A clinical research article entitled "Impact of Tear Film Stability on Corneal Refractive Power Measurement and Surgical Planning for Cataract" was recently published in the journal Advances in Ophthalmology Practice and Research by the cataract department of Tianjin Medical University Eye Hospital. Dr. Yuanfeng Jiang and Dr. Xiteng Chen are the co-first authors of the paper, and Professors Fang Tian and Shaochong Bu serve as the corresponding authors.
Impact of tear film stability on corneal refractive power measurement and surgical planning for cataract（click for the access of the original article）
01 Highlights
With growing patient expectations for postoperative visual quality, precise intraocular lens (IOL) power calculation has become a critical determinant of cataract surgery success. Corneal refractive power is a key parameter in IOL calculation. As the tear film constitutes the first optical interface on the corneal surface, its stability significantly affects the accuracy of corneal measurements. However, more than 50% of elderly patients with cataracts experience varying degrees of tear film instability or dry eye disease, a factor often overlooked in clinical practice, potentially leading to increased risk of postoperative refractive error.
This study is the first to systematically reveal the crucial role of tear film stability in preoperative measurements for cataract surgery, providing scientific evidence to enhance surgical precision.
Using a prospective cohort design, the research team divided 45 patients with age-related cataracts into two groups: a tear film instability group (tear film breakup time ≤ 5 seconds) and a control group. Two sets of measurements were taken 10 minutes apart using a non-invasive tear film analyzer (Keratograph SM) and an optical biometer (IOL Master 700). Variability in corneal refractive power (K and TK), astigmatism (KCA and TCA), and six different IOL power calculation formulas was analyzed and compared.
Key Findings:
1.Increased Measurement Variability
In the tear film instability group, measurement variability was significantly higher for the flat keratometry reading (Kf), mean keratometry (K), and corneal astigmatism (KCA) compared to the control group (P < 0.05). Total keratometry (TK) and total corneal astigmatism (TCA) were also affected, indicating that even when posterior corneal surface data are included, tear film instability compromises measurement repeatability.
2.Discrepancies in IOL Calculation Formulas
The SRK-T formula showed significantly greater variability in calculated IOL power in the tear film instability group (median difference: 0.09 D vs. 0.04 D, P = 0.044). In contrast, newer generation formulas such as Barrett Universal II were less affected, suggesting the need for careful formula selection in clinical settings.
3.Dynamic Mechanism Analysis
Tear film breakup leads to irregularities in the corneal surface optical interface, especially along the flat meridian, exacerbating measurement fluctuations. The study also found a significant negative correlation between tear film stability and non-invasive tear breakup time (NIBUT), further confirming the importance of managing tear film health preoperatively.
Clinical Implications:
This study is the first to demonstrate, via non-invasive assessment, the impact of tear film stability on preoperative planning for cataract surgery. The findings support the following clinical recommendations:
- Preoperative Assessment: Include tear film stability evaluation as a standard component of preoperative cataract screening, especially in elderly patients or those with dry eye symptoms.
- Intervention Strategies: Actively manage tear film instability with artificial tears, lipid supplements, and other ocular surface treatments.
- Formula Optimization: Avoid using formulas like SRK-T that are sensitive to tear film instability; instead, opt for more robust formulas such as Barrett Universal II.
Future Directions:
The research team plans to expand the sample size and conduct longitudinal follow-up of postoperative refractive outcomes to validate the long-term benefits of preoperative tear film intervention. Lead researcher Dr. Yuanfeng Jiang commented:
"Ocular surface health is the cornerstone of precision refractive cataract surgery. We aim to explore more personalized treatment strategies to help patients achieve optimal visual outcomes."
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