Adjunctive Oral Vitamin D Supplementation Enhances Tear Secretion in Patients with Refractive Errors and Dry Eye Syndrome: A Double-Blind Randomized Controlled Trial

Abstract

Refractive errors often coexist with dry eye syndrome (DES), exacerbated by vitamin D deficiency through impaired tear film stability and inflammation. This trial assessed whether adjunctive oral vitamin D enhances the efficacy of artificial tears in refractive error-associated DES. A double-blind randomized controlled trial enrolled 45 adult patients (aged 17–45 years) with refractive errors and confirmed DES at the Refraction Ophthalmology Outpatient Clinic of a tertiary teaching hospital. Participants were randomized 1:1 to artificial tears monotherapy (Group A, n=23) or combination therapy with 1000 IU oral cholecalciferol daily plus artificial tears (Group B, n=22) for four weeks. Primary outcomes were serum 25-hydroxyvitamin D [25(OH)D] levels and DES parameters including Schirmer's test, tear break-up time (TBUT), meibomian gland evaluation (MGE), and Ocular Surface Disease Index (OSDI). After dropouts, 39 patients were analyzed (monotherapy n=21, combination n=18). Monotherapy showed a paradoxical vitamin D category shift (normal: 52.38% to 38.10%; p<0.001) with stable Schirmer test 1 (4.76% abnormal; p=0.048 bilaterally); Schirmer test 2, TBUT, MGE, and OSDI were non-significant. Combination therapy improved vitamin D status (p<0.001), Schirmer test 1 (22.22% to 11.11%; p=0.039), and Schirmer test 2 (44.44% to 27.78%; p=0.007). No significant intergroup differences in dry eye severity (p=0.541 baseline; p=0.647 post-intervention); significant within-group severity reduction for combination therapy (mild DES: 61.11% to 83.33%; p=0.045) versus monotherapy (p=0.133). Adjunctive oral vitamin D supplementation to artificial tears significantly improves vitamin D status and tear secretion in refractive error-associated DES, with superior within-group dry eye severity reduction compared to monotherapy.