Migrating scleral explants.

Anterior migration of an extrascleral explant is an uncommon complication following buckling procedures. We report five patients where the explant cheesewired through the rectus muscle insertion following retinal detachment surgery. Muscles were not disinserted at the time of surgery in any case. Ocular motility problems were only seen in two patients. The probable mechanisms of this hitherto unreported complication are discussed.

Age-related normal tolerance intervals for retinal vascular response to systemic autonomic nerve stimulation.

This study establishes the age-adjusted tolerance intervals for retinal vascular responses to sustained handgrip contraction (a test of sympathetic nerve function). Forty adult subjects (mean age: 39.7 +/- 14.1 years, range: 20 to 72 years; 19 males) were included in the final analysis. Mean percentage calibre change in response to sustained handgrip contraction in this population was -5.61% with a significant correlation between subject age and percentage retinal vessel calibre change (p less than 0.001). Mean retinal arteriolar calibre change in response to systemic autonomic stimulation varied significantly with age: between -8.48% at age 20 years and -2.06% at age 70 years with a mean of -5.95% at the mean age of 39.7 years. The standard deviation is 3.04% and the 95% confidence intervals were set between +/-6.17%. This autoregulatory reflex appears to be inversely related to age.

Retinal vessel responses to systemic autonomic stimulation in fellow eyes of patients with retinal vein occlusion.

The retinal vessel calibre responses to systemic autonomic stimulation were studied in fellow eyes of 11 patients with central retinal vein occlusion (CRVO) and 10 patients with branch retinal vein occlusion (BRVO), using sustained isometric muscle contraction as the stimulus. These vessel responses were compared to those of a control group of 11 subjects of similar ages. The changes in retinal vessel calibre were measured using the Quantimet Image Analyser. There was no significant difference in mean arteriolar constriction during isometric muscle contraction (mean +/- SEM) between the CRVO group (6.0 +/- 1.34%) and the BRVO group (5.4 +/- 0.31%), (p greater than 0.05), and between either of these groups compared with the control group (7.4 +/- 1.20%), (p greater than 0.50). Similarly there was no significant difference in mean venule responses between the groups (CRVO 4.9 +/- 0.48%; BRVO 4.6 +/- 0.63%; control subjects 3.8 +/- 0.90%; p greater than 0.05). The diastolic blood pressure responses were similarly not significantly different between the 3 groups (CRVO 22.3 +/- 1.27, range + 17 to 29 mmHg; BRVO 25.8 +/- 2.9 mmHg, range 18 to 45 mmHg; control subjects 21.3 +/- 1.7 mmHg, range 16 to 35 mmHg), (p greater than 0.10). The implications of the results are discussed.

Impaired autoregulation of the retinal vasculature and microalbuminuria in diabetes mellitus.

The relationship between microalbuminuria and retinal vessel responses to sustained handgrip contraction was studied in a group of 20 diabetic patients. The diabetics were divided into two groups based on their albumin excretion rates (AER): Group 1 (AER less than or equal to 10 mcg/min) consisted of ten diabetic patients, mean age 55.8 +/- 3.9 years (mean +/- SEM); five IDDM and five NIDDM. Group 2 (AER greater than 10 mcg/min) comprised ten diabetic patients: mean age 56.8 +/- 3.04 years; six IDDM and four NIDDM. Both groups were similar in that there were no significant differences between mean age, type of diabetes, mean duration of diabetes, glycaemic control or mean resting blood pressures. Group 2 diabetics had a higher incidence of autonomic dysfunction than Group 1, based on the results of four standard tests of autonomic nerve function. There were significantly decreased retinal vessel responses to sustained handgrip contraction in Group 2 diabetics (mean arteriolar constriction 0.1 +/- 0.32%, and mean venule constriction 1.0% +/- 0.99%) compared with Group 1 diabetics (mean arteriolar constriction 6.9 +/- 1.69%, and mean venule constriction 4.2 +/- 0.05%). Retinopathy was slightly worse in Group 2. The implications of the association of microalbuminuria (AER greater than 10 mcg/min) and loss of retinal vessel reactivity to sustained handgrip contraction are discussed.

The effect of cervical sympathectomy on retinal vessel responses to systemic autonomic stimulation.

The retinal vessel calibre responses to systemic sympathetic stimulation, were studied in nine patients (eight male; mean age: 31.7 years; range: 19-58 years) with unilateral disruption of their cervical sympathetic tract. All patients had ipsilateral decreased/absent facial sweating and a Horners syndrome, evidence of unilateral sympathetic denervation. Both eyes of each patient were studied and the results were analysed in two groups: the group of nine sympathectomised eyes and the control group of unaffected fellow eyes. During handgrip contraction there was a significant difference in the mean retinal arteriolar constriction (mean +/- SEM) between the group of sympathectomised eyes (4.6 +/- 0.89%) and control eyes (7.1 +/- 1.13%), p less than 0.01. Similarly, there was a significant difference in mean venule constriction during sustained handgrip contraction between the group of sympathectomised eyes (1.5 +/- 0.67%) and control eyes (4.9 +/- 0.98%), p less than 0.05. There was no significant difference in the mean rise in diastolic blood pressure between the two groups: control eyes +27.9 +/- 2.38 mmHg and sympathectomised eyes +27.8 +/- 2.25 mmHg. There was no correlation between the blood pressure and retinal vessel responses in either group. These results suggest that the sympathetic nervous system plays an integral role in retinal blood flow regulation.

Intraocular pressure responses to systemic autonomic stimulation in diabetes mellitus.

The acute changes in intraocular pressure during sustained handgrip contraction (2.5 minutes duration) and the Valsalva manoeuvre (15 seconds duration), both standard tests of autonomic nerve function were studied in 14 diabetic patients and 14 similar aged control subjects. During sustained handgrip contraction, diastolic blood pressure increased by 16.35 +/- 1.87 mmHg in the diabetic patients and 21.36 +/- 0.66 mmHg for the control group. Mean intraocular pressure decreased by 0.71 +/- 0.43 mmHg in the diabetics, p less than 0.05 and 0.64 +/- 0.27 mmHg, p less than 0.01) in the control group. There was no correlation between the blood pressure and the intraocular pressure responses in either group. On release of handgrip contraction, mean recovery intraocular pressure over 5 minutes was significantly lower than mean baseline values for the two groups; control: baseline 14.78 +/- 0.49 to 14.14 +/- 0.67, p less than 0.001 and diabetic: 14.57 +/- 0.65 to 13.86 +/- 0.72, p less than 0.001. During the Valsalva manoeuvre, there was a significant rise in intraocular pressure in the control (+7.85 +/- 0.75 mmHg, p less than 0.001) and the diabetic group (+7.93 +/- 1.18 mmHg, p less than 0.001). 5 minutes after release of intrathoracic pressure, mean recovery intraocular pressure remained significantly below baseline values for the two groups. The Valsalva ratios were in the normal range for the control group (1.21 to 2.2) while 2 diabetics had abnormal ratios.

Responses of the retinal circulation to systemic autonomic stimulation in diabetes mellitus.

The retinal vessel calibre responses to systemic sympathetic stimulation, were studied in 22 randomly selected diabetic patients (mean age +/- SEM: 54.7 +/- 2.59 years, range 25-73; 13 IDDM, 9 NIDDM; 4 females), using sustained isometric muscle contraction as the stimulus. At a different session the integrity of the autonomic nerve function in these diabetic patients was assessed using 3 standard tests of autonomic nerve function, based on cardiovascular reflexes. Diabetic patients with an intact autonomic nervous system: Group 1, (n = 11, mean age: 54.9 +/- 4.55 years, 7 IDDM 4 NIDDM) showed a mean arteriolar constriction of 9.2% (SEM 2.89, p less than 0.01) and a mean venule constriction of 5.1% (SEM 1.73, p less than 0.02), for a mean rise in diastolic blood pressure of 23.7 mmHg (SEM 2.19 range: 13-33). There were no significant mean retinal vessel responses however, in diabetics with autonomic dysfunction (Group 2): mean arteriolar constriction of 1.2% (SEM 1.38 p greater than 0.05) and venule constriction of 2.1% (SEM 1.38, p greater than 0.05); for a mean rise in diastolic blood pressure of 19.8 mmHg (SEM 4.49, range: 2-50). There was no correlation between the rise in diastolic blood pressure and the retinal arteriolar constriction in the 2 groups (Group 1:r = 0.45, p greater than 0.01 and Group 2: r = 0.56, p greater than 0.05). Duration, type and control of diabetes were not significantly different between the 2 groups. The severity of retinopathy was slightly worse in Group 2 compared to Group 1. These results point to an association between autonomic neuropathy and failure of regulation of retinal blood flow.

Intraocular pressure responses to systemic autonomic stimulation.

The intraocular pressure (IOP) responses to two standard tests of autonomic nerve function were studied in 15 healthy subjects, mean age 33 years (range: 20-64). Both tests are based on cardiovascular reflexes: (1) The rise in diastolic blood pressure provoked by sustained isometric muscle contraction, a response mediated by the sympathetic nervous system and (2) The heart-rate responses to the Valsalva manoeuvre, a response mediated by the parasympathetic nervous system. During sustained isometric exercise, the mean IOP decreased significantly from baseline values of 12.60 mmHg (SEM 0.55) to 11.26 mmHg (SEM 0.32, p less than 0.05) while mean diastolic blood pressure increased by 20.80 mmHg (range: +12 to +53 mmHg). However there was no direct correlation between them (r = -0.05). Post exercise the mean IOP remained significantly lower than baseline values for five minutes (p less than 0.01). During the Valsalva manoeuvre, there was a significant increase in IOP of 7.20 mmHg from a baseline of 12.80 mmHg (SEM 0.45) to 20.00 mmHg (SEM 0.78, p less than 0.001); during the recovery period, mean IOP was significantly lower than baseline values at 12.13 mmHg (SEM 0.39, p less than 0.05). The mean Valsalva ratio was normal at 1.68 (range: 1.2-2.6). The possible mechanisms involved in these responses are discussed.

Intra-ocular pressure changes during rapid sequence induction of anaesthesia. A comparison between thiopentone and suxamethonium and thiopentone and atracurium.

The changes in intra-ocular pressure associated with two different anaesthetic induction and tracheal intubation techniques were compared (n = 30). After pre-oxygenation, Group A received thiopentone (5 mg/kg) followed by suxamethonium (1.5 mg/kg), both within 25 seconds, and Group B atracurium (0.5 mg/kg) followed by thiopentone (5 mg/kg) again both within 25 seconds. Tracheal intubation occurred after one minute in Group A and 2 minutes in Group B to allow for full paralysis. In Group A intra-ocular pressure did not alter significantly from baseline and the maximum increase was only 0.93 mmHg. The statistical type II error risk was consistently below 55% and all 95% confidence limits included negative values. Intra-ocular pressure in Group B was consistently lower than baseline (p less than 0.05) but with a longer induction-intubation interval. These results therefore provide valuable information about the 'balance of risks' when choosing a muscle relaxant for an inadequately starved patient with a penetrating eye injury.

Retinal circulation responses to systemic autonomic nerve stimulation.

The retinal vessel calibre responses to controlled stimulation of the autonomic nervous system were studied in 10 healthy subjects, using sustained isometric muscle contraction as stimulus. Each subject was studied twice using different mydriatic agents, (1) g.tropicamide 1% a parasympatholytic agent and (2) g. phenylephrine 10% a sympathetic agonist. In the tropicamide study, there was a mean arteriolar constriction of 8.1% (SEM 1.67, p less than 0.001) and venule constriction of 3.7% (SEM 0.85, p less than 0.001) with a mean rise in diastolic blood pressure of 27.4 mmHg (SEM 2.95, range: 13-45 mmHg). When g. phenylephrine 10% was used, there was a mean arteriolar constriction of 8.6% (SEM 1.68, p less than 0.001) and venule constriction of 4.8% (SEM 1.22, p less than 0.001) with a mean rise in diastolic blood pressure of 29.2 mmHg (SEM 2.56, range: 17-44 mmHg). There was no significant difference in retinal vessel calibre in the recovery phase compared to baseline phase (p greater than 0.05) or between the two mydriatic agents on vessel responses (p greater than 0.05). There was no correlation between the rise in diastolic blood pressure and the degree of retinal vessel constriction, during handgrip contraction in either study. This study has demonstrated a significant association between retinal vessel calibre and systemic autonomic nerve stimulation. The possible mechanisms for the retinal vessel constriction observed in this study are discussed.