The correlation between full moon and admission volume for penetrating injuries at a major trauma centre in South Africa.

BACKGROUND: The possible effect of full moon on admission volume of trauma centres is a well-mentioned phenomenon that has been perpetuated worldwide. We aimed to review the correlation between full moon and admission volume and to interrogate any possible relationship on admission for penetrating trauma. METHODS: A retrospective study from 2012 to 2018 at Pietermaritzburg Metropolitan Trauma Service (PMTS), South Africa. RESULTS: A total of 8 722 patients were admitted. Eighty-three per cent (7 242/8 722) were male and the mean age was 29 years. The total number of days during the study period was 1 953, 66 of which were 'full moon' (FM) days and 1 887 were 'non-full moon' (NFM) days. There was no significant difference between gender or age distribution. The mean number of admissions per day on FM days compared with NFM days was not significant (4.1 vs 4.5, p = 0.583). A total of 3 332 patients with penetrating trauma were admitted. This constituted 42% (113/271) of admission on FM days and 38% (3 219) on NFM days, which is not statistically significant (p = 0.229). Subgroup analysis did not demonstrate any significant difference between the number of stab wounds - 28% (77/113) vs 25% (2 124/3 219) - or gunshot wounds - 13% (16/113) vs 12% (990/3 219) - between FM and NFM days. CONCLUSION: The correlation between full moon and trauma admission is unfound in our setting. The perpetuating notion that 'it must be full moon tonight' is likely to be an urban myth with no scientific evidence for such a claim.

Selective Nonoperative Management of Abdominal Stab Wounds with Isolated Omental Evisceration is Safe: A South African Experience.

BACKGROUND AND AIMS: Selective nonoperative management of abdominal stab wound is well established, but its application in the setting of isolated omental evisceration remains controversial. The aim of the study is to establish the role of selective nonoperative management in the setting of isolated omental evisceration. MATERIALS AND METHODS: A retrospective study was conducted over an 8-year period from January 2010 to December 2017 at a major trauma center in South Africa to determine the outcome of selective nonoperative management. RESULTS: A total of 405 consecutive cases were reviewed (91% male, mean age: 27 years), of which 224 (55%) cases required immediate laparotomy. The remaining 181 cases were observed clinically, of which 20 (11%) cases eventually required a delayed laparotomy. The mean time from injury to decision for laparotomy was <3 h in 92% (224/244), 3-6 h in 6% (14/244), 6-12 h 2% (4/244), and 12-18 h in 1% (2/244). There was no significant difference between the immediate laparotomy and the delayed laparotomy group in terms of length of stay, morbidity, or mortality. Ninety-eight percent (238/244) of laparotomies were positive and 96% of the positive laparotomies (229/238) were considered therapeutic. CONCLUSION: Selective nonoperative management for abdominal stab wound in the setting of isolated omental evisceration is safe and does not result in increased morbidity or mortality. Clinical assessment remains valid and accurate in determining the need for laparotomy but must be performed by experienced surgeons in a controlled environment.

Hanging-related injury in Pietermaritzburg, South Africa.

BACKGROUND: Hanging is a common form of self-harm, and emergency care physicians will not infrequently be called upon to manage a survivor.Despite the relative frequency of the injury, there is a paucity of literature on the topic and the spectrum and incidence of associated injuries are poorly described. OBJECTIVES: To review experience with management of victims of hanging at a major trauma centre in South Africa. METHODS: All patients treated by the Pietermaritzburg Metropolitan Trauma Service following a hanging incident between December 2012 and December 2018 were identified from the Hybrid Electronic Medical Registry. Basic demographics were recorded, and the management and outcome of each patient were noted. RESULTS: During the 6-year period under review, a total of 154 patients were seen following a hanging incident. The mean age was 29.4 years. There were 24 females (15.6%) and 130 males (84.4%). The vast majority (n=150; 97.5%) had attempted suicide, and only 4 hangings (2.5%) were accidental. A total of 92 patients (60.9%) had consumed alcohol prior to the incident. There were 23 patients with a Glasgow Coma Score (GCS) <9 (severe traumatic brain injury (TBI)), 14 with a GCS of 9 - 12 (moderate TBI) and 117 with a GCS >12 (mild TBI). A total of 7 patients (4.5%) required intensive care unit admission, and 25 (16.2%) required intubation. The following extracranial injuries were documented on computed tomography scans: hyoid bone fractures (n=2), cervical spine fracture (n=10), mandible fracture (n=4) and oesophageal injury (n=1). Intracranial pathology was evident on 27.0% of scans, with the most common finding being global cerebral ischaemia. The mortality rate was 2.5% (4/154). CONCLUSIONS: Hanging is a common mechanism of self-harm. It is associated with significant injuries and mortality. The acute management of hanging should focus on airway protection followed by detailed imaging of the head and neck. Further work must attempt to include mortuary data on hanging.

Discrepancy in clinical outcomes of patients with gunshot wounds in car hijacking: a South African experience.

INTRODUCTION: Discrepancy in outcomes between urban and rural trauma patients is well known. We reviewed our institutional experience with the management of gunshot wounds (GSWs) in the specific setting of car hijacking and focused on clinical outcome between rural and urban patients. METHODS: A retrospective review was conducted at a major trauma centre in South Africa over an 8-year period for all patients who presented with any form of GSWs in car hijacking settings. Specific clinical outcomes were compared between rural and urban patients. RESULTS: A total of 101 patients were included (74% male, mean age 34 years). Fifty-five per cent were injured in rural areas and the remaining 45% (45/101) were in the urban district. Mean time from injury to arrival at our trauma centre was 11 hours for rural and 4 hours for urban patients (p < 0.001). Seventy-six per cent (76/101) sustained GSWs to multiple body regions. Sixty-three of the 101 (62%) patients required one or more operative interventions. In individual logistic regressions adjusted for sex and number of regions injured, rural patients were 9 (95% CI: 1.9-44.4) and 7 (95% CI: 2.1-24.5) times more likely than urban patients to have morbidities or required admissions to intensive care respectively. The risk of death in rural patients was 36 (95% CI: 4.5-284.6) times higher than that of urban patients. CONCLUSION: Patients who sustained GSWs in carjacking incidents that occurred in rural areas are associated with significantly greater morbidity and mortality compared with their urban counterparts. Delay to definitive care is likely to be the significant contributory factor, and improvement in prehospital emergency medical service is likely to be beneficial in improving patient outcome.

The spectrum of animal related injuries managed at a major trauma centre in South Africa.

BACKGROUND: Humans come into contact and interact with an array of animals in a number of areas and environments. We set out to review our experience with animal-related injuries in Pietermaritzburg, KwaZulu-Natal, South Africa. METHOD: All patients who sustained an injury secondary to an interaction with an animal in the period December 2012-December 2017 were identified from the Hybrid Electronic Medical Registry (HEMR). RESULTS: There were 104 patients in the study sample. The mean age of patients in the study was 32.8 years, with a range from 1 to 76 years old. 75% (n = 78) were male and 25% (n = 26) female. Out of the 104 animal-related injuries, 67 were blunt trauma, 39 penetrating trauma and 3 a combination of blunt and penetrating trauma. The species causing trauma included dogs (53), horses (29), cows (18), buffalo (1), warthog (1), impala (1) and a single goat (1). The median time from injury to hospitalisation was 46.62 hours (range from 0 to 504 hours). Injuries occurred to the head (n = 32), face (n = 9), neck (n = 32), abdomen (n = 22), urogenital system (n = 6), upper limb (n = 39) and lower limb (n = 39). The Injury Severity Score (ISS) mean for the patients was 8.16, the range 1-4, the median 9 and the standard deviation 6.88. In 49 patients the treatment was non-operative. In the remaining 55 patients, a total of 68 operative procedures were required. Operations included wound debridement/surgical washout (n = 38), laparotomy (n = 9), arterial repair/ligation (n = 8), skin graft (n = 4), craniotomy (n = 5), fasciotomy (n = 2), amputation (n = 1), and placement of an ICP monitor (n = 1). 49 of these operations were for patients with dog bite injuries. The mean hospital stay was 0.13 days with a range of 0-4 days. Four patients were admitted to the Intensive Care Unit (ICU) and two patients died. CONCLUSION: Human interactions with animals may result in injuries which require surgical treatment. The most common animal injury is a dog bite but in the case of the larger domestic farm animals, blunt force type injuries and goring can result in significant injuries which require complex surgical interventions.

Quantifying the burden of trauma imaging on the CT scan service at a major trauma centre in South Africa.

BACKGROUND: Imaging is an integral part of trauma management and the huge burden of trauma in South Africa places substantial pressures on radiology resources. This study aims to provide a holistic overview of the burden of trauma imaging and the cost of trauma to a busy CT scanning facility at a tertiary hospital in South Africa. METHOD: We set out to describe and quantify the impact of blunt poly-trauma on CT scanning services at Grey's Hospital in Pietermaritzburg. We aimed to provide a holistic assessment in terms of use of equipment and staff, cost to the hospital and overall usage of CT scanning. RESULTS: Over the four-year study period, 1572 patients required a CT scan following blunt torso trauma (mean age: 30 years, 81% males). Of the 1572 patients, 625 had a chest radiograph (40%), 383 a cervical spine X-ray (24%), 347 a pelvic X-ray (22%), 292 a skull X-ray (18%), 193 a limb X-ray (12%), 133 an abdominal radiograph (8%), and 86 a FAST scan (5%). The 1572 CT included: 967 head, 568 neck, 65 chest, 241 abdominal, 228 pelvic, 12 upper limb, 38 lower limb and 394 had full body (Pan) CT scan. The mean total cost of the CT scanning for blunt poly-trauma is ZAR 12 000. The total cost of CT scanning for blunt poly-trauma is 0.92% of the total hospital expenditure. Roughly 7.8% of the total hours worked by the CT scanner over the time period under review was dedicated to blunt poly-trauma. CONCLUSION: Blunt poly-trauma is a preventable disease, which has a major financial impact on the healthcare system in general. This study has documented the tremendous burden it places on an already stretched CT scanning service.

The spectrum of self inflicted injuries managed at a major trauma centre in South Africa.

BACKGROUND: Infantile hypertrophic pyloric stenosis (IHPS) is the thickening of both muscle layers of the pylorus and is most commonly found in first-born males. It usually presents with projectile, non-bilious vomiting. Late presentation leads to severe dehydration and malnutrition with deranged serum-electrolytes and acid-base imbalance delaying treatment and prolonging hospital stay. This study aims to evaluate the profile, management and outcome of IHPS at a tertiary hospital in Bloemfontein, South Africa. METHOD: The study was a retrospective, descriptive record review including all patients with IHPS admitted to Universitas Hospital from January 2008 to February 2016. Of the 22 patients admitted, files for 19 patients were available for inclusion. RESULTS: Sixteen (84.2%) of the 19 patients were male. Of the 11 patients with available birth order, two were first-, two second-, six third- and one fourth-born. The patients' ages ranged from 27 to 194 days (median 51 days). The most common symptoms were projectile vomiting (78.9%) and poor weight gain (68.4%). Six patients had no ultrasound done, and 17 patients underwent a Ramstedt-pyloromyotomy. Eight patients received atropine as part of their initial management. The duration of symptoms ranged from 1 to 58 days (median 14 days). There was no reported mortality. The length of stay ranged from 2 to 60 days (median 7 days). CONCLUSION: The gender distribution and age at presentation were in keeping with the literature but not the birth order. The delay before surgery emphasises the poor general health and deranged biochemical state the patients present at the hospital.

Primary repair of duodenal injuries: a retrospective cohort study from a major trauma centre in South Africa.

BACKGROUND AND AIMS: The management of duodenal trauma remains controversial. This retrospective audit of a prospectively maintained database was intended to clarify the operative management of duodenal injury at our institution and to assess the risk factors for leak following primary duodenal repair. MATERIALS AND METHODS: This was a retrospective study undertaken at the Pietermaritzburg Metropolitan Trauma Service, Pietermaritzburg, South Africa. Operative techniques used for duodenal repair were recorded. Our primary outcome was duodenal leak in the postoperative period. Patients from January 2012 to December 2016 were included. All duodenal injuries were graded according to the American Association for the Surgery of Trauma (AAST) grading. Only patients who had a primary repair were included in the final analysis. RESULTS: During the five-year data collection period, a total of 562 patients underwent a trauma laparotomy; of which 94 patients sustained a duodenal injury. A primary pyloric exclusion and gastro-jejunostomy (PEG) was performed in three patients. These three were then excluded from further analysis. Of the 91 primary duodenal repairs, seven (8%) subsequently leaked. These were managed by PEG in three and by secondary repair and para-duodenal drainage in four. The two physiological parameters most associated with subsequent leak were lactate and pH level. There was a significantly higher mortality rate for those who leaked vs those who did not leak. Chi-squared test revealed a significant difference in the leak rate between AAST I (0%), AAST-II (1.6%) and AAST-3 (66.7%) grade injuries (p <0.01). CONCLUSION: The trend towards primary repair of duodenal injuries appears to be justified. However duodenal leak remains a significant risk in certain high risk patients and strategies to manage injuries in this subset requires further work.

Pre-operative asymptomatic bacteriuria: a risk factor for prosthetic joint infection?

BACKGROUND: Infection is a rare complication following implantation of prosthetic material into a joint. The impact of asymptomatic bacteriuria (ASB) before elective operations and the subsequent risk of prosthetic joint infection (PJI) are not well understood. AIMS: To assess the prevalence of ASB amongst patients undergoing total arthroplasty of the hip and knee; and to determine the rates of PJI diagnosed within two years of the arthroplasty and if ASB is an independent risk factor for developing PJI. METHODS: Patients who had total/unicondylar knee or total hip arthroplasty were reviewed retrospectively over a five-year period. Pre-operative urine samples within one year of surgery were analysed, and those with ASB were identified. The primary outcome was PJI within the first postoperative year. FINDINGS: In total, 5542 patients were included. Of these, 4368 had a pre-operative urine culture recorded. The prevalence of ASB was 140 of 4368 (3.2%). The overall PJI rate was 56 of 5542 (1.01%). Of those with PJI, 33 had a pre-operative urine sample recorded. The infection rates were 5% (seven of 140) in the ASB group, 0.61% (26 of 4228) in the no-ASB group and 1.96% (23 of 1174) in the group without a urine sample (P < 0.001). The ASB isolate was the same micro-organism as the PJI isolate in one of the seven cases. CONCLUSION: The association between ASB and PJI is statistically significant, but the urine isolates did not relate to the isolates in the prosthetic joint, suggesting that the relationship is unlikely to be causal.

A raised serum lactate level is an independent predictor of in-hospital mortality in patients with isolated cerebral gunshot wounds.

BACKGROUND: Cerebral gunshot wounds (CGSWs) represent a highly lethal form of traumatic brain injury, and triaging these patients is difficult. The prognostic significance of the serum lactate level in the setting of CGSWs is largely unknown. OBJECTIVES: To examine the relationship between elevated serum lactate levels and mortality in patients with isolated CGSWs. METHODS: A retrospective review of the regional trauma registry was undertaken at the Pietermaritzburg Metropolitan Trauma Service, South Africa, over a 5-year period from 1 January 2010 to 31 December 2014. All patients with an isolated CGSW were included. RESULTS: A total of 102 patients with isolated CGSWs were identified. Of these, 92.2% (94/102) were male. The mean age (standard deviation) was 29 (8) years, and the in-hospital mortality rate was 21.6% (22/102). The mean serum lactate level was significantly higher among non-survivors than among survivors (6.1 mmol/L v. 1.3 mmol/L; p<0.001). Lactate levels among non-survivors were <2 mmol/L in 4.5%, 2 - 3.99 mmol/L in 9.1%, 4 - 5.99 mmol/L in 36.4% and ≥6 mmol/L in 50.0%. The odds ratio for mortality with a lactate level of 4 - 5.99 mmol/L was 67 (95% confidence interval (CI) 1.7 - 2 674.2), while for a lactate level of ≥6 mmol/L it was 1 787 (95% CI 9.0 - 354 116.1). The serum lactate level accurately predicted mortality even after adjustment for other variables. Based on a receiver operating curve analysis, an optimal cut-off of 3.3 mmol/L for serum lactate as a predictor for mortality was identified (area under the curve = 0.957). CONCLUSIONS: CGSWs are associated with significant mortality, and a raised serum lactate level appears to be an independent predictor of in-hospital mortality. It is a potentially useful adjunct in the resuscitation room for identifying patients with a very poor prognosis.

Validation of the Baragwanath mortality prediction score for cerebral gunshot wounds: the Pietermaritzburg experience.

INTRODUCTION: Cerebral gunshot wounds (GSW) are highly lethal injuries. To date, only one clinical scoring system to predict mortality in a developing world setting has been described. This is the Baragwanath mortality prediction score ("ABC": admission blood pressure, brain matter spillage and consciousness level). MATERIALS AND METHODS: We performed a retrospective review of prospectively entered data for a cohort of patients with isolated cerebral GSWs over a 5-year period (January 2010-December 2014) in our institution. We aimed to validate the Baragwanath ABC mortality prediction score in our population. RESULTS: During the 5-year study period, 102 patients with isolated cerebral GSWs were reviewed, 22% (22/102) of which died. Based on the total ABC score (1-5), the mortality was 0% for 1, 21% for 2, 67% for 3, 92% for 4, and 100% for 5. The ABC score has a sensitivity of 82% (95% CI 60-95%), specificity of 96% (95% CI 89-99%), PPV of 86% (95% CI 66-96%) and NPV of 95% (95% CI 86-99%). CONCLUSIONS: The Baragwanath mortality prediction score accurately predicts non survival of patients with a cerebral GSW in our patient cohort. Further validation studies in other populations are required before this system can be widely adopted.

The correlation between ATLS and junior doctors' anatomical knowledge of central venous catheter insertion at a major trauma centre in South Africa.

OBJECTIVE: To review the ability of junior doctors (JDs) in identifying the correct anatomical site for central venous catheterization (CVC) and whether prior Advanced Trauma Life Support (ATLS) training influences this. DESIGN: We performed a prospective, observational study using a structured survey and asked a group of JDs (postgraduate year 1 [PGY1] or year 2 [PGY2]) to indicate on a photograph the exact site for CVC insertion via the internal jugular (IJV) and the subclavian (SCV) approach. This study was conducted in a large metropolitan university hospital in South Africa. RESULTS: A total of 139 JDs were included. Forty-four per cent (61/139) were males and the mean age was 25 years. There were 90 PGY1s (65%) and 49 PGY2s (35%). Overall, 32% (45/139) were able to identify the correct insertion site for the IJV approach and 60% (84/139) for the SCV approach. Of the 90 PGY1s, 34% (31/90) correctly identified the insertion site for the IJV approach and 59% (53/90) for the SCV approach. Of the 49 PGY2s, 29% (14/49) correctly identified the insertion site for the IJV approach and 63% (31/49) for the SCV approach. No significant difference between PGY1 and 2 were identified. Those with ATLS provider training were significantly more likely to identify the correct site for the IJV approaches [OR=4.3, p=0.001]. This was marginally statistically significant (i.e. p>0.05 but <0.1) for the SCV approach. CONCLUSIONS: The majority of JDs do not have sufficient anatomical knowledge to identify the correct insertion site CVCs. Those who had undergone ATLS training were more likely to be able to identify the correct insertion site.

The effect of a concomitant renal injury on the outcome of colonic trauma.

BACKGROUND: The management of colon injuries has steadily evolved over the course of the last half century. So too has the management of renal trauma. It is not clear from the literature as to whether concomitant colon and renal injuries carry increased risk of morbidity and mortality, and whether this combination of injuries necessitates a specifically tailored management approach. METHODS: A retrospective review was carried out for the period January 2012 to December 2016. All patients over the age of 18 years who were subjected to laparotomy for penetrating trauma (gunshot wounds or stab wounds) and who sustained an intra-operatively proven colonic injury were included in this study. Operative management and outcomes were investigated. A direct comparison was made between patients with a combined colonic and renal injury and those with only a colonic injury. RESULTS: Over the five-year period a total of 268 patients sustained a colonic injury. The 239 patients with a colonic injury (Group A) were compared to the 29 patients with a combined colonic and renal injury (Group B). Regarding the management of the colonic injuries, there were no differences in the rates of primary repair, anastomosis, exteriorization, or damage control surgery between groups A and B. As for the management of the renal injury, 14 were not explored at laparotomy; in 12 a nephrectomy was performed and in 3 the renal injury was repaired. The nephrectomy cohort were more likely to have undergone damage control surgery, to be admitted to ICU, to receive a colostomy, and had higher mortality. While there was no difference in the need for damage control surgery or mortality between groups, Group B had a significantly greater need for ICU admission. Morbidity was similar between the two groups - in particular, there was no difference in the rates of either gastro-intestinal complications or acute kidney injury between the two groups. CONCLUSION: In patients with combined colon and renal injuries, it seems reasonable to treat each organ on its own merit, without the expectation of increased morbidity or mortality. In the non-damage control setting, most colonic injuries may be safely repaired, and a peri-renal haematoma that is not expanding or actively bleeding may be safely left alone.

The accommodation of lens implants.

Efforts devoted to the production of accommodative lens implants may be premature as there is conflicting information about the functional performance of the aged ciliary muscle which may determine their performance. Additional doubts exist on the performance of the ageing lenticular capsule in connection with some types of implant. Not only do these matters need resolving, but the change in the optical power of the eye needs also to be large enough for reading glasses to become unnecessary. However, not all these strictures apply to the development of accommodative lens implants for children who may be aphakic following operations, e.g. for congenital cataracts.

Ethnic variability of the vasculature of the optic disc in normal and glaucomatous eyes.

PURPOSE: Although disc pallor is associated with glaucoma, the structural macro-anatomy of the disc vasculature has received little attention, and possible ethnic differences have not been considered. Accordingly we studied the distribution of blood vessels crossing the rim of the optic disc. METHODS: Thirty normal controls, and 50 glaucomatous cases with a unilaterally impaired visual field were studied. The sample populations included white Caucasian, and African and Afro/Caribbean volunteers. A b/w photographic method of imaging the blood vessels crossing the rim of the optic disc was used, the illuminant being green. The prints used in the analysis had been masked during their exposure to enhance contrast. The numbers of vessels, grouped into large (~60nm), medium (~30nm), and small (~10nm) lumina, were counted, the disc images being divided radially into eight equal sectors. RESULTS: While the large vessels crossed the rim mainly along the vertical, the small ones did so mainly in the horizontal. The distribution of the medium vessels was unpolarized but their crossings predominated on the nasal side. The vessel patterns differed significantly between the two ethnic groups as regards both number and distribution along the rim of the disc, the smaller vessels being more numerous in Caucasian eyes (p~0.02). Rim crossings by vessels were smaller in glaucomatous eyes in both ethnic groups. In normal eyes there was a statistically significant age-related decline in the number of small vessels after the age of 20 years. CONCLUSIONS: There exists a statistically significant inverse relation between the number of capillaries crossing the disc rim and the vertical cup/disc ratio. Caucasian rims show the larger number of capillaries crossing. (Eur J Ophthalmol 2004; 14: #-507).

Ethnic variability of the vasculature of the optic disc in normal and in glaucomatous eyes.

PURPOSE: Although disc pallor is associated with glaucoma, the structural macro-anatomy of the disc vasculature has received little attention, and possible ethnic differences have not been considered. Accordingly we studied the distribution of blood vessels crossing the rim of the optic disc. METHODS: Thirty normal controls, and 50 glaucomatous cases with a unilaterally impaired visual field were studied. The sample populations included white Caucasian, and African and Afro/Caribbean volunteers. A b/w photographic method of imaging the blood vessels crossing the rim of the optic disc was used, the illuminant being green. The prints used in the analysis had been masked during their exposure to enhance contrast. The numbers of vessels, grouped into large (approximately 60nm), medium (approximately 30nm), and small (approximately 10nm) lumina, were counted, the disc images being divided radially into eight equal sectors. RESULTS: While the large vessels crossed the rim mainly along the vertical, the small ones did so mainly in the horizontal. The distribution of the medium vessels was unpolarized but their crossings predominated on the nasal side. The vessel patterns differed significantly between the two ethnic groups as regards both number and distribution along the rim of the disc, the smaller vessels being more numerous in Caucasian eyes (p approximately 0.02). Rim crossings by vessels were smaller in glaucomatous eyes in both ethnic groups. In normal eyes there was a statistically significant age-related decline in the number of small vessels after the age of 20 years. CONCLUSIONS: There exists a statistically significant inverse relation between the number of capillaries crossing the disc rim and the vertical cup/disc ratio. Caucasian rims show the larger number of capillaries crossing.

On the age-related prevalence of anisometropia.

Data on the prevalence of non-amblyopic anisometropia amongst adults throughout the world were tabulated and plotted as a function of age. The global picture reveals a systematic rise in the prevalence of anisometropia with age, the fitted linear regression having a significant positive slope of 1% (p < 0.0005) for every 7 years. The distribution may embrace a juvenile rise and a later, post-presbyopic one, perhaps due to neuro-senescence.