Retinal Vessel Diameter Changes in Relation to Dark Adaptation and Acute Hyperglycemia.

The purpose of this experimental clinical study was to assess the effects of dark adaptation and acute changes in glycemia on retinal vessel diameters in men. The study included 14 patients (mean age 63 years, range 48-74 years) with type 2 diabetes mellitus and minimal or no diabetic retinopathy. Retinal vessel diameters were assessed using infrared photography before and after dark adaptation, first while fasting and then at peak hyperglycemia during an oral glucose tolerance test (OGTT). Dark adaptation was accompanied by retinal vasodilatation, both during fasting (mean glycemia 7.6 ± 1.7 mM) and postprandial hyperglycemia (15.7 ± 4.2 mM). When fasting, the increase in vein diameter during dark adaptation was 2.0% after 20 min (P=0.018) and 2.9% after 40 min (P=0.010). When subjects were hyperglycemic, the increase during dark adaptation was 2.8% for retinal vein diameters (P=0.027) and 2.0% for retinal artery diameters after 20 min (P=0.002) and 1.7% for retinal artery diameters after 40 min (P=0.022). For identical conditions of light/dark adaptation, retinal vessels were dilated when subjects were fasting compared to postprandial hyperglycemia. Thus, darkness and fasting were both associated with retinal vasodilation in this short-term experiment in patients with type 2 diabetes. Future studies should determine whether both the stimuli of vasodilation lead to retinal hyperperfusion, which would support that they may be involved in the aggravation of diabetic retinopathy.

Automated refraction is stable 1 week after uncomplicated cataract surgery.

PURPOSE: To compare automated refraction 1 week and 1 month after uncomplicated cataract surgery. METHODS: In this prospective cohort study, we recruited patients in a 2-month period and included consecutive patients scheduled for bilateral small-incision phacoemulsification cataract surgery. The exclusion criteria were (i) corneal and/or retinal pathology that could lead to automated refraction miscalculation and (ii) surgery complications. Automated refraction was measured 1 week and 1 month after surgery. RESULTS: Ninety-five patients met the in- and exclusion criteria and completed follow-up. The mean refractive shift in spherical equivalent was -0.02 dioptre (D) between 1 week and 1 month after surgery and not statistical significant (p = 0.78, paired t-test). The magnitude of refractive shift in either myopic or hyperopic direction was neither correlated to age, preoperative corneal astigmatism, axial length nor phacoemulsification energy used during surgery (p > 0.05 for all variables, regression analysis). The refractive target was missed with 1.0 D or more in 11 (12%) patients. In this subgroup, the mean refractive shift in spherical equivalent was 0.49 D between 1 week and 1 month after surgery with a trend towards statistical significance (p = 0.07, paired t-test). There was no difference in age, preoperative corneal astigmatism, axial length or phacoemulsification energy used during surgery compared to the remainder of the patients (p > 0.05 for all variables, unpaired t-test). CONCLUSION: Automated refraction is stabile 1 week after uncomplicated cataract surgery, but there is a trend towards instability, if the refractive target is missed with 1.0 D or more.

Baseline haemoglobin A1c influences retinal function after long-term insulin pump therapy.

PURPOSE: The purpose of the study was to characterize the long-term effect of insulin pump therapy (CSII) on electroretinography and dark adaptometry and to examine the influence of baseline glycaemic control on retinal function in patients with type 1 diabetes mellitus. METHODS: This prospective observational extension study enrolled 13 patients out of 17 who completed a primary 1-year study of the effect of CSII on retinal function. Twelve patients were still on CSII at follow-up. The extension study included a single examination 3.5 years (range 3.0-4.0 years) after initiation of CSII of one study eye per patient. Procedures included full-field electroretinography (ERG), dark adaptometry, optical coherence tomography, and fundus photography. RESULTS: Mean ERG amplitudes 3.5 years after initiation of CSII were 15-43 % lower than at baseline (all p < 0.05) and 21-45 % lower than after 1 year on CSII. The mean rate of dark adaptation had returned to baseline after a transient 13 % (p = 0.0024) acceleration at the 1-year visit. Reduction of ERG amplitudes between 1 and 3.5 years was statistically associated predominantly with baseline haemoglobin A1c (HbA1c) ≥ 8.7 % and, to a smaller extent, with HbA1c reductions larger than 1.9 % after initiation of CSII. No significant changes in ERG amplitudes were found in patients with baseline HbA1c < 8.7 % and HbA1c reductions smaller than 1.9 %. CONCLUSIONS: Deterioration of subclinical retinal function from 1 to 3.5 years after initiation of CSII was associated predominantly with poorer metabolic control before initiation of CSII. Analyses of retinal function may supplement structural and morphological characteristics in the study of diabetic complications.

Cone pathway function in relation to asymmetric carotid artery stenosis: correlation to blood pressure.

PURPOSE: To examine retinal function in relation to retinal perfusion pressure in patients with carotid artery stenosis. METHODS: Thirteen patients with carotid artery stenosis without clinical eye disease underwent assessment of ophthalmic artery systolic blood pressure (OSP) by ocular pneumoplethysmography, carotid artery obstructive disease by ultrasonography, intraocular pressure by applanation tonometry, retinal perfusion by fluorescein angiography and retinal function by multifocal electroretinography (mfERG). Data analysis compared the eye on the most stenotic side with the fellow eye in the same patient. RESULTS: Ophthalmic systolic pressure was 95.8 ± 13.1 mmHg on the side with the highest degree of carotid artery stenosis (mean 94.0%) and 111.7 ± 10.3 mmHg in the fellow eyes on the side with the lesser degree of stenosis (mean 33.9%). Summed mfERG implicit times (N1 and P1) were 3.4% and 2.0% longer (p = 0.013 and 0.021), and N1 and P1 amplitudes were 18.0% and 16.0% (p = 0.0041 and 0.020) lower in eyes on the side with the higher stenosis compared with the contralateral eyes. Shorter implicit times and higher amplitudes were correlated with higher brachial systolic arterial blood pressure (p = 0.0028, 0.011, 0.041 for N1, P1, N2 implicit times, respectively, and p = 0.0086, 0.016, 0.040 for N1, P1, N2 for amplitudes, respectively, corrected for OSP). CONCLUSION: Cone function deviation was observed in clinically healthy eyes on the side with highest degree of carotid artery stenosis and was found correlated to arterial blood pressure.

Prolonged multifocal electroretinographic implicit times in the ocular ischemic syndrome.

Purpose. To examine retinal function in chronic ocular ischemia using multifocal electroretinography (mfERG). Methods. Thirteen patients with unilateral ocular ischemic syndrome (OIS) underwent assessment of ophthalmic systolic blood pressure by ocular pneumoplethysmography, carotid artery patency by ultrasonography, intraocular pressure (IOP) by applanation tonometry, retinal perfusion by fluorescein angiography, and retinal function by mfERG. Results. Ophthalmic systolic blood pressure was 67.0 +/- 11.6 mm Hg in eyes with OIS and 106.1 +/- 18.0 mm Hg in fellow eyes, whereas IOP was 13.8 +/- 3.2 and 14.4 +/- 1.7 mm Hg, respectively. Summed mfERG implicit times (N1, P1, N2) were prolonged in eyes with OIS, by 7.6%, 6.2%, and 7.5%, respectively, compared with fellow eyes (P < or = 0.0048). The retardation of retinal function was significant outside the macula, whereas the assessment of responses from the central retina was limited by high variance. Second-order kernel (first slice) summed implicit times (N1, P1, N2) were also prolonged in OIS, by 6.6%, 7.3%, and 6.8%, respectively (P < or = 0.0058). Of the amplitudes, only the second-order N2 amplitude was significantly abnormal, being reduced by 23.2% in OIS (P = 0.011). Conclusions. The function of the outer and middle layers of the retina was found to be suppressed in chronic ocular hypoperfusion. The moderate delay in retinal function does not appear to explain the prominent photopic symptom of diffuse glare in bright light, and the delay could be evidence of a functional adaptation that serves to maintain and optimize signaling under conditions of compromised perfusion. (ClinicalTrials.gov number, NCT00403195.).