employed for measuring axial length (AL), anterior chamber depth (ACD), and lens thickness (LT).[5,6,7] However, limitations such as corneal compression, inter-operator variability, and the risk of transmitting infections have led to an increased preference for non-contact optical biometry methods.[6,7]

Swept-source optical coherence tomography (SS-OCT), integrated into devices such as the IOLMaster 700 (Carl Zeiss Meditec, Germany), represents a significant advancement in ocular biometry.[8-11] This technology provides high-resolution imaging with deeper tissue penetration, allowing for precise measurements of AL, keratometry (both anterior and posterior), white-to-white (WTW) corneal diameter, central corneal thickness (CCT), ACD, and LT.[12-14] The combination of SS-OCT imaging and telecentric keratometry has notably enhanced measurement repeatability, particularly in eyes with dense cataracts, thereby improving intraocular lens (IOL) power calculation accuracy.

Despite these technological advantages, optical biometry may fail in approximately 8–17% of cases, especially in eyes with dense nuclear sclerosis, posterior subcapsular cataracts, or other media opacities.[15-18] In such instances, A-scan ultrasonography remains a crucial supplementary tool, offering dependable measurements of essential biometric parameters. Studies have shown that employing both modalities in tandem can increase the proportion of eyes achieving postoperative refraction within ±1.0 dioptre of the target from 82.5% to as high as 94.3%.[18,19]

Numerous investigations have reported ocular biometric norms in Asian populations using optical coherence-based techniques. However, limited data are available that directly compare biometric parameters derived from A-scan ultrasonography and optical biometry specifically in Indian eyes. To date, only one study from Central India has attempted to correlate axial length with ocular and systemic variables using ultrasound, without incorporating partial coherence interferometry (PCI) or other optical techniques.[20]

Considering the ethnic and anatomical diversity across the Indian population, understanding the level of agreement between different biometric modalities is vital for optimizing IOL power calculations. The present study aims to systematically compare ocular biometric parameters obtained using A-scan ultrasonography and optical biometry in Indian eyes undergoing phacoemulsification at a tertiary care center. Through this comparative analysis, the study seeks to evaluate the concordance between modalities, assess clinical reliability, and explore their implications for routine cataract surgery planning in resource-constrained settings.

This prospective, comparative clinical study was conducted at the Department of Ophthalmology, at a tertiary care center for over a period of 18 months. The objective of the study was to compare ocular biometric measurements obtained using applanation A-scan ultrasonography and swept-source optical coherence tomography (SS-OCT)–based optical biometry in Indian eyes undergoing phacoemulsification.

Patients aged 40 to 70 years, diagnosed with age-related cataract, and scheduled to undergo uneventful phacoemulsification with posterior chamber intraocular lens (IOL) implantation were recruited for the study. Informed written consent was obtained from all participants, and the study protocol was approved by the Institutional Ethics Committee in accordance with the Declaration of Helsinki.

A total of 100 eyes from 100 patients were included. Each participant underwent a comprehensive ophthalmic evaluation, including uncorrected and best-corrected visual acuity, slit-lamp biomicroscopy, intraocular pressure measurement, and dilated fundus examination. Detailed medical history and relevant systemic investigations were also recorded.

Preoperative ocular biometry was performed using two different modalities:

• Group A (n = 50): Optical biometry was conducted using the IOLMaster 700 (Carl Zeiss Meditec AG, Germany), which utilized SS-OCT technology to measure axial length (AL), anterior chamber depth (ACD), lens thickness (LT), white-to-white corneal diameter, and anterior and posterior keratometry.
• Group B (n = 50): Applanation A-scan ultrasonography (Appasamy Associates, India) was employed to measure AL, ACD, and LT through the contact technique.

All measurements were performed by a single trained operator to minimize interobserver variability. Only scans with optimal quality and signal-to-noise ratios, as per manufacturer guidelines, were included for analysis.

Phacoemulsification surgeries were performed by experienced surgeons using a standardized technique under either topical or peribulbar anesthesia. A foldable acrylic IOL was implanted in all eyes. Patients were followed postoperatively, and refraction was recorded at 1, 2, and 3 months to assess refractive outcomes and the predictive accuracy of each biometry modality.

Patients with corneal opacities or degenerations, glaucoma, retinal or optic nerve pathology, diabetic or hypertensive retinopathy, vitreous degeneration, previous ocular trauma or surgery, or macular degeneration were excluded from the study.

The primary outcome was the comparison of biometric parameters specifically axial length, anterior chamber depth, and lens thickness between the two techniques. Secondary outcomes included the accuracy of postoperative refractive prediction and the proportion of eyes achieving refraction within ±0.50 dioptres and ±1.00 dioptres of the intended target.

Table 1: Sex Distribution in Group A and Group B (n = 50 each)

This table 1 compares the gender distribution between the two study groups—Group A (Immersion A-scan) and Group B (Optical Biometry), each consisting of 50 patients. In Group A, males constituted 52% (26 individuals), while females accounted for 48% (24 individuals), resulting in a male-to-female ratio of 1.08:1. In contrast, Group B had 44% males (22 individuals) and 56% females (28 individuals), with a male-to-female ratio of 0.79:1. These figures suggest a nearly balanced gender representation in both groups, with a slightly higher proportion of females in Group B.

Table 2: Age Distribution of Patients in Group A and Group B (n = 50 each)

This table 2 categorizes the patients based on age groups across both cohorts. Among the 50 patients in Group A, 16% (8 individuals) were aged between 40–50 years, 60% (30 individuals) were in the 51–60 years range, and 24% (12 individuals) were aged 61–70 years. Group B showed a slightly different distribution, with 20% (10 individuals) in the 40–50 age range, 56% (28 individuals) in the 51–60 range, and 24% (12 individuals) in the 61–70 range. This table demonstrates that the majority of patients in both groups were between 51–60 years of age.

Table 3: Distribution of Patients According to BCVA in Group A and Group B (n = 50 each)

                                  BCVA -(Best-Corrected Visual Acuity)

This table 3 presents the distribution of best-corrected visual acuity (BCVA) in both groups before surgery and at a 1-month follow-up. Pre-operatively, most patients had moderate to poor vision. For example, 56% had BCVA between <6/18–6/60 and 30% had BCVA between 6/12–6/18. Only 4% had good vision in the 6/6–6/9 range. However, after 1 month of follow-up, the majority (84%) had improved to the 6/6–6/9 range, indicating significant visual recovery. Very few patients (2%) remained in the moderate vision category (<6/18–6/60), and no patients had vision worse than 6/60 postoperatively. This table emphasizes the effectiveness of the intervention in restoring vision.

Table 4: Comparison of BCVA Preoperatively and at 1-Month Follow-Up (n = 60 eyes)

This table 4 simplifies the BCVA data into two categories: worse than 6/12 and 6/12 or better. Before surgery, 90% (54 out of 60 eyes) had BCVA worse than 6/12. At one month post-op, only 13.3% (8 eyes) remained in this category, showing a statistically significant improvement in visual acuity (p < 0.001). This reinforces the visual gains observed in Table 3 and supports the clinical effectiveness of the procedures used in both groups.

Table 5: Comparison of Mean Axial Length (mm) by Two Methods

This table 5 compares the mean axial length of the eye as measured by two different techniques—Immersion A-scan and Optical Biometry. The mean axial length in Group A was 23.08 ± 0.42 mm, while in Group B it was slightly longer at 23.42 ± 0.39 mm. The difference between these two methods was statistically significant (p = 0.037), indicating a measurable variance between the two techniques in determining axial length, which may affect intraocular lens power calculations.

Table 6: Comparison of Actual Post-operative Refraction

                       (Spherical Equivalent in Diopters)

This table 6 highlights the post-operative refractive outcomes (spherical equivalent in diopters) between Group A and Group B. Group A had a mean post-operative refraction of −0.42 D, while Group B had a slightly closer-to-target mean refraction of −0.25 D. The difference between the two was statistically significant (p = 0.032), suggesting that optical biometry may provide more accurate refraction outcomes than immersion A-scan.

In the present study, the demographic distribution across both groups was comparable, with a slight male predominance in the immersion A-scan group (52%) and a marginal female predominance in the optical biometry group (56%). These findings are consistent with observations made by DONGARE SD, et al., (2024). [21] The majority of participants in both groups fell within the 51–60 years age range, reflecting the typical demographic profile of patients presenting with age-related cataracts in the Indian population. This trend aligns with previous literature, notably the study by Vashist P, et al. (2011), [22] which highlighted a similar age pattern among cataract patients. Such balanced demographics helped minimize potential bias in outcome comparisons between the two groups.

Postoperative visual outcomes demonstrated marked improvement in both cohorts. Prior to surgery, 90% of patients exhibited a best-corrected visual acuity (BCVA) worse than 6/12, indicative of moderate to severe visual impairment. One month postoperatively, this proportion significantly declined to 13.3%, with 84% of patients achieving a BCVA in the range of 6/6 to 6/9. These findings underscore the effectiveness of cataract surgery when combined with accurate biometry in restoring functional vision. This is further supported by Joshi AK, et al., (2019), [23] who reported that although optical biometry devices provide greater accuracy than immersion ultrasound, their high cost and limited applicability in cases with dense cataracts pose certain challenges.

While both biometry methods yielded positive visual outcomes, notable differences emerged in biometric measurements and refractive predictability. The mean axial length (AL) measured using optical biometry was significantly higher (23.42 ± 0.39 mm) compared to the immersion A-scan method (23.08 ± 0.42 mm), with a statistically significant p-value of 0.037. This discrepancy can be attributed to the non-contact nature of optical biometry, which eliminates corneal compression and provides enhanced resolution and reproducibility.

In a separate study, Attar HH, et al., [24] reported similar findings, where 150 eyes were evaluated and the BCVA improved from counting fingers to 6/18 preoperatively, with 84% of patients achieving 6/9 postoperatively. Similarly, Joshi AK, et al., [25] observed that among patients assessed preoperatively and at a 30-day follow-up, 32 had BCVA ranging from <3/60 to 1/60 preoperatively, while 54 patients achieved BCVA between 6/6 and 6/9 postoperatively.

Furthermore, the mean postoperative spherical equivalent refraction was closer to emmetropia in the optical biometry group (−0.25 ± 0.16 D) compared to the immersion A-scan group (−0.42 ± 0.24 D), with this difference also reaching statistical significance (p = 0.032). These findings indicate that optical biometry yields more accurate intraocular lens (IOL) power calculations and improved refractive outcomes. This is corroborated by Nenning M, et al., (2024), [26] who noted that the advent of optical biometry has significantly enhanced the precision of axial length measurements, which is critical for accurate IOL power estimation.

Although both modalities led to substantial visual improvements, the superior precision and reproducibility of optical biometry make it a preferred choice in routine clinical practice, particularly when targeting precise refractive outcomes such as in premium IOL implantation. Nonetheless, immersion A-scan remains a dependable and accessible alternative, especially in patients with dense cataracts or other media opacities where optical biometry may not be feasible. Mandlik HR, et al., (2020) [27] emphasized that immersion ultrasound biometry remains a reliable and cost-effective technique, particularly beneficial in cases where optical methods are limited by media opacities.

The study's findings highlighted that, the importance of accurate biometry in cataract surgery outcomes. While the advantages of optical biometry are evident, especially in terms of precision and refractive accuracy, the role of immersion A-scan remains indispensable in resource-limited settings. By understanding the limitations of this study, including the modest sample size and single-center design, further research with larger, multicentric trials is recommended to confirm these findings and assess the performance of both techniques across various clinical scenarios.

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