Biomedical subjects

M J Doughty

Publications and source records attributed to M J Doughty.

At least 19 recordsLinked to original sources

PubMed2003

Is manual counting of corneal endothelial cell density in eye banks still acceptable? The French experience.

AIM: To examine the differences in manual endothelial cell counting methods in French eye banks and to analyse whether these differences could explain some substantial discrepancies observed in endothelial cell density (ECD) for corneas made available for transplant. METHODS: A questionnaire was sent to the 22 eye banks asking for details of the technical features of the light microscopes used, the microscope calibration, strategy for cell counting, the technical staff, and the method of presenting endothelial data. RESULTS: All eye banks responded and 91% (20/22) used only manual counting methods, in real time, directly through a microscope, and 62 different technicians, with varying experience, were involved in such counting. Counting of cells within the borders of a grid that were in contact with two adjacent borders was the most common method (17/22, 77%). Of the eight banks (8/22, 36%) that did not calibrate their microscopes, six reported the highest ECD values. Of the 14 others (64%), six applied a "magnification correcting factor" to the initial cell counts. In five of these cases, the corrected ECD was lower than estimated on initial count. Most of the banks (12/22, 55%) counted 100 cells or less in one to six non-adjacent zones of the mosaic. 14 of the banks (14/22, 64%) also graded cell polymegethism while seven (7/22, 32%) also graded pleomorphism ("hexagonality"). CONCLUSIONS: Lack of microscope calibration appears to be the leading cause of variance in ECD estimates in French eye banks. Other factors such as differences in counting strategy, the evaluation of smaller numbers of cells, and the different extent of experience of the technicians may also contribute to intraobserver and interobserver variability. Further comparative studies, including cross checking and the outcome of repeated counts from manual methods, are clearly needed with cross calibration to a computer based image archiving and analysis system.

Calibration↗

PubMed2002

A semi-automated assessment of cell size and shape in monolayers, with optional adjustment for the cell-cell border width-application to human corneal endothelium.

Measurements of large numbers of feature sizes within defined domains (e.g. cell areas within cell-cell borders) can be a time-consuming activity, but automation that includes defining such domains has not be proven to be very reliable. Other alternatives are therefore needed, and the goal of the present studies was both to develop a semi-automated (interactive) measurement system for cell areas and to carefully compare the output to that obtained using a manual digitiser pad method. A particular interest was in the contribution made by the cell-cell border zones. Non-contact specular micrographs of central corneal endothelium were obtained from 20 white male adults, aged 40-60 years. An overlay of the endothelial image was generated manually, from which the areas of around 200 cells were measured manually with a digitiser pad and also by a computer-assisted scanning method. The pad data was typed into a spread sheet along with details of the number of cell apices (sides). The computerised analysis identified borders of the same cells on the overlay, reduced these borders to a minimum, and then assessed cell area by the pixel count along with the number of neighbouring cells (to give cell sides data). The average cell area was 393 +/- 28 and 422 +/- 29 microm(2) (mean+/-SD) by the digitiser pad and computer-based methods, respectively. The average areas for each cell type were 153, 270, 392, 519 and 685 microm(2) for 4-, 5-, 6-, 7- and 8-sided cells, respectively. Assessment of the relationship between cell area and the number of cell sides (area-side relationships) showed a highly significant and positive correlation (P<0.001; r(2)=0.865). Comparing the two methods, the average cell area was 7.5% higher in the computer scan method, and this is attributed to the fact that the contribution made by the cell borders (the para-cellular space) had been essentially eliminated. A proportional correction factor can be applied to add back the cell borders/intercellular space to the computerised output, and examples are given based on using the average data from digitiser pad for each cell type. In conclusion, a computer assisted method has been developed to simultaneously provide data on the variance in cell areas (polymegethism) and cell shape (pleomorphism) from overlays of 200 cells from human corneal endothelial images, with the cell border zone corrected to allow for a finite para-cellular space.

Adult↗

PubMed2002

Morphometry of the corneal endothelium in glassblowers compared to non-glassblowers.

Acute exposure to high levels of IR radiation (IRR) can damage the endothelial cell layer of the human cornea, but the impact of chronic lower-dose exposure has not been assessed objectively. The corneal endothelium of 10 individuals who had occupational exposure to IRR as glassblowers (average 16 years) was examined by photo-slitlamp biomicroscopy, the endothelial mosaic assessed by morphometry, and compared to 10 non-glassblowers (controls). The analyses reveal the glassblowers to have higher than expected endothelial cell density (ECD, average 3371+/-304 cells/mm(2) compared to a control value of 3072+/-198 cells/mm(2)), a higher variance in cell area, and a lower percentage of the most-prevalent cell type, i.e. the six-sided cells (average 52.0+/-12.2%, compared to controls of 64.1+/-6.6%). Analyses of the sizes of different cell types (four-, five-, six-sided, etc.) indicate that the cells in both groups are proportionately larger as the number of sides increases, but that this area-side relationship is different in the glassblowers, who had both smaller and larger cells compared to controls. Two other cases had even higher cell density values (>5000 cells/mm(2)) and <50% six-sided cells. Occupational exposure to a mixture of IRR, perhaps some UVR as well as thermal convection effects, can apparently result in morphological changes in the human corneal endothelium. These may be the result of IRR-stimulated cell division.

Endothelium, Corneal↗

PubMed2001

Changes in hydration, protein and proteoglycan composition of the collagen-keratocyte matrix of the bovine corneal stroma ex vivo in a bicarbonate-mixed salts solution, compared to other solutions.

Many solutions have been used to investigate the swelling properties of the mammalian corneal stroma but few of the solutions resemble the expected extracellular matrix fluid of the corneal stroma, and little information is available on whether incubation ex vivo causes significant changes in the gross composition of the stroma. From quality-selected recent post-mortem eyes of adult cattle, stroma preparations were cut from the central part of the cornea. The time-dependent changes in wet mass were assessed over 9 h at 37 degrees C, and the preparations then dried. Various solutions of known pH (6.88-8.32) and osmolality (<50-327 mosmol/kg) were used, and were assayed for protein and proteoglycan after the incubation. The rates and extent of stromal swelling were lowest in a glucose-supplemented mixed salts solution containing 35 mM bicarbonate (0.5% CO2) solution, marginally greater in a mixed salts solution containing 35 mM bicarbonate (5% CO2) or similar non-bicarbonate mixed salts solutions (including BSS), and progressively greater in phosphate-buffered saline (PBS), various phosphate buffers (10-67 mM) and saline solutions (0.025-1%), and greatest in water. The initial rates of swelling ranged from 44 to 451 mg/h and the secondary rates from 9 to 106 mg/h. In all solutions, protein and proteoglycans were detected, but these ranged from around 1 to 10% of the samples with the bicarbonate-buffered solutions, to around 30% with the use of some phosphate buffers or saline.

Animals↗

PubMed2001

Influence of chronic alcohol abuse and ensuing forced abstinence on static subjective accommodation function in humans.

PURPOSE: Acute alcohol ingestion can change accommodation, but the long term effects of sustained alcohol consumption on accommodative function have not been studied in detail. This study was thus undertaken on individuals with a history of alcohol abuse. METHODS: Thirty-seven male individuals aged 25-56 years (average 40 years) from an alcohol rehabilitation centre in Inverness, Scotland, were assessed on admission and after a week of forced abstinence. The results were compared to a paired age-matched set of control male subjects. The static amplitude of accommodation was measured by an RAF rule, and the pupil size measured with a pupil gauge. RESULTS: On admission, the group mean measured amplitude of accommodation was 4.7 +/- 2.2 D (mean +/- SD). These values for the alcoholics were lower than age-matched controls (of 5.9 +/- 2.9 D). The slope of the age-dependent decline in RAF rule accommodation measures was significantly smaller for the alcoholics compared to controls (at 0.215 +/- 0.027 D/year versus 0.332 +/- 0.015 D/year, respectively; p < 0.001), with the younger alcoholics showing a greater impairment. Following abstinence, there was no measurable change in accommodation measured, indicating the lower amplitude in the alcoholics was not attributable to circulatory alcohol levels. The resting pupil diameter in the alcoholics was 4.37 +/- 0.63 mm compared to the controls of 3.97 +/- 0.75 mm, with a higher incidence of small pupils (< or = 3 mm) in the controls. CONCLUSIONS: The results indicate that chronic alcohol use can adversely affect subjective static accommodation, especially in younger alcoholics, as well as cause slight mydriasis.

Accommodation, Ocular↗

PubMed2001

A descriptive and quantitative study of the keratocytes of the corneal stroma of albino rabbits using transmission electron microscopy.

The present morphometric study was designed to assess the dimensions and shape of keratocytes and their nuclei by transmission electron microscopy, and to assess these features in relation to the stromal lamellae. Corneas from 10 albino rabbits were fixed in 2% glutaraldehyde in cacodylate buffer (pH 7.4, 300 mOsm/kg) and embedded in Spurr's epoxy resin. Both transverse and coronal thin sections through the corneal stroma were prepared. The stromal lamellae had an average thickness of 2.45+/-1.15 microm. The average cell thickness of the keratocytes was 1.34+/-0.46 microm (range 0.49-4.76 microm), with the apparent cell thickness being related to the average anterior-posterior thickness of the adjacent lamellae (r = 0.424, P = 0.001)). The relative length and thickness of the cell nucleus, in transverse section, was measured to be 0.65+/-0.13 and 0.76+/-0.10 of the cell body section respectively. As assessed by planimetry, the area of the keratocyte cell body viewed in coronal section was 292+/-118 microm2, with a nucleus-to-cytoplasm ratio of 0.437+/-0.295. The electron micrographs confirmed the presence of gap junctions between keratocyte cell processes, and the occasional presence of centrioles in the cells. Some keratocyte processes were observed to extend from one face of the lamellae to the other, suggesting anterior-to-posterior cell communication. These studies indicate that the keratocyte cell thickness is influenced by the physical pressure exerted by adjacent stromal lamellae. The cell nucleus, while a dominant feature in transverse section, has a normal size in relation to the cell cytoplasm when viewed in coronal section.

Albinism↗

PubMed2001

Video-assessment of tear meniscus height in elderly Caucasians and its relationship to the exposed ocular surface.

PURPOSE: An adequate volume of tears is considered essential to prevent desiccation of the exposed ocular surface, especially in elderly individuals. Few assessments of tear meniscus height (TMH) have however been reported for elderly individuals. METHODS: Close-up images of the lower marginal tear strip were obtained by videography over about 30 s in 56 elderly individuals (38 women, 18 men; 71 +/- 5 years of age) without significant eye disease and having a functional lacrimal system (Schirmer test). From such an "en face" view, the vertical height of the tear meniscus (TMH) at the lower eyelid was measured from stopped video frames. Firstly, TMH was assessed at the mid-point of the eyelid from five frames separated by 5 s; these values were averaged to give a time-averaged assessment of TMH (a tTMH value). Secondly, a position-averaged method (pTMH) was used in which TMH was assessed at 5 locations along the eyelid margin from a single frame that included several mm of marginal tear strip, and an average value calculated. The videographs were also used to assess palpebral aperture and the exposed ocular surface, a 1 min Schirmer test measure (closed eye) was also made, and keratometry data was available for most subjects. RESULTS: A wide range of average values was encountered for both tTMH (range 0.057 to 0.271 mm) and pTMH (0.031 mm to 0.325 mm). The group-averaged tTMH value was 0.172 +/- 0.047 mm (median 0.164 mm) while the group-averaged pTMH value was 0.171 +/- 0.058 mm (median 0.168 mm), with no difference being found between the two methods (p = 0.84, paired t-test). With either method, the apparent TMH value was greater when the exposed ocular surface value (average 1.68 +/- 0.51 cm(2)) was lower and vice versa, and was statistically-significant for the tTMH measures (p = 0.02, r = 0.32), but not the pTMH measures (p = 0.18, r = 0.18). Neither TMH measure was related to the Schirmer test values or to central corneal curvature. CONCLUSIONS: The results indicate that healthy elderly individuals can be expected to have a measurable lower marginal tear strip, and that objective assessment of this may be a useful alternative to the Schirmer test. A possible association was found between the measures of TMH and the palpebral aperture height (and thus the exposed ocular surface), and so might need to be considered when TMH is assessed.

Aged↗

PubMed2001

Consideration of three types of spontaneous eyeblink activity in normal humans: during reading and video display terminal use, in primary gaze, and while in conversation.

PURPOSE: To consider the conditions under which the so-called spontaneous (endogenous) eyeblink activity has been assessed by different investigators over the last 75 years and to consider the most appropriate terminology. The reason for this analysis was to try to identify why such different values for the spontaneous eyeblink rate (SEBR) have been reported. METHODS: A retrospective evaluation of published articles was carried out to identify whether the SEBR assessments were consistently dependent on the activity of the subjects while spontaneous eyeblink activity was being investigated. These were compared with assessments of SEBR in young adult subjects under equivalent conditions. RESULTS: Assessments of spontaneous eyeblink activity revealed that SEBR in a reading posture is lower than that in primary gaze, and SEBR is higher when subjects are in conversation. Such differences are also generally found in literature reports, especially if the primary gaze assessment is carried in silence. Electrophysiological measures of SEBR yield slightly higher values compared with observational techniques. Statistical analysis (with calculation of 95% confidence interval values) indicate that reading-SEBR should be between 1.4 and 14.4 eyeblinks/min, primary gaze-SEBR between 8.0 and 21.0 eyeblinks/min and conversational-SEBR between 10.5 and 32.5 eyeblinks/min for normal adults. CONCLUSIONS: It is inappropriate to simply state a value for spontaneous eyeblink rate because it is so dependent on experimental conditions. It is further proposed that reports of SEBR measures should be prefixed by these experimental conditions, namely reading-SEBR, primary gaze-SEBR (in silence) and conversational-SEBR.

Adult↗

PubMed2000

Swelling of the collagen-keratocyte matrix of the bovine corneal stroma ex vivo in various solutions and its relationship to tissue thickness.

AIM: The mammalian corneal stroma, like some other connective tissues, can absorb fluid, swell and become oedematous. Since studies on the corneal stroma have been carried out with different types of preparations and solutions, inter-study comparisons are very difficult. A study was thus undertaken on a standardised preparation to assess the relative magnitude of this swelling and its relationship to thickness of the preparations. METHODS: From selected recent post-mortem eyes of adult cattle, stroma preparations were cut from the central part of the cornea. These preparations were immersed in various solutions of known pH and osmolality, and the time-dependent changes in wet mass were assessed over 9 h at 37 degrees C. The relative rates and magnitude of the swelling of the tissue were then compared. RESULTS: A reference value for stromal swelling was obtained by incubation in a 35 mM bicarbonate-buffered mixed salts solution equilibrated with 5% CO2-air (pH 7.60) where a 3.39-fold increase in wet mass and a 4.58-fold increase in thickness was realised in 9 h, at an initial rate of 76 +/- 3%/h. The swelling was essentially the same in an organic buffer-mixed salt solution (pH 7.5) but progressively greater in phosphate-buffered saline (pH 7.5), a range of phosphate buffers (10-67 mM, pH 7.5), NaCl solutions (0.025-1%) and with gross swelling observed in water (where a 15.9-fold increase in wet mass occurred along with a 25-fold increase in thickness, at an initial rate of 643 +/- 62%/h). Overall, the wet mass changes were strongly related to thickness (P < 0.001). CONCLUSIONS: The results confirm that the selection of solution(s) for studies on corneal stromal swelling is critical. The swelling (oedema) is lower in a physiologically-relevant solution (similar to the aqueous humour of the eye). This indicates that the swelling tendency of the corneal stroma has been overestimated in the past, and that a similar discrepancy may also exist for studies on other connective tissues ex vivo when non-physiological experimental solutions are used.

Animals↗

PubMed2000

Assessment of the reliability of human corneal endothelial cell-density estimates using a noncontact specular microscope.

PURPOSE: We sought to determine the variance in endothelial cell density (ECD) estimates for human corneal endothelia. METHODS: Noncontact specular micrographs were obtained from white subjects without any history of contact lens wear, or major eye disease or surgery; subjects were within four age groups (children, young adults, older adults, senior citizens). The endothelial image was scanned, and the areas from > or =75 cells measured from an overlay by planimetry. The cell-area values were used to calculate the ECD repeatedly so that the intra- and intersubject variation in an average ECD estimate could be made by using different numbers of cells (5, 10, 15, etc.). RESULTS: An average ECD of 3,519 cells/mm2 (range, 2,598-5,312 cells/mm2) was obtained of counts of 75 cells/ endothelium from individuals aged 6-83 years. Average ECD estimates in each age group were 4,124, 3,457, 3,360, and 3,113 cells/mm2, respectively. Analysis of intersubject variance revealed that ECD estimates would be expected to be no better than +/-10% if only 25 cells were measured per endothelium, but approach +/-2% if 75 cells are measured. CONCLUSION: In assessing the corneal endothelium by noncontact specular microscopy, cell count should be given, and this should be > or =75/ endothelium for an expected variance to be at a level close to that recommended for monitoring age-, stress-, or surgery-related changes.

Adult↗

PubMed2000

Reassessment of the corneal endothelial cell organisation in children.

AIM: To assess uniformity of the corneal endothelial cell mosaic in children. METHODS: 36 healthy children (5-11 years old, 16 boys, 20 girls) were assessed by specular microscopy. Endothelial cell density (ECD) was calculated from measured cell areas, and the number of sides/cell noted. RESULTS: Average values for ECD and cell areas were 3987 cells/mm(2) (95% CI 3806 to 4168 cells/mm(2)) and 278 (SD 85) mm(2) respectively, with normal distribution (COV 28. 2%, range 17.4 to 39.2%) and with the average percentage of six sided cells being 66.6% (8.8%). Cell area was positively correlated to number of cell sides (p <0.01, r(2)=0.993), but the percentage of six sided cells was negatively correlated to ECD (p <0.01, r=0.493). CONCLUSION: A high ECD occurs in children, but this does not mean there is a high percentage of "hexagons".

Cell Count↗

PubMed2000

Comparison of grading schemes to quantitative assessments of nucleus-to-cytoplasmic ratios for human bulbar conjunctival cells collected by impression cytology.

PURPOSE: To quantitatively assess the measured nucleus-to-cytoplasm (N/C) ratios for sets of bulbar conjunctival cells categorised by a subjective grading scheme (0-3). METHODS: Impression cytology samples were taken from the nasal bulbar conjunctiva of 37 individuals (aged 22 to 74 years) without any significant eye disease. The sheets of cells were generally stained with Giemsa, photographed and 35 mm slides prepared. The images were graded 0 to 3 according to the scheme of Nelson [Cornea 7, 71-81 (1988)] and approximately 35 contiguous cells from each image measured by planimetry from an overlay. RESULTS: Analysis of 1097 cells revealed that the N/C ratios ranged from 1.395 to 0.056 and correlated well with the grading. The average N/C ratio (range for +/- 1.96 SD) for each grade was 0.607 (0.983 to 0.531) for grade 0, 0.533 (0.759 to 0. 333) for grade 1, 0.291 (0.427 to 0.155) for grade 2, and 0.154 (0. 228 to 0.080) for grade 3. CONCLUSIONS: N/C ratios can be assessed from conjunctival impression cytology samples and appear to be sufficiently consistent to allow for a designated range of cell N/C ratios to be specified for each grade.

Adult↗

PubMed2000

Further analysis of the size and shape of cells obtained by impression cytology from the exposed portion of the human bulbar conjunctiva.

PURPOSE: To assess whether the size of the cells obtained by conjunctival impression cytology can be quantitatively assessed by measurement of the longest dimension of the cells. METHODS: Under topical benoxinate anaesthesia, cells were removed from the normally exposed nasal bulbar conjunctival surface using a 0.4 micron pore diameter filter (Biopore filter; type Millcell-CM). The filters were stained with haematoxylin after ethanol denaturation, photographed at 40 x magnification, and 35 mm slides prepared. An optical overlay method was used to outline the borders of sets of 30-35 contiguous cells on each image. The cell area, longest and shortest dimensions were measured by planimetry to an accuracy of +/- 3%. RESULTS: Analyses of 20 sets of samples, from individuals aged 21 to 48 years and without clinically significant ocular surface disease, revealed a median cell area of 133 micron 2 (n = 621, range 46-1602 micron 2; average 212 micron 2), a median longest dimension of 13.9 microns (range 6.6-68.8 microns; average 16.9 microns) and a shorter dimension of 10.0 microns (range 4.7-43.0 microns; average 11.9 microns); the distributions of values indicated bimodality. Most cells had a long:short ratio (L:S ratio) value between 1.00 and 1.80, but 11.9 +/- 6.1% of the cells had L:S ratios between 1.80 and 4.60. The overall relationship between the longest dimension and the area of the cells was nonlinear, with cells having larger L:S ratios having disproportionately smaller areas. CONCLUSIONS: The superficial conjunctival cells are small, and their longest dimensions are systematically related to area. Analyses of cell shape indicate further possible ways of identifying different cells on the bulbar conjunctiva. Compared to literature values, there is a substantial overlap in longest dimensions of the conjunctival cells with those of cells that can be collected off the corneal surface. This means that superficial conjunctival and corneal cells cannot be distinguished simply on the basis of measurements of the long dimension.

Adult↗

PubMed1999

Re-assessment of the potential impact of physiologically relevant pH changes on the hydration properties of the isolated mammalian corneal stroma.

The pH sensitivity of the swelling of the mammalian corneal stroma was reinvestigated to assess whether or not there were detectable differences in the hydration properties of this collagen-keratocyte matrix within a physiologically relevant range (as opposed to extremes of acid or alkaline pH) and at a physiologically relevant temperature. From recent post-mortem eyes of adult cows, square (8 x 8 mm) samples of corneal stroma were prepared and incubated in an isotonic, buffered (HEPES etc.), mixed salts solution with added glucose at 37 degrees C. The time-dependent changes in wet mass were assessed over 24 h. The rate and magnitude of stromal swelling were different within the range of pH 6.5-8.5. The wet mass of stromal samples increased almost 2-fold within 1 h, and then at lesser rates to realise 3.25-3.75-fold and 4-5-fold increases in wet mass by 9 h and 24 h respectively. The maximum increases were observed at pH 7.25-7.5, with most of the effect being the result of differences in the initial rate of swelling. The discontinuous swelling and the pH effect on the rates of swelling were also evident when the data were fitted to a previous kinetic model (Elliott et al., J. Physiol. (Lond.) 298 (1980) 453-470). It is concluded that pH changes in the physiological range can have a small but reproducible impact on the swelling kinetics of the isolated mammalian corneal stroma ex vivo.

Animals↗

PubMed1999

Assessment of the effects of cetylpyridium chloride on water content of the collagen-keratocyte matrix of the mammalian corneal stroma ex vivo.

The effects of cationic surfactants on the time-dependent increases in hydration of the corneal stroma were investigated to assess if the contribution of the proteoglycans could be titrated and how it might relate to the maximum and minimum swelling properties of the corneal stroma. From recent post-mortem eyes from adult sheep, square (8 x 8 mm) samples of corneal stroma were prepared and incubated in isotonic neutral pH mixed salts solution with added glucose, or pure water, at 37 degrees C. The time-dependent changes in wet mass were assessed over 24 h in the absence or presence of 0. 001-2% w/v cetylpyridium chloride (CPC) or benzalkonium chloride (BAC). The rate and magnitude of stromal swelling was reduced in a concentration-dependent fashion by the surfactants. In mixed salts solution, 100% inhibition of swelling could be achieved at 2% CPC and BAC. In pure water, the relative swelling was much more substantial and could only be attenuated by CPC.

Animals↗

PubMed1999

The acinar and ductal organisation of the tarsal accessory lacrimal gland of Wolfring in rabbit eyelid.

The purpose of this study was to objectively assess the tarsal accessory lacrimal gland of Wolfring and its excretory duct by transmission electron microscopy (TEM). The upper eyelid of 6 female grey rabbits (2 kg) was fixed in the fully extended configuration with buffered glutaraldehyde. At the tarsal/orbital portion of the palpebral conjunctiva, a series of prominent acinar glands were located by both light microscopy and TEM. Cells within the acini were characterised by apical tight junctions and desmosomal connections as well as abundant intra-cytoplasmic osmophillic (secretory) granules. The apical surfaces were profusely decorated with microvilli-like extensions. In the vicinity of the acini, and traversing over several millimetres of adjacent sub-epithelial parenchyma and epithelium, was an extensive system of duct-like spaces lined with secretory cells decorated with microvilli. These ducts run a tortuous course within the palpebral conjunctival epithelium leading to crypt-like termination's along the eyelid inner surface. The tarsal accessory lacrimal gland of Wolfring thus has an acinar structure similar to the main lacrimal glands, and its ducts are lined by secretory cells along the entire tortuous course towards the palpebral conjunctival surface, where the ducts emerge at multiple points at the tarsal/orbital portion of the surface.

Animals↗

PubMed1999

Re-wetting, comfort, lubricant and moisturizing solutions for the contact lens wearer.

In recent years there have been significant changes in perspective and availability of eyedrops designed to provide comfort to the contact lens wearer. This review addresses the reasons why there is a need for these types of products and considers their potential impact on the corneal and conjunctival surface. The methods of assessment of these solutions are discussed and the range of current products and options for the UK practitioner are detailed.

Journal Article↗

PubMed1999

The cornea swells in the posterior direction under hydrogel contact lenses.

Two mathematical models were developed to describe the topographical corneal swelling response to hydrogel contact lenses and the effect of these changes on refractive error. In one, corneal thickness changes resulted in deformation of the anterior corneal surface. In the other, the posterior surface only was deformed. Refractive error, corneal thickness and corneal shape were monitored in a sample of adapted contact lens wearers with one eye patched for 4 h while wearing a soft contact lens. The experimental data were most consistent with the model in which the posterior surface only was deformed.

Contact Lenses, Hydrophilic↗