PREOPERATIVE MEASUREMENT OF TEAR FILM HYPEROSJMOLARITY

Preoperative measurement of tear film hyperosmolarity appears to be a useful tool for identifying individuals at risk for a suboptimal visual outcome after LASIK and who might especially benefit from intensive therapy for dry eye disease, said David C Eldridge OD, at the 2012 annual meeting of the Association for Research in Vision and Ophthalmology. Dr Eldridge, vice-president of clinical affairs, TearLab Corporation, reported findings from a post hoc analysis of data collected in a prospective, multicentre study in which 128 patients (256 eyes) undergoing bilateral-sequential VisXR wavefront-guided LASIK with IntralaseR flaps were randomised to three days of preoperative QID use of an ocular lubricant (BlinkR Tears, AMO) or no pre-treatment. Eight highly experienced LASIK surgeons performed the procedures using the same technology, but their own standard medication regimen.

However, all patients used the ocular lubricant QID for one month after surgery. All surgeons were masked to the osmolarity measurement throughout the three-month period. To determine if tear osmolarity measured before starting any ocular lubricant treatment using a point-of-care osmometer (TearLab Osmolarity System) predicted postoperative visual acuity outcomes, patients were divided into hyperosmolar (≥308 mOsml/L; n = 48) and normal (<308 mOsml/L; n = 81) groups. The results showed the normal osmolarity group had a statistically significant better outcome. At three months after surgery, mean UCVA in the right and left eyes of hyperosmolar patients was 20/26 and 20/28, respectively, compared with 20/19 for both eyes in patients with normal osmolarity. Mean BCVA in the hyperosmolarity patients was about 20/19 for both eyes and not significantly different from the mean BCVA in the normal group, he reported. “The importance of maximising tear film stability preoperatively to improve outcomes after laser vision correction surgery has been realised for some time. It is particularly important in patients undergoing a customised ablation to assure capture of an accurate wavefront that will guide the laser ablation. Preferably, we would be able to identify at-risk hyperosmolar patients preoperatively and target them with interventions for modifying their risk factor rather than using a shotgun approach that treats all patients with the same standard regimen. Our findings suggest that surgeons should measure tear osmolarity before surgery to identify patients with dry eye disease.â€

Dr Eldridge added that data collected in the study are also consistent with information reported in the 2007 Report of the International Dry Eye Workshop showing that tear film osmolarity has a higher positive predictive value for detecting dry eye disease than any other conventionally used diagnostic tests. Ocular surface staining was also performed preoperatively, but was a very insensitive indicator of dry eye as the average score in hyperosmolar patients was just 0.2 on a scale of zero to four, he explained. UCVA data were also measured at one month after surgery, when required four times/day postoperative ocular lubricant use had just ended, and the means were 20/20 in both eyes of hyperosmolar patients and 20/20 and 20/19 for the patients with normal preoperative tear osmolarity. “The divergence in visual acuity outcomes between the normal and hyperosmolar patients in the interval from one to three months suggests that in selected at-risk (hyperosmolar) patients, it may be important to maintain dry eye therapy for an extended period of time,†Dr Eldridge said.