Heredity may play a role in determining IOP, according to a twin study conducted by Britain"s King"s College London School of Medicine. The study also aimed to determine whether the use of different instruments influences calculation of eye IOP heritability.

A total of 422 twin pairs (211 monozygotic [MZ], 211 dizygotic [DZ]) were recruited to participate from the TwinsUK Adult Twin Registry at St. Thomas" Hospital, London. Investigators measured IOP using Goldmann applanation tonometry; a subset of twins were also measured using the Ocular Response Analyzer (ORA) and the Dynamic Contour Tonometer (DCT). Investigators then compared the covariance of IOP within MZ and DZ pairs using genetic modeling techniques to determine the relative contribution of genes and environment to the variation in IOP in this population.

The mean IOP for Goldmann applanation tonometry was 15.4 (SD 2.7) mmHg (range, 8.7 to 26.2 mmHg). The MZ correlations were significantly higher than DZ for IOP measured by Goldmann applanation tonometry, DCT and ORA. Correlation coefficients for MZ:DZ twins were: Goldmann applanation tonometry, 0.57:0.39; DCT, 0.62:0.36; Goldmann-correlated ORA (IOPg), 0.73:0.47. Modeling suggested heritability for Goldmann applanation tonometry IOP of 0.62, with individual environmental factors accounting for 0.38 of the variation.

The study demonstrates that genetic effects are important in determining IOP in this twin population. IOP readings differed depending upon the instrument used, resulting in different heritability values; genetic factors explained 62 percent, 63 percent and 74 percent of the variation in IOP using Goldmann applanation tonometry, DCT and ORA IOPg, respectively. Environmental factors determined the remainder of the variation.

Researchers at California"s Jacobs Retina Center at the Shiley Eye Center conducted a retrospective, observational case-control and interventional case series study to assess the incidence of vitreomacular adhesion and traction in AMD. The researchers also aimed to evaluate surgical treatment in a subset of patients with choroidal neovascularization (CNV) that is nonresponsive to anti-neovascular growth factor (anti-VEGF) treatment.

Spectral optical coherence tomography, combined with simultaneous scanning laser ophthalmoscope (Spectral OCT/SLO), was performed in 170 eyes of 94 older patients, 61 of whom had exudative AMD, 59 of whom had nonexudative AMD and 50 of whom were control participants. Investigators determined the presence of hyaloid adhesion to the posterior pole as well as vitreomacular traction (VMT). Five patients with VMT underwent surgical hyaloid removal. Best-corrected visual acuity (BCVA) and retinal thickness were evaluated as outcomes.

Hyaloid adhesion was present in 17 eyes with exudative AMD (27.8 percent), 15 eyes with nonexudative AMD (25.4 percent) and eight control eyes (16 percent). Significant difference was found among the groups. Among the eyes with hyaloid adhesion, VMT appeared in 10 eyes (59 percent) with exudative AMD, two eyes (13 percent) with nonexudative AMD and one control eye (12 percent). VMT was associated with the severity of AMD. The area of hyaloid adhesion was significantly smaller than, and concentric to, the area of CNV complex in eyes with exudative AMD. Eyes with VMT that underwent surgery experienced a modest improvement of BCVA and decrease of retinal thickness.

Based on these results, the authors conclude that hyaloid adhesion to the macula is associated with AMD and frequently causes VMT in eyes with CNV. Tractional forces may antagonize the effect of anti-VEGF treatment and cause pharmacological resistance in a subpopulation of patients. They point out that future studies are needed to define the role of vitreoretinal surgery in such cases.