Antemortem vitreous potassium may strengthen postmortem interval estimates.

The purpose of this letter is to highlight that postmortem interval estimates using vitreous potassium concentrations may be further optimised by calibration against antemortem vitreous samples.

Biochemical analysis of the living human vitreous.

BACKGROUND: To date, our understanding of the biochemical composition of the living human vitreous relies on extrapolations from animal or human post-mortem studies. METHODS: This was a cross-sectional study of vitreous samples from 27 individuals scheduled for retinal surgery within a tertiary hospital. From each vitreous sample, the concentrations of sodium, potassium, chloride, calcium, magnesium, glucose, lactate, ß- hydroxybutyrate, copper, zinc, selenium, iron, ferritin and transferrin and osmolality were measured. Perioperative serum samples were also obtained for comparison. RESULTS: The following vitreous mean ± standard deviation (95% confidence interval of the mean) was observed for each analyte: sodium, 146.7 ± 3.3 (145.4-148.0) mmol/L; potassium, 5.73 ± 0.86 (5.39-6.08) mmol/L; chloride, 121.6 ± 2.6 (120.6-122.7) mmol/L; calcium, 1.128 ± 0.518 (0.923-1.333) mmol/L; magnesium, 0.900 ± 0.158 (0.838-0.962) mmol/L; glucose, 2.97 ± 0.98 (2.58-3.36) mmol/L; lactate, 3.97 ± 1.09 (3.54-4.40) mmol/L; osmolality, 289.5 ± 6.9 (286.6-292.5) mOsm/kg; BOHB, 0.0937 ± 0.0472 (0.0750-0.1124) mmol/L; copper, 0.519 ± 0.269 (0.412-0.625) µmol/L; zinc, 1.95 ± 1.09 (1.52-2.38) µmol/L; selenium, 0.1035 ± 0.0276 (0.0923-0.1146) µmol/L; iron, 3.11 ± 1.40 (2.56-3.66) µmol/L; ferritin, 19.5 ± 10.3 (15.5-23.6) µg/L; transferrin, 0.0878 ± 0.0526 (0.0670-0.1086) g/L. Vitreous biochemistry was not significantly different between male and female participants. Vitreous biochemistry was significantly different between non-diabetic and diabetic participants. Vitreous biochemistry was significantly different from the vitreous substitute BSS Plus (Alcon, USA). The vitreous extracted from living humans was markedly different from the commonly reported reference values obtained from animal studies. CONCLUSIONS: The current data provide hitherto unavailable information about the biochemical composition of the living human vitreous.

The effect of central retinal venous pressure in patients with central retinal vein occlusion and a high mean area of nonperfusion.

PURPOSE: To evaluate the effect of central venous pressure (CVP) on visual outcomes and retinal ischemic consequences in patients with central retinal vein occlusion (CRVO). DESIGN: Prospective, single-center cohort study. PARTICIPANTS: Eighty-eight patients with CRVO and a high overall mean area (21.6 disc areas) of capillary nonperfusion (CNP) who were followed for 18 months before the availability of intravitreal therapy and who were offered standard care of the time. METHODS: Patients were evaluated at baseline and at 3, 8, and 18 months. At each study visit, measurements of CVP, best-corrected visual acuity (BCVA), area of CNP, retinal fluorescein transit time (FTT), and an evaluation for rubeosis iridis were performed. MAIN OUTCOME MEASURES: Evaluation of the effect of different levels of CVP on BCVA, retinal blood flow, and the development of retinal ischemia and rubeosis iridis. RESULTS: Mean BCVA was significantly higher in patients with lower CVP at all time points (P<0.0001). The area of CNP increased significantly with higher levels of CVP and progressed with time. The development of rubeosis iridis was significantly associated with CVP at all time points and was present in 5.6%, 27.9%, and 88.9% of those with low, moderate, and high CVP levels, respectively (P<0.0001), at the 18-month conclusion. Retinal blood flow as measured by FTT was reduced with higher levels of CVP. Spontaneous lowering of CVP had beneficial effects on BCVA, although this diminished with time. CONCLUSIONS: Eyes with increased CVP after more severe CRVO demonstrate significantly reduced vision, reduced retinal blood flow, a higher incidence of rubeosis iridis, and larger areas of CNP that correlate with the degree of CVP elevation.

Recurrent third nerve palsy as the presenting feature of neurofibromatosis 2.

Neurofibromatosis 2 (NF2) is a rare autosomal dominant disorder associated with the development of multiple central and peripheral nervous system tumors. Patients with NF2 are often diagnosed in adulthood, with symptoms of an isolated tumor or hearing loss associated with vestibular schwannomas. Diagnosing NF2 in children is complicated by the fact that the diagnostic criteria often are not met at presentation and there is usually no family history of the disease. The authors describe the diagnostic challenge posed by a pediatric patient who developed a relapsing and remitting third nerve paresis and was later diagnosed with NF2. A mechanism for the recurrent cranial mononeuropathy is proposed.