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Biomedical subjects

M T Benson

Publications and source records attributed to M T Benson.

At least 19 recordsLinked to original sources
PubMed2006

Subjective and objective performance of the Lenstec KH-3500 "accommodative" intraocular lens.

AIM: To determine whether eyes implanted with the Lenstec KH-3500 "accommodative" intraocular lenses (IOLs) have improved subjective and objective focusing performance compared to a standard monofocal IOLs. METHODS: 28 participants were implanted monocularly with a KH-3500 "accommodative" IOL and 20 controls with a Softec1 IOL. Outcome measures of refraction, visual acuity, subjective amplitude of accommodation, objective accommodative stimulus response curve, aberrometry, and Scheimpflug imaging were taken at approximately 3 weeks and repeated after 6 months. RESULTS: Best corrected acuity with the KH-3500 was 0.06 (SD 0.13) logMAR at distance and 0.58 (0.20) logMAR at near. Accommodation was 0.39 (0.53) D measured objectively and 3.1 (1.6) D subjectively. Higher order aberrations were 0.87 (0.85) microm and lower order were 0.24 (0.39) microm. Posterior subcapsular light scatter was 0.95% (1.37%) greater than IOL clarity. In comparison, all control group measures were similar except objective (0.17 (0.13) D; p = 0.032) and subjective (2.0 (0.9) D; p = 0.009) amplitude of accommodation. Six months following surgery, posterior subcapsular scatter had increased (p<0.01) in the KH-3500 implanted subjects and near word acuity had decreased (p<0.05). CONCLUSIONS: The objective accommodating effects of the KH-3500 IOL appear to be limited, although the subjective and objective accommodative range is significantly increased compared to control subjects implanted with conventional IOLs. However, this "accommodative" ability of the lens appears to have decreased by 6 months post-surgery.

Accommodation, Ocular↗
PubMed2005

The management of primary rhegmatogenous retinal detachment not involving the fovea.

AIM: To establish the likelihood of, and risk factors associated with, progression of 'macula-on' retinal detachment. METHODS: A multi-centre prospective observational study of patients with acute retinal detachment, not involving the fovea, was conducted over a 6-month period. Data collected included duration of symptoms, visual acuity, presence of posterior vitreous detachment, retinal drawings and subretinal fluid (SRF) distance from the fovea at a minimum of two time points. RESULTS: A total of 82 data sets from 15 institutions were analysed. Of 82 cases 11 (13%) demonstrated progression of fluid. Mean progression in those cases which progressed was 2.3 disc diameters (dd) and the average rate of progression was 1.80 dd/day. Binary regression analysis failed to reveal any statistically significant risk factors for progression. Multiple regression analyses were made to identify risk factors. With distance of SRF from fovea at operation as a function, distance of SRF at presentation was the only statistically significant risk factor. In all, 26% of patients underwent surgery out-of-hours. A total of 83% patients achieved a 6-week best-corrected vision of 6/9 or better. CONCLUSION: Most retinal detachments in this study did not progress within the first few days. The distance of SRF from the fovea at presentation was the only statistically significant risk factor for progression to foveal detachment.

Acute Disease↗
PubMed2004

Surgical treatment and outcome of patients with giant retinal tears.

OBJECTIVE: To report the management and outcome in retinal detachments associated with giant retinal tears (GRTs). METHODS: Retrospective, case note analysis of patients treated between November 1991 and June 2002 at a tertiary referral hospital. RESULTS: The case notes of 29 patients (24 males, 5 females) with a follow-up ranging from five months to 7 years were reviewed. In all, 25 eyes had retinal detachments with macular involvement and 10 patients had myopia more than 6 D. All patients underwent vitrectomy. A total of 23 patients had heavy liquid and 16 had scleral explants; 28 patients had silicone oil and one had C3F8 tamponade. Intraoperative complications included lens trauma and iatrogenic GRT. Six eyes had recurrent retinal detachment and needed multiple surgical procedures. At the last follow-up, 25 patients had anatomically attached retinas. In all, 18 fellow eyes were treated prophylactically. Three patients had total retinal detachment and marked PVR. The visual acuity improved in 20 eyes. CONCLUSION: GRTs are more common in patients with high myopia. With newer techniques of surgical treatment of GRTs, the anatomical and visual outcomes are more favourable.

Adolescent↗
PubMed2003

Retinal detachment and the second stage of labour: a survey of regional practice and literature review.

Following several referrals for 'assessment', obstetricians in the West Midlands Health Region were surveyed regarding patients perceived to be at high risk of retinal detachment during the second stage of labour. A questionnaire was sent to 95 practicing obstetricians. This was a four-item questionnaire, based on four identifiable categories of referral to the ophthalmologist, by the obstetricians. It also covered the perceptions of the obstetricians of the ocular problem in relation to their obstetric clinical decision. With a 70% response rate, a significant number of obstetricians consider that certain ophthalmic conditions predispose to retinal detachment during labour. Even though they hold this view, the obstetricians generally do not modify their obstetric practice in response to any perceived ophthalmic risk. Such a view is not borne out by current literature, with no evidence to support a causative link between labour and rhegmatogenous (versus serous) retinal detachment, even in eyes predisposed to that condition.

Female↗
PubMed2002

Macular hole surgery with silicone oil.

PURPOSE: Macular hole surgery usually involves gas tamponade which necessitates a variable period of postoperative posturing in a face-down position. A number of patients find this difficult or impossible for medical or social reasons. This study reviews our experience of macular hole surgery using silicone oil tamponade with no restriction of posturing. METHODS: Sixteen consecutive cases of macular hole (stage III/IV) surgery where silicone oil was used for tamponade were reviewed. Group A patients were unable for medical or social reasons to maintain a face-down posture and Group B patients had previous failed surgery with gas tamponade. RESULTS: Anatomical closure of hole was achieved in 81% (13/16) of all cases and 88% (7/8) of cases with no previous surgery (Group A) with a mean follow-up of 7.5 months (range 4-24 months). Mean visual improvement (log(MAR) value of visual acuity) for Group A and Group B were 0.41 and 0.03, respectively. CONCLUSIONS: The success rate of macular hole surgery using silicone oil as tamponade, in cases with no previous surgery, is comparable to that achieved when gas is used as tamponade. Although good anatomical success can be achieved in cases with previous failed surgery, the visual outcome is less rewarding. Silicone oil is an alternative to gas tamponade for macular hole surgery in patients who are unable or unwilling to posture. However, it has to be borne in mind that silicone oil tamponade is not without risks.

Aged↗
PubMed2002

Biometry of the silicone oil-filled eye: II.

PURPOSE: In phakic silicone oil-filled eyes, removal of the silicone oil can be combined with phacoemulsification and intraocular lens (IOL) implantation. True axial length (AL) of the silicone oil-filled (viscosity 1300 centistokes) eye can be estimated from the measured AL (MAL) obtained on A and/or B scan echography, by multiplying MAL by a conversion factor of 0.71. IOL power can then be calculated using current biometry formulae (SRK/T). This study aims to evaluate the conversion factor in clinical practice. METHODS: Eleven patients undergoing combined removal of silicone oil and phacoemulsification with IOL implant were studied. Patients were divided into two groups. In Group 1 (seven patients), the IOL was placed in the capsular bag and in Group 2 (four patients) the IOL was placed in the ciliary sulcus. Calculated AL (CAL) was obtained by multiplying the MAL of the silicone oil-filled eye (as measured on A or B scan ultrasonagraphy) by the conversion factor of 0.71. IOL power was then estimated using the CAL in the SRK/T formula. The spherical equivalent of the postoperative refractive error was compared to predicted refractive error. RESULTS: The mean difference in actual and predicted refractive error was 0.74 dioptres (D) (standard deviation 0.75 D) for Group 1 and 1.31 D (standard deviation 1.4 D) for Group 2. CONCLUSIONS: The conversion factor of 0.71 corrects for the apparent increase in AL induced by silicone oil of viscosity 1300 centistokes. This allows accurate prediction of the required IOL power in eyes undergoing combined cataract extraction, removal of silicone oil and lens implant. Sulcus placement of the IOL gives a less predictable result than placement in the capsular bag.

Biometry↗
PubMed2000

Nitric oxide synthase and cGMP activity in the salivary glands of the American dog tick Dermacentor variabilis.

We colocalized nitric oxide synthase (NOS) activity in epithelial cells that surround the salivary gland duct in female Dermacentor variabilis with NADPH diaphorase histochemistry and immunohistochemistry using a polyclonal anti-endothelial NOS. Using size-exclusion chromatography, a fraction with a molecular mass of about 185 kDa that had diaphorase activity was eluted from tick salivary gland homogenate. This fraction converted arginine to citrulline with the production of nitric oxide (NO), which was detected by using electron spin resonance spectroscopy. The complete activity of the diaphorase fraction was dependent on NADPH, FAD, tetrahydrobiopterin, calmodulin, (CaM), and Ca(2+), but was not dependent on dithiothreitol. The arginine analog N(G)-monomethyl-L-arginine inhibited the activity of this fraction. NO and arginine activated soluble guanylate cyclase to produce cGMP in dopamine-stimulated isolated salivary glands. Dopamine-stimulated isolated salivary glands treated with tick saline containing either EDTA, the NOS inhibitor N(G)-nitro-L-arginine methyl ester, or the calcium/CaM binding inhibitor W-7 showed no increase in cGMP. The NO donor sodium nitroprusside significantly increased cGMP levels in unstimulated isolated salivary glands. A possible function for NO in salivation by this ixodid tick is discussed.

Animals↗
PubMed2000

Visual function and subjective quality of life compared in subjects with acquired macular disease.

PURPOSE: To determine the objective measures of visual function that are most relevant to subjective quality of vision and perceived reading ability in patients with acquired macular disease. METHODS: Twenty-eight patients with macular disease underwent a comprehensive assessment of visual function. The patients also completed a vision-related quality-of-life questionnaire that included a section of general questions about perceived visual performance and a section with specific questions on reading. RESULTS: Results of all tests of vision correlated highly with reported vision-related quality-of-life impairment. Low-contrast tests explained most of the variance in self-reported problems with reading. Text-reading speed correlated highly with overall concern about vision. CONCLUSIONS: Reading performance is strongly associated with vision-related quality of life. High-contrast distance acuity is not the only relevant measure of visual function in relation to the perceived visual performance of a patient with macular disease. The results suggest the importance of print contrast, even over print size, in reading performance in patients with acquired macular disease.

Adult↗
PubMed1999

The posterior vitreous detachment clinic: do new retinal breaks develop in the six weeks following an isolated symptomatic posterior vitreous detachment?

PURPOSE: Symptomatic posterior vitreous detachment (PVD) is sometimes associated with sight-threatening retinal tears or retinal detachment. Patients are usually reviewed twice because it is believed that retinal breaks may develop within 6 weeks of a PVD and as such the management of a PVD consumes significant resources. The aim of this study was to find the frequency of retinal breaks developing within 6 weeks of an isolated PVD using the same experienced examiner at both visits. METHOD: Patients presenting to the eye casualty with symptomatic PVD were examined by the casualty staff. Those with a retinal break or retinal detachment were referred directly for treatment and those with only a PVD were seen within 8 days in the PVD clinic. They were examined by a vitreo-retinal Fellow using indirect ophthalmoscopy and a 20 D lens with scleral indentation. The position and nature of any retinal abnormalities were noted and compared with those described in the casualty notes. Those with sight-threatening breaks were referred for treatment and the remainder were reviewed 5 weeks later when the presence of any new breaks was noted. RESULTS: One hundred and seven patients were referred to the PVD clinic over a 6-month period, of whom 2 did not have a PVD. At the first visit to the PVD clinic 6 patients had round holes anterior to the equator, 2 had equatorial horseshoe tears and 1 had lattice with holes. At the second visit, 2 additional patients had round holes anterior to the equator but in both the retina had been obscured by vitreous haemorrhage at the first visit. No patient in whom a full examination was possible at the first visit developed further retinal pathology. CONCLUSION: These results demonstrate the need to perform a full examination of the peripheral retina with scleral indentation at the time of presentation and emphasise the importance of finding a vitreous haemorrhage following a symptomatic PVD. If no retinal breaks are detected by thorough examination at presentation, further reviews, in the absence of increasing symptoms, may not be necessary.

Adult↗
PubMed1999

Biometry of the silicone oil-filled eye.

PURPOSE: The advent of silicone oil tamponade has resulted in improved success rates in complicated retinal detachment surgery. Its use, however, can induce cataract formation in phakic eyes. In selected patients, removal of silicone oil can be combined with phacoemulsification of the cataract and intraocular lens (IOL) implantation, thus avoiding a further operation. This, however, poses a problem when trying to decide the power of IOL to be used, since the echographically measured axial length (AL) of an eye is greater in the presence of silicone oil. We performed ultrasound examination in the presence of silicone oil of viscosity 1300 centistokes, in order to determine whether the measured AL varied from the true AL by a constant factor. METHODS: The ALs of 7 phakic eyes were measured by A-mode echography, with and without silicone oil of viscosity 1300 centistokes in the posterior segment. The retina was attached in all cases. The control group consisted of 6 phakic eyes with attached retinae undergoing vitrectomy without the use of silicone oil. The ALs in the control group were measured before and after vitrectomy. RESULTS: The mean ratio of true AL to measured AL in the presence of silicone oil was 0.71 (standard deviation 0.01; range 0.70-0.73; median 0.71) in the 7 eyes in this study. In the control group, vitrectomy appeared to have no significant effect on AL. CONCLUSIONS: We have established a constant which corrects for the apparent increase in AL induced by silicone oil of viscosity 1300 centistokes. This conversion factor, when used in existing biometry formulae (SRK/T), allows estimation of the power of IOL required in eyes undergoing combined cataract extraction, removal of silicone oil and lens implantation.

Biometry↗
PubMed1998

Surgical excision of subfoveal neovascular membranes.

BACKGROUND: Subfoveal choroidal neovascular membranes (CNV) are a cause of significant visual impairment. Laser treatment of such lesions results in visual loss. Surgical excision of CNV may allow stabilisation or improvement of vision. A series of results of surgical excision are presented. METHODS: The records for 43 eyes of 40 consecutive patients undergoing surgical excision of CNV not associated with age-related macular degeneration (AMD) were reviewed retrospectively. Statistical analyses of the relationship between pre-operative factors and post-operative visual results were made. Improvement or worsening of visual acuity was defined as a change of more than 2 lines of Snellen acuity. RESULTS: In 79.1% of patients visual acuity was improved or unchanged following surgery, and in 20.9% there was a reduction of Snellen acuity. There was no statistically significant association between visual outcome and age, gender, duration of visual symptoms, cause of CNV, presence of subretinal haemorrhage, elevation of retina by subretinal fluid, prior laser surgery, or the presence of pre-operative or intraoperative subretinal haemorrhage. There was a possible association between the non-use of gas tamponade and an increased chance of reduced vision. Visual loss was more likely in those eyes with good pre-operative visual acuity. Recurrence of CNV was noted in 10 (23%) eyes; repeat surgery was not associated with a worse visual outcome. CONCLUSIONS: Surgical excision of CNV not related to AMD is a promising technique. More meaningful assessment of visual function in these patients will allow refinement of case selection.

Adolescent↗
PubMed1995

Effects of pharmacological modulation of intracellular signalling systems on retinal pigment epithelial cell attachment to extracellular matrix proteins.

Complication of retinal detachment by proliferative vitreoretinopathy (PVR) is common. In the contraction of intraocular collagen matrices which occurs in PVR cell proliferation, migration and adhesion seem to be more important than any inherent cellular contractility. The aim of this study was to investigate the pharmacological inhibition of adhesion of retinal pigment epithelial cells to extracellular matrices. The adherence of human RPE lines to a range of ten substrates was assessed to determine their preferred substrates for attachment. The effect of pharmacological inhibitors and stimulators of protein kinase C, cyclic AMP and calcium/calmodulin intracellular signal transduction systems on attachment to substrates was investigated. RPE cells showed a clear substrate preference for fibronectin, and slight preference for collagen type I. Modulation of the protein kinase C and cAMP pathways had relatively minor effects upon RPE attachment. Increasing intracellular calcium concentration reduced RPE attachment to 12% of control, whilst reducing intracellular calcium had a less marked, although significant effect. Down-regulation of calmodulin reduced attachment to 17% of control. The drug tamoxifen, and the experimental calmodulin antagonist J8, produced significant inhibition of attachment even when cells had been allowed to adhere for 24 h prior to exposure to these agents. The adhesion of RPE to extracellular matrices may be markedly affected by drugs which modulate the intracellular calcium and calmodulin signalling systems. Calmodulin antagonists warrant further investigation as possible pharmacological inhibitors of PVR.

Animals↗
PubMed1995

Cytokine modulation of adhesion molecule expression on human retinal pigment epithelial cells.

PURPOSE: The purpose of this study was to assess qualitatively the expression of adhesion molecules by human retinal pigment epithelium (RPE) and to study their regulation by inflammatory cytokines. These molecular events and the role played by inflammatory cytokines are important for selective lymphocyte trafficking into the eye during uveitis. METHODS: Expression of intracellular adhesion molecule-1 (ICAM-1), endothelial leukocyte adhesion molecule-1 (ELAM-1), platelet endothelial cell adhesion molecule-1 (PECAM-1), and vascular adhesion molecule (VCAM-1) by early passage human RPE cells was assessed by flow cytometry. In addition, the regulation of the expression of these molecules by the inflammatory cytokines interleukin-1 beta (IL-1 beta), IL-6, tumor necrosis factor alpha (TNF alpha), and interferon gamma (IFN gamma) was determined. Reverse transcription-polymerase chain reaction (RT-PCR) was used to characterize further adhesion molecule expression. RESULTS: Flow cytometric analysis determined that ICAM-1 was constitutively expressed on RPE cell lines and that in the presence of TNF alpha, IFN gamma, and IL-1 beta, there was a median fold increase in expression of 4.4, 5.4, and 4.4, respectively. In contrast, flow cytometric analysis of ELAM-1, PECAM-1, and VCAM-1 indicated that these adhesion molecules were not constitutively expressed at the cell surface; only the expression of VCAM-1 was upregulated by the presence of cytokines. The results of RT-PCR on RPE cells indicated that mRNA for all the adhesion molecules was present constitutively in some RPE cultures. After activation with IFN gamma, TNF alpha, and IL-1 beta, RT-PCR analysis showed that the number of RPE cell lines expressing all the adhesion molecules increased. CONCLUSIONS: ICAM-1 expression is markedly upregulated by inflammatory cytokines. Although mRNA for other adhesion molecules is expressed in RPE cells and is enhanced by inflammatory cytokines, this does not necessarily reflect the cell surface protein expression. Thus, the expression of adhesion molecules by RPE cells, and the subsequent recruitment of specific leukocytes, may be determined by the local cytokine environment.

Base Sequence↗