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Biomedical subjects

C R Canning

Publications and source records attributed to C R Canning.

At least 19 recordsLinked to original sources
PubMed1995

Survey of colour contrast sensitivity in non-ophthalmic users of blue-green wavelength argon lasers.

BACKGROUND: Previous studies have shown that ophthalmologists using blue-green argon laser may suffer subtle defects in their colour vision. A reduction in colour contrast sensitivity in the tritan colour confusion axis, an early manifestation of blue cone photoreceptor injury by the high energy photons of the laser, has been demonstrated and has prompted a reappraisal of laser safety in ophthalmology. Argon laser is also frequently used in scientific research, often at higher power output and for longer periods than is used in clinical practice. The scientists operating these lasers are at risk of developing similar phototoxic retinal injury. METHODS: The colour contrast sensitivity of 18 scientists who regularly use short wavelength argon laser was investigated. RESULTS: Eye protection was infrequently used and individuals had been subjected to between 580 and 7200 hours of cumulative laser exposure during the course of their research. CONCLUSION: The use of blue-green argon laser by the scientists investigated was not associated with a significant reduction in colour contrast sensitivity.

Adult↗
PubMed1994

A comparison of the efficacy of Holmium laser sclerostomy ab externo versus trabeculectomy in the treatment of glaucoma.

We compared 15 patients who had undergone Holmium laser sclerostomy ab externo with 15 who had had trabeculectomy. In the short term, laser sclerostomy led to adequate control of intraocular pressure, but in the longer term it compared unfavourably with trabeculectomy in terms of efficacy, complications and reoperation rate. At 1 year follow-up, 8 patients in the laser group had had to undergo a second operation compared with none in the control trabeculectomy group, and 7 were still on glaucoma medication compared with 2 in the control group. Iris prolapse into the internal sclerostomy ostium within 2 months accounted for most failures, and was only partially amenable to Nd:YAG peripheral iridectomy. This common complication seems to be related to anterior chamber depth. There also appears to be a tendency for blockage of the sclerostomy with cellular or fibrinous debris. Recent literature is reviewed and modifying strategies discussed.

Adult↗
PubMed1993

Patient satisfaction following vitreoretinal surgery.

A postal questionnaire was used to study patient satisfaction in 149 consecutive patients undergoing vitreoretinal surgery in Southampton. Of the 123 patients who responded, 70 (60%) felt that their vision improved following surgery. Fifty-eight patients (47%) stated that their vision was not as good as they had hoped it would be, and multiple logistic regression analysis showed that this response reflected a poorer visual outcome in this group. Despite this, 116 (94%) of those replying stated that the operation had been worth while. All 5 patients who felt that their operations had not been worth while had undergone retinal detachment surgery. This high level of satisfaction may be attributable to realistic expectations, as 116 patients (94%) replied that the procedures had been adequately explained.

Adult↗
PubMed1993

The effect of pilocarpine on the glaucomatous visual field.

Patients with chronic open angle glaucoma are traditionally managed by medical therapy during the early stages of the disease. Pilocarpine is a well established topical agent, but suffers troublesome sequelae, the most apparent of which is pupillary constriction. This study assesses the effect of miosis (produced by one drop of 2% pilocarpine) on the static threshold perimetry of 20 subjects with chronic open angle glaucoma and documented visual field loss, using the 30-2 program of the Humphrey field analyser. Following miosis, the Statpac mean defect deteriorated by an average of -1.49 dB compared with baseline (p = 0.004). This dB deterioration is twice that reported in studies on younger normal subjects following miosis. The decrease in mean defect showed a positive correlation with the degree of pupillary constriction, the correlation being greater in those eyes with a miosed pupil diameter of 2 mm or less. There was no significant decrease in the other Statpac global indices following miosis. A parallel study using the fellow eye of the same glaucoma patients showed a high degree of intertest variability, but no significant learning or fatigue effect. We conclude that pilocarpine-induced miosis causes a significant deterioration in visual field in a population of patients with chronic open angle glaucoma: this factor should be considered when choosing therapy for glaucoma particularly in cases where field loss approaches the permitted legal minimum for driving.

Aged↗
PubMed1991

Colour contrast sensitivity changes caused by peripheral retinal laser photocoagulation.

Macular phototoxicity is known to occur with laser use, and there is evidence that the wavelength of the light used influences this effect. In this study, a computer based colour contrast sensitivity test was used to assess the immediate macular effects of photocoagulation of peripheral flat retinal holes in otherwise normal retinas, using blue-green (488 and 514 nm), yellow (577 nm), orange (595 nm) or red (647 nm) laser light. The laser aiming beam was not allowed to traverse the macula at any stage during treatment. No protan or deutan axis threshold changes were noted in the 17 patients tested irrespective of the laser wavelength used. Tritan axis sensitivity was significantly reduced one hour after treatment with the blue-green laser, but no tritan axis change was found after treatment with longer wavelength lasers. The effect was no longer present the day after treatment in the subjects tested. The results show that even peripheral retinal treatment with blue-green laser can cause acute macular phototoxicity.

Color Perception↗
PubMed1991

Posterior lens capsule abscess due to Propionibacterium acnes and Staphylococcus epidermidis following extracapsular cataract extraction.

A case of posterior lens capsular abscess occurring many months after an extracapsular cataract extraction is presented. This was caused by a mixed infection involving Propionibacterium acnes and Staphylococcus epidermidis. The significance of Staph epidermidis after such a long postoperative period is uncertain, but the case shows features typical of secondary endophthalmitis due to P acnes, including a long delay in onset and a grumbling course not brought under control by medical treatment. It supports the theory that the nidus of infection is localised in the posterior lens capsule by showing development of a visible capsular abscess with associated vitreous involvement. The subsequent removal of the capsule and vitreous, despite leaving the intraocular lens in place, led to complete resolution of the inflammation. Both organisms have previously been found to be sequestered in the posterior lens capsule by histological and microbiological examination of excised capsular specimens. It is important to consider them as possible causative agents in the formation of a postoperative capsular abscess.

Abscess↗
PubMed1990

Treatment of diffuse diabetic macular oedema: a comparison between argon and krypton lasers.

We report the results of a randomised treatment trial of macular grid photocoagulation in 91 eyes with diffuse diabetic macular oedema followed up for at least two years comparing Krypton red with Argon blue/green lasers. At two years, macular oedema had improved equally in both groups, and the visual acuity was unchanged or better in 85% of eyes treated with Argon and in 79.5% of eyes treated with Krypton laser. No statistically significant differences were observed between the two groups in terms of visual acuity or the degree of oedema. We conclude that the observed effect of grid laser treatment in diffuse diabetic macular oedema did not depend on the wavelength of the laser light used in this study.

Adult↗
PubMed1989

Using argon laser blue light reduces ophthalmologists' color contrast sensitivity. Argon blue and surgeons' vision.

Color contrast sensitivity was measured in laser operators before and after laser use. After argon blue-green laser treatment sessions, sensitivity was reduced for colors lying along a tritan color-confusion line for several hours. This acute effect is due to specular "flash-backs" from the aiming beam off the surface of the contact lens. It is caused only by argon 488-nm light, when the aiming beam intensity is high. In addition, a correlation has been demonstrated between the number of years of laser experience and a chronic reduction in tritan color contrast sensitivity. It is suggested that repeated acute changes caused by the argon lasers may cause cumulative effects and produce a chronic threshold elevation. A simple method of eliminating the acute effect is documented.

Adult↗
PubMed1989

Delayed suprachoroidal haemorrhage after glaucoma operations.

Delayed suprachoroidal haemorrhage occurred in 13 eyes in a consecutive series of 432 cases undergoing trabeculectomy or anterior chamber (A/C) tube drainage operations. Aphakia and vitrectomy were associated with an increased risk of haemorrhage, whilst advanced age, myopia, systemic hypertension and high preoperative intraocular pressure were not. Haemorrhage occurred more often after A/C tube drainage operations than after trabeculectomy. An explanation for this may be that eyes requiring A/C tube drainage operations have had multiple previous operations including lens extraction and vitrectomy, have a higher pre-operative intraocular pressure and a greater fall in pressure after operation when compared to eyes undergoing trabeculectomy. Post-operative hypotony should be avoided in high-risk eyes.

Adolescent↗
PubMed1989

Doppler ultrasound velocity mapping of extra-ocular muscles: a preliminary report.

Colour doppler imaging and conventional spectral doppler/B-mode techniques were used to detect and quantify rectus muscle movement during voluntary saccades. A velocity gradient was evident in all muscles studied--low velocities near the muscle origin at the back of the orbit increasing linearly to a maximum near the muscle insertion on the globe. A consistent reduction in velocity occurred along muscles injected with botulinum toxin. Doppler ultrasound complements current clinical eye movement recording techniques--electronystagmography, infrared light reflection methods and magnetic induction methods--insofar as it detects movement in parts of the muscle itself rather than movement of the globe secondary to muscle contraction. Future developments in colour doppler imaging will make the technique clinically more applicable.

Botulinum Toxins↗
PubMed1988

Neodymium: YAG laser iridotomies--short-term comparison with capsulotomies and long-term follow-up.

This study addresses three aspects of anterior segment Nd:YAG laser treatment--acute endothelial damage, as assessed by endothelial specular photomicrography (ESP), acute and long-term intraocular pressure (IOP) changes, and long-term iridotomy patency. The acute ESP and IOP changes in 26 eyes (21 patients) after Nd:YAG laser iridotomies were compared to 39 eyes (37 patients) after Nd:YAG laser capsulotomy. Similar endothelial damage occurred in both groups, although less damage was noted in the group of 9 eyes in which capsulotomies were undertaken in the presence of an intraocular lens. In a parallel study 53 eyes (44 patients) were followed for a mean of 83 weeks (19 months) from the time of Nd:YAG iridotomy. There were no late closures and no late rises in IOP. The level of acute IOP rise after treatment did not predict long-term IOP. We conclude that Nd:YAG iridotomy is an effective procedure in the long-term, and that both iridotomy and capsulotomy are accompanied by noteworthy acute endothelial changes and intraocular pressure rises.

Cornea↗
PubMed1988

Doppler ultrasound studies of the ophthalmic artery.

The doppler frequency shift of ultrasound pulses scattered off red blood cells in the ophthalmic artery can be detected and used as an index of velocity of flow in the artery. The doppler shift is shown to be responsive to changes in ocular blood flow induced by changes in mean arterial blood pressure at the level of the eye and changes in intraocular pressure. The technique may be useful in the study of eye disease in which blood flow is altered. Doppler frequency shifted signals have also been detected within the coats of the eye.

Blood Flow Velocity↗
PubMed1988

Doppler ultrasound of orbital vessels.

The techniques of doppler ultrasound have been applied to blood vessels within the orbit. The doppler frequency shifts of ultrasonic pulses scattered from blood cells moving within orbital vessels are a measure of velocities rather than the amount of blood flow. The doppler signal from the ophthalmic artery behind the globe is responsive to changes in ocular blood flow. Blood flow can also be detected at the optic nerve head, and from the coats of the eye adjacent to the nerve head. Flow rate in the ophthalmic artery is reduced following retrobulbar anaesthesia. The source of the pulsatile retrograde flow signal which can be detected in some cases of internal carotid stenosis is located in the region of the ophthalmic artery.

Anesthesia, Local↗
PubMed1988

Ocular quinine toxicity.

A case of ocular quinine toxicity is described which showed the typical acute visual loss and subsequent recovery. Vermiform motion of the pupil was noted 48 hours after overdose. This acute effect has not been reported before. Although acute systemic intoxication may respond to removal of quinine from the gut and circulation, there is no evidence that any treatment affects the visual prognosis. The action of quinine on the retina is unknown. We suggest it may block cholinergic neurotransmission in the inner synaptic layer.

Adult↗