PubMed Health⌕ Search

Biomedical subjects

Nathan Efron

Publications and source records attributed to Nathan Efron.

54 records · Page 3Linked to original sources
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↗
PubMed2004

On the etiology of keratocyte loss during contact lens wear.

PURPOSE: To employ confocal microscopy to investigate the etiology of keratocyte loss after short-term contact lens wear by monitoring quantitative changes in keratocyte density. METHODS: Twenty neophyte subjects aged 26 +/- 3 years participated in the study, which was conducted over the course of three experimental sessions. In the first session, one eye of each subject was fitted with a silicone hydrogel contact lens, and the other eye served as the control. Both corneas were exposed to an anoxic environment for 2 hours. Ultrasound pachometry and confocal microscopy were performed on both eyes at baseline, immediately after the experiment and 2 hours post experiment. This procedure was repeated after 72 hours, but in this case one eye of each subject was fitted with a hyper-Dk rigid contact lens, and the fellow eye served again as the control. In the third experimental session, each subject was asked to periodically rub one eye only. Tear samples collected from the rubbed and control eyes were assayed for epidermal growth factor (EGF), hepatocyte growth factor (HGF), and interleukin (IL)-8. RESULTS: The increase in corneal thickness was similar in the experimental and control eyes. Both anterior and posterior keratocyte densities decreased in the experimental eyes compared with the control eyes, in all sessions. EGF and IL-8 concentrations were increased in the rubbed eyes compared with the control eyes. CONCLUSIONS: It is hypothesized that the mechanical stimulation of the corneal surface, due to the physical presence of a contact lens, induces the release of inflammatory mediators that cause keratocyte dysgenesis or apoptosis.

Adult↗
PubMed2004

Short-term physiologic response in neophyte subjects fitted with hydrogel and silicone hydrogel contact lenses.

PURPOSE: To investigate the short-term physiologic response to three soft lens materials with different oxygen permeability characteristics. METHODS: Forty-three neophytes were randomly prescribed Acuvue 2, Acuvue Advance (Johnson & Johnson Vision Care), or Focus Night & Day (CIBA Vision) for 4 weeks on a daily-wear basis. A further 19 subjects did not wear lenses (control). Experimental and control subjects were examined 2 and 4 weeks after dispensing. Ocular physiologic response was measured with a slitlamp biomicroscope in a strictly masked fashion. RESULTS: Limbal redness increased in the Acuvue 2 group compared with the other two groups. Conjunctival redness increased more in the Acuvue 2 group than in the Acuvue Advance group. More conjunctival staining was seen with the Acuvue Advance and Focus Night & Day groups compared with the Acuvue 2 group. Increased scores for papillary conjunctivitis were seen in the Focus Night & Day group compared with the Acuvue Advance group. CONCLUSIONS: The reduced level of limbal redness seen with the Acuvue Advance and Focus Night & Day groups suggests that these lenses provide more oxygen to the ocular surface than the Acuvue 2 lens to a degree that can be observed clinically. The conjunctival staining response was similar for the Acuvue Advance and Focus Night & Day groups. The results for the Acuvue Advance and Focus Night & Day groups for papillary conjunctivitis may reflect differences in their material and surface properties.

Adult↗
PubMed2003

Confocal microscopic evaluation of particles at the corneal flap interface after myopic laser in situ keratomileusis.

PURPOSE: To investigate the appearance and origin of interface particles in the cornea after myopic laser in situ keratomileusis (LASIK) using the confocal microscope. SETTING: Department of Optometry and Neuroscience, UMIST, Manchester, United Kingdom. METHODS: An in vivo slit-scanning, real-time confocal microscope (Tomey ConfoScan P4) fitted with an Achroplan(R) 40X/0.75 NA immersion objective (Zeiss) was used to examine the morphology of the central cornea in 6 patients (12 eyes) at the initial visit (before surgery) and 1 week and 1, 3, and 6 months after LASIK for myopia. RESULTS: In all eyes, several interspersed particles of variable size and brightness were observed 1 week after surgery at the flap interface. The overall density of these particles decreased with time (F = 14.34, P =.01). For analysis, the particles were divided by density into high brightness and low brightness. The low-brightness particles significantly decreased with time (F = 13.26, P =.02). The high-brightness particles remained constant in density at all postoperative visits (F = 1.3, P =.15). CONCLUSIOINS: The particles of low reflectivity may represent 1 or more types of remains. It is unclear whether the low-reflectivity particles will eventually disappear. The high-reflectivity particles may represent fine metallic debris arising from the mechanical drive mechanism and/or the disposable knife of the microkeratome. If they are metallic and magnetic, they could be cleared during surgery (immediately before flap replacement) using a specially adapted magnet.

Adult↗
PubMed2003

Environmental impact of three replacement modalities of soft contact lens wear.

PURPOSE: To illustrate the environmental impact of three contact lens replacement modalities, and to place this into a broader environmental context. METHODS: Environmental impact was calculated by sorting the packaging used in the supply of three representative contact lens systems into their constituent materials (liquid, plastic, paper, metal and glass), determining their mass, calculating the annualised consumption by a typical contact lens wearer, and factoring the data against published indices of the environmental impact of the constituent materials. RESULTS: Conventional lens wear had the highest impact and planned replacement lens wear (monthly disposable) had the lowest impact. CONCLUSIONS: The overall environmental impact of waste generated thorough the use of contact lens products by the end consumer is insignificant (0.5%) compared with the amount of waste generated in our everyday life.

Journal Article↗
PubMed2003

The combined influence of knowledge, training and experience when grading contact lens complications.

PURPOSE: A study was conducted to evaluate the influence of knowledge, training and experience (clinical skills set) when assessing the severity of contact lens complications. METHODS: Nine optometrists (who were in possession of a relevant clinical skills set) and nine 'non-optometrists' (subjects without the clinical skills set) were each invited to grade - to the nearest 0.1 increment - an image of each of 16 contact lens complications using Efron Grading Scales for Contact Lens Complications. This procedure was repeated 2 weeks later, yielding a total data base comprising 576 individual grading estimates. RESULTS: The mean of the test and retest grading estimates was the same for the optometrists (2.8 +/- 0.7) and the non-optometrists (2.6 +/- 0.9) (F1,15,1 = 1.3, p = 0.26); that is, non-optometrists can grade accurately. Median grading reliability for optometrists (+/-0.41) was lower than (i.e. superior to) that for non-optometrists (+/-0.67) (p = 0.001). Non-optometrists tended to display a reluctance to grade by interpolation and to less reliably grade subtle clinical signs. CONCLUSIONS: When averaged over several attempts, non-optometrists will arrive at similar estimates of severity to optometrists when grading ocular complications of contact lens wear; however, they will do so less reliably. The relative contribution of the three attributes of the clinical skills set to grading performance is presently unclear.

Clinical Competence↗
PubMed2003

Experience and training as determinants of grading reliability when assessing the severity of contact lens complications.

PURPOSE: A study was conducted to investigate the influence of experience and training on grading reliability when assessing the severity of contact lens complications. METHODS: Twenty-three optometry students who were unfamiliar with the use of grading scales each used the Efron Grading Tutor computer program to ascertain grading reliability at an 'initial' experimental session and a 'final' session 3 weeks later. Twelve subjects (the 'trained' group) were given a tutorial on grading techniques and were asked to complete two grading exercises between the initial and final sessions. The other 11 subjects (the 'untrained' group) received no such training between the two sessions. Differences in grading reliability between the initial and final grading sessions were evaluated. RESULTS: Grading reliability was superior (lower) for the combined subject cohort at the final session (mean +/- standard deviation 0.33 +/- 0.12) compared with the initial session (0.46 +/- 0.25) (p = 0.004). However, there was no difference in the improvement in grading reliability between the two groups. CONCLUSIONS: Grading reliability improves statistically with some experience, although perhaps not to a clinically meaningful extent. No added benefit can be derived from supplemental training.

Clinical Competence↗
PubMed2003

Morphology of corneal nerves in soft contact lens wear. A comparative study using confocal microscopy.

The aim of this study was to evaluate corneal innervation in soft contact lens wearers using the Tomey Confoscan confocal microscope (40x/0.75 objective lens). Three distinct age- and sex-matched subject groups were involved, including extended soft (hydrogel and silicone-hydrogel) contact lens wearers, overnight soft (hydrogel) contact lens wearers, and non contact lens wearers. A number of variables were objectively measured, subjectively evaluated, or graded in order to investigate the distribution and morphology of corneal nerves. For most of the evaluated parameters, no statistically significant differences were found. However, qualitative observations showed noticeable differences in corneal nerve appearance among the different subject groups; the degree of corneal oedema was suggested as the main causative factor. In conclusion, neither the short-term (overnight wear) nor the long-term (12-month extended wear) soft contact lens wear appeared to affect the morphology and/or distribution of corneal nerves as viewed with confocal microscopy.

Adult↗
PubMed2003

The case against rigid contact lenses.

Rigid lens fitting has been an integral part of contact lens practice for decades. However, rigid lens fitting has been constantly declining since soft lenses were introduced in the 1970s to whereby, world wide, rigid lenses constitute less than 10% of new contact lens fits. It seems that many practitioners correctly or incorrectly believe that rigid lenses only need to be prescribed in specialized or extenuating circumstances. This discussion article examines the international decline in rigid lens fitting and seeks to explain the cause of this trend. I conclude that rigid lenses will be virtually obsolete by the year 2010.

Contact Lenses↗
PubMed2003

Comfort response to rigid and soft hyper-transmissible contact lenses used for continuous wear.

PURPOSE: To assess subjective comfort during the first three months of continuous wear of hyper-transmissible soft and rigid contact lenses. METHODS: One hundred subjects (50 experienced wearers and 50 neophytes) were fitted with either the Focus Night & Day lens (CIBA Vision, Duluth, GA) or the Z alpha lens (Menicon, Nagoya, Japan). Comfort was monitored at regular intervals using a vertical analog comfort scale. RESULTS: Good comfort scores (generally indicating very comfortable lenses) were recorded for the two soft lens groups (experienced and neophytes) and the experienced rigid lens group; these scores remained approximately constant throughout the study. Comfort reported by neophyte rigid lens wearers was initially recorded as being between slightly uncomfortable and comfortable; however, after 1 week of daily wear and 1 night of overnight wear, the mean comfort score of this group reached a level that was similar to that recorded by subjects in the other three study groups. CONCLUSION: The comfort data presented in this study can be used by clinicians to anticipate the subjective response of both new and existing lens wearers to new-generation hyper-transmissible soft and rigid contact lenses.

Adult↗
PubMed2003

In vivo dehydration of silicone hydrogel contact lenses.

PURPOSE: To benchmark the performance of new-generation silicone hydrogel contact lenses in terms of their in vivo hydration characteristics and to highlight the possible clinical ramifications of any changes observed. METHODS: Thirteen subjects (four men and nine women with a mean age of 24.8 +/- 5.0 years) wore a silicone hydrogel lens (PureVision, Bausch & Lomb, Rochester, NY) in one eye and a conventional hydrogel lens (ACUVUE 2, Johnson & Johnson Vision Care, Jacksonville, FL) in the other eye for 4 weeks on an extended-wear basis. A gravimetric method was used to determine lens water content and dehydration during the intended lifespan of the lenses. RESULTS: For the PureVision lens, the water content was 38.3% +/- 0.9%, 35.2% +/- 1.1%, and 35.3% +/- 1.7% at baseline and after 2 and 4 weeks of wear, respectively (F=28.4, P<0.0001). For the ACUVUE 2 lens, the water content was 58.1% +/- 0.6% and 52.1% +/- 1.3% at baseline and after 2 weeks of wear, respectively. Thus, after 2 weeks of wear, absolute dehydration was 2.8% +/- 1.8% and 6.0% +/- 1.3% for the PureVision and ACUVUE 2 lenses, respectively (t=6.8, P<0.0001). The mass of deposition was calculated to be 568 +/- 457 microg for the PureVision lens and 1,660 +/- 499 microg for the ACUVUE 2 lens (t=5.1, P=0.0003). CONCLUSIONS: The ACUVUE 2 lens underwent a greater degree of lens dehydration, causing a reduction in oxygen permeability (3.6 barrer), and deposition after 2 weeks of extended wear. The loss of water from the PureVision lens was paradoxically associated with a 6.0-barrer increase in oxygen permeability after 4 weeks of extended wear.

Adult↗
PubMed2002

Validation of computer morphs for grading contact lens complications.

Abstract An alternative to the use of printed grading scales for assessing the severity of contact lens-induced ocular pathology is to use computer-generated grading morphs. This technique involves manipulation of a continuously variable movie sequence until this matches the severity of the condition being observed. To validate the use of computer morphs, nine experienced optometrists were each invited to grade - to the nearest 0.1 increment - an image of each of 16 contact lens complications, using printed scales (Efron Grading Scales for Contact Lens Complications) and computer morphs (Efron Grading Morphs). This entire procedure was repeated approximately 2 weeks later, yielding a total data base comprising of 576 individual grading estimates. Good accuracy was achieved using computer morphs, as evidenced by the similarity between the mean of the test and retest grading estimates for the printed scales (2.8 +/- 0.7) and the computer morphs (2.6 +/- 0.8) (F1,8 = 2.7, p = 0.14). There was no difference in median reliability between the printed scales (+/- 0.41) and the computer morphs (+/- 0.43) (Z = 0.1, p = 0.95). Computer morphs are thus considered to have been validated in view of their accuracy and reliability compared with printed scales. In addition, computer morphs offer considerable utility in terms of computer-based clinical record keeping, teaching and learning, and clinical research.

Computer Graphics↗
PubMed2002

Confocal microscopic observations of the human cornea following overnight contact lens wear.

BACKGROUND: Striae and folds are observed with a slitlamp biomicroscope in the cornea following overnight contact lens wear. These phenomena are poorly understood. The aim of this study is to employ confocal microscopy to observe and document these and other morphological changes in the human cornea following overnight contact lens wear. METHODS: Slitlamp biomicroscopy, slit-scanning confocal microscopy and ultrasonic pachometry were performed on both eyes of 13 subjects (3M, 10F, age 24 +/- 3 years) before and after eight hours overnight wear of a -3.00 D Bausch & Lomb one day disposable soft contact lens (Dk/t = 15.1 x 10(-9) [cm/sec] x [ml O2/ml x mmHg]) in one eye; the other non-lens-wearing eye acted as a control. RESULTS: Following sleep, both corneas were swollen (lens-wearing eye 11.8 +/- 3.8 per cent; control eye 2.1 +/- 1.9 per cent) and the stroma of both corneas displayed an apparent reduction in keratocyte density (lens-wearing eye 21 per cent; control eye 10 per cent). Folds were observed with the slitlamp biomicroscope and long, straight, dark, orthogonal lines were observed with the confocal microscope, in the posterior stroma of the oedematous lens-wearing eyes. Such features were not observed in the control eyes. The keratocytes appeared less distinct with greater levels of corneal oedema. CONCLUSION: The apparent loss of keratocytes following overnight lens wear is an optical artefact that can be explained in terms of corneal oedema causing volumetric tissue expansion and a loss of optical clarity, which hampers keratocyte detection. These findings place the onus on researchers postulating a loss of stromal keratocytes following clinical interventions, such as contact lens wear, to account for the effects of oedema.

Adult↗
PubMed2002

Confocal microscopic observations of stromal keratocytes during extended contact lens wear.

BACKGROUND: The aim of this study was to monitor changes in keratocyte density during extended contact lens wear and to explore the possible role of hypoxia and oedema in any changes observed. METHODS: Twenty-three neophyte myopic subjects wore a high Dk/t lens (PureVision) in one eye and a low Dk/t lens (Acuvue 2) in the other eye on an extended wear basis for six months. Slit-scanning confocal microscopy and ultrasonic pachometry were performed on both eyes at baseline (before lens wear), after three and six months of lens wear, and one week after cessation of lens wear (the 'post-cessation' visit). RESULTS: No differences were established between the two lenses or between the three study visits for anterior stromal keratocyte density (KD). Posterior stromal KD was similar for the two lenses throughout the study. However, there was an overall drop in posterior KD of 14 per cent in both eyes at the six-month visit, compared to the initial visit. Posterior KD at the six-month visit was no different from that at the post-cessation visit. Corneal thickness was similar for the two lenses at the initial and post-cessation visits, but was three per cent greater for the eye wearing the Acuvue 2 lens at the six-month visit. CONCLUSION: Extended contact lens wear causes a loss of keratocytes; this loss cannot be attributed to contact lens-induced hypoxia and/or oedema, or to an artifact of confocal microscopy relating to presence of residual oedema. It is postulated that lens-induced keratocyte loss may be related to the physical presence of contact lenses creating some mechanical effect.

Adult↗
PubMed2002

Comparative clinical performance of two silicone hydrogel contact lenses for continuous wear.

BACKGROUND: Silicone hydrogel soft contact lenses are now available for use on a 30-day continuous wear basis. The aim of this study was to compare the clinical performance of two such lenses. METHODS: In a single-centre, randomised, subject-masked, two-period crossover study, 30 subjects wore a pair of PureVision lenses (Bausch & Lomb) and a pair of Focus Night & Day lenses (CIBA Vision), alternately, for successive eight-week periods. Assessment was made of lens fit and surface characteristics, logMAR visual acuity, ocular response and subjective reaction. RESULTS: Lens fit, deposition and post-lens debris were similar for the two lens types. High contrast visual acuity was statistically significantly better for the PureVision lens, as was the subject-reported quality of vision, although these differences were not considered clinically significant. For both lenses, limbal and conjunctival redness reduced throughout the duration of the study, whereas there was a slight increase in the overall amount of corneal staining. The incidence of mucin balls peaked four weeks after commencing lens wear and began to decline thereafter; more mucin balls were noticed in subjects wearing Focus Night & Day lenses. No differences between the lenses were observed for any other biomicroscopic signs. CONCLUSIONS: This study demonstrates similar clinical performance with the two silicone hydrogel lenses evaluated. We believe that, with careful monitoring, both of these new-generation lenses can be prescribed for continuous wear.

Adult↗