Biomedical subjects

Clare O'Donnell

Publications and source records attributed to Clare O'Donnell.

9 recordsLinked to original sources

PubMed2006

Corneal hydration control in contact lens wearers with diabetes mellitus.

PURPOSE: The purpose of this study was to assess the acute swelling and recovery response to contact lens-induced corneal hypoxia in diabetic patients who wear contact lenses. METHODS: A thick, low water content, soft contact lens was fitted under a light patch to one eye of 23 diabetic patients and one eye of 23 nondiabetic control subjects in a single-masked, controlled clinical study. After 2.5 hours an ultrasonic pachymeter was used to measure the induced corneal edema and the rate at which the cornea recovered to baseline thickness. RESULTS: The induced corneal edema was significantly less for the diabetic patients compared with the nondiabetic control subjects (p = 0.004). The corneas of the diabetic patients were found to recover from the induced edema at a similar rate to the corneas of the nondiabetic control subjects (p = 0.28). CONCLUSIONS: Diabetes mellitus alters aspects of corneal hydration control.

Adult↗

PubMed2005

An evaluation of corneal nerve morphology and function in moderate keratoconus.

PURPOSE: To investigate corneal nerve morphology and corneal sensitivity in keratoconus. METHODS: The central cornea of 13 subjects with keratoconus and 13 age-matched control subjects was assessed using in vivo confocal microscopy and corneal aesthesiometry. RESULTS: Significant differences in corneal nerve fibre density were found between the subjects with keratoconus and the control subjects (keratoconus versus control; 1018.3+/-489.6 microm versus 1820.7+/-789.5 microm; p = 0.006). The mean diameter of nerve fibres in the stroma was found to be greater in subjects with keratoconus compared to control subjects (keratoconus versus control; 10.2+/-4.6 microm versus 5.5+/-1.9 microm; p = 0.007). The orientation of corneal nerve fibres in the subjects with keratoconus appeared to be altered from the predominantly vertical orientation seen in the control subjects. Corneal touch threshold was found to be similar in the two groups, although the subjects with keratoconus using contact lens correction had reduced corneal sensitivity compared to the contact lens-wearing control subjects (keratoconus with contact lenses versus controls with contact lenses; 1.18+/-0.19 g/mm2 versus 0.98+/-0.05 g/mm2; p = 0.03). CONCLUSION: This study reveals significant reductions in nerve density in the keratoconic cornea. The thickened stromal nerve fibres observed in the keratoconic corneas may explain why prominent corneal nerves are often seen using slit lamp biomicroscopy in keratoconic patients.

Adult↗

PubMed2005

Corneal endothelial abnormalities associated with thalidomide toxicity.

PURPOSE: To describe bilateral corneal endothelial abnormalities associated with thalidomide toxicity. METHODS: Observational case report. RESULTS: A 30-year-old man, born with bilateral hypoplastic upper limb defects (phocomelia) caused by thalidomide toxicity, presented with bilateral symmetrical corneal endothelial changes resembling guttata without corneal edema. Pachymetry, specular microscopy, and confocal microscopy were performed. Biomicroscopy findings over a 10-year follow-up showed no changes. CONCLUSIONS: Nonprogressive bilateral corneal endothelial changes resembling cornea guttata should possibly be included in the ocular manifestations of thalidomide toxicity. We postulate that thalidomide may have affected the migration and development of the mesenchymal neural crest cells, which are the developmental precursors of the corneal endothelium and stroma.

Abnormalities, Drug-Induced↗

PubMed2005

Agreement and repeatability of central thickness measurement in normal corneas using ultrasound pachymetry and the OCULUS Pentacam.

PURPOSE: To compare the accuracy and repeatability of the OCULUS Pentacam (a new Scheimpflug-based imaging system) with ultrasound pachymetry in the measurement of central corneal thickness (CCT). METHODS: CCT was measured in 21 subjects (21 normal corneas) on 2 separate occasions by the same examiner, using an Allergan-Humphrey 850 ultrasonic pachymeter and an OCULUS Pentacam instrument. RESULTS: Mean values of CCT for both visits for each instrument were 534 +/- 47 microm and 528 +/- 45 microm using the ultrasonic pachymeter and the Pentacam, respectively. Plots of differences against means displayed relatively good agreement (limits of agreement were -13.0 to +26.6 microm). The repeatability (limits of agreement) of the ultrasound pachymeter was -18.3 to +17.7 microm, while for the OCULUS Pentacam it was -24.1 to +21.1 microm. CONCLUSIONS: Our data showed that the Pentacam instrument provided measurements that were slightly but systematically lower than the measurements provided by ultrasonic pachymetry, which is currently the clinical gold standard method. The results, coupled with a unique ability to image and analyze the anterior chamber in vivo, make the OCULUS Pentacam a promising new instrument for anterior eye evaluation.

Adult↗

PubMed2004

Grading of corneal transparency.

AIM: To examine the academic literature on the grading of corneal transparency and to assess the potential use of objective image analysis. METHOD: Reference databases of academic literature were searched and relevant manuscripts reviewed. Annunziato, Efron (Millennium Edition) and Vistakon-Synoptik corneal oedema grading scale images were analysed objectively for relative intensity, edges detected, variation in intensity and maximum intensity. In addition, corneal oedema was induced in one subject using a low oxygen transmissibility (Dk/t) hydrogel contact lens worn for 3h under a light eye patch. Recovery from oedema was monitored over time using ultrasound pachymetry, high and low contrast visual acuity measures, bulbar hyperaemia grading and transparency image analysis of the test and control eyes. RESULTS: Several methods for assessing corneal transparency are described in the academic literature, but none have gained widespread use in clinical practice. The change in objective image analysis with printed scale grade was best described by quadratic parametric or sigmoid 3-parameter functions. 'Pupil image scales' (Annunziato and Vistakon-Synoptik) were best correlated to average intensity; however, the corneal section scale (Efron) was strongly correlated to variations in intensity. As expected, patching an eye wearing a low Dk/t hydrogel contact lens caused a significant (F = 119.2, p < 0.001) 14.3% increase in corneal thickness, which gradually recovered under open eye conditions. Corneal section image analysis was the most affected parameter and intensity variation across the slit width, in isolation, was the strongest correlate, accounting for 85.8% of the variance with time following patching, and 88.7% of the variance with corneal thickness. CONCLUSION: Corneal oedema is best determined objectively by the intensity variation across the width of a corneal section. This can be easily measured using a slit-lamp camera connected to a computer. Oedema due to soft contact lens wear is not easily determined over the pupil area by sclerotic scatter illumination techniques.

Journal Article↗

PubMed2004

A hyper-Dk piggyback contact lens system for keratoconus.

PURPOSE: To report the fitting of a hyper-Dk piggyback contact lens system in a case of keratoconus. METHODS: Case report. RESULTS: A patient with keratoconus, suboptimal visual acuity, corneal neovascularization, and marked conjunctival hyperemia, who was intolerant of rigid gas-permeable contact lenses, was fitted with a novel piggyback contact lens system that incorporated a hyper-oxygen transmissible hydrogel contact lens, on top of which was fitted a hyper-oxygen transmissible rigid gas-permeable lens. This novel contact lens system provided a significant improvement in visual acuity, comfort, and lens wear time. There was a marked reduction in corneal vascularization and ocular hyperemia. CONCLUSIONS: This hyper-Dk piggyback contact lens system satisfied the ocular and visual requirements of this patient, for whom other nonsurgical options for vision correction had been unsuccessful. This system has potential application in the visual rehabilitation of other cases of corneal irregularity, including unsuccessful refractive surgery, ocular trauma, and keratoplasty. Piggyback contact lens systems require the same level of expertise to fit as basic forms of soft and rigid contact lenses. The hyper-oxygen transmissible lens materials available make these dual-lens systems a viable option for the compromised cornea.

Biocompatible Materials↗

PubMed2004

Corneal endothelial cell morphometry and corneal thickness in diabetic contact lens wearers.

PURPOSE: To assess corneal endothelial cell morphometry and corneal thickness in diabetic patients who wear contact lenses. METHODS: Images of the central corneal endothelium were analyzed quantitatively and qualitatively and corneal thickness was measured in a group of diabetic patients (type 1, N = 26; type 2, N = 4) who wear soft contact lenses and in a group of nondiabetic age-matched control subjects who were also contact lens wearers. RESULTS: Endothelial cell characteristics and corneal thickness values were similar for the two groups (p > 0.05). Four of the diabetic patients (and none of the nondiabetic patients) displayed folds in the endothelial mosaic. CONCLUSIONS: The morphometry of corneal endothelial cells and central corneal thickness values in diabetic patients who wear soft contact lenses were not appreciably different from those found in lens-wearing control subjects.

Adult↗

PubMed2004

Non-compliance with lens care and maintenance in diabetic contact lens wearers.

We hypothesize that diabetic contact lens wearers may represent a special group displaying higher levels of compliance with their lens care regimens as a result of learned behaviour relating to maintenance of their diabetic condition. To test this hypothesis, a prospective, single centre, controlled, masked study was performed whereby 29 diabetic contact lens patients and 29 non-diabetic control subjects were issued with disposable hydrogel contact lenses and a multipurpose lens care regimen. All participants were given identical instruction on lens care and maintenance. Compliance levels were assessed at a 12-month aftercare appointment by demonstration and questionnaire. Twenty-four different aspects of compliance were scored, 12 by observation and 12 by questionnaire report, of which only two showed a significant difference between the diabetic and control groups. Although the combined population of contact lens wearers was generally compliant, there were examples of non-compliance in both groups. Neither the duration of diabetes nor the degree of metabolic control appeared to have a significant effect on compliance. The results suggest that eye care practitioners cannot assume that diabetic patients will be more compliant with contact lens care and maintenance than non-diabetic patients.

Adolescent↗

PubMed2004

Corneal nerve tortuosity in diabetic patients with neuropathy.

PURPOSE: Corneal confocal microscopy is a reiterative, rapid, noninvasive in vivo clinical examination technique capable of imaging corneal nerve fibers. Nerve fiber tortuosity may indicate a degenerative and attempted regenerative response of nerve fibers to diabetes. The purpose of this study was to define alterations in the tortuosity of corneal nerve fibers in relation to age, duration of diabetes, glycemic control, and neuropathic severity. METHODS: The cornea and collected images of the subbasal nerve plexus of 18 diabetic patients (stratified into mild, moderate, and severe neuropathic groups using conventional clinical measures of neuropathy) and 18 age-matched nondiabetic control subjects were scanned, and a novel mathematical paradigm was applied to quantify the extent of nerve tortuosity, which was termed the tortuosity coefficient (TC). RESULTS: TC was significantly different between the four clinical groups (F(3) = 12.2, P < 0.001). It was significantly greater in the severe neuropathic group than in control subjects (P < 0.003) and in the mild (P < 0.004) and moderate (P < 0.01) neuropathic groups. TC did not correlate significantly with the age (r = -0.003, P > 0.05), duration of diabetes (r = -0.219, P > 0.05), or hemoglobin A1c (HbA1c; r = 0.155, P > 0.05) of diabetic patients. CONCLUSIONS: Corneal confocal microscopy allows rapid, noninvasive in vivo evaluation of corneal nerve tortuosity. This morphologic abnormality relates to the severity of somatic neuropathy and may reflect an alteration in the degree of degeneration and regeneration in diabetes.

Cornea↗