Abstract
Abstract: :
Purpose: The present study was designed to determine whether elevated vitreous lactate concentration is a viable substance that can be directly correlated with ganglion cell damage and optic neuropathy associated with a mechanical model of glaucoma. It was also intended to demonstrate the noninvasive nature of proton nuclear magnetic resonance (H–NMR) spectroscopy for sequential in vivo measurements of lactate that may be useful in the early detection and diagnosis of glaucoma. Methods:A 50 µl volume of 20 µm diameter latex beads was injected into the anterior chamber of the eye in an anesthetized New Zealand White rabbit to block aqueous outflow and create an elevated intraocular pressure (IOP). The contralateral eye served as the control by receiving an equal volume injection of vehicle without the latex beads. Eye pathology was assessed by: measuring the intraocular pressure throughout the study; using H–NMR spectroscopy to non–invasively measure any changes in vitreous lactate concentrations over time that may be associated with the progression of the pathophysiology; and carrying out light microscopy to characterize and correlate any changes in the retina histology and population of ganglion cells including the nerve fiber layer thickness. Results:A mean value of 9 mm Hg was recorded for IOPs in control and experimental eyes prior to the injection of latex beads into the anterior chamber. Although some experimental eyes developed a peak IOP of 26 mm Hg over a twelve–day interval, the mean value of the IOP was 17.7 ± 5.3 mm Hg; concurrently IOPs in control eyes remained unchanged. At the start, the baseline vitreal lactate levels were 3.87 mM and were unchanged in control eyes; however, in eyes with elevated IOP, vitreal lactate concentrations rose to 9.45 mM with a mean of 6.99 ± 1.45 mM. The nerve fiber layer of the temporal medullary ray area in control eyes had a mean thickness of 157.52 µm, whereas in eyes with elevated IOP, the mean thickness was reduced to 66.27 µm or 57.9% of the control value. A smaller reduction of only 13.24 % was found in the nasal medullary ray areas in which control eyes had a mean thickness of 60.49 µm compared to a thickness of 52.48 µm for eyes with elevated IOP. Conclusion:Results demonstrated that H–NMR spectroscopy could be used to follow vitreal concentrations of lactate over time and that increases in lactate could be correlated with both elevated IOP and the reduction of nerve fiber layer thickness.
Keywords: intraocular pressure • nerve fiber layer • pathology: experimental