Biomedical subjects

A G Casswell

Publications and source records attributed to A G Casswell.

At least 19 recordsLinked to original sources

PubMed2003

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; HbA(1c) 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 HbA(1c) (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 HbA(1c), 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.

Adolescent↗

PubMed2001

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.

Aged↗

PubMed2001

Effectiveness of apraclonidine 1% in preventing intraocular pressure rise following macular hole surgery.

AIM: To determine the efficacy of apraclonidine hydrochloride 1% in preventing intraocular pressure (IOP) spikes following idiopathic macular hole (IMH) surgery with platelet adjunct and intraocular gas tamponade. METHODS: This is a prospective, double masked, randomised study to compare apraclonidine hydrochloride 1%, an alpha(2) agonist, with a placebo in the prevention of IOP rises following macular hole surgery. Each patient was randomly selected to receive either the study drug or the placebo; one drop was instilled in the conjunctival sac 2 hours preoperatively and on completion of the procedure. IOP was measured at baseline and at 1, 3, 6, 24, 48 hours, and 2 weeks postoperatively. Blood pressure and heart rate were also recorded at baseline and at 3 and 24 hours postoperatively. Macular hole repair surgery was performed as standardised in the unit with a vitrectomy, platelet concentrate, and complete fill of the vitreous cavity with perfluoropropane gas (C(3)F(8)) at a concentration of 16%. RESULTS: 25 patients (26 eyes) were enrolled. 12 eyes received apraclonidine hydrochloride 1% (mean age 70.7; range 62-78 years) and 14 eyes received the placebo (mean age 70.0; range 57-81 years). At baseline evaluation the mean IOP was 15.6 mm Hg for the study group and 14.3 mm Hg for the placebo group. The mean postoperative IOP at 1 hour, 3 hours, 6 hours, and 24 hours was 10.6, 9.6, 8.2, and 14.0 mm Hg in the apraclonidine group. In the control group at the same time intervals the mean IOP was 23.4, 17.5, 19.2, and 24.7 mm Hg. These readings were statistically significant different: 1 hour (p=0.0001); 3 hours (p=0.0015); 6 hours (p<0.0001); and 24 hours (p=0.019), the readings at 48 hours and 2 weeks were not statistically significant different (p=0.15 and p=0.59). Only one of the patients in the study group had an IOP above 25 mm Hg at any time. In the control group an IOP above 25 mm Hg was found in seven patients (50%) at the 1 hour postoperative measurement. At 2 weeks the IOP was recorded below 25 mm Hg in all patients. No statistically significantly difference was noted between the two groups regarding the systolic or diastolic blood pressure values and the heart rate records. No local or systemic adverse reactions were observed. CONCLUSIONS: Apraclonidine hydrochloride 1% appears to be an efficacious and safe drug in the prophylaxis of early postoperative IOP elevations in patients undergoing macular hole surgery.

Adrenergic alpha-Agonists↗

PubMed2000

Clinical evaluation of 'local contrast enhancement' for oral fluorescein angiograms.

PURPOSE: To describe and assess the clinical impact of 'local contrast enhancement' on oral fluorescein angiograms. METHODS: Oral fluorescein angiograms (OFA) were performed on 12 patients with a range of diabetic retinopathy. The digital images were processed using two enhancement techniques: histogram equalization, a widely available method; and 'local contrast enhancement'. Twelve control images and 24 enhanced images were randomised and subjectively graded for clarity between 1 and 100 on a visual analogue scale by two masked observers. A score of 50% was chosen as the cut-off for clinically useful images. RESULTS: The mean score for the unenhanced images was 38.8% (SD 19.4); the histogram equalization performed better at 54.7% (SD 10.0) (p = 0.016) and 'local contrast enhancement' at 69.4% (SD 13.6) (p < 0.001). These results equate to a 14.7% improvement in comparison with histogram equalization and a 30.3% improvement with the 'local contrast enhancement' technique. All the 'local contrast enhancement' images were clinically useful, compared with 58.3% of the histogram equalization images (chi 2 2.08, p = 0.2), and 33.3% of the control images (chi 2 = 6.75, p = 0.01). CONCLUSION: This pilot study has demonstrated the power of 'local contrast enhancement' techniques for low-contrast fluorescein angiograms. Using 'local contrast enhancement' oral fluorescein angiograms can give high-quality images and may allow safer patient investigation.

Administration, Oral↗

PubMed2000

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.

AIDS-Related Opportunistic Infections↗

PubMed1999

Vitrectomy for phacolytic glaucoma in a patient with homocystinuria.

PURPOSE: To determine the successful treatment of unilateral phacolytic glaucoma by vitrectomy and trabeculectomy in a patient with homocystinuria whose lens had dislocated into the vitreous at least 15 years earlier. METHODS: In a 32-year-old woman with homocystinuria, bilateral dislocation of the lens into the vitreous, and phacolytic glaucoma in her left eye a three-port pars plana vitrectomy was performed with the patient under general anesthesia. The lens was removed and a trabeculectomy fashioned. Special precautions for general anesthesia included preoperative aspirin and compression stockings for thromboembolic prophylaxis and intraoperative dextrose infusion, 5%, to maintain intravascular volume and prevent hypoglycemia. RESULTS: The intraocular pressure and uveitis resolved postoperatively with improvement in the visual acuity and intraocular pressure, which returned to normal without further treatment. CONCLUSIONS: Phacolytic glaucoma is best resolved by removal of the exciting lens material. Pars plana vitrectomy with the patient under general anesthesia can be carried out safely despite the risks traditionally associated with homocystinuria.

Adult↗

PubMed1998

What effect does laser photocoagulation have on driving visual fields in diabetics?

Although laser panretinal photocoagulation (PRP) for proliferative diabetic retinopathy is known to cause peripheral field constriction, the risks of failing the UK driving field test following treatment are currently unclear as the small number of previous studies have conflicting results. Following PRP using only argon laser with a 500 microns spot size, both uniocular and binocular Esterman visual fields from 60 diabetic patients were assessed by the Chairman of the Visual Standards Sub-Committee of the Royal College of Ophthalmologists. Forty-two per cent of uniocular fields from treated eyes failed. Twelve per cent of binocular fields from those having bilateral PRP failed. Type II diabetes was associated with a significant increase in the risk of failure. Although there is a high risk of failure in any given treated eye, 88% of diabetics will pass a binocular field test, even if both eyes are treated.

Adult↗

PubMed1998

How good are we at assessing driving visual fields in diabetics?

PURPOSE/BACKGROUND: Following laser panretinal photocoagulation (PRP) for proliferative diabetic retinopathy, patients are at risk of failing the UK driving visual field test due to loss of peripheral field. Although a definition of the minimum field requirement exists, differences in its interpretation may influence whether fields pass or fail. Currently it is not known how fields are interpreted in practice nor to what extent this affects failure rates. METHODS: Uniocular and binocular Esterman visual fields from 60 diabetic patients following PRP were examined both by the chairman of the Visual Standards Sub-Committee of the Royal College of Ophthalmologists and separately by four consultant ophthalmologists. The results were analysed (1) to assess the extent of agreement and (2) to identify, from the chairman's results, the field deficits that are still compatible with passing. RESULTS: Agreement was generally good for binocular fields but was only moderate for uniocular fields. In up to 15% of binocular fields and 43% of uniocular fields the chairman's decision was different from that of the consultants. Several key aspects of the field that influence a pass/fail decision are identified. CONCLUSIONS: Substantial differences in the assessment of driving visual fields following RPR currently exist between consultants and the chairman of the Visual Standards Sub-Committee. Using the information presented here to guide assessment it is now possible to reduce this variation.

Automobile Driver Examination↗

PubMed1997

Chromatic-contrast threshold impairment in diabetes.

A prospective study was carried out to investigate acquired colour-vision deficits in diabetics using an automated, computer-controlled, cathode-ray-tube based test of chromatic contrast. Chromatic-contrast thresholds estimates were measured along both a red/ green (constant S-cone) confusion axis and a tritan (constant M/L-cone) confusion axis for 305 eyes of 305 diabetics. The diabetic data were partitioned into groups based on a clinical categorisation of retinopathy. The diabetic data were compared with both age-matched and 'lens-equated' control data obtained from a bank of 347 normal subjects. Further analysis of differences between diabetic-status groups was performed. Associations between chromatic contrast threshold estimates and age, duration of disease, and severity of both macular oedema and ischaemia were investigated. The diabetic group was found to have significantly reduced chromatic-contrast threshold estimates when compared with normal controls, even in the absence of retinopathy. This reduction in chromatic contrast was predominantly tritanopic in nature. Interestingly, no reduction in red/green chromatic-contrast threshold estimate was found in diabetics without retinopathy. The tritan deficit seen in diabetics without retinopathy was strongly correlated with duration of disease, but when adjustments were made to account for the effects of duration-dependent lens yellowing, the tritan deficit was no longer apparent. A correlation between both the severity of macular oedema and severity of ischaemia with chromatic-contrast loss was established. Acquired reductions in both red/green and tritan chromatic-contrast threshold estimates seen in diabetics are strongly correlated with the severity of retinopathy. The results provide evidence that the specific tritan deficits seen in diabetics can be explained by the effects of lens yellowing rather than by selective damage of the blue cone system as has been hypothesised by other groups. The results provide support for the potential use of automated CRT-based tests of colour vision in diabetic retinopathy screening protocols.

Adolescent↗

PubMed1996

Do Mersilene sutures need to be removed after cataract surgery?

A major disadvantage of nylon sutures is the need to remove them post-operatively to prevent suture fracture and irritation. Mersilene (polyester) sutures do not hydrolyse or disintegrate and are in theory superior to nylon. Fifty-two consecutive patients were examined an average of 3 years after uncomplicated extracapsular cataract extraction with corneal sections sutured with interrupted 11/0 polyester. It was found that 29% had suture-related problems and required, or had previously undergone, suture removal for reasons other than high astigmatism. The most common problem was a loose stitch with adherent mucus and corneal vascularisation (17% of patients at review). Sixty-six per cent of patients with loose sutures reported discomfort. We would not advocate prophylactic removal, but patients with polyester sutures should be advised to return if they become symptomatic.

Astigmatism↗

PubMed1996

Radiotherapy treatment of age-related subfoveal neovascular membranes in patients with good vision.

This prospective study investigated whether low-dose ionising radiotherapy preserved vision and caused membrane regression in patients with age-related subfoveal neovascular membranes (SFNVMs) or vascularised pigment epithelial detachments (PEDs) and relatively good initial visual acuities. Twenty-five patients with initial Snellen acuities of 6/24 or better were treated with low-dose external beam radiotherapy. Of the patients with SFNVMs, visual acuities were maintained or improved in 58% at 6 months and 53% at 1 year. Neovascular membrane size was assessed by image analysis and showed some regression in 47% and 41% at 6 and 12 months respectively. These results suggest that patients with SFNVMs and good vision may benefit from radiotherapy, faring better than previous reports of the natural history of this condition. Conversely, patients with vascularised PEDs did not appear to benefit from radiotherapy. Only 17% maintained their vision at 1 year and 33% suffered retinal pigment epithelial tears. The results from patients with SFNVMs and good initial vision, excluding those with vascularised PEDs, are encouraging however, any benefit from this treatment needs to be proven by controlled trials with long follow-up.

Aged↗

PubMed1996

May I bend down after my cataract operation, doctor?

We reviewed the records of 21 patients with posttraumatic wound dehiscence following cataract surgery to establish the cause of injury and assess the complications and outcome following injury. Wound dehiscence most commonly resulted from patients knocking their eye accidentally with their own hand, and falls were the second most frequent cause. None of these patients suffered injury as a result of bending down. Eyes that had undergone cataract surgery through corneal sections were more prone to wound dehiscence than those operated on via a limbal approach. The visual outcome following repair was good in the majority of cases, but eyes with expulsion of lens implant and/or vitreous loss tended to have a relatively poor outcome.

Aged↗

PubMed1996

A comparative study of the efficacy of 2.5% phenylephrine and 10% phenylephrine in pre-operative mydriasis for routine cataract surgery.

It is common practice in many ophthalmic units to administer multiple applications of 10% phenylephrine in combination with an anti-cholinergic agent to ensure adequate pupil mydriasis prior to routine cataract surgery. Phenylephrine is a pure alpha-1 adrenoreceptor agonist known to produce marked systemic vasoconstriction and associated hypertension with occasional profound reflex bradycardia. Many reviews have suggested caution in the use of 10% phenylephrine in the elderly or hypertensive patient. In a prospective, randomised trial we have assessed pupil dilation comparing the efficacy of 10% phenylephrine (53 patients) versus 2.5% phenylephrine (62 patients). When administered in conjunction with 1% cyclopentolate four times over 1 hour pre-operatively, 2.5% phenylephrine was found to be as effective as 10% phenylephrine in the initiation and maintenance of mydriasis during both extracapsular and phacoemulsification cataract extraction.

Aged↗

PubMed1996

Colour vision in diabetic and normal pseudophakes is worse than expected.

Automated colour vision testing in pseudophakes showed unexpected results. Chromatic discrimination sensitivity was measured in 22 diabetic pseudophakes with no retinopathy, 23 diabetic pseudophakes with background retinopathy and 34 non-diabetic pseudophakes. These results were compared with those in age-matched normal and diabetic phakic subjects, all of whom had good vision. The diabetics were also matched for retinopathy grading and duration of diabetes. In all three groups, red-green discrimination sensitivity was worse in the pseudophakes when compared with the corresponding phakic subjects (normals, p < 0.001; no retinopathy, p = 0.467; background retinopathy, p = 0.057). However, tritan vision was marginally worse in the normal pseudophake group but was better in the two diabetic pseudophake groups, when compared with phakic controls. This may be due to a reduction in tritan sensitivity in age-matched phakic controls from the effects of increased lens yellowing with age.

Aged↗

PubMed1995

White-centered retinal hemorrhages as an early sign of preeclampsia.

PURPOSE/METHOD: We examined a pregnant patient who had symptomatic white-centered retinal hemorrhages. Severe preeclampsia rapidly developed despite the patient not having hypertension, proteinuria, or edema at initial examination. RESULTS/CONCLUSIONS: Retinal hemorrhages gradually resolved without treatment and visual acuity returned to 20/20 six months after emergency delivery of a healthy infant. Retinal or choroidal vascular abnormalities in pregnant patients may be caused by early preeclampsia and immediate obstetric referral is indicated.

Adult↗

PubMed1995

Endophthalmitis after routine intra-ocular surgery in an asplenic patient.

A 72-year-old asplenic man developed an acute early pneumococcal endophthalmitis after a routine endocapsular cataract extraction with poor final visual outcome. It is recognized that splenectomy increases the risk and severity of pneumococcal infections. Our patient had not received pneumococcal vaccination or been prescribed prophylactic antibiotics since his splenectomy or at the time of surgery. Failure of these measures to occur may have affected visual outcome.

Aged↗

PubMed1994

Decentration of the posterior chamber lens implant: a comparison of capsulorhexis with endocapsular surgery.

The optical effect of posterior chamber lens decentration is a well-recognised complication of cataract surgery causing significant symptoms even with the larger-diameter implant optics available. In this paper we present the results of a study of implant decentration occurring with extracapsular surgery, in which we compared a group of patients with one tear in the anterior capsule with a second group with two tears in the anterior capsule. Our findings show that lens decentration is greater in those patients with two tears of the anterior capsule, and this difference is statistically significant.

Aged↗

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↗