Biomedical subjects

Andrew KC Lam

Publications and source records attributed to Andrew KC Lam.

3 recordsLinked to original sources

PubMed2001

Daytime variation of pulsatile ocular blood flow (POBF) in normal Chinese.

BACKGROUND: Pulsatile ocular blood flow (POBF) measurement is a new parameter to aid the understanding of the aetiology of low-tension glaucoma. There has been one study reporting the diurnal variation of POBF. However, that study involved eight subjects only. This study investigated the daytime variation of POBF with a greater sample size. METHODS: Twenty-four young Chinese subjects (12 males and 12 females) were recruited. The mean age of our subjects was 23.6 years and only the right eye was analysed. All the subjects were screened for glaucoma and the POBF was measured at three-hourly intervals from 9:00 am to 9:00 pm with an OBF tonometer (OBF Labs, UK, Ltd). The Goldmann intraocular pressure (IOP) and 'erect arm' systemic blood pressure (BP) were also measured. RESULTS: The IOP was found to be higher in the daytime, reaching the highest at noon (mean of 14.29 mmHg) and gradually reduced to the lowest at 9:00 pm (mean of 12.99 mmHg). The change was marginally significant (repeated measures ANOVA, P = 0.05). The POBF demonstrated a trend to increase from 9:00 am, mean of 605.5 &mgr;l/min, to 9:00 pm, 720.1 &mgr;l/min (repeated measures ANOVA, P < 0.01). Student-Newman-Keuls post hoc test indicated that the difference was mainly due to the comparisons between the 9:00 am and 9:00 pm results and the 9:00 am and 6:00 pm results. The pulse amplitude did not vary significantly. The mean blood pressure also demonstrated a significant variation (repeated measures ANOVA, P < 0.01). In the analysis of covariance, no significant effects of mean blood pressure on POBF and pulse amplitude were revealed. CONCLUSIONS: The variation in POBF was due to factors other than systemic blood pressure. Practitioners should consider POBF variation in repeated measurements, for example when monitoring the medical treatment for glaucoma. Further study on POBF variation is required over a complete circadian cycle.

Journal Article↗

PubMedDate not supplied

Fourth nerve palsy with monovision.

The fourth cranial nerve is the most vulnerable cranial nerve. Its damage gives rise to a vertical ocular deviation and usually the patient comes with a right head-tilt. The Parks-Bielschowsky three-step test is a simple and useful test for identifying the paretic extraocular muscle, giving rise to such a vertical ocular deviation. A case of long-standing fourth nerve palsy in a 45-year-old woman is reported. Monovision spectacles were prescribed to give the patient satisfactory distant and near vision.

Journal Article↗

PubMedDate not supplied

The effect of myelination on perimetry and retinal nerve fibre analysis.

BACKGROUND: Myelinated retinal nerve fibres around the optic nerve head can lead to an enlargement of blind spot with kinetic perimetry. Presumably extensive myelination will also decrease the visual sensitivity with static perimetry. This study reports the effect of myelination on static perimetry in several patients. Scanning laser polarimetry can measure the retinal nerve fibre layer thickness around the optic nerve head in vivo. This technique was applied at the myelination to investigate its effect on retinal nerve fibre layer thickness determination. METHODS: Four eyes of three subjects with myelination around the optic nerve head were tested with Bjerrum screen at one metre to measure the blind spot size. They were followed by Humphrey Visual Field Analyser with a custom pattern to quantify the threshold level at the blind spot region. A GDx Nerve Fiber Analyser was used to measure the retinal nerve fibre layer thickness around the optic nerve head. RESULTS: All the patients demonstrated an enlargement of the blind spot, with different extents, corresponding to the area of myelination. Threshold testing revealed a depression in the myelinated regions. The results for retinal nerve fibre layer were not conclusive with two eyes demonstrating thickening and two eyes showing no effect from myelination. CONCLUSIONS: A static field test with a modern visual field analyser may help to quantify the effect of myelination on visual sensitivity. More studies on the effect of myelination on retinal nerve fibre layer thickness measurement are suggested with more subjects involved.

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