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Biomedical subjects

N Efron

Publications and source records attributed to N Efron.

At least 19 recordsLinked to original sources
PubMed2000

Hydrogel contact lens ageing.

PURPOSE: To determine if hydrogel lens water content decreases over wearing periods of up to four weeks; that is, demonstrate an 'ageing' effect. METHODS: Six subjects (4 males, 2 females; age range: 34.8 +/- 11.0 years) wore each of the following lenses for one month: Acuvue, Frequency 38, Gentle Touch and Proclear. Pre-insertion and post-removal lens water content was measured daily by the subjects using an Atago CL-1 Soft Contact Lens Refractometer for a 28 day period. Post-insertion and pre-removal comfort was recorded over the same period. RESULTS: A significant lens ageing effect was noted whereby the pre-insertion lens water content decreased significantly over the 28 day cycle for all lenses (P < 0.05). The pattern for daily dehydration remained consistent for the 28 day period for the Acuvue lens and the Gentle Touch lens but decreased for the Frequency 38 lens and the Proclear lens. Comfort decreased significantly by the end of the day for three of the four lens types investigated. CONCLUSIONS: It is apparent that the extent of lens dehydration changes over time, and that this pattern of change is different for different lens types. The associated loss of oxygen performance with dehydration is demonstrated. These data will assist practitioners in understanding the clinical effects of soft lens dehydration over time.

Adolescent↗
PubMed1999

Ocular temperature in carotid artery stenosis.

PURPOSE: To explore the potential application of wide-field, color-coded infrared ocular thermography in the investigation of carotid artery stenosis (CAS). METHODS: Ocular thermography and color duplex ultrasonography were undertaken in a masked study of 24 asymptomatic, consecutively presenting patients who were examined for vascular occlusive disease. RESULTS: Linear regression analysis indicated that there was a significant negative correlation between ocular surface temperature and the degree of CAS (r = -0.67, p < 0.001). Similar results were demonstrated between the relative difference in CAS (right - left) and the relative difference in ocular surface temperature (right - left) (r = -0.67, p < 0.001). CONCLUSIONS: These results indicate that the circle of Willis and the other anastomoses within the brain are unable to compensate fully for the reduction in blood flow on the affected side. Noncontact ocular temperature measurement has potential as both a screening test and a supplementary diagnostic clinical test for CAS.

Body Temperature↗
PubMed1999

Hydrogel contact lens dehydration and oxygen transmissibility.

PURPOSE: Oxygen transmissibility is a key determinant of the physiological response of the cornea to contact lens wear. Because transmissibility is related to hydrogel water content, we conducted a study to determine the change in water content during lens wear and to quantify the impact any such change would have on transmissibility. METHODS: In a double masked clinical investigation, two subjects each wore 17 different pairs of contact lenses. Water content was measured before lens wear at 35 degrees C and immediately after 4 hours of contact lens wear. Contact lens oxygen transmissibilities were calculated on each occasion. RESULTS: The absolute changes in water content for the 17 lenses varied from +0.5% to -5.3%. For some lenses, this change in water content altered the lens oxygen transmissibilities to a clinically significant degree. The changes in water content and oxygen transmissibilities were greatest with FDA Group IV lenses. CONCLUSIONS: Dehydration during contact lens wear can alter the oxygen transmissibility of hydrogel lenses, and in some situations, this factor may be clinically significant.

Contact Lenses, Hydrophilic↗
PubMed1999

Clinical performance of an innovative back surface multifocal contact lens in correcting presbyopia.

PURPOSE: This prospective study was designed to subjectively and objectively evaluate the performance of an aspheric multifocal back surface rigid gas permeable (RGP) contact lens. The multifocal element of this lens design consisted of an aspheric optical zone that varied according to the patient's ametropia, corneal topography, and required reading addition. METHODS: We fit 28 presbyopic subjects with an aspheric multifocal back surface RGP contact lens (age range: 45 to 68 years). Reading additions ranged from +0.75 D to +2.50 D. Subjects were assessed initially and at 2, 6, and 12 weeks for ocular changes, visual performance, and subjective responses. RESULTS: We required 116 RGP lenses to achieve an acceptable fit and visual acuity in 28 subjects (55 eyes). At the final visit, the distance logMAR acuity with the multifocal contact lens (+0.12 +/- 0.10) was not statistically different (t = -0.623, P = -0.5388) from spectacle acuity at the initial visit (+0.10 +/- 0.12). The near logMAR acuity with the multifocal contact lens at the final visit (0.36 +/- 0.12) was not statistically different from that for near acuity with spectacles at the initial visit (0.33 +/- 0.13). No slit lamp signs worsened during the study. A reduction in myopia of 0.67 D was noted by the final visit. Spectacle blur was noted if the acuity at the initial refraction was compared to the acuity with the same refraction at the final visit (t = -3.287, P = 0.0028) but not when the refractive changes were incorporated (t = 1.058, P = 0.3127). All subjects rated the performance of the lenses very highly: comfort, 86%; distance acuity, 83%; near acuity, 73%; and stability of vision, 74%. Twenty-four subjects (86%) chose the multifocal contact lens as their preference. CONCLUSION: We demonstrated that a multifocal design is able to provide acceptable distance and near correction for presbyopic patients. The aspheric geometry required can be optimized for a given patient by considering his/her degree of ametropia, as well as the corneal topography.

Aged↗
PubMed1998

Grading scales for contact lens complications.

Grading scales have been developed to assist practitioners in recording the level of severity of ocular complications of contact lens wear. Eight common complications are depicted in five levels of severity--from grade 0 (normal) to grade 4 (severe). The intersubject variance in grading was determined to be 1.0 scale units, which by coincidence concurs exactly with the key design strategy of the grading scales that each grading step of 1.0 corresponds to a clinically significant difference in severity.

Contact Lenses↗
PubMed1998

Non-compliance in optometric practice.

The purposes of this paper is to explore how some of the recent and future changes relating to the optometric profession could affect non-compliant behaviour among patients. Non-compliance has been widely documented and discussed in numerous health care fields and is understood to be the responsibility of both the practitioner and patient working in a health care partnership. At least one third of patients have been reported to be non-compliant with health care recommendations which can result in the poor outcome of a treatment, secondary medical problems, dissatisfaction, frustration and the wasting of health resources. In recent years contact lens complications have been linked with non-compliant behaviour with contact lens care and maintenance regimens which has led to several media scares over contact lens related hygiene risks and has heightened interest in the issue of non-compliance in the field of optometry. Shared care schemes have already been adopted in some areas of the United Kingdom and if therapeutic pharmaceutical agents are introduced to the list of drugs permitted for use by optometrists in the future the issue of non-compliance will become even more poignant. Every optometrist needs to be aware of the high probability of non-compliant behaviour among patients, the consequences of this non-compliance and the steps that can be taken to enhance compliance in different areas of eye-care.

Contact Lenses↗
PubMed1997

Corneal temperature changes during photorefractive keratectomy.

PURPOSE: Corneal temperature changes in photorefractive keratectomy (PRK) have been implicated in the aetiology of subepithelial haze. This study was undertaken to quantify the temperature change during this surgical procedure. METHODS: Non-contact, colour-coded ocular thermography was performed by using an infrared detection system during PRK on a group of 12 subjects. RESULTS: Mean (+/-SD) central ocular surface temperature (OST) after epithelial debridement was 29.15 +/- 0.39 degrees C. Mean peak OST during PRK was 37.77 +/- 0.67 degrees C, with most of the temperature increase occurring during the first 15 s. Factors such as ablation depth, optical correction, and procedure duration were not demonstrated to have a significant effect on corneal temperature during the procedure, suggesting a complex relation between-PRK parameters and the change in corneal temperature. CONCLUSIONS: Previous work suggested that corneal collagen denatures at approximately 39 degrees C, and it has been demonstrated that corneal temperature may be elevated to this level during routine PRK. Further research is indicated into the effects of preoperative cooling and pausing in treatment to reduce temperature changes.

Collagen↗
PubMed1997

A prospective study of the effect of education on non-compliant behaviour in contact lens wear.

The contact lens practitioner and patient present a specific case for the study of non-compliance in areas such as hygiene, solution use, appointment attendance and wearing times. Education is one of the factors thought to influence compliance among patients in general health care situations and contact lens practitioners are encouraged to educate patients in the care and maintenance of contact lenses. A prospective, randomized, controlled and double masked study was performed to assess the effect of a 'compliance enhancement strategy' on levels of compliance among contact lens wearers over twelve months. Eighty experienced contact lens patients were randomly allocated to two experimental groups. A standard level of contact lens instruction was applied to the first group and in addition the compliance enhancement strategy was applied to patients assigned to the second group. The strategy consisted of extra education for patients using a video, booklets, posters, a checklist and a health care contract. Patients were given free supplies of ReNu multipurpose solution and Medalist 38 soft contact lenses (Bausch and Lomb, Rochester, New York). Compliance levels were assessed at a twelve month aftercare appointment by demonstration and questionnaire. The results indicate that the compliance enhancement strategy had little significant effect on the compliance levels of the patients to who it was applied. The population of contact lens wearers were generally very compliant and the contact lenses and care regimen were clinically successful. The possibility that the assessment of non-compliance was not adequately sensitive to highlight small differences in non-compliant behaviour is discussed. The standard level of education applied to this sample of contact lens patient were adequate to ensure generally high levels of compliance with the simple care and maintenance regimen recommended.

Adolescent↗
PubMed1996

Distribution of oxygen across the surface of the human cornea during soft contact lens wear.

PURPOSE: To determine whether tear mixing occurs beneath soft contact lenses, we examined the effect of blinking on the oxygen distribution across the corneal surface beneath a nonuniform thickness lens. METHODS: A custom-designed twin polarographic oxygen sensor assembly was used to simultaneously measure the equivalent oxygen percentage (EOP) at central and peripheral corneal locations of 10 human subjects beneath a -6.00 D thin-design hydroxyethyl mathacrylate (HEMA) lens. A -0.25 D lens served as a control. Each lens was worn for 5 min under static (no blinking) and dynamic (12 and 60 blinks/min) conditions. RESULTS: A significantly greater EOP (p = 0.006) was observed at the central (vs. peripheral) cornea during static and dynamic lens wear; central and peripheral oxygenation were unaffected by blinking. CONCLUSIONS: Tear mixing is insignificant beneath thin-design HEMA lenses; therefore, oxygenation across the corneal surface beneath such lenses is best predicted from the lens thickness profile rather than average thickness.

Adolescent↗
PubMed1996

Scratch resistance of rigid contact lens materials.

Practitioners have long recognised the importance of determining the extent of scratching on the surface of rigid contact lenses when deciding on lens replacement. Despite this, little research has been undertaken to define this problem. The extent of scratching of rigid contact lens materials was evaluated and this property was related to material oxygen permeability and refractive index. One hundred and forty lenses made from 28 different rigid materials were evaluated in a masked and randomised manner. Scratches were created on the front surface of the lenses using an apparatus that was specifically designed and constructed for this experiment. The extent of scratching was quantitatively evaluated using a computer-based scanning and image analysis system. The oxygen permeability of all materials was measured using the polarographic method. An Atago N3000 hand-held refractometer was used to measure the refractive index of these materials. Three significant correlations were revealed: an inverse relationship (r = -0.813, P < 0.0001) between oxygen permeability and refractive index; a positive relationship (r = 0.511, P < 0.008) between oxygen permeability and the extent of scratching; and an inverse relationship (r = -0.539, P < 0.0058) between refractive index and the extent of scratching. The information generated in this study concerning scratch resistance of rigid contact-lens materials may assist the contact lens industry and contact lens practitioners in developing and prescribing rigid lenses with optimal performance characteristics.

Contact Lenses↗
PubMed1996

Regular replacement of extended wear rigid gas permeable contact lenses.

PURPOSE: While the benefits of planned replacement of soft contact lenses have been investigated, the question of whether there are any clinical benefits to planned replacement of rigid gas permeable (RGP) lenses does not appear to have been addressed experimentally. We aimed to determine the benefits of regular replacement of extended wear RGP contact lenses. METHODS: We conducted a prospective, single-center, controlled, double-masked study of 39 RGP lens wearers. The subjects were divided into two groups and wore extended wear Quantum 2 lenses (Dk = 120) for 12 months. Subjects in Group I replaced lenses every 3 months, whereas those in Group II were not scheduled to replace their lenses. The integrity of the lenses and the ocular responses to lens wear were monitored in both groups every three months. RESULTS: Compared to lenses worn by subjects in Group I, lenses worn by Group II subjects showed significantly more mucous coating, lens binding, and corneal staining over time (P < 0.05; ANCOVA). There was no difference in microcystic or tarsal conjunctiva response, lens comfort, refractive change, or visual acuity between the two groups. CONCLUSIONS: We advocate that to maintain optimal lens integrity and ocular health, RGP lenses used for extended wear should be replaced every 3 to 6 months.

Adult↗
PubMed1996

Life expectancy of rigid gas permeable and high water content contact lenses.

PURPOSE: The purpose of this study was to evaluate the life expectancy of various rigid gas permeable (RGP) lens materials used on a daily wear basis and to compare these results with the life expectancy of a matched group of soft lens wearers. METHODS: We retrospectively analyzed the records of 600 contact lens wearing patients (300 soft contact lens users and 300 RGP lens users fit between September 1987 and September 1994. None of the subjects wore lenses on a planned replacement system. For the purpose of the study, RGP lenses were divided into three groups: < or = 40 Dk were considered low-Dk; 41-89 Dk were considered mid-Dk; and > or = 90 Dk were considered high-Dk. All soft lenses were high water content lenses (> or = 60% water content). Lenses were included if they were replaced due to loss, breakage, deposition, or poor wettability but not if replaced because of changes in fit or prescription. RESULTS: The mean (+/- SD) life-spans of each lens type in months were 19.9 +/- 17 for low-Dk RGP lenses, 15.9 +/- 13.3 for mid-Dk RGP lenses, 9.0 +/- 8.2 for high-Dk RGP lenses, and 6.4 +/- 5.2 for high water content soft lenses. Statistical analysis using a one-way ANOVA on ranks indicated that these results were statistically significant (P < 0.0001). CONCLUSIONS: Patients should be informed that high-Dk lenses (RGP and soft) provide substantial clinical benefits and that they should except to replace high-Dk RGP lenses after approximately 6 months. This lends further credence to the use of high-Dk lenses on a planned replacement basis.

Adult↗
PubMed1995

Infrared thermography of the tear film in dry eye.

Infrared ocular thermograms were recorded for a group of 36 dry eye patients and for 27 age- and sex-matched controls. Mean ocular surface temperature was greater in the dry eye group (32.38 +/- 0.69 degrees C) compared with the control group (31.94 +/- 0.54 degrees C; p < 0.01). In addition, there was a greater variation of temperatures across the ocular surface in the dry eye group, illustrated by the difference in temperature between the limbus and the centre of the cornea (0.64 +/- 0.20 degrees C in dry eye patients compared with 0.41 +/- 0.20 degrees C in the control group; p < 0.001). This parameter was also shown to be greater in dry eye patients who displayed either a fast tear break-up time or a poor Schirmer's test result. Infrared thermography is a non-invasive and objective technique that may prove a useful research tool for study of the tear film, its deficiencies and its various treatment modalities.

Adult↗
PubMed1994

Non-compliance in general health care.

An increased interest in non-compliance has been demonstrated by the great number of papers recently published on the subject. A review of the relevant literature shows a pattern emerging of at least one third of clients being non-compliant. This can result in a hazard to health, a waste of health resources and much frustration for practitioners and clients in many areas of health care. There are multiple factors which appear to be related to non-compliance in a complex and interdependent way. These factors can be described under three main headings: the client, the treatment and disorder, and the clinic interactions. Compliance is summarized as the shared responsibility of practitioner and client in a health care partnership. The purpose of this paper is to review the extensive literature on compliance in general health care and to present a set of guidelines for the enhancement of compliance in the form of a general model.

Attitude to Health↗
PubMed1994

Non-compliance in contact lens wear.

Non-compliance is emerging as a critical issue in the contact lens field. This problem has been studied at depth in general health care situations and is seen as the responsibility of both practitioner and patient (client) working in a health care partnership. The contact lens practitioner and patient present a specific case for the study of non-compliance in areas such as hygiene, solution use, appointment attendance and wearing times. From 40 to 91% of contact lens patients have been reported as non-complaint in the use of recommended care and maintenance regimens and many of these are confused or ignorant about their behaviour. In order to arrive at a general set of conclusions from the studies published to date, it is important to understand the methodology of each study, it purpose, the definition of non-compliance used and the way the results were analysed and described. This review summarizes the research into non-compliance in the contact lens field to data. A set of general conclusions is drawn and a model for compliance in the context of contact lens practice is proposed.

Age Factors↗
PubMed1993

Potential applications of ocular thermography.

Thermography is an investigative technique which allows rapid color-coded display of the temperature across a wide surface by means of infrared detection. We describe an ocular thermographic study of a normal population and present case studies describing the application of this technique for patients with ocular disease. We found that 95% of the normal population have an interocular temperature difference (temperature of center of right cornea minus temperature of center of left cornea) of 0.60 degrees or less. There appears to be a greater difference in temperature between the limbus and the center of the cornea in patients with dry eyes. This technique has potential for evaluating tear film disorders and inflammatory conditions, for monitoring the progress of such conditions, and for evaluating the efficacy of various treatments.

Acanthamoeba Keratitis↗