Justin Cooper , 2025-05-16 17:17:00
Key takeaways:
- Keratometry measurements showed significant variability in patients with unstable tear film before cataract surgery.
- Artificial tears and other appropriate treatments should be considered.
When conducting IOL power calculation, tear film instability significantly influences various measurements of corneal refractive power and astigmatism, making errors in the calculation more likely, according to a study.
“The measurement of corneal refractive power is one of the most important biometric values for IOL calculation in cataract surgical planning,” Yuanfeng Jiang, of Tianjin Medical University Eye Hospital, China, and colleagues wrote in Advances in Ophthalmology Practice and Research. “Although it has been previously reported that optical biometry devices provide fairly reliable measurements of corneal refractive power in normal eyes, the clinical evidence regarding their tolerance level for tear film instability is still insufficient.”
When conducting IOL power calculation, tear film instability significantly influences various measurements of corneal refractive power and astigmatism, making errors in the calculation more likely. Image: Adobe Stock
Jiang and colleagues conducted a prospective observational study of 45 patients undergoing preoperative evaluation for age-related cataract surgery.
Patients’ tear films were assessed using the Keratograph 5M (Oculus). Depending on their noninvasive breakup time, they were split into two groups: those with “stable” or “critical” tear film (n = 23), serving as the control group, and those with “unstable” tear film (n = 22).
After 30 minutes, patients underwent two consecutive keratometry assessments using the IOLMaster 700 (Zeiss), spaced at least 10 minutes apart. The differences between these two measurements were compared between the control group and those with unstable tear film.
“Previous researches have almost always interfered with the tear film itself to some extent when evaluating its stability,” the researchers wrote. “The noninvasive detection method used in our study successfully and objectively avoided this issue.”
Compared with the control group, the group with tear film instability had significantly higher variability in multiple keratometry measurements, including standard keratometry measures (Kf and K), keratometric corneal astigmatism, total keratometry (TKf and TK) and total corneal astigmatism.
The only IOL power calculation formula to be significantly affected by these differences was the SRK-T formula. Using that formula, the IOL power calculation had a median variability of 0.09 D in the group with tear film instability and 0.04 D in the control group.
However, all formulas included in the IOLMaster 700 (including the Barrett Universal II, Barrett Universal II TK, Haigis, Haigis TK and SRK-T TK) showed increased variability as noninvasive breakup time decreased.
Overall, the results support “the theory that an unhealthy tear film would have a negative impact on corneal measurements,” the researchers wrote.
“Based on noncontact assessment of tear film stability, we demonstrated that an unstable tear film reduces the repeatability of preoperative corneal refractive power measurements in cataract patients, resulting in an increase in the variability of IOL calculation formulas,” Jiang and colleagues wrote. “Therefore, for patients with severe tear film instability, appropriate treatment should be actively pursued, such as the use of artificial tears, lipid supplements and biologic tear substitutes.
“Our findings emphasize that ocular surface homeostasis should not be neglected in preoperative planning for precision refractive cataract surgery, including astigmatism management.”
Perspective
This study offers critical clinical insight: Unstable tear film can reduce the repeatability of corneal power and astigmatism measurements, which may compromise IOL power calculations in cataract patients. For optometrists involved in preoperative assessments, this emphasizes the importance of addressing tear film instability or dry eyes before obtaining biometry. Although total keratometry and multiple IOL calculation formulas were used, only the SRK-T formula showed a statistically significant variability, indicating it may be particularly vulnerable to poor tear film quality. However, even when statistical significance was absent, wider interquartile ranges across all formulas suggest clinically relevant unpredictability. The results affirm what many clinicians observe in practice: Dry eye, common in aging cataract populations, can distort measurements even with advanced devices like the IOLMaster 700. Optometrists must consider treating tear film instability before cataract surgery planning to improve surgical outcomes and patient satisfaction. A potential shortcoming of the study is its small sample size, which limits broader generalizability. Additionally, newer formulas like the Kane or Hill-RBF were analyzed only post hoc and did not show significant changes, warranting further study. Overall, this research reinforces the need for stable ocular surface conditions when precision matters most.
Disclosures: Sesah reports no relevant financial disclosures.
