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Biomedical subjects

A S Jacks

Publications and source records attributed to A S Jacks.

9 recordsLinked to original sources
PubMed2003

Spontaneous retinal venous pulsation: aetiology and significance.

Spontaneous retinal venous pulsation is seen as a subtle variation in the calibre of the retinal vein(s) as they cross the optic disc. The physical principles behind the venous pulsations has been the point of much debate. Initial theories suggested that the pulsation occurred because of the rise in intraocular pressure in the eye with the pulse pressure. This article presents an argument that this is not the case. The pulsations are in fact caused by variation in the pressure gradient along the retinal vein as it traverses the lamina cribrosa. The pressure gradient varies because of the difference in the pulse pressure between the intraocular space and the cerebrospinal fluid. The importance of this is that as the intracranial pressure rises the intracranial pulse pressure rises to equal the intraocular pulse pressure and the spontaneous venous pulsations cease. Thus it is shown that cessation of the spontaneous venous pulsation is a sensitive marker of raised intracranial pressure. The article discusses the specificity of the absence of spontaneous venous pulsation and describes how the patient should be examined to best elicit this important sign.

Blood Pressure↗
PubMed1999

Using the second instrument peripheral corneal incision in phacoemulsification as a blow-off valve.

PURPOSE: To assess the rise in intraocular pressure following phacoemulsification and whether it can be modified by the architecture of the peripheral corneal incision for the second instrument. SETTING: Frimley Park Hospital, Frimley, United Kingdom. METHOD: Forty-two patients had intraocular pressures measured from both eyes preoperatively, then underwent routine scleral section phacoemulsification. They were randomly assigned to perpendicular (blow-off valve) and oblique (water-tight) peripheral corneal incision groups. Postoperative intraocular pressures were measured at 3, 6, 12 and 18 hours. Pressures from the unoperated eyes were used as controls. Aqueous release from the second instrument peripheral corneal incisions and frown scleral incision were assessed using the Seidel's test. RESULTS: There was a rise in intraocular pressure in both groups compared to the control eyes (mean 10.95+/-2.19 mmHg, P<0.00005) at 6 hours. The difference between the groups was significant at 12 hours (mean difference 3.35 mmHg, P<0.05); 63.6% of the perpendicular incisions and 15% of the oblique incisions were Seidel's positive. The frown incision did not leak. CONCLUSION: This study documents the natural history of the rise in intraocular pressure following phacoemulsification peaking at 6 hours. Pharmacological agents should be administered to cover this period. The perpendicular peripheral corneal incision had a tendency to act as a blow-off valve allowing release of aqueous when intraocular pressures were elevated in the first 18 hours following phacoemulsification. This phenomenon is likely to result in a reduction in rise of intraocular pressure compared to the oblique peripheral corneal incision group which tended to be water-tight.

Aged↗
PubMed1997

Paediatric cycloplegia: a new approach.

BACKGROUND: Cycloplegia is a traumatic experience for most children, as guttae cyclopentolate stings on instillation into the conjunctival sac. This may result in inadequate cycloplegia, difficulty in further examination and a child who is scared of both the doctor and the ophthalmology department. Guttae proxymetacaine hydrochloride 0.5% (Ophthaine, Proparacaine) is a topical local anaesthetic that does not sting on instillation. METHODS: Eighty-eight consecutive children in the paediatric clinic were assessed. The response of the patient to previous use of cyclopentolate alone was assessed by the parents of the child using a grading scheme. The use of proxymetacaine prior to instillation of cyclopentolate was then assessed using the same grading system. RESULTS: Seventy per cent of the children who received cyclopentolate alone were assessed to have cried and been unhappy. Ninety-one per cent of the children who received cyclopentolate after proxymetacaine were assessed to have shown no adverse reaction to the cycloplegia and remained happy. CONCLUSION: This study shows that use of proxymetacaine prior to cyclopentolate results in atraumatic cycloplegia in children. This can confer multiple benefits on the doctor-patient relationship.

Anesthetics, Local↗
PubMed1990

2',3'-cyclic nucleotide phosphohydrolase activity determined using an image analyzer detection system.

The activity of 2',3'-cyclic nucleotide phosphohydrolase (CNPase) was assayed using high-performance thin-layer chromatography (HPTLC) and an image analyzer detection system. The assay system was used to study a possible inhibitory effect by aminoguanidine on CNPase specific activity. One advantage of using a fixed-time HPTLC system over a real-time spectrophotometric system for an enzyme activity study was that apparent inhibition of the enzyme due to interference of the assay system (chromophore inhibition, etc.) was avoided. In addition, due to the increased accuracy of the image analyzer over conventional methods of TLC plate analysis, a rapid and more accurate measurement of HPTLC plates was possible which required only nanomole amounts of substrate. Also, a digital image of each plate analyzed was stored indefinitely in the computer's memory for future reference. The measurements of CNPase specific activity made using this system compared favorably to those found in recent literature.

2',3'-Cyclic Nucleotide 3'-Phosphodiesterase↗
PubMed1989

A biochemical study of optic nerve myelin isolated by a micromethod from different aged rats.

A micromethod was used to study myelin from individual rat optic nerves as a function of age. Protein and galactolipid content as well as 2',3'-cyclic nucleotide phosphohydrolase (CNPase) activity at ages 2, 4, 22, and 28 months were determined. Protein content increased significantly at 22 months and decreased at advanced age. Galactolipid content increased significantly at 28 months while CNPase activity decreased. The ratios of protein to galactolipid and CNPase to galactolipid changed with changing age. These data suggest that, unlike the central nervous system, specific biochemical parameters of the optic nerve change with age.

Aging↗