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.

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.

Differential diameter responses in macular and peripheral retinal arterioles may contribute to the regional distribution of diabetic retinopathy lesions.

BACKGROUND: Diabetic retinopathy is assumed to be due to impaired retinal autoregulation, involving both pressure autoregulation and metabolic autoregulation. The disease displays regional differences, with signs of hyperperfusion in the macular area and capillary occlusion with retinal ischemia in the peripheral retinal areas. It can be hypothesized that these regional differences in the occurrence of retinopathy lesions may reflect differences in the capacity of retinal arterioles to autoregulate the diameter of retinal arterioles. METHODS: Seventeen normal persons and two matched groups of patients with respectively diabetic maculopathy and proliferative diabetic retinopathy were examined. The diameter change of a macular and a peripheral retinal arteriole during an increase in the arterial blood pressure induced by isometric exercise, during an increase in retinal metabolism induced by flicker stimulation, and during both stimulus paradigms simultaneously were studied using the dynamic vessel analyzer (DVA). RESULTS: During isometric exercise, the diameter response was reduced in both macular and peripheral retinal arterioles in the two groups of patients with diabetes mellitus. During flicker stimulation, the diameter response was significantly reduced in patients with proliferative diabetic retinopathy, but there was no significant difference between the responses of macular and peripheral arterioles. During simultaneous isometric exercise and flicker stimulation, there was no difference between the diameter response of macular arterioles in the three groups, whereas the diameter response of macular arterioles was significantly lower in normal persons and significantly higher in persons with proliferative diabetic retinopathy as compared to peripheral arterioles. CONCLUSIONS: Regional differences in the disturbances of the diameter response to increased blood pressure may contribute to the regional differences in the distribution of diabetic retinopathy lesions. In the central retinal areas, the diameter response to increased blood pressure and retinal metabolism interacted in a way that may potentially protect this area from ischaemia, whereas this protective mechanism was absent in the peripheral retinal arterioles. An elucidation of the mechanisms underlying diameter regulation to increased blood pressure and retinal metabolism, and the interaction between these two mechanisms, may help in understanding the pathophysiology of diabetic retinopathy.

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.].

Increased blood pressure induces a diameter response of retinal arterioles that increases with decreasing arteriolar diameter.

PURPOSE: To study the diameter response of retinal arterioles as a function of the arteriolar diameter. METHODS: Ten healthy young volunteers aged 22 to 33 years were subjected to diameter measurement of four successive segments of a retinal arteriole with a retinal vessel analyzer (RVA). At each of the segments, the diameter response during an increase in the systemic blood pressure (mean arterial pressure [MAP]) induced by isometric exercise was compared to the diameter of the arterioles during rest. RESULTS: The isometric exercise induced a significant contraction of the studied vessel segments averaging 2.5% +/- 0.4% (P < 0.0001, n = 40). There was a significant negative correlation between the baseline diameter of the studied vessel segments and the diameter response induced by isometric exercise (P = 0.02). CONCLUSIONS: The blood pressure-induced diameter response of retinal arterioles increased with decreasing diameter of the vessels. The results indicate that the distal retinal arterioles play a major role in the regulation of retinal blood flow.

[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.

[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.

Bradykinin relaxation in small porcine retinal arterioles.

PURPOSE: To study changes in the spontaneous diameter of small retinal arterioles and bradykinin (BK)-induced vasodilation during inhibition of the synthesis of nitric oxide (NO), prostaglandins (PGs), and cytochrome P450 2C8/9-dependent endothelial-derived hyperpolarizing factor (EDHF). METHODS: Forty-eight isolated porcine arterioles with a diameter of approximately 70 microm were mounted in a double-barreled pipette system placed in an organ bath, and diameter changes were studied under isobaric conditions. After an equilibration period, the arterioles were incubated with inhibitors of the synthesis of NO, PGs, or cytochrome P450 2C8/9-dependent EDHF, and spontaneous diameter changes were studied. Subsequently, the arterioles were precontracted, and the diameter was assessed after addition of BK in cumulative concentrations. RESULTS: Inhibition of NOS elicited a significant decrease in the spontaneous diameter of the vessels (P = 0.028), whereas no change in the spontaneous diameter was induced by inhibition of PG or cytochrome P450 2C8/9 dependent EDHF synthesis (P = 0.35 and P = 0.75, respectively). The vasodilating effect of BK was decreased by inhibition of NO (P = 0.002) but not by inhibition of prostaglandin or cytochrome P450 2C8/9-dependent EDHF synthesis (P = 0.82 and P = 0.94, respectively). CONCLUSIONS: The results suggest the presence of a spontaneous release of NO, which keeps the retinal microcirculation dilated under normal conditions. The finding of BK-induced relaxation being dependent on the NO synthase (NOS), but not on PGs or cytochrome P450 2C8/9-dependent EDHF may be of importance for understanding the microcirculatory effects of pharmacologic compounds affecting the BK metabolism, such as angiotensin-converting enzyme (ACE) inhibitors.

Adenosine relaxation in small retinal arterioles requires functional Na-K pumps and K(ATP) channels.

PURPOSE: To study the effect of Na-K pump and K(ATP) channel inhibition on the diameter and the adenosine-induced vasodilation of small retinal arterioles. METHODS: Thirty isolated porcine arterioles with a diameter of approximately 70 microm were mounted in a double-barrelled pipette system placed in an organ bath, and diameter changes were studied under isobaric no-flow conditions. After an equilibration period, the arterioles were incubated with the Na-K pump inhibitors ouabain and low K(+) medium or the K(ATP) channel inhibitor glibenclamide, and spontaneous diameter changes were studied. Subsequently, the arterioles were precontracted and the adenosine concentration response curve was measured with and without the presence of inhibitors. RESULTS: Inhibition of the Na-K pump elicited a significant decrease in the spontaneous diameter of the vessels (P = 0.047), whereas no change in the spontaneous diameter was induced by inhibition of the K(ATP) channels (P = 0.754). Inhibition of the Na-K pump with ouabain or with low K(+) medium, as well as inhibition of the K(ATP) channels with glibenclamide, both diminished the adenosine induced vasodilation (P = 0.003, P = 0.01, and P = 0.003, respectively). CONCLUSION: The adenosine-induced vasodilation of small retinal arterioles involves the K(ATP) channels and the Na-K pump. Changes in the metabolism of adenosine as well as the activity of the K(ATP) channels or the Na-K pump can be expected to influence the retinal blood flow.

Myogenic response in isolated porcine retinal arterioles.

PURPOSE: To study the myogenic response in large and small porcine retinal arterioles and the effects of blockade of L-type voltage gated calcium channels on the myogenic response. METHODS: Eleven large (outer diameter 137.7 +/- 4.5 micro m) and fourteen small (77.3 +/- 3.7 micro m) isolated porcine retinal arterioles were studied for myogenic response while mounted between two double-barrelled pipette systems. The intraluminal pressure was varied from 0 to 140 cm H( 2)O (0-103 mmHg) and the diameter changes of the arterioles were registered. The pressure-diameter relation was determined for arterioles in calcium-containing and calcium free solutions and during inhibition of the L-type voltage gated calcium channels with nifedipine. RESULTS: Both large and small retinal arterioles showed a decrease in diameter as the intraluminal pressure was increased, but no significant difference was found between large and small arterioles (p = 0.39). Blockade of voltage gated calcium channels significantly abolished the myogenic response (p = 0.010 and p = 0.005, large and small arterioles respectively). CONCLUSIONS: The results indicate that myogenic responses are present throughout the retinal arteriolar system and that L-type voltage gated calcium channels are involved in transforming the stretch of retinal vascular smooth muscle cells induced by an increase in intraluminal pressure into a contraction.

[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.

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.

The incidence of retinal detachment after cataract surgery.

PURPOSE: To estimate the cumulative risk of retinal detachment (RD) after routine cataract surgery by phacoemulsification. SETTING: Department of Ophthalmology, Aarhus University Hospital, Denmark METHODS: Retrospective cohort study based on 12.222 consecutive cataract surgeries in 7.856 patients using phacoemulsification over a 6 year period from 2000 to 2005. Cases with a diagnosis of RD were identified through the procedure-coding database at the Medical Registry of Aarhus University Hospital, which is based on Diagnosis Related Groups (DRG) and used to report to the Danish Patients Registry (LPR). For each case the age of the patient, gender, axial length, surgical complications, postoperative Nd:YAG capsulotomy and time interval between cataract surgery and RD were recorded. RESULTS: The mean follow-up time was 64.8 months (range 26.2-97.6 months). Forty-eight (48) cases of RD were identified making an overall cumulative risk of 0.39%. As compared to the normal incidence of RD reported in the Scandinavian literature, the relative risk of RD following cataract surgery was about 2.3 times that of the natural incidence. As compared to the average cataract group, the group of RD following cataract surgery was characterized by a younger mean age (60.5 vs. 73.7 years), male gender (58.3% vs 34.8%), longer axial lengths (24.56 vs 23.25 mm) and a higher frequency of surgical complications (10.4% vs 1.8%) (p<0.001) but not a higher frequency of Nd:YAG capsulotomy (p>0.05), CONCLUSIONS: The cumulative risk of RD after lens surgery was about 2.3 times the natural incidence but seems to be lower than that of older reports. SYNOPSIS: Retinal detachment following cataract surgery is associated with young age, male gender, long axial lengths and surgical complications. The cumulative risk of RD after lens surgery was about 2.3 times the natural.

Lack of effect of short-term treatment with amlodipine and lisinopril on retinal autoregulation in normotensive patients with type 1 diabetes and mild diabetic retinopathy.

PURPOSE: Diabetic retinopathy is characterized by morphological changes in the retina secondary to disturbances in retinal blood flow. It has been shown that antihypertensive treatment has a protective effect on the development of diabetic retinopathy, and evidence suggests that inhibitors of the renin-angiotensin system have a protective effect beyond the antihypertensive effect. The background for this additional effect is unknown but might be related to an effect on retinal autoregulation. METHODS: In a double-blinded, two-way cross-over study, 25 normotensive patients with type 1 diabetes (T1D) aged 20.6-33.9 (mean 27.9) with mild retinopathy were randomized to receive either 5 mg of the calcium channel blocker (CCB) amlodipine for 14 days followed by a washout period and treatment with 10 mg of the angiotensin converting enzyme (ACE) inhibitor lisinopril for another 14 days or the two treatments in the reverse order. Using a Dynamic Vessel Analyzer (DVA), the diameter response of retinal arterioles during an acute increase in the blood pressure induced by isometric exercise, during flicker stimulation and during both stimulus conditions simultaneously was studied before and during the two treatments periods. RESULTS: Amlodipine and lisinopril induced a similar non-significant decrease in the arterial blood pressure. At baseline, the arterial diameter decreased by 2.4 ± 0.9% (p = 0.004) during isometric exercise, increased by 2.2 ± 0.9% (p = 0.019) during flicker stimulation and increased by 1.8 ± 0.9% (p = 0.03) during the combined stimulus conditions. Neither of the antihypertensive drugs amlodipine (p = 0.76) or lisinopril (p = 0.11) changed the diameter response of retinal vessels significantly; however, the two treatments induced a different response in the veins during combined exercise and flicker (p = 0.021). CONCLUSIONS: Short-term treatment with amlodipine and lisinopril had no significant effect on retinal autoregulation in young normotensive patients with T1D and mild retinopathy, and this lack of effect was similar for the two drugs. A possible normalizing effect of antihypertensive treatment on retinal autoregulation was not observed; however, it might take longer time to improve autoregulation than to reduce the arterial blood pressure.

Use of the retinal vessel analyzer in ocular blood flow research.

The present article describes a standard instrument for the continuous online determination of retinal vessel diameters, the commercially available retinal vessel analyzer. This report is intended to provide informed guidelines for measuring ocular blood flow with this system. The report describes the principles underlying the method and the instruments currently available, and discusses clinical protocol and the specific parameters measured by the system. Unresolved questions and the possible limitations of the technique are also discussed.

Interaction between flicker-induced vasodilatation and pressure autoregulation in early retinopathy of type 2 diabetes.

BACKGROUND: Diabetic retinopathy is accompanied with changes in the autoregulation of retinal blood flow secondary to changes in the systemic blood pressure and the retinal metabolism. In the present study we tested the working hypothesis that there is an interaction between these mechanisms that might be relevant for understanding and treating flow disturbances in diabetic retinopathy. METHODS: Fifty-four persons divided into three age and sex matched groups were studied: Group 1: twenty normal persons. Group 2: fourteen patients with type 2 diabetes mellitus and no diabetic retinopathy. Group 3: twenty type 2 diabetic patients with minimal diabetic retinopathy and a diabetes duration similar to that of the patients in group 2. Using the Retinal Vessel Analyzer (RVA) the diameter response of retinal arterioles was studied in all groups after an increase in the blood pressure by isometric exercise, during exposition to 8 Hz flickering light, and during simultaneous exposition to both stimulus conditions. RESULTS: The increased blood pressure induced by isometric exercise induced a non-significant vasoconstriction in the normal persons and in the diabetic patients without retinopathy (p=0.10 and p=0.84 respectively), and a non-significant vasodilatation in the diabetic patients with mild retinopathy (p=0.10). The flicker stimulus elicited a significant vasodilatation of retinal arterioles that decreased significantly from the normal persons to the diabetic patients without and with retinopathy (linear regression, p<0.01). The flicker-induced vasodilatation was not significantly affected by a simultaneous increase in the arterial blood pressure in normal persons (p=0.85). Conversely, in the diabetic patients the reduced diameter response during flicker was counteracted by a simultaneous increase in the blood pressure, to a level not differing significantly from the response of normal persons (p=0.75). CONCLUSIONS: Intervention studies aimed at modifying perfusion in retinal disease should consider the interaction between different mechanisms for autoregulating retinal blood flow. New treatment modalities for retinal vascular disease might need to target several mechanisms of tone control in retinal arterioles simultaneously.