Investigators at Toronto's Hospital of Sick Children Research Institute conducted a study aimed at determining whether any common variants in the gene for vascular endothelial growth factor (VEGF) are associated with long-term renal and retinal complications in Type I diabetes.

The study included 1,369 white subjects with Type I diabetes from the Diabetes Control and Complications Trial (DCCT)/Epidemiology of Diabetes Interventions and Complications (EDIC) study. Subjects had an average of 17 retinal photographs and 10 renal measures over 15 years. In the DCCT/EDIC, investigators studied 18 single nucleotide polymorphisms (SNPs) in VEGF that represent all linkage disequilibrium bins and tested them for association with time to development of severe retinopathy (SR), 3-step or greater progression of retinopathy, clinically significant macular edema, persistent microalbuminuria and severe nephropathy.

A global multi-SNP test showed a highly significant association of VEGF SNPs with SR; all other outcomes were non-significant. In survival analyses controlling for covariate risk factors, eight SNPs showed significant association with SR. The most significant single-SNP association was rs3025021. Family-based analyses of SR provided evidence of excess transmission of C at rs699947, T at rs3025021 and the C-T haplotype from both SNPs. Multi-SNP regression analysis including 15 SNPs and allowing for pairwise interactions independently selected six significant SNPs. The data demonstrates that multiple VEGF variants are associated with the development of SR in Type I diabetes.

When keratorefractive surgery is used to treat a central corneal diameter smaller than the resting pupil, visual symptoms of polyopia, ghosting, blur, haloes and glare may result. Although progress has been made to enlarge the area of surgical treatment to extend beyond the photopic pupil, geometric limitations can pose restrictions to extend the treatment beyond the mesopic pupil diameter and can lead to impediments in night vision. The size of the treated area that has achieved good optical performance has been defined as the functional optical zone (FOZ). This study by Spain's Universidad de Murcia describes three objective methods to measure the FOZ.

Researchers evaluated corneal topography examination results from one eye of 34 unoperated normal eyes and 32 myopic eyes corrected by laser in situ keratomileusis (LASIK) in three ways. First, a uniform axial power method, FOZ(A), assessed the area of the postoperative cornea within a +/- 0.5D window centered on the mathematical mode. Second, FOZ was determined based on the corneal wavefront true root mean squared (RMS) error as a function of the simulated pupil size, FOZ(R). Third, FOZ was determined from the radial modulation transfer function (MTF), established at the retinal plane as a function of pupil size, FOZ(M).

For normal eyes, mean for the FOZ(A) method was 7.6 mm, for the FOZ(R) method 9.1 mm and for the FOZ(M) method 7.7 mm. For LASIK-corrected eyes, mean for the FOZ(A) method was 6.0 mm, for the FOZ(R) method 6.9 mm and for the FOZ(M) method 6.0 mm. Overall, an average decrease of 1.8 mm in the FOZ was found after the LASIK procedure. Correlations between the FOZ methods after LASIK showed acceptable and statistically significant values.

The authors suggest that these methods will be useful in characterizing more fully corneal treatment profiles after keratorefractive surgery. Because of its ease of implementation, direct spatial correspondence to corneal topography and good correlation to the other more computationally intensive methods, the semiempiric uniform axial power method, FOZ(A), appears most practical in use. The authors believe that the ability to measure the size of the FOZ should permit further evolution of keratorefractive surgical lasers and their algorithms to reduce the night vision impediments that can arise from FOZs that do not encompass the entire mesopic pupil.