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Biomedical subjects

J A Davison

Publications and source records attributed to J A Davison.

At least 19 recordsLinked to original sources
PubMed2001

Cloning, expression and chromosomal location of NKX6B TO 10Q26, a region frequently deleted in brain tumors.

Nkx6-2 (former Gtx) is a murine-homeobox-containing gene localized distally on Chromosome (Chr) 7. Analysis of the expression pattern, together with DNA binding assays, suggests that this gene product might be important for differentiated oligodendrocyte function and in the regulation of myelin gene expression. We now report on the cloning and characterization of the human homolog (NKX6B). DNA sequence analysis of an 11-kb genomic fragment revealed that the complete human gene spans 1.2 kb and is composed of three exons. NKX6B is predicted to encode a polypeptide of 277 amino acids with 97% identity to mouse Nkx6-2. Northern blot experiments showed that NKX6B expression is tightly controlled in a tissue-specific fashion with the highest site of expression being the brain. Finally, using STS content mapping and RH analyis, we demonstrated that NKX6B maps to the 10q26, a region where frequent loss of heterozygosity has been observed in various malignant brain tumors. These results may implicate NKX6B as a candidate tumor suppressor gene for brain tumors, particularly for oligodendrogliomas.

Amino Acid Sequence↗
PubMed2000

Positive and negative dysphotopsia in patients with acrylic intraocular lenses.

PURPOSE: To report the incidence, management, and prevention of patient reports of glare and streaks around a point source of light or a dark shadow in the temporal field of vision after acrylic intraocular lens (IOL) implantation. SETTING: A private practice. METHODS: Cases in which patients complained vigorously of dysphotopsia were catalogued prospectively during the implantation experience in 6668 consecutive eyes having surgery between January 1995 and June 1999. The techniques of topical-intracameral anesthesia, temporal clear corneal incisions, and phacoemulsification were used in all cases. Alternate IOL styles were selected for use from July 1999 to April 2000. RESULTS: Fourteen cases (0.2%) were identified. The complaints resolved in 1, were diminished in 1, and were tolerated without change in 7. Five eyes of 4 patients required IOL exchange with capsular bag placement of a poly(methyl methacrylate) (PMMA) or silicone lens for resolution of symptoms. Selecting alternate IOL styles reduced the incidence of dysphotopsia. CONCLUSIONS: Glare and streaks from a point source of light represent positive photic expressions of dysphotopsia, and temporal dark shadows represent similar negative photic expressions. Both appear to be associated with shiny square-edge optics made of high-refractive-index acrylic polymer. Intraocular lenses of PMMA and silicone with rounded edges, along with square-edge acrylic IOLs with nonreflective edges, appear less likely to cause clinically significant pseudophakic dysphotopsia.

Acrylates↗
PubMed1999

Performance comparison of the Alcon Legacy 20000 1.1 mm TurboSonics and 0.9 mm MicroTip.

PURPOSE: To compare the efficiencies of the operative procedures, the changes in postoperative corneal endothelial cell density (ECD), and incision performance after cataract surgery using 2 different phacoemulsification tips. SETTING: Wolfe Clinic, Marshalltown, Iowa, USA. METHODS: A randomized prospective study of 119 consecutive cases was conducted. All patients were adults having phacoemulsification using a modified in situ fracture technique. All cases were done by 1 surgeon using the Alcon Legacy 20000 phacoemulsification machine with normal vacuum cassettes and tubing. One of 2 45 degree phacoemulsification tips was used: the 1.1 mm TurboSonics (n = 65) or the 0.9 mm MicroTip (n = 54). Measurements at the time of surgery included metered phacoemulsification time and mean phacoemulsification power. Corneal keratometry and ECD by contact specular microscopy were determined preoperatively and 10 weeks postoperatively. RESULTS: The mean metered phacoemulsification time was statistically significantly different between the 2 groups: 1.1 mm TurboSonics = 1.25 minutes; 0.9 mm MicroTip = 1.66 minutes. The mean ultrasound power was also significantly different: 1.1 mm TurboSonics = 52.98%; 0.9 MicroTip = 49.07%. Loss of corneal ECD was not significantly different: 1.1 mm TurboSonic = 3.68%; 0.9 mm MicroTip = 5.79%. Mean diopters of induced incisional keratometric flattering was similar: 1.1 mm TurboSonics, 0.32 diopters (D) +/- 0.61 (SD); 0.9 mm MicroTip, 0.25 +/- 0.49 D. There were no cases of anterior radial capsule tear, posterior capsule tear, vitreous loss, iris aspiration, suture closure, or incision leak. CONCLUSIONS: Although a longer mean metered phacoemulsification time was required with the 0.9 mm MicroTip, corneal endothelial cell loss and incisional keratometric performance were not different from those of cases in which the larger 1.1 mm TurboSonics tip was used. Both tips can be used effectively and safely for phacoemulsification of the human cataract.

Cataract Extraction↗
PubMed1999

Performance comparison of the Alcon Legacy 20000 1.1 mm TurboSonics and 0.9 mm Aspiration Bypass System tips.

PURPOSE: To compare the efficiencies of the operative procedures and the reductions in postoperative corneal endothelial cell density (ECD) after cataract surgery using 2 different phacoemulsification tips and their associated cassettes and tubing. SETTING: Wolfe Clinic, Marshalltown, Iowa, USA. METHODS: A randomized prospective study of 100 consecutive cases was conducted. All patients were adults having phacoemulsification using a hybrid in situ fracture technique. All cases were performed by 1 surgeon using the Alcon Legacy 20000 phacoemulsification machine. One of 2 45 degree phacoemulsification tips and associated cassettes and tubing were used: the 1.1 mm TurboSonics with normal tubing (n = 47) or the 0.9 mm Aspiration Bypass System (ABS) tip with high-vacuum cassettes and tubing (n = 53). Measurements at the time of surgery included metered phacoemulsification time, percentage power used, total time spent in the phacoemulsification process, and milliliters of balanced salt solution (BSS) used. Corneal ECD was determined preoperatively and 10 weeks postoperatively. An independent statistician performed 2-sample t tests or Wilcoxon rank sum tests on the data. RESULTS: There were no cases of anterior radial capsule tear, posterior capsule tear, vitreous loss, iris aspiration, incision leak, or suture closure. There was no correlation between amount of corneal ECD loss and any operative variable measured. Similar measurements for the 1.1 mm TurboSonics and the 0.9 mm ABS included, respectively, ECD loss 7.34% and 8.22%; metered phacoemulsification time 1.29 and 1.22 minutes; total time of the phacoemulsification process 113 and 105 seconds. There were statistically significant differences between the 1.1 mm TurboSonics tip and 0.9 mm ABS tip performance in mean power percentage overall (52% versus 48%) and overall BSS volume used (85 versus 76 mL). CONCLUSIONS: The 0.9 mm ABS phacoemulsification tip used with the high-vacuum cassette and tubing provided the physical advantages of tip-size reduction while requiring similar ultrasonic power and BSS volumes as the 1.1 mm TurboSonics tip with standard cassette and tubing. Together, they provide a wider available dynamic range in which to integrate ultrasonic power, higher vacuum, and higher aspiration flow rates to improve the efficiency and ease of use than the standard 1.1 mm TurboSonics cataract operation.

Cataract Extraction↗
PubMed1998

Clinical comparison of the Alcon 20,000 Legacy and 10,000 Master phacoemulsification units.

PURPOSE: To determine whether the use of the Alcon 20,000 Legacy phacoemulsification unit requires less phacoemulsification time and causes fewer intraoperative complications than the Alcon 10,000 Master unit. SETTING: Private practices in Kansas City, Missouri, and Marshalltown, Iowa, USA. METHODS: This prospective study comprised 400 consecutive cases of phacoemulsification with intraocular lens (IOL) implantation performed using the Alcon 20,000 Legacy unit by a high-volume phacoemulsification surgeon (n = 200) and a moderate-volume surgeon (n = 200). Data included age, phacoemulsification time, and surgical complications. The control study was a retrospective review of the same data from the previous 200 cases done by each surgeon with the Alcon 10,000 Master unit. RESULTS: In the combined series of 400 cases done with the 10,000 Master unit, mean age was 72.7 years and mean phacoemulsification (i.e., ultrasound) time, 1.97 minutes. There were 2 cases (0.50%) of vitreous loss and 3 cases (0.75%) of posterior capsule tear without vitreous loss. The total complication rate for both surgeons was 1.25% with the 10,000 Master. In the combined series of 400 cases done with the 20,000 Legacy unit, mean age was 72.5 years and mean phacoemulsification time, 1.50 minutes. There were no cases of vitreous loss and 1 case (0.25%) of posterior capsule tear without vitreous loss. The total complication rate for both surgeons was 0.25% with the 20,000 Legacy. The difference in complication rates between the two machines was not significant. Phacoemulsification time with the 20,000 Legacy unit was significantly less than with the 10,000 Master unit for both surgeons (P < or = .001 and .05, respectively). CONCLUSION: The Alcon series 20,000 Legacy unit proved to be a safe, reliable, and highly effective instrument for modern cataract extraction and IOL implantation that required significantly less phacoemulsification time than the 10,000 Master unit.

Adolescent↗
PubMed1993

A technique for prevention of sudden pressure loss on emptying of irrigation bags during arthroscopic surgery using gravity-fed irrigation systems.

Gravity-fed irrigation systems in arthroscopic surgery are safe and cheap, but visualization can be impaired by fluctuations in in-flow pressure, which leads to bleeding and temporary disruption of surgery. We describe a gravity-fed irrigation system using differential hydrostatic pressures in sequentially arranged irrigation bags that can be independently raised and lowered. This technique maintains a relatively steady flow and intra-articular pressure, thereby improving the quality of irrigation without having to resort to the more expensive pressure infusion systems, and minimizing the need for surgery under tourniquet.

Arthroplasty↗
PubMed1993

Capsule contraction syndrome.

Capsule contraction syndrome is an exaggerated reduction in anterior capsulectomy and capsular bag diameter after extracapsular cataract surgery. While rarely seen with can-opener-style capsulectomies with anterior radial capsular tears, it is relatively frequent with capsulorhexis. It is particularly common in patients with pseudoexfoliation and in eyes with a history of moderately severe uveitis. Its effects, which include extreme reduction in the capsulectomy opening, malposition of the opening, reduction in equatorial capsular diameter, and displacement of the IOL, seem more exaggerated in small capsulorhexis openings and in the older patient. Neodymium: YAG laser radial anterior relaxing capsulotomies done within three weeks of cataract surgery reduce the sphincter effect of the contraction and lessen the chronic zonular-traction-related complications of the condition, which may include spontaneous IOL dislocation and retinal detachment.

Aged↗
PubMed1993

Keratometric comparison of 4.0 mm and 5.5 mm scleral tunnel cataract incisions.

Postoperative keratometric astigmatism was analyzed in 276 consecutive cases of phacoemulsification and posterior chamber lens implantation performed by one surgeon. The series was divided into two groups: one received 4.0 mm incisions and the other 5.5 mm incisions. Incision design was triplanar and required suture closure, i.e., all wounds were closed with two X-pattern 10-0 nylon sutures. Using the Cravy method, an insignificant difference in induced astigmatism was found between the groups at one day, two weeks, and one year after surgery. The average induced diopters of astigmatism for the 4.0 mm group was +0.80 +/- 0.94 at one day, +0.49 +/- 0.73 at two weeks, and -0.34 +/- 0.91 at one year; for the 5.5 mm group it was +0.69 +/- 1.07 at one day, +0.41 +/- 0.85 at two weeks, and -0.23 +/- 1.01 at one year. Two-week uncorrected visual acuity of 20/40 or better was similar for both groups. Seventy-six percent of the 4.0 mm group and 68% of the 5.5 mm group had acuities of 20/40 or better. A significant difference in the incidence of immediate postoperative hyphema was noted. The overall hyphema incidence was 9%, with a 14% and 4% incidence for 5.5 mm and 4.0 mm incisions, respectively.

Astigmatism↗
PubMed1993

Undesired light images associated with ovoid intraocular lenses.

Ovoid intraocular lenses (IOLs) accounted for approximately 35% of the lenses implanted in 1991. Despite their popularity among surgeons, patient observations and complaints suggest that ovoid lenses are associated with undesired optical images postoperatively. A pilot clinical study was carried out to test that hypothesis. A multicentered investigation of 289 cases with well-centered IOLs determined that 45% of 168 patients with ovoid lenses observed unwanted optical phenomena at some time after surgery, whereas 17% of 121 patients with round IOLs had similar complaints. Based upon the preliminary clinical study a laboratory investigation was designed to assess optical performance differences between ovoid and round IOLs. One testing system used scatterometry and a second, ray tracing analysis. Both methods determined that the truncated, thickened edge of ovoid lenses was associated with significant light scattering, possibly accounting for the extraneous light images observed by some patients. The results of the clinical and laboratory investigations suggest that undesired optical images produced by ovoid IOLs are due to lens shape rather than to the reduced dimension of the optic.

Cataract Extraction↗