The Prevalence Of Hyperosmolarity And Its Influence On Light Scatter In Patients Undergoing Cataract Surgery

Increased tear osmolarity can impact corneal health and is a central mechanism of ocular surface disease. Evidence suggests hyperosmolarity can also cause light scatter, resulting in fluctuating vision and biometry measurements. Pre-cataract surgery, this can cause intraocular lens power calculation errors, resulting in unexpected refractive error post-surgery, and ultimately patient dissatisfaction. Post-surgery, these fluctuations can also result in patient dissatisfaction despite achievement of target refraction. Given the interdependency between cataract surgery and osmolarity, determining hyperosmolarity rates pre- and post-surgery, and how this affects vision, may help to address patient dissatisfaction with surgical outcomes. 

This abstract presents data from two prospective, observational studies conducted at two sites (Cincinnati Eye Institute, Cincinnati, Ohio, USA; Servicio de Oftalmología, Hospital Universitario Virgen de la Arrixaca, Murcia, Spain) to investigate the prevalence of hyperosmolarity (PS) and its effect on light scatter (LSS), respectively. Patients presenting for pre-surgical cataract evaluation were randomly selected for inclusion in the studies. 

Patients were bilaterally assessed for osmolarity using the ScoutPro osmolarity system using a cut-off of ≥315 mOsm/L to define normal- and hyperosmolarity. Patients in the LSS were grouped according to osmolarity status (normal, n=10; hyperosmolar, n=11). Eighty patients were included in the PS, 44% of which were hyperosmolar. Osmolarity, symptom severity, tear film break-up time (TBUT), and meibomian gland disease (MGD) were assessed at baseline in both studies. Contiguous, 20-second ocular scatter index (OSI) scans were also performed in the LSS; eligible patients had a score of ≥4.0. Patients were followed up at 30 days (PS) and 90 days (LSS) post-surgery.  

In the PS, of the 56% of patients who had normal osmolarity pre-surgery, 32% became hyperosmolar post-surgery. Of the 44% of patients who were hyperosmolar pre-surgery, 52% achieved normal osmolarity post-surgery, despite topical corticosteroid, NSAID, antibacterial, and artificial tear treatment during the postoperative period. In the LSS, variation in light scatter as measured by OSI correlated with osmolarity status at baseline (mean±standard deviation OSI: 0.33±0.11 normal osmolarity, 0.65±0.30 hyperosmolar; p<0.005). OSI did not correlate with staining (p=0.891), TBUT (p=0.749), symptoms (p=0.719), or MGD status (p=0.852) when patients were stratified at baseline by these measures. 

These studies show that hyperosmolarity is highly prevalent pre- (44%) and post- (40%) cataract surgery, including one-third of patients becoming hyperosmolar post-surgery. Importantly, the light scatter caused by hyperosmolarity is only detectable when patients are stratified by osmolarity and not by other standard measures. These results suggest hyperosmolarity should be measured both pre- and post-surgery to ensure sources of light scatter can be detected and vision outcomes and patient satisfaction optimised.