Biomedical subjects

Han-Bor Fam

Publications and source records attributed to Han-Bor Fam.

8 recordsLinked to original sources

PubMed2006

Corneal elevation indices in normal and keratoconic eyes.

PURPOSE: To determine an index that distinguishes keratoconus and keratoconus-suspect eyes from normal eyes with Orbscan (Bausch & Lomb) corneal elevation maps. SETTING: Department of Ophthalmology, Tan Tock Seng Hospital, Singapore, and iLaser Centre, Island Hospital, Penang, Malaysia. METHODS: In this initial phase of this multicenter nonrandomized retrospective study, 1 eye of 166 normal subjects, 15 keratoconus patients, and 11 keratoconus suspects was examined at 1 clinic. The anterior best-fit sphere (BFS), posterior BFS, anterior elevation, posterior elevation, and maximum and minimum keratometries were analyzed. Two indices with the highest sensitivity and specificity classifying these conditions were identified using receiver operating characteristic curves. These 2 indices were evaluated in a subsequent validation study using 1 eye of 221 normal subjects, 43 keratoconus patients, and 23 keratoconus suspects from another clinic. RESULTS: The anterior elevation and anterior elevation ratio (anterior elevation ratio = anterior elevation/anterior BFS) best classified the different groups. An anterior elevation ratio of 0.5122 mm or less had 99% sensitivity and 95.2% specificity while a ratio 16.5 mum or less had 80.1% sensitivity and 80.8% specificity in discriminating normal eyes from keratoconus and keratoconus suspects. The results were similar in the validation study. In addition, these anterior elevation and anterior elevation ratio cutoff values had high sensitivity and specificity in identifying keratoconus suspects from normal eyes in the validation study. CONCLUSION: Anterior corneal elevation parameters are clinically relevant measures for detecting keratoconus and suspected keratoconus eyes.

Adult↗

PubMed2006

Relationship between the corneal surface and the anterior segment of the cornea: An Asian perspective.

PURPOSE: To determine the values for the anterior best-fit sphere (BFS) and posterior BFS in an Asian population using the Orbscan II (Bausch & Lomb) slit-scanning Placido disk corneal topographer. SETTING: Hospital-based refractive surgery center. METHODS: This prospective nonrandomized study comprised of 1 eye of 724 subjects. The eyes were measured with the Orbscan II. Default settings were used to generate relative elevation maps. Anterior BFS, posterior BFS, mean keratometry (K(mean)), spherical equivalent (SE), horizontal white-to-white size (WTW), and anterior chamber depth (ACD) were analyzed. RESULTS: The mean spherical equivalent (SE) in the 724 eyes was -5.32 diopters (D) +/- 2.88 (SD). The anterior BFS and posterior BFS were normally distributed, with a mean of 43.05 +/- 1.37 D and 52.43 +/- 2.03 D, respectively. The regression equation of anterior BFS and posterior BFS was posterior BFS = 0.443 + 1.208 anterior BFS (r(2) = 0.667, P<.01). The ratio of posterior BFS to anterior BFS was 1.22 +/- 0.03. The anterior BFS was significantly correlated to posterior BFS (P<.01), K(mean) (P<.01), and horizontal WTW (P<.01) but not to SE (P = .28). The posterior BFS was significantly correlated to K(mean) (P<.01) and the horizontal WTW (P<.01) but not to SE (P = .70). CONCLUSION: There was a close relationship between the various corneal parameters, which is significant in refractive surgery and intraocular lens calculation and design.

Adolescent↗

PubMed2006

Efficacy of measuring visual performance of LASIK patients under photopic and mesopic conditions.

INTRODUCTION: The aim of the study was to compare the visual performance of LASIK eyes measured using high-contrast logMAR letter charts under bright (photopic) and dim (mesopic) conditions. MATERIALS AND METHODS: A total of 46 subjects (35 +/- 8 years of age) undergoing LASIK procedures were recruited for the study. The best spectacle-corrected visual acuity (BSCVA) of each subject was measured using the high-contrast ETDRS logMAR chart under photopic and mesopic conditions at 3 visits: preoperative (Pre), 1 month postoperative (Post1) and 3 months postoperative (Post3). The differences in logMAR scores for the right eyes only were analysed for the Pre-Post1 (n = 46), Pre-Post3 (n = 18) and Post1-Post3 (n = 16) comparisons. RESULTS: The logMAR scores of subjects were worse at the 1-month postoperative visit than preoperatively, and improvement in visual performance was seen at the 3-month postoperative visit. These changes in visual performance became more evident under mesopic conditions. The means and standard errors of the differences in logMAR scores for the Pre-Post3 (0.097 +/- 0.020) were slightly larger than those of the Pre-Post1 (-0.067 +/- 0.019) and Post1-Post3 (0.031 +/- 0.012) comparisons. Under mesopic conditions, the visual performance of the subjects was statistically significant for the 3 comparisons, but not under photopic conditions. CONCLUSION: High-contrast logMAR chart performed under mesopic conditions has the potential to replace visual acuity measured under photopic conditions in providing more reliable representation of postoperative visual outcomes of LASIK eyes. Eye doctors should consider performing this vision test routinely to gauge the success of LASIK surgery.

Adult↗

PubMed2005

Post-LASIK myopic shift after a trek in the North Pole.

Bilateral laser in situ keratomileusis was performed in a 37-year-old male ethnic Chinese adventurer. Eight weeks postoperatively, the patient made an unassisted trek to the geographic North Pole. After 2 weeks in this environment, a myopic shift of more than -1.50 diopters occurred in both eyes. The myopic shift resolved over 2 months when the patient returned to a tropical climate. Using Orbscan corneal topography, we propose that the myopic shift was attributed to biomechanical changes in the cornea induced by corneal dehydration in the Arctic environment.

Adult↗

PubMed2005

Corneal honeybee sting.

BACKGROUND: We report the complications and management of a retained bee sting injury to the cornea. The case highlights the acute and chronic management of an uncommon injury and its pathogenesis. METHODS: A 67-year-old man was attacked by a swarm of bees and was referred for severe chemosis on the right eye. A retained corneal bee stinger (ovipositor) was seen but removal was only partially successful. He subsequently developed a large corneal epithelial defect, anterior uveitis, intractable glaucoma, traumatic cataract, toxic optic neuropathy, and corneal scarring. We reviewed the literature on corneal bee sting injuries and their complications. RESULTS: Inflammation was controlled with topical steroids and the patient underwent a combined phacoemulsification and trabeculectomy with mitomycin-C for uncontrolled glaucoma. However, optic neuropathy did not resolve. INTERPRETATION: Corneal bee sting injuries are uncommon but can result in severe sight-threatening complications such as toxic optic neuropathy. Early recognition of the possible complications and appropriate treatment may help to prevent permanent loss of vision. Removal of a retained corneal bee stinger remains controversial.

Aged↗

PubMed2005

Orbscan global pachymetry: analysis of repeated measures.

PURPOSE: The Orbscan II is a hybrid slit-scanning and Placido disc corneal topographer capable mapping global pachymetry over a 10-mm corneal diameter. In this study, the repeatability of the Orbscan global pachymetry was determined. METHODS: Five consecutive Orbscan examinations were performed on one eye of 20 healthy volunteers by one examiner in one session. Mean, standard deviation, range of readings, and coefficient of variance were calculated for the central, thinnest point and global pachymetry. RESULTS: Orbscan repeatability for the central pachymetry was 3.62 microm (95% confidence interval [CI], 0.57-6.66) with a coefficient of variance of 0.67% (95% CI, 0.09-1.25) and intraclass correlation coefficient (ICC) of 0.978 (95% CI, 0.959-0.990). Thinnest point pachymetry had a repeatability of 4.25 microm (95% CI, 1.19-7.31) with a coefficient of variance of 0.80% (95% CI, 0.19-1.42) and ICC of 0.973 (95% CI, 0.950-0.988). Global pachymetry had a coefficient of variance <1.5% in the central 4 mm and <<2.5% across the entire cornea. Global pachymetry showed an area of greatest repeatability (<< +/- 5 microm) within a central 3.0-mm horizontal and 4.0-mm vertical diameter. DISCUSSION: Orbscan is capable of giving repeatable pachymetry readings that are comparable to the ultrasound pachymeter within the central and thinnest point of the cornea. There is a gradual loss of repeatability toward the peripheral cornea possibly as a result of a lack of overlapping data points.

Confidence Intervals↗

PubMed2004

Evaluation of biofilm formation on nylon sutures removed from clinically noninfected eyes after cataract surgery.

PURPOSE: To determine the presence of bacterial biofilm on nylon sutures removed from clinically noninfected eyes after cataract surgery. SETTING: The Eye Institute, Tan Tock Seng Hospital, Singapore, Singapore. METHODS: Sutures were removed from 10 eyes after cataract surgery at different time periods. Immediately after removal, the sutures were fixed and dehydrated. All sutures were viewed by scanning electron microscopy, and 6 were also viewed by transmission electron microscopy (TEM). RESULTS: There was no evidence of bacterial biofilm formation on the nylon sutures. Significant cellular debris was seen, mainly at the knots. Clusters of coccoid-shaped structures were visible; however, examination by TEM showed they were not bacteria. CONCLUSION: There was no evidence of biofilm formation on sutures removed after cataract surgery from clinically noninfected eyes.

Aged↗

PubMedDate not supplied

Effect of higher-order wavefront aberrations on binocular summation.

PURPOSE: To determine the effect of individual Zernike wavefront aberrations on binocular summation and binocular visual acuity. METHODS: A 0.25-microm wavefront aberration of second, third and fourth order Zernike modes were introduced into a set of log minimum angle of resolution unit (logMAR) visual acuity charts convolved by CTView. Subjects were dilated and fitted with an artificial pupil of 3 mm. For each set of charts, right eye, left eye, and binocular acuity was measured. The gain in binocular visual acuity over monocular visual acuity was defined as binocular summation. The visual acuity lost binocularly reading aberrated charts was normalized for each subject and defined as the aberration induced loss in acuity. RESULTS: Binocular summation was 10.0% (95% limits of agreement 8.8 to 11.1%) in the unaberrated state and ranged from 17.3 to 3.4% in the Zernike modes studied. Binocular summation was greatest in defocus followed by coma and astigmatism. The aberration induced loss in monocular and binocular acuity was higher for Zernike modes with low angular frequency compared to those with high angular frequency. Linear regression showed a significant relationship between aberration-induced loss of visual acuity and binocular summation. CONCLUSIONS: A fixed amount of root mean square (RMS) aberration has a varied effect on binocular vision depending on the angular frequency and radial order of Zernike mode. Binocular vision has a positive effect in reducing the visual impact of aberrations as Zernike modes that suffer from the most loss of visual acuity also experience the greatest amounts of binocular summation.

Adult↗