Lionel G Ripley

Assessment of colour vision as a screening test for sight threatening diabetic retinopathy before loss of vision

Aim: To assess the effects of sight threatening diabetic retinopathy (STDR) on colour vision and to evaluate automated tritan contrast threshold (TCT) testing for STDR screening before significant visual loss. Method: Patients were recruited from a hospital based photographic screening clinic. All subjects underwent best corrected Snellen visual acuity (BCVA) and those with 20/30 vision or worse were excluded. Automated TCT was performed with a computer controlled, cathode ray tube based technique. The system produced a series of sinusoidal, standardised equiluminant chromatic gratings along a tritan confusion axis. Grading of diabetic retinopathy was made by one of the team of experienced ophthalmic registrars (SpR) using slit lamp biomicroscopy and a 78D lens; HbA1c and urine albumin were also tested. Results: Patients with STDR had significantly worse TCT despite normal BCVA (p<0.0001). TCT yielded a sensitivity of 100% for detecting diabetic maculopathy and 94% for STDR with a specificity of 95%. Logistic regression analyses showed that TCT (p<0.001) and HbA1c (p<0.05) correlated significantly with the presence of STDR but duration of diabetes, urine albumin counts, and BCVA failed to show any significant correlation. No associations between TCT and duration of disease, TCT and HbA1c, and TCT and urine albumin counts were found. Conclusion: Tritan colour vision deficiency was observed in patients with STDR despite their normal BCVA. These results indicate that automated TCT assessment is an effective and clinically viable technique for detecting STDR, particularly diabetic maculopathy, before visual loss.

The ultimate Aberdeen knot

INTRODUCTION The Aberdeen knot has been shown to be stronger and more secure than a surgeons knot for ending a suture line. No data exist as to the ideal configuration of the Aberdeen knot. The Royal College of Surgeons of England in their Basic Surgical Skills Course, 2002 recommended six throws. The aim of this experiment is to find the ideal combination of throws and turns. MATERIALS AND METHODS Aberdeen knots of various configurations were tied in 0-PDS suture (Ethicon, Johnson and Johnson). Each configuration was tied 10 times. A materials testing machine was used to test the knots to destruction in a standardised manner. RESULTS The knots were seen to behave in two ways. They either slipped and unravelled, or broke. Knots tied with fewer than three throws were unreliable. Knots tied with three throws and two turns appear to be the strongest configuration. Adding further throws and turns does not increase the strength of an Aberdeen knot. CONCLUSIONS An Aberdeen knot tied with three throws and two turns is the ultimate Aberdeen knot.

Chromatic contrast thresholds as a prognostic test for visual improvement after macular hole surgery: color vision and macular hole surgery outcome.

Purpose To evaluate the relationship between preoperative chromatic contrast thresholds, postoperative visual acuities (VA), and visual improvement after macular hole surgery. Methods A consecutive series of patients with Stage II to IV macular holes was studied before macular hole surgery. Preoperative chromatic contrast thresholds, VA, and reading acuity were analyzed in relation to the postoperative visual function. The chromatic contrast thresholds were measured using a computerized cathode ray tube-based system along red-green and tritan confusion axes. Results Preoperative and postoperative chromatic contrast thresholds were elevated significantly in affected eyes (P < 0.001). Preoperative VA showed a strong correlation with postoperative VA (r = 0.66, P < 0.001) but a weak correlation with visual improvement (r = −0.33, P = 0.03). Red-green contrast threshold correlated strongly with both the distance visual improvement (r = −0.77, P < 0.001) and reading visual improvement (r = -0.61, P < 0.001). Tritan contrast threshold, however, showed a slightly weaker correlation (distance: r = −0.63, P < 0.001; reading: r = −0.47, P < 0.005). Conclusions These results suggest that chromatic contrast thresholds, especially the red-green contrast threshold, represent a better prognostic guide for visual improvement after macular hole surgery than VA measurement.

Screening for CMV retinitis using chromatic discrimination thresholds and achromatic contrast sensitivity

BACKGROUND Many patients with cytomegalovirus retinitis (CMVR) are unaware of visual disturbance so screening is advocated for patients with HIV and low CD4 counts. Many tests of retinal function have been recommended but few are effective at detecting CMVR. We assess the potential of chromatic discrimination thresholds and achromatic contrast sensitivity as screening tests for patients with CMVR. METHOD 11 HIV+ patients with CMVR, 16 age matched HIV+ patients, and 29 age matched controls were recruited. Visual acuity, chromatic discrimination thresholds, and achromatic contrast sensitivity were measured. Fundal examination was performed by slit lamp biomicroscopy for HIV+ patients. Those with CMVR were photographed and the CMVR graded from the photographs. RESULTS Loss of chromatic discrimination was found in patients with CMVR (tritan p<0.0005, red/green p<0.05). The same group had deterioration in achromatic contrast sensitivity at 2.2, 3.4, and 10 cpd (p<0.05). There was correlation between the zone of CMVR with chromatic gratings (tritan r=0.83, p<0.005). No statistically significant difference was found between the HIV+ patients and the controls for all tests (p>0.1). CONCLUSIONS HIV+ patients with CMVR have a loss of chromatic discrimination and achromatic contrast sensitivity and this may be used to screen HIV+ patients for CMVR.

Sealing the Acetabular Notch : Does it Improve Cement Penetration in the Acetabulum?

Since the advent of cemented hip replacements inthe 1950s, outcomes of cementing techniques in the stem have improved significantly. These improvements have not translated as readily to the acetabulum. This article suggests further techniques of improving cementiig techniques in the acetabulum.

The Distribution of Cement Penetration into Bovine Acetabular Bone Utilising Various Pressurisation Techniques

Most mechanical failures of acetabular fixation within ten years of primary cemented hip replacement are attributable to a failure to achieve good initial fixation of bone and cement. Several studies have suggested that to achieve good fixation between bone and cement between 3 mm and 5 mm of cement penetration into bone is desirable. Whilst several acetabular cement pressurisation systems exist, little is known about the effects of cement pressurisation on the pattern of penetration of cement into cancellous bone within the pelvis. The current paper assesses the penetration of bone cement into bovine acetabular bone by various pressurisation techniques. We found that pressurisation with the use of a swab in glove or the DePuy pressuriser led to improvement in cement penetration both in terms of maximum depth and also percentage cover of the cup by cement (p<0.05). There was no significant difference in mean maximal penetration between the use of the pressuriser and the swab in a glove technique (p=0.3). If only a plain cup was used as a pressuriser, the penetration achieved was significantly lower in comparison to use of a pressuriser (p<0.02). When compared to previously documented acrylic models, the pattern of intrusion noted in the bovine model was different: penetration was lower at the equatorial and base regions of the acetabulum.