Biomedical subjects

Leon N Davies

Publications and source records attributed to Leon N Davies.

7 recordsLinked to original sources

PubMed2007

Advances in anterior segment imaging.

PURPOSE OF REVIEW: Imaging of the crystalline lens and intraocular lens is becoming increasingly more important to optimize the refractive outcome of cataract surgery, to detect and manage complications and to ascertain advanced intraocular lens performance. This review examines recent advances in anterior segment imaging. RECENT FINDINGS: The main techniques used for imaging the anterior segment are slit-lamp biomicroscopy, ultrasound biomicroscopy, scheimpflug imaging, phakometry, optical coherence tomography and magnetic resonance imaging. They have principally been applied to the assessment of intraocular lens centration, tilt, position relative to the iris and movement with ciliary body contraction. SUMMARY: Despite the advances in anterior chamber imaging technology, there is still the need for a clinical, high-resolution, true anatomical, noninvasive technique to image behind the peripheral iris.

Anterior Eye Segment↗

PubMed2006

Clinical evaluation of rebound tonometer.

PURPOSE: To evaluate the reliability and repeatability of intraocular pressure (IOP) measurements using a new rebound tonometer. METHODS: Intraocular pressure was measured in 42 healthy human eyes of subjects aged 18-30 years (mean +/- standard deviation [SD] 21.5 +/- 3.2 years) using the ICare Rebound and Goldmann tonometers in two separate sessions. RESULTS: Intraocular pressure measurements were found to read slightly, but not significantly, higher with the ICare tonometer compared with the Goldmann instrument in both sessions (first session: mean bias +/- SD + 0.50 +/- 2.33 mmHg; second session: mean bias +/- SD + 0.52 +/- 1.92 mmHg). Limits of agreement between repeated readings were +/- 5.11 mmHg for measurements taken with the ICare tonometer, compared with +/- 3.15 mmHg for measurements taken with the Goldmann method. CONCLUSION: Measurement of IOP in normal, healthy subjects using the ICare rebound tonometer produced a small, statistically insignificant, positive bias when compared with the Goldmann tonometer. Intersessional repeatability of IOP taken with the ICare is poorer than that of IOP taken with the Goldmann tonometer, but is comparable with that of other non-Goldman-type tonometers currently available.

Adolescent↗

PubMed2005

The macular mapping test: a reliability study.

BACKGROUND: Age-related macular degeneration (ARMD) is the leading cause of visual disability in people over 60 years of age in the developed world. The success of treatment deteriorates with increased latency of diagnosis. The purpose of this study was to determine the reliability of the macular mapping test (MMT), and to investigate its potential as a screening tool. METHODS: The study population comprised of 31 healthy eyes of 31 participants. To assess reliability, four macular mapping test (MMT) measurements were taken in two sessions separated by one hour by two practitioners, with reversal of order in the second session. MMT readings were also taken from 17 age-related maculopathy (ARM), and 12 AMD affected eyes. RESULTS: For the normal cohort, average MMT scores ranged from 85.5 to 100.0 MMT points. Scores ranged from 79.0 to 99.0 for the ARM group and from 9.0 to 92.0 for the AMD group. MMT scores were reliable to within +/- 7.0 points. The difference between AMD affected eyes and controls (z = 3.761, p = < 0.001) was significant. The difference between ARM affected eyes and controls was not significant (z = -0.216, p = 0.829). CONCLUSION: The reliability data shows that a change of 14 points or more is required to indicate a clinically significant change. This value is required for use of the MMT as an outcome measure in clinical trials. Although there was no difference between MMT scores from ARM affected eyes and controls, the MMT has the advantage over the Amsler grid in that it uses a letter target, has a peripheral fixation aid, and it provides a numerical score. This score could be beneficial in office and home monitoring of AMD progression, as well as an outcome measure in clinical research.

Adult↗

PubMed2005

Ametropia and ocular biometry in a U.K. university student population.

PURPOSE: The prevalence of myopia is known to vary with age, ethnicity, level of education, and socioeconomic status, with a high prevalence reported in university students and in people from East Asian countries. This study determines the prevalence of ametropia in a mixed ethnicity U.K. university student population and compares associated ocular biometric measures. METHODS: Refractive error and related ocular component data were collected on 373 first-year U.K. undergraduate students (mean age = 19.55 years +/- 2.99, range = 17-30 years) at the start of the academic year at Aston University, Birmingham, and the University of Bradford, West Yorkshire. The ethnic variation of the students was as follows: white 38.9%, British Asian 58.2%, Chinese 2.1%, and black 0.8%. Noncycloplegic refractive error was measured with an infrared open-field autorefractor, the Shin-Nippon NVision-K 5001 (Shin Nippon, Ryusyo Industrial Co. Ltd, Osaka, Japan). Myopia was defined as a mean spherical equivalent (MSE) less than or equal to -0.50 D. Hyperopia was defined as an MSE greater than or equal to +0.50 D. Axial length, corneal curvature, and anterior chamber depth were measured using the Zeiss IOLMaster (Carl Zeiss, Jena, GmBH). RESULTS: The analysis was carried out only for white and British Asian groups. The overall distribution of refractive error exhibited leptokurtosis, and prevalence levels were similar for white and British Asian (the predominant ethnic group) students across each ametropic group: myopia (50% vs. 53.4%), hyperopia (18.8% vs. 17.3%), and emmetropia (31.2% vs. 29.3%). There were no significant differences in the distribution of ametropia and biometric components between white and British Asian samples. CONCLUSION: The absence of a significant difference in refractive error and ocular components between white and British Asian students exposed to the same educational system is of interest. However, it is clear that a further study incorporating formal epidemiologic methods of analysis is required to address adequately the recent proposal that juvenile myopia develops principally from "myopiagenic" environments and is relatively independent of ethnicity.

Adolescent↗

PubMed2005

Non-invasive phakometric measurement of corneal and crystalline lens alignment in human eyes.

We describe a non-invasive phakometric method for determining corneal axis rotation relative to the visual axis (beta) together with crystalline lens axis tilt (alpha) and decentration (d) relative to the corneal axis. This does not require corneal contact A-scan ultrasonography for the measurement of intraocular surface separations. Theoretical inherent errors of the method, evaluated by ray tracing through schematic eyes incorporating the full range of human ocular component variations, were found to be larger than the measurement errors (beta < 0.67 degrees , alpha < 0.72 degrees and d < 0.08 mm) observed in nine human eyes with known ocular component dimensions. Intersubject variations (mean +/- S.D.: beta = 6.2 +/- 3.4 degrees temporal, alpha = 0.2 +/- 1.8 degrees temporal and d = 0.1 +/- 0.1 mm temporal) and repeatability (1.96 x S.D. of difference between repeat readings: beta +/- 2.0 degrees , alpha +/- 1.8 degrees and d +/- 0.2 mm) were studied by measuring the left eyes of 45 subjects (aged 18-42 years, 29 females and 16 males, 15 Caucasians, 29 Indian Asians, one African, refractive error range -7.25 to +1.25 D mean spherical equivalent) on two occasions.

Adolescent↗

PubMed2004

Cling film as a barrier against CJD in Goldmann-type applanation tonometry.

PURPOSE: To determine the feasibility of taking intra-ocular pressure (IOP) readings with Goldmann-type applanation tonometer probe covered with cling film to avoid transmission of Creutzfeldt-Jakob disease (CJD). METHODS: Data were collected on two occasions from the right eyes of 30 healthy subjects using a Perkins applanation tonometer. On each occasion, a single tonometry measurement was made with and without cling film covering. RESULTS: Cling film covering brought about a statistically significant IOP bias (-0.8 mmHg on first occasion and -1.17 mmHg on second occasion). The 95% limits of agreement, between readings made with and without cling film covering, were +/-3.4 mmHg on first occasion; +/-2.5 mmHg on second occasion. A statistically significant reduction of inter-sessional repeatability was observed for readings taken with cling film (+/-5.2 mmHg) compared to those made without (+/-3.9 mmHg). CONCLUSIONS: Even if the above findings are found to be acceptable, given the known intra-subject variations of this type of tonometry (+/-4 mmHg), ethical and legal considerations relating to the barrier properties of cling film are likely to prevent its routine use by optometrists.

Adult↗

PubMed2004

Reliability, normative data, and the effect of age-related macular disease on the Eger Macular Stressometer photostress recovery time.

PURPOSE: To assess repeatability and reproducibility, to determine normative data, and to investigate the effect of age-related macular disease, compared with normals, on photostress recovery time measured using the Eger Macular Stressometer (EMS). METHOD: The study population comprised 49 healthy eyes of 49 participants. Four EMS measurements were taken in two sessions separated by 1 h by two practitioners, with reversal of order in the second session. EMS readings were also taken from 17 age-related maculopathy (ARM), and 12 age-related macular degeneration (AMD), affected eyes. RESULTS: EMS readings are repeatable to within +/-7 s. There is a statistically significant difference between controls and ARM affected eyes (t = 2.169, p = 0.045), and AMD affected eyes (t = 2.817, p = 0.016). The EMS is highly specific, and demonstrates sensitivity of 29% for ARM, and 50% for AMD. CONCLUSIONS: The EMS may be a useful screening test for ARM, however, direct illumination of the macula of greater intensity and longer duration may yield less variable results.

Adolescent↗