• Patients with floppy lid syndrome (FES) may have structural changes that could signal risk for glaucoma development, says a study in the May 2015 Cornea.¹ Researchers in Spain performed a corneal biomechanical evaluation on 208 eyes—72 with FES and 136 without FES—of 107 patients, measuring corneal hysteresis (CH), corneal resistance factor (CRF), central corneal thickness (CCT), Goldmann-correlated intraocular pressure (IOPg) and corneal-compensated intraocular pressure (IOPcc). Noncontact IOP and all corneal biomechanical properties were measured using the Ocular Response Analyzer (Reichert).

Mean CH was significantly lower in patients with FES compared with those without FES (i.e., 9.51 ± 1.56 vs. 11.66 ± 9.11), which may “constitute a risk factor for glaucoma due to an association with the response of the corneoscleral shell and the ocular vasculature to IOP-induced stress,” say the researchers. Interestingly, mean CH remained statistically significant after adjusting for age and apnea-hypoapnea index, but mean CRF and mean IOPcc did not. There was no statistically significant difference in Goldmann-correlated IOP and CCT.

1. Royo MM, de Ribot AM, Sanchez-de-la-Torre M, et al. Corneal biomechanical properties in floppy eyelid syndrome. Cornea. 2015 May;34(5):521-4. 

• Hybrid contact lenses with tear vaults of more than 100μm may be detrimental to corneal health because of inadequate surface oxygen supply, reports a study in the March 2015 Eye & Contact Lens.¹ Slit lamp and OCT evaluations found that fitting hybrids with the manufacturers’ recommended tear vault of 100μm or less resulted in acceptable corneal surface oxygen values, around 100mm Hg, while vaults greater than 100μm created less ideal corneal surface pO₂—as low as 0mm Hg. 

The researchers had hoped to find an acceptable way to calculate corneal surface pO₂ under a hybrid lens, but inconsistent results between the slit lamp and OCT limited reliability. Despite the study’s limitations, it highlights the need for a better clinical method for measuring corneal surface pO₂—similar to methods used for soft, silicone hydrogel and rigid contact lenses. Such testing would help clinicians better fit hybrids. Until then, the researchers advise fitting hybrid contact lenses with modest vaults to provide adequate oxygen supply.

1. Lee KLY, Nguyen DPA, Edrington TB, and Weissman BA. Calculated in situ tear oxygen tension under hybrid contact lenses. Eye & Contact Lens. 2015 Mar;41(2):111-116.

Multifocal Halo Reduction Possible?
A new lens surface modification that smoothes out surface discontinuities could reduce the halo effect commonly experienced by patients with multifocal intraocular or contact lenses, reports a study in the December 2014 Optics Communications.¹ Coauthor Zeev Zalevsky, PhD, of Israel’s Bar-Ilan University says “the proposed surfacing technique can be very important in significantly improving [vision], especially the night vision performance of any IOL for presbyopia correction,” noting that it could in theory be added to any multifocal lens. 

1. Limon O, Zalevsky Z. Ophthalmic halo reduced lenses design. Optics Communications. 2014 Dec;342:253-8.