Effect of Low‐Level Light Therapy on Ocular Surface Parameters in Patients Undergoing Cataract Surgery: A Prospective Double‐Masked Randomized Controlled Clinical Trial

Effect of Low‐Level Light Therapy on Ocular Surface Parameters in Patients Undergoing Cataract Surgery: A Prospective Double‐Masked Randomized Controlled Clinical Trial

August 27, 2025

ABSTRACT
Introduction: Postoperative dry eye disease (DED) remains a frequent complication that
can reduce patient satisfaction and surgical outcomes. Low-level light therapy (LLLT) is a
non-invasive technology that has shown posi‐ tive outcomes in managing DED. This study aimed to assess the prophylactic application of perioperative LLLT for improving ocular sur‐face parameters and symptoms in consecutive patients undergoing cataract surgery.

Methods: In this prospective, double-masked, randomized sham-controlled study, patients
scheduled for cataract surgery were randomized to receive either periocular LLLT or sham treatment 1 week before and 1 week after surgery. Ocular surface assessments, including
Ocular Surface Disease Index (OSDI) questionnaire, tear film break-up time (BUT), Schirmer
test type I, tear osmolarity, and corneal fluorescein staining (Oxford score), were performed preoperatively before the first treatment/sham session (T0), and postoperatively 1 week (T1) and 1 month postoperatively (T2). All patients received the same postoperative therapy.

Results: Out of 98 patients randomized to
LLLT (50 patients) or sham treatment (48
patients), 89 patients (45 males, 44 females;
mean age of 73.75 ± 7.95 years) completed
the study. Unlike controls, the LLLT group
showed significant improvements from T0 to
T1 and T2 for OSDI scores (respectively, from
26.62±15.42 to 15.53±12.04 and 13.36±11.69;
p < 0.001) and BUT values (respectively, from
5.76 ± 3.99 to 6.69 ± 4.48 and 8.38 ± 4.53;
p = 0.002), and from T0 to T2 for tear osmolar‐
ity (respectively, from 300.69±14.19 mOsm/l to
296.11±12.30 mOsm/l; p=0.048). No significant
differences were found in Schirmer test values
within or between the two groups. No adverse
effects were reported.

Conclusions: Perioperative LLLT is a safe, well-
tolerated, and effective treatment for preventing

iatrogenic DED in cataract surgery. Integrating
LLLT into the routine perioperative care may
enhance patient satisfaction and overall out‐
comes in the setting of cataract surgery.
Clinical Trial Registration Number :
NCT07067294, retrospectively registered on
05.07.2025.

Summary

  • Population: 98 adults scheduled for cataract surgery (89 completed; mean age ~74).

  • Design: Prospective RCT, LLLT vs sham, double-masked.

  • Intervention: Two periocular LLLT sessions with a 633 ± 10 nm device (15 min) — one week pre-op and one week post-op; controls got a look-alike “demo” light at <30% power.

  • When measured: Pre-op (T0), 1 week post-op (T1), 1 month post-op (T2).

  • Outcomes: Symptoms (OSDI), tear breakup time (BUT), Schirmer I, tear osmolarity, and Oxford corneal staining. 

Key results (LLLT vs sham)

  • Symptoms (OSDI): Improved with LLLT (26.6 → 15.5 at T1 → 13.4 at T2; p<0.001), but worsened in controls; between-group differences significant at T1 and T2.

  • Tear stability (BUT): Increased in LLLT (5.8 s → 8.4 s at T2; p=0.002); no meaningful change in controls.

  • Tear osmolarity: Decreased with LLLT (300.7 → 296.1 mOsm/L at T2; p=0.048) but increased in controls (296.7 → 306.2; p=0.002); between-group difference at T2 p<0.001.

  • Corneal staining: Stable with LLLT; worse in controls (significant at T1).

  • Schirmer I: No differences (aqueous volume unchanged).

  • Safety: No adverse events reported; treatment was well tolerated. 

Why this matters

  • Prophylaxis works: Doing two short LLLT sessions around surgery reduced the typical post-op dry-eye symptom spike and stabilized the tear film.

  • Osmolarity as a sensitive marker: The divergent osmolarity trend (down with LLLT, up in controls) supports osmolarity as a useful peri-op biomarker to track ocular-surface stress/recovery.

  • Mechanism consistent with PBM: The authors attribute benefits to photobiomodulation (mitochondrial/anti-inflammatory effects), plus potential support of meibomian function via endogenous eyelid heating—fitting known PBM pathways. 

Practical takeaways for peri-op cataract care

  • If you’re optimizing the ocular surface: Consider two 15-min periocular LLLT sessions (one pre-, one post-op) in addition to standard drops.

  • What to monitor: OSDI, BUT, osmolarity, and Oxford staining show the intervention’s effect; Schirmer may not move (since volume isn’t the main issue).

  • Safety/flow: Non-invasive, quick, operator-light; integrates easily into clinic workflow. 

Limitations / open questions

  • Follow-up only 1 month: Durability beyond 3–6 months remains to be shown.

  • Generalizability: Single-center; real-world but with standard exclusions.

  • Registration timing: Trial was retrospectively registered (NCT07067294), so future work should prospectively register and extend follow-up. 

Bottom line: In this RCT, periocular 633 nm LLLT given one week before and after cataract surgery was safe and improved symptoms, tear stability, osmolarity, and early epithelial integrity compared with sham. It’s a plausible peri-operative add-on to reduce iatrogenic dry eye after cataract surgery.