Shenelle Wickramarathna
Background
CT head scans are among the most frequently requested imaging studies in both emergency and outpatient medicine. While they offer rapid and critical diagnostic insight, they also come with a less visible risk: unintended radiation exposure to the eyes. The ocular lens is one of the most radiosensitive tissues in the human body (1). Even a single exposure to ionising radiation can increase the risk of cataract formation, and there is evidence that with repeated imaging, the risk accumulates (2).
National guidance from bodies such as the Royal College of Radiologists (RCR) recommends that the lenses be excluded from the scan field whenever clinically appropriate (3). However, in real-world settings, compliance is often poor. In many departments, patient positioning is suboptimal, gantry tilt is underused, and high clinical workloads can make safety adjustments feel optional. As a result, lens exclusion tends to be deprioritised, forming a systemic blind spot in imaging safety and, ultimately, in long-term ophthalmic outcomes.
This audit was undertaken to assess how often the lens is actually excluded in practice, and whether a simple, low-cost intervention led by radiographers could make a meaningful difference in reducing preventable radiation exposure to the eye.
Aims
This audit was designed with the following objectives:
- To establish baseline compliance with lens exclusion in outpatient CT head imaging across three NHS hospital sites.
- To introduce a targeted, low-cost quality improvement intervention focused on optimising lens protection.
- To re-audit practice following intervention and quantify any improvement in compliance with lens exclusion.
Methods
A two-cycle retrospective audit was conducted across three NHS hospital sites, anonymised here as Site 1, Site 2, and Site 3. For each cycle, we manually reviewed 150 outpatient CT head scans, 50 from each site, selected from routine outpatient lists over a one-week period.
To ensure the clinical appropriateness of lens exclusion, we excluded any scans where the indication required orbital visualisation (e.g., trauma, diplopia, or known orbital pathology). The remaining scans were assessed using axial images and scout views to determine whether the lenses were within the field of view.
Each scan was categorised into one of three groups:
- Both lenses excluded
- One lens included
- Both lenses included
Scans where both lenses were excluded were considered compliant with best-practice guidance on lens sparing.
After the first audit cycle (Cycle 1), we introduced a multi-pronged quality improvement intervention at all three sites. First, we raised awareness through departmental presentations and displayed visual prompts near CT control areas, including scan alignment diagrams and RCR guidance on lens exclusion. Second, we offered short refresher training for radiographers, focusing on the use of gantry tilt and how to align the scan plane with the supraorbitomeatal line. Finally, staff were encouraged to optimise patient positioning when feasible, using techniques such as chin tucking or head support cushions.
Several weeks later, the second audit cycle (Cycle 2) was carried out using the same methodology.
Results
The first audit cycle revealed consistently poor compliance across all sites. At Site 1, just one of the 50 scans (2%) excluded both lenses. Site 2 showed slightly better performance, with 4 scans (8%) meeting compliance. Site 3 again mirrored Site 1, with just one compliant scan (2%). In total, only 6 out of 150 scans (4%) excluded both lenses — meaning that in 96% of cases, patients were exposed to unnecessary ocular radiation.
Following the intervention, the second cycle showed a clear and substantial improvement. At Site 1, 24 out of 50 scans (48%) achieved full lens exclusion. Site 2 showed 25 compliant scans (50%), while Site 3 achieved 21 compliant scans (42%). Combined, 70 out of 150 scans (47%) excluded both lenses, marking an 11-fold increase in compliance compared to baseline.
Statistical analysis using Fisher’s exact test confirmed this improvement to be highly significant (p < 0.0001), highlighting the impact of targeted radiographer-led interventions in changing practice. While there remains a gap from the ideal of 100% compliance, the findings represent a major step forward in reducing preventable radiation to the eyes.
Conclusion
This multisite audit uncovered a widespread, modifiable issue in routine CT head imaging: the consistent inclusion of the lenses despite guidance advocating for their exclusion when possible. At baseline, fewer than 1 in 20 scans excluded both lenses, a striking figure considering the simplicity of the intervention required. By equipping radiographers with visual prompts, technique refreshers, and positioning tips, compliance rose to nearly 1 in 2 scans across all sites. This reflects not only a statistically significant improvement but also a clinically meaningful one in terms of long-term visual health.
It’s important to note that full compliance is not always possible. In some cases, such as patients with reduced consciousness, limited neck mobility, or urgent imaging requirements, it may be clinically unfeasible to reposition the head or adjust gantry tilt. Additionally, equipment limitations may restrict the degree of tilt achievable. These are not failures of practice but reflections of the real-world context in which imaging is delivered.
Nonetheless, this audit reinforces the idea that lens protection should be embedded into everyday radiological workflows. Radiographers are well-positioned to lead this change with support from local guidelines, educational resources, and ongoing audit cycles. As the number of CT head scans continues to grow year-on-year, the cumulative radiation burden to patients also rises, making it more important than ever to ensure we are not trading diagnostic speed for long-term visual harm.
References
1. Hamada N, Azizova T V., Little MP. An update on effects of ionizing radiation exposure on the eye. Br J Radiol. 2020 Nov 1;93(1115):20190829.
2. Chodick G, Bekiroglu N, Hauptmann M, Alexander BH, Freedman DM, Doody MM, et al. Risk of Cataract after Exposure to Low Doses of Ionizing Radiation: A 20-Year Prospective Cohort Study among US Radiologic Technologists. Am J Epidemiol. 2008 Jul 15;168(6):620–31.
3. The Royal College of Radiologists. Head CT – Lens Exclusion. 2008. Available at: https://www.rcr.ac.uk/career-development/audit-quality-improvement/auditlive-radiology-templates/head-ct-lens-exclusion/ (Accessed: 30 October 2025).