Oxygenation differs among white matter hyperintensities, intersected fiber tracts and unaffected white matter.

White matter hyperintensities of presumed vascular origin are frequently observed on magnetic resonance imaging in normal aging. They are typically found in cerebral small vessel disease and suspected culprits in the etiology of complex age- and small vessel disease-related conditions, such as late-onset depression. White matter hyperintensities may interfere with surrounding white matter metabolic demands by disrupting fiber tract integrity. Meanwhile, risk factors for small vessel disease are thought to reduce tissue oxygenation, not only by reducing regional blood supply, but also by impairing capillary function. To address white matter oxygen supply-demand balance, we estimated voxel-wise capillary density as an index of resting white matter metabolism, and combined estimates of blood supply and capillary function to calculate white matter oxygen availability. We conducted a cross-sectional study with structural, perfusion- and diffusion-weighted magnetic resonance imaging in 21 patients with late-onset depression and 21 controls. We outlined white matter hyperintensities and used tractography to identify the tracts they intersect. Perfusion data comprised cerebral blood flow, blood volume, mean transit time and relative transit time heterogeneity-the latter a marker of capillary dysfunction. Based on these, white matter oxygenation was calculated as the steady state cerebral metabolic rate of oxygen under the assumption of normal tissue oxygen tension and vice versa. The number, volume and perfusion characteristics of white matter hyperintensities did not differ significantly between groups. Hemodynamic data showed white matter hyperintensities to have lower blood flow and blood volume, but higher relative transit time heterogeneity, than normal-appearing white matter, resulting in either reduced capillary metabolic rate of oxygen or oxygen tension. Intersected tracts showed significantly lower blood flow, blood volume and capillary metabolic rate of oxygen than normal-appearing white matter. Across groups, lower lesion oxygen tension was associated with higher lesion number and volume. Compared with normal-appearing white matter, tissue oxygenation is significantly reduced in white matter hyperintensities as well as the fiber tracts they intersect, independent of parallel late-onset depression. In white matter hyperintensities, reduced microvascular blood volume and concomitant capillary dysfunction indicate a severe oxygen supply-demand imbalance with hypoxic tissue injury. In intersected fiber tracts, parallel reductions in oxygenation and microvascular blood volume are consistent with adaptations to reduced metabolic demands. We speculate, that aging and vascular risk factors impair white matter hyperintensity perfusion and capillary function to create hypoxic tissue injury, which in turn affect the function and metabolic demands of the white matter tracts they disrupt.

Ray-tracing Analysis of the Corneal Power From Scheimpflug Data.

PURPOSE: To describe a method by which mapped corneal elevation data can be used for ray-tracing analysis of the effective corneal power. METHODS: Mapped elevation data of the front and back surface of the cornea exported by a clinical Scheimpflug camera was triangulated into a polygonal format and imported into a commercial optical engineering software. The focal length of the cornea was determined by exact ray tracing analysis of the distance giving the sharpest point spread function (PSF) at the selected image plane. The effective corneal power could then be determined as the reciprocal of the observed focal length "reduced to air." The corneal power determined by the ray-tracing procedure was checked for reproducibility and effect of pupil size and finally compared with standard keratometry methods. RESULTS: Twenty random cases referred for cataract or refractive lens surgery were investigated. The ray-traced corneal power was found to be highly reproducible with a maximum error of 0.023 diopters (D) between repeated ray-tracing experiments. The mean ray-traced corneal power of 42.34 D (assuming a 3-mm pupil) was found to be 1.02 D lower than the standard keratometry reading assuming a keratometric index of 1.3375 (P < .001). The ray-traced corneal power was found to be higher than the true net power (P < .01) but not significantly different from the total corneal refractive power reported by the Scheimpflug device (P > .05). The ray-traced corneal power increased 0.31 D when the pupil size increased from 3 to 5 mm, which was attributed to spherical aberration. CONCLUSIONS: Exact ray tracing can be used on mapped tomography data to analyze for the effective corneal power. This technique was found to be highly reproducible and may be a promising tool in the analysis of the true power of the cornea of any shape. [J Refract Surg. 2018;34(1):45-50.].

[Toric intraocular lenses correct astigmatism in connection with surgery for cataract].

Cataract surgery is traditionally regarded as a primarily sight-restoring procedure. However, with the improvement of surgical techniques and intraocular lenses the procedure has evolved into a refractive procedure as well. With the recent advent of toric intraocular lenses (t-IOL) surgeons now have the potential to correct pre-existing astigmatism in addition to the correction of myopia and hyperopia by the implantation of an appropriate t-IOL, carefully selected according to both its spherical and cylindrical power. The benefit for the patient is an improved vision without spectacles.

Precision of 5 different keratometry devices.

To compare the precision among currently available keratometry devices. The corneal power was measured on two separate visits with the Nidek TonoRef II Autorefractor/Keratometer, the Zeiss IOLMaster 500, the Haag-Streit Lenstar LS 900, the Oculus Pentacam, and the Oculus Keratograph 4M. The precision was evaluated as the mean absolute intersession difference (MAD) between the corneal power measurements for each patient. Only the non-operated eye was included in the study. The Keratograph was found to have the highest MAD (0.215 D), which was significantly different from the other devices except for the IOLMaster. Nidek ARK had the lowest MAD (0.097 D), but this was not significant compared to Pentacam (0.124 D), Lenstar (0.132 D), or IOLMaster (0.140 D). Only one out of 29 patients had a precision difference exceeding 0.25 D with the Nidek ARK. Among the devices studied, the Nidek ARK was found to have the highest and the Keratograph was found to have to the lowest precision for the measurement of corneal power.

[Steroid treatment and risk of glaucoma]. / Steroidbehandling og risiko for glaukom.

The risk of steroid-induced elevation of intraocular pressure and glaucoma is clinical relevant and require monitoring of patients at risk. The risk depends on route of administration, potency and individual risk factors such as primary open glaucoma (POAG), first-degree relative with POAG, age (children) and myopia. Steroid-induced elevation of intraocular pressure is most commonly associated with ocular application and systemic administration but may occur after periocular cutaneous application and nasal and inhalation therapy in patients with individual risk factors.

[Steroid treatment and risk of glaucoma].

The risk of steroid-induced elevation of intraocular pressure and glaucoma is clinical relevant and require monitoring of patients at risk. The risk depends on route of administration, potency and individual risk factors such as primary open glaucoma (POAG), first-degree relative with POAG, age (children) and myopia. Steroid-induced elevation of intraocular pressure is most commonly associated with ocular application and systemic administration but may occur after periocular cutaneous application and nasal and inhalation therapy in patients with individual risk factors.

Improvement of mild retinopathy in type 2 diabetic patients correlates with narrowing of retinal arterioles. A prospective observational study.

PURPOSE: Diabetic retinopathy is one of the leading causes of blindness in the Western world. The disease is characterized by morphological lesions secondary to disturbances in retinal blood flow assumed to be related to disturbances in retinal autoregulation. However, there is a need for elucidating the relation between disturbances in diameter regulation of retinal vessels and the development of diabetic retinopathy in longitudinal studies. METHODS: Sixty-four patients with type 2 diabetes mellitus were subjected to measurement of pressure autoregulation of retinal arterioles using the Dynamic Vessel Analyzer (DVA) and measurement of retinal thickness using OCT scanning, and after a mean of 6.8 years, 42 of the patients were re-examined. The vascular response was compared in patients in whom retinopathy had disappeared, was unchanged, or had worsened. RESULTS: At baseline, hemoglobin A1c (HbA1c) was significantly higher in the patients who would later experience worsening of diabetic retinopathy than in the other groups, but had been reduced at the follow-up examination. During the follow-up period, the resting diameter of retinal arterioles decreased significantly in the patients who experienced improvement in diabetic retinopathy but was unchanged in the other groups, whereas both the diameter response of retinal arterioles to isometric exercise and retinal thickness increased non-significantly with worsening of retinopathy. CONCLUSIONS: The development of diabetic retinopathy is related to the diameter of retinal arterioles. Future clinical intervention studies should aim at investigating the effects of normalizing arteriolar diameters in diabetic retinopathy.

Acute hyperinsulinemia increases the contraction of retinal arterioles induced by elevated blood pressure.

Diabetic retinopathy is accompanied by disturbances in retinal blood flow, which is assumed to be related to the diabetic metabolic dysregulation. It has previously been shown that normoinsulinemic hyperglycemia has no effect on the diameter of retinal arterioles at rest and during an increase in the arterial blood pressure induced by isometric exercise. However, the influence of hyperinsulinemia on this response has not been studied in detail. In seven normal persons, the diameter response of retinal arterioles to an increased blood pressure induced by isometric exercise, to stimulation with flickering light, and to the combination of these stimuli was studied during euglycemic normoinsulinemia (protocol N) on one examination day, and euglycemic hyperinsulinemia (protocol H) on another examination day. Isometric exercise induced significant contraction of retinal arterioles at all examinations, but during a repeated examination the diameter response was significantly reduced in the test persons following the N protocol and increased in the persons following the H protocol. Flicker stimulation induced a significant dilatation of retinal arterioles at all examinations, and the response was significantly higher during a repeated examination, irrespective of the insulin level. Repeated exposure to isometric exercise reduces contraction, whereas repeated exposure to flickering light increases dilatation of retinal arterioles in vivo. Hyperinsulinemia increases contraction of retinal arterioles induced by isometric exercise.

Spontaneous high frequency diameter oscillations of larger retinal arterioles are reduced in type 2 diabetes mellitus.

PURPOSE: Diabetic retinopathy is characterized by morphological changes in the retina secondary to disturbances in retinal blood flow. Vasomotion is a mechanism for regulating blood flow by spontaneous oscillations in the diameter of retinal resistance arterioles, and has been shown to be disturbed outside the eye in diabetic patients. Therefore, the purpose of the present study was to characterize spontaneous oscillations in the diameter of retinal arterioles in normal persons and in persons with different severity of diabetic retinopathy. METHODS: Video recordings of the retina were performed in 19 normal persons and three matched groups of type 2 diabetic patients with no retinopathy, mild retinopathy, and diabetic maculopathy. Continuous recordings of a larger retinal arteriole during rest and during an increase in the arterial blood pressure induced by isometric exercise were subjected to power spectrum analysis of spontaneous oscillations in vessel diameter. RESULTS: During rest the oscillations in the diameter of retinal arterioles with high frequencies were significantly reduced in patients with diabetic retinopathy. Increased arterial blood pressure did not change the oscillations in normal persons, but further reduced the oscillations in diabetic patients. CONCLUSIONS: Spontaneous high frequency oscillations in the diameter of larger retinal arterioles are reduced in type 2 diabetic patients, and are further reduced during an increase in the arterial blood pressure. The finding may reflect changes in the vascular walls of importance for diagnosing and predicting the visual prognosis in patients with diabetic retinopathy.