Nicola Pritchard

A multi‐centre study of lapsed contact lens wearers

Purpose:  Discontinuation from contact lens wear has been identified as a contributing factor in the lack of growth of contact lens use in Europe. The purpose of this study was to determine the proportion of lapsed contact lens wearers that can be refitted successfully with contact lenses and to evaluate the reasons for discontinuation from contact lens wear.

The ocular response to extended wear of a high Dk silicone hydrogel contact lens

Purpose: A four‐month extended wear clinical trial was conducted to compare die ocular effects of a high Dk Balafilcon A silicone hydrogel lens and a low Dk HEMA 38.6 per cent H2O soft lens.

Influence of age on peripheral refraction

To investigate how age affects peripheral refraction we measured objective peripheral refraction for 55 young subjects (24+/-4 years) and 41 older subjects (59+/-3 years) out to 35 degrees eccentricity in temporal and nasal visual fields. Subjects were compared in 1D subgroups based on central spherical equivalent refractions (low hypermetropes +0.54 D to +1.51 D, emmetropes +0.50 D to -0.49 D, low myopes -0.50 D to -1.49 D, moderate myopes -1.50 D to -2.58 D). Overall, young and older subjects with similar refractive corrections had similar peripheral refraction components. Both age groups showed relative hypermetropic shifts in the peripheral fields as myopia increased and also decreases in peripheral astigmatism J180 as myopia increased. J45 varied little across the visual field with linear relationships occurring between J45 and visual field angle for all but one subgroup (older emmetropes). Peripheral refraction in emmetropes to moderate myopes is relatively unaffected by age for healthy eyes of similar refractive errors.

Repeatability of Measuring Corneal Subbasal Nerve Fiber Length in Individuals With Type 2 Diabetes

Purpose: To analyze the repeatability of measuring nerve fiber length (NFL) from images of the human corneal subbasal nerve plexus using semiautomated software. Methods: Images were captured from the corneas of 50 subjects with type 2 diabetes mellitus who showed varying severity of neuropathy, using the Heidelberg Retina Tomograph 3 with Rostock Corneal Module. Semiautomated nerve analysis software was independently used by two observers to determine NFL from images of the subbasal nerve plexus. This procedure was undertaken on two occasions, 3 days apart. Results: The intraclass correlation coefficient values were 0.95 (95% confidence intervals: 0.92–0.97) for individual subjects and 0.95 (95% confidence intervals: 0.74–1.00) for observer. Bland-Altman plots of the NFL values indicated a reduced spread of data with lower NFL values. The overall spread of data was less for (a) the observer who was more experienced at analyzing nerve fiber images and (b) the second measurement occasion. Conclusions: Semiautomated measurement of NFL in the subbasal nerve fiber layer is highly repeatable. Repeatability can be enhanced by using more experienced observers. It may be possible to markedly improve repeatability when measuring this anatomic structure using fully automated image analysis software.

Subjective and objective measures of corneal staining related to multipurpose care systems.

An objective, digital-imaging method of measuring corneal staining was evaluated in 24 subjects wearing soft contact lenses. The method was used to compare the clinical performance of common multipurpose care systems (MPS) for soft contact lens care. Subjects used three different MPS, one containing polyquaternium-1 (PQ) and two containing polyhexanide (PX1 and PX2), for 2 weeks in a randomised, single-masked (investigator) crossover study. Corneal staining induced with the three MPS was analysed using an image-processing program (ImageTool, UTHSCSA Version 2, University of Texas, USA). Conjunctival hyperaemia and papillae were also evaluated. The intraclass correlation coefficient was similar with image analysis to that of investigator grading (0.876, 0.879, respectively). Significant differences in staining response were detected using the objective method. There was significantly less staining area with polyquaternium-1 (PQ) than polyhexanide (PQ: 0.12 mm(2), PX2: 0.91 mm(2)). Inferior palpebral papillae were significantly greater with PX2 than with PQ (1.0, 0.7 (0-4), respectively). The technique was shown to be an effective method of evaluating different corneal staining responses. Bilateral corneal staining in three or more quadrants is useful in the diagnosis of MPS-related staining.

Neural and optical limits to visual performance in myopia.

We investigated the relative importance of neural and optical limitations to visual performance in myopia. A number of visual performance measures were made on all or subsets of 121 eyes of emmetropic and myopic volunteers aged 17-35 years. These tests included visual measures that are mainly neurally limited (spatial summation out to +/-30 degrees in the horizontal visual field and resolution acuity out to +/-10 degrees in the horizontal visual field) and central ocular aberrations. We found that myopia affected the neurally limited tests, but had little effect on central higher order aberration. The critical area for spatial summation increased in the temporal visual field at 0.03 log units/dioptre of myopia. Resolution acuity decreased at approximately 0.012 log units/dioptre of myopia. Losses of visual function were slightly greater in the temporal than in the nasal visual field. The observed visual deficit in myopia can be explained by either global retinal expansion with some post-receptor loss (e.g. ganglion cell death) or a posterior polar expansion in which the point about which expansion occurs is near the centre of the previously emmetropic globe.

In vivo confocal microscopy of the bulbar conjunctiva.

Background:  The aim of this work is to develop a more complete qualitative and quantitative understanding of the in vivo histology of the human bulbar conjunctiva.

Confocal microscopy of the bulbar conjunctiva in contact lens wear.

Purpose: The aim of this study was to investigate the capabilities of laser scanning confocal microscopy (LSCM) for undertaking qualitative and quantitative investigations of the response of the bulbar conjunctiva to contact lens wear. Methods: LSCM was used to observe and measure morphological characteristics of the bulbar conjunctiva of 11 asymptomatic soft contact lens wearers and 11 healthy volunteer subjects (controls). Results: The appearance of the bulbar conjunctiva is consistent with known histology of this tissue based on light and electron microscopy. The thickness of the bulbar conjunctival epithelium of lens wearers (30.9 ± 1.1 μm) was less than that of controls (32.9 ± 1.1 μm) (P < 0.0001). Superficial and basal bulbar conjunctival epithelial cell densities in contact lens wearers were 91% and 79% higher, respectively, than that in controls (P < 0.0001). No difference was observed in goblet and Langerhans cell density between lens wearers and controls. Conjunctival microcysts were observed in greater numbers, and were larger in size, in lens wearers compared with controls. Conclusions: The effects of contact lens wear on the human bulbar conjunctiva can be investigated effectively at a cellular level using LSCM. The observations in this study suggest that contact lens wear can induce changes in the bulbar conjunctiva such as epithelial thinning and accelerated formation and enlargement of microcysts, increased epithelial cell density, but has no impact on goblet or Langerhans cell density.

Corneal Confocal Microscopy Predicts 4-Year Incident Peripheral Neuropathy in Type 1 Diabetes

OBJECTIVE This study determined if deficits in corneal nerve fiber length (CNFL) assessed using corneal confocal microscopy (CCM) can predict future onset of diabetic peripheral neuropathy (DPN). RESEARCH DESIGN AND METHODS CNFL and a range of other baseline measures were compared between 90 nonneuropathic patients with type 1 diabetes who did or did not develop DPN after 4 years. The receiver operator characteristic (ROC) curve was used to determine the capability of single and combined measures of neuropathy to predict DPN. RESULTS DPN developed in 16 participants (18%) after 4 years. Factors predictive of 4-year incident DPN were lower CNFL (P = 0.041); longer duration of diabetes (P = 0.002); higher triglycerides (P = 0.023); retinopathy (higher on the Early Treatment of Diabetic Retinopathy Study scale) (P = 0.008); nephropathy (higher albumin-to-creatinine ratio) (P = 0.001); higher neuropathy disability score (P = 0.037); lower cold sensation (P = 0.001) and cold pain (P = 0.027) thresholds; higher warm sensation (P = 0.008), warm pain (P = 0.024), and vibration (P = 0.003) thresholds; impaired monofilament response (P = 0.003); and slower peroneal (P = 0.013) and sural (P = 0.002) nerve conduction velocity. CCM could predict the 4-year incident DPN with 63% sensitivity and 74% specificity for a CNFL threshold cutoff of 14.1 mm/mm2 (area under ROC curve = 0.66, P = 0.041). Combining neuropathy measures did not improve predictive capability. CONCLUSIONS DPN can be predicted by various demographic, metabolic, and conventional neuropathy measures. The ability of CCM to predict DPN broadens the already impressive diagnostic capabilities of this novel ophthalmic marker.

Corneal Markers of Diabetic Neuropathy

Diabetic neuropathy is a significant clinical problem that currently has no effective therapy, and in advanced cases, leads to foot ulceration and lower limb amputation. The accurate detection, characterization and quantification of this condition are important in order to define at-risk patients, anticipate deterioration, monitor progression, and assess new therapies. This review evaluates novel corneal methods of assessing diabetic neuropathy. Two new noninvasive corneal markers have emerged, and in cross-sectional studies have demonstrated their ability to stratify the severity of this disease. Corneal confocal microscopy allows quantification of corneal nerve parameters and noncontact corneal esthesiometry, the functional correlate of corneal structure, assesses the sensitivity of the cornea. Both these techniques are quick to perform, produce little or no discomfort for the patient, and are suitable for clinical settings. Each has advantages and disadvantages over traditional techniques for assessing diabetic neuropathy. Application of these new corneal markers for longitudinal evaluation of diabetic neuropathy has the potential to reduce dependence on more invasive, costly, and time-consuming assessments, such as skin biopsy.