Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UMLS:C0595921 (intraocular pressure)
 11,750 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Glaucomatous optic neuropathy is a primary pathological condition responsible for visual dysfunction due to glaucoma. However, how intraocular pressure and other risk factors lead to glaucomatous optic neuropathy is not fully understood. Given that static or kinetic visual field tests for evaluating visual dysfunction in glaucomatous optic neuropathy are a subjective assessments based on a psychophysical principle, the development of a tool for objective assessment of the visual field is needed. In this study, we attempt to elucidate the pathophysiology of glaucomatous optic neuropathy and to refine a modality for the objective assessment of the visual dysfunction due to it. Aquaporin (AQP) water channels are located primarily in the plasma membrane. These proteins form either a homo- or hetero-tetramer and allow water to cross the plasma membrane bi-directionally. The transmembrane water movement through AQPs is critically involved in the maintenance of normal neuronal activity. Among the 13 isoforms indentified so far, AQP-4 is known to be expressed in the retrobulbar portion of the optic nerve. However, the optic nerve head, the primary pathological site of glaucomatous optic neuropathy, reportedly does not express AQP-4. We found that in control rats, astrocytes throughout the optic nerve express AQP-9. The chronic elevation of intraocular pressure due to cauterization of three episcleral veins substantially reduced both gene expression and immunoreactivity of AQP-9, whereas it did not change the AQP-4 gene or protein expression in the retrobulbar portion of the optic nerve. These findings are implicated in the chronic elevation of intraocular pressure in astrocytes. Similar findings were also observed in the eyes of a monkey with angle-laser-induced ocular hypertension and of a human with primary open-angle glaucoma. AQP-9 was also expressed in the cell bodies of retinal ganglion cells in control rats and its expression was significantly reduced in the eyes of rats with ocular hypertension. Recently, the astrocyte-to-neuron lactate shuttle hypothesis has been proposed. This hypothesis suggests that lactate generated by glucose during glycolysis in astrocytes is used by neurons as an energy substrate. Given that AQP-9 belongs to an aquaglyceroporin subfamily and allows solutes other than water (e.g., lactate) to cross the plasma membrane, chronic ocular hypertension may perturb this physiological passage of lactate. Thus, lactate as the energy substrate may be unable to be transported from astrocytes to retinal ganglion cells at the cell bodies and axons due to the reduction of AQP-9 expression by astrocytes at the optic nerve head and retinal ganglion cells. The multifocal visual evoked potential (mfVEP) is an objective visual field test, which enables the recording of cortical potential corresponding to 60 local retinal areas simultaneously. Evidence is accumulating that the signal-to-noise ratio (SNR) has been enhanced by recording mfVEPs from multiple channels at the same time. However, previous studies evaluated the mfVEPs mostly in Caucasians. It has not yet been proven whether this strategy is applicable to Japanese people who have a skull frame that may be different from that of Caucasians. We calculated the relative position of the calcarine landmark for electrode placement during the mfVEP recording, from brain MRI images of 200 individuals, which were found to be 1 cm lower than those reported in Caucasians with a statistical significance. Then, we recorded mfVEPs from 110 normal controls using three channels and conducted receiver-operating characteristic (ROC) curve analysis of the overlap of SNR distribution at signal and noise windows. We found that a combination of one horizontal channel straddling the inion with either one of the two perpendicular vertical channels yielded the largest area under the ROC curve (AUC). Next, we showed that the SNR-AUC exhibited a similar diagnostic performance to, and a significant correlation with, a total deviation of the Humphrey visual field in 56 eyes with mild to moderate glaucomatous damage, which exhibited a mean deviation of -15 dB or less, and in 62 control eyes. In contrast, a topographical agreement in defining abnormal locations based on probability plots between the Humphrey visual field and mfVEP testing was moderate. The SNR-AUC may be used as a global index, analogous to the mean deviation of the Humphrey visual field, to quantify diffuse functional loss due to glaucomatous optic neuropathy, in contrast to the previously proposed cluster analysis of the mfVEP probability plots, which is a strategy more suitable to diagnosing local sensitivity loss.
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PMID:[New insights into the pathogenesis of glaucomatous optic neuropathy and refinement of the objective assessment of its functional damage]. 2256 5

Optical coherence tomography (OCT) provides a new dimenstion in ophthalmology because it allows evaluation of the pathology in vivo, and provides information to assist the management of macular disease and glaucoma. It is necessary to differentiate the diagnosis of glaucoma from diseases of the optic nerve and of the visual pathway. This study evaluates the usefulness of OCT in detecting disorders of the optic nerve and visual pathway. In addition, the pathogenesis of glaucomatous optic neuropathy (GON), the most common optic neuropathy, was investigated by focusing on the dynamics of aquaporin. I. Evaluation of optic nerve and visual pathway disorders by optical coherence tomography. The swinging flashlight test is an easy, sensitive, objective test to detect relative afferent pupillary defects (RAPD). The number of RAPD detected by the swinging flashlight test was closely correlated with the ratio of retinal nerve fiber layer thickness (RNFLT) between the two eyes of 20 cases of unilateral optic atrophy. OCT could assess the amount of RAPD that reflected an asymmetrical functional disturbance of the optic nerves, as a structural difference. The time courses of RNFLT and ganglion cell complex (GCC) changes' were observed immediately following the time of injury in 4 cases of traumatic optic neuropathy. OCT revealed that both the RNFLT and GCC decreased rapidly from 2 weeks after the injury until 20 weeks later. The RNFLT decreased significantly in the horizontal direction in comparison to the perpendicular direction in 34 eyes from the cases of optic chiasm syndrome. This means that OCT could quantitatively detect the band atrophy of the optic disc in optic chiasm syndrome. Measuring the RNFLT showed a thinning of RNFLT in the perpendicular direction in comparison to the horizontal direction in ipsilateral eyes and thinning in the horizontal direction in comparison to the perpendicular direction in the contralateral eyes in optic tract syndrome. Measuring the GCC showed a thinning of the GCC in the temporal hemifield to the central fovea of the ipsilateral eyes, and thinning of the GCC in the nasal hemifield of the contralateral eyes. This means that OCT could detect the structural changes of hourglass atrophy in the ipsilateral eye and band atrophy in the contralateral eye at the optic disc as well as the homonymous hemianopia in the visual field. OCT was useful in evaluating the optic nerve and visual pathway disorders, but there were also some limitations. The thinning area of RNFLT measured by OPTVue and Cirrus were in entirely opposite directions in cases of optic chasm syndrome. The reason was attributed to the better performance of RTVue in measuring a thin RNFLT on the nasal side of the optic disc in comparison to Cirrus. The specific characteristics of the instruments should be considered when the results of OCT are evaluated. II. Dynamics of aquaporin in the optic nerve Aquaporin (AQP) is a membrane protein that forms a water channel to facilitate water crossing the plasma membrane. AQP-4 was originally thought to be expressed in the optic nerve, but it is expressed only in the retrobulbar medullated region of the optic nerve and the expression of AQPs in the optic disc has not been detected. This study investigated the expressions of AQPs in the optic nerve in rat, monkey and human. The results demonstrate that only AQP-9 was expressed at the unmedullated pre-lamina cribrosa and lamina cribrosa regions, and both AQP-4 and AQP-9 were expressed at the medullated retrobulbar region. Astrocytes were observed to express AQP-9, because AQP-9 immunoreactivity was identical to that of glial fibrillary acidic protein. Elevated intraocular pressure substantially reduced AQP-9 expression in the optic nerve, whereas expression of AQP-4 was not changed in rat eyes. The same phenomena were also observed in the monkey eye with ocular hypertension as well as human eye with glaucoma. AQP-9 is an aquaglyceroporin that allows solutes such as lactate rather than water to cross the cell membrane. The astrocyte-to-neuron lactate shuttle hypothesis has been proposed, in which lactate transported from astrocytes is used by neurons as an energy substrate. Reduction of AQP-9 expression in the optic nerve head under elevated intraocular pressures might be closely related to the pathogenesis of GON.
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PMID:[New insights into the study of optic nerve diseases]. 2363 Dec 54