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Biomedical subjects

T W Hahn

Publications and source records attributed to T W Hahn.

33 records · Page 2Linked to original sources
PubMed1994

Excimer laser photorefractive keratectomy for myopia: two-year follow-up.

We evaluated the results of photorefractive keratectomy (PRK) with an excimer laser on 45 consecutive myopic eyes (23 patients) that were followed two years or more. The myopic range was from -2.00 diopters (D) to -6.00 D with astigmatism less than 1.50 D. Uncorrected visual acuity better than 20/25 was achieved in 88.9% of all cases two years postoperatively. Best corrected visual acuity was equal to or better than preoperatively in 95.6% of eyes. The difference between the attempted and achieved correction was within +/- 1.00 D in 91.1% two years postoperatively. Keratometric readings and central corneal thickness showed a gradual restoration until six months postoperatively and then stabilized. The cornea was clear in 66.7% of the eyes. The most common subjective complaint was decreased night vision two years after PRK. From our experience, excimer laser PRK is a predictable and effective surgical method to correct myopia up to -6.00 D in a single-step procedure.

Adult↗
PubMed1993

Excimer laser ablation of conjunctival epithelial melanosis.

Two patients with conjunctival epithelial melanosis received a 193 nm argon fluoride excimer laser treatment. In both patients the melanosis was easily removed with a smoothing technique using the excimer laser. The ablated area showed normal appearing conjunctiva. The lesion did not recur during the eight-month follow-up. Therapeutically, the excimer laser can be used to treat benign conjunctival lesions as well as superficial corneal diseases.

Adult↗
PubMed1993

Two-step annular tectonic lamellar keratoplasty in severe Terrien's marginal degeneration.

We present a case of severe Terrien's marginal degeneration treated with two-step annular lamellar keratoplasty. Both eyes of the patient had peripheral corneal thinning with ectasia around the entire corneal circumference. First, an annular-shaped ectatic lesion was defined and removed, and donor tissue of the same size and shape was sutured on the recipient bed with 10-0 nylon. Four months later, the same operation was performed in the fellow eye. This procedure allows corneal astigmatism to be controlled either by suture removal or resuturing, thereby substantially improving visual acuity. No complications occurred during 1 1/2 years of follow up.

Astigmatism↗
PubMed1992

Secondary intraocular lens implantation in aphakia.

We retrospectively studied secondary intraocular lens (IOL) implantation in 165 aphakic patients (162 eyes) from May 1983 to August 1989. Seventy-five eyes (46.3%) had secondary IOL implantation; these included seven cases of trans-sulcus scleral fixation of the posterior chamber lens. The remaining 87 eyes could not have secondary IOL implantation because of the ocular conditions. The most common reason for secondary implantation was to relieve the discomfort caused by spectacles or contact lenses (56.2%). An anterior chamber lens was used in 43 eyes (57.3%) and a posterior chamber lens in 32 eyes (42.7%). Final postoperative visual acuity of 20/40 or better was achieved in 92.0% of the eyes with posterior chamber lenses, in 71.4% of the eyes with anterior chamber lenses, and in 57.1% of the eyes with scleral-fixated posterior chamber lenses. Endothelial cell loss was greater in the eyes with anterior chamber lenses than in the eyes with posterior chamber lenses. Of the cases that could be followed, 83.3% showed endothelial cell loss of less than 30% at six months postoperatively. Postoperative complications such as cystoid macular edema, persistent fibrinous membrane formation, and neovascular glaucoma occurred in only ten (13.3%) of the 75 eyes that had secondary implantation. These complications occurred more frequently in eyes that had anterior chamber lenses with anterior vitrectomy. There were no noticeable complications in the eyes that had trans-sulcus scleral fixation of posterior chamber lenses. Updrawn pupil, prolapsed vitreous, and peripheral anterior synechia were common conditions preventing secondary IOL implantation.

Adult↗
PubMedDate not supplied

Acridine orange staining for rapid diagnosis of Acanthamoeba keratitis.

Acanthamoeba keratitis is uncommon, but one of the most severe infectious diseases of the cornea. Delayed diagnosis or misdiagnosis as bacterial or herpes simplex keratitis leads to extensive corneal inflammation and profound visual loss. Therefore, accurate and rapid diagnosis of Acanthamoeba keratitis is essential for successful treatment and good prognosis. We evaluated the usefulness of acridine orange staining from corneal scrapings and contact lens solutions for the rapid diagnosis of four consecutive cases of Acanthamoeba keratitis. Gram stain and culture on nonnutrient agar plates with Escherichia coli overlay were also made. Corneal scrapings stained with acridine orange revealed yellow-to-orange polygonal, cystic structures consistent with the appearance of Acanthamoeba among inflammatory cells and the corneal epithelial cells. The contact lens case solutions of two patients also showed numerous cysts with double wall. Some organisms from the third patient were identified as Acanthamoeba castellani and others as Acanthamoeba lugdunensis. Based on the acridine orange staining results in four cases of Acanthamoeba keratitis, this stain is recommended as a simple and reliable method for the rapid diagnosis of this disease.

Acanthamoeba↗
PubMedDate not supplied

Effect of bradykinin on cultured bovine corneal endothelial cells.

PURPOSE: To clarify the effect of bradykinin on cytosolic free calcium mobilization and cell proliferation in cultured bovine corneal endothelial cells (BCEC). METHODS: The cytosolic free calcium concentration (Ca2+]i) was measured with the InCa(TM) Imaging System after the treatment of bradykinin (10(-11) to 10(-7) M) alone or with the pretreatments of EGTA, bradykinin receptor (Bk1 and Bk2) antagonists and an inhibition of phospholipase C (U-73122). Also, the effect of bradykinin on cell proliferation in BCEC was evaluated using cell counts. RESULTS: In BCEC, [Ca2+]i in the resting state was 87 +/- 9 nM. Bradykinin induced an increment of [Ca2+]i in a concentration-dependent manner and its 50% effective concentration was approximately 5 x 10(-11) M. A [Ca2+]i increment at 10(-8) M bradykinin was inhibited with the pretreatment of EGTA, an extracellular calcium chelator. U-73122 (5 x 10(-6) M) attenuated the bradykinin-induced [Ca2+]i increment. The pretreatment of HOE-140 (Bk2 antagonist) almost attenuated the bradykinin (10(-8) M)-induced [Ca2+]i increase, but des-Arg9-[Leu(8)]-bradykinin (Bk1 antagonist) did not suppress it. To investigate the physiological effect of bradykinin, the effect of bradykinin on cell proliferation was studied. 10(-8) M of bradykinin produced a significant increase in cell numbers. This mitogenic effect of bradykinin was inhibited by the Bk2 antagonist. CONCLUSIONS: Bradykinin-induced stimulation of the signal transduction pathway in BCEC is coupled with the Bk2 type receptor. Furthermore, bradykinin produces the mitogenic effect in BCEC.

Animals↗
PubMedDate not supplied

Photorefractive keratectomy for undercorrected myopia after radial keratotomy: two-year follow up.

We evaluated the clinical results of excimer laser photorefractive keratectomy (PRK) on 18 myopic eyes of 13 patients with residual myopia after radial keratotomy. Follow up was 24 months or more and the time interval between radial keratotomy and PRK ranged from 12 to 94 months. Patients were divided into two groups for analysis based on their preoperative myopia: group 1 (-6.00 diopters (D) or less), group 2 (more than -6.00 D). Uncorrected visual acuity at 2 years follow up was 20/40 or better in 86% (group 1) and 50% (group 2). Mean manifest refractive change was from -3.55 D to -0.91 D in group 1 and from -7.44 D to -2.50 D in group 2. Predictability within 1.00 D between attempted and achieved correction was 71.4% (group 1) and 80% (group 2). Most complications were transient except decreased spectacle corrected visual acuity in one eye--a complication also reported by others. Glare (61%) and decreased vision at night (50%) were the most troublesome subjective symptoms. These results show that previous radial keratotomy may not influence the myopic correction of PRK. Planned two-stage myopic correction (PRK after radial keratotomy) in high myopia can be considered a useful technique.

Adult↗
PubMedDate not supplied

Sequence of precursor polyprotein gene (segment A) of infectious bursal disease viruses isolated in Korea.

The coding regions of segment A of two recent Korean very virulent (vv) infectious bursal disease virus (IBDV) isolates (KK1 and KSH) and one atypical IBDV isolate (K310) were amplified by reverse transcriptase-polymerase chain reaction, sequenced, and compared with published sequences for IBDV. The overall amino acid sequence similarity of the KK1 and KSH strains compared with foreign vvIBDV strains was between 97.43% and 98.02%. The KK1 and KSH strains, like vvIBDV strains, share unique amino acid residues at positions 222(A), 256(I), 294(I), and 299(S). The sequence of K310 strain was markedly different from other IBDV strains. The K310 strain had 12, 2, and 1 unique amino acid substitutions in the VP2 hypervariable region, VP4, and VP3 gene, respectively, and 3 of 12 substitutions in a VP2 hypervariable region were found in two hydrophilic regions known to be involved in antigenic determination. Also, the K310 strain had 222(S) and 254(S), which were found in variant IBDV strains. The SWSASGS heptapeptide is conserved in all Korean IBDV isolates. By phylogenetic analysis, KK1 and KSH were categorized in one group with foreign vvIBDV isolates, but K310 isolate was categorized in a separate group that was differentiated from the other IBDV strains compared. The K310 strain seemed to be evolved from a separate lineage of IBDV strain.

Amino Acid Substitution↗
PubMedDate not supplied

Some problems after photorefractive keratectomy.

We analyzed the data from 1821 patients (2920 eyes) who received photorefractive keratectomy (PRK) to investigate the postoperative complications which cause a significant decrease in visual acuity. A corneal haze of grade 2 or more developed in 9 patients (11 eyes, 0.38%) and corticosteroid-induced ocular hypertension occurred in 3 patients (4 eyes, 0.14%). Three patients (4 eyes) who had corneal haze of grade 2 or more underwent repeated photorefractive keratectomy and one patient (2 eyes) with steroid-induced ocular hypertension underwent trabeculectomies. A decrease of best spectacle corrected visual acuity of two lines or more was detected in 7 patients (8 eyes, 0.27%), caused by irregular astigmatism, steroid-induced cataract, incidental choroidal neovascular membrane, and an unknown origin. Good predictability and stabilization after photorefractive keratectomy was maintained at the 2 year follow-up. However, some subjective symptoms were reported by many patients and some complications occurred in a minority of eyes despite the excellent visual outcome in a large majority.

Cornea↗
PubMedDate not supplied

Photorefractive keratectomy in 202 myopic eyes: one year results.

We performed one-step procedures of photorefractive keratectomy (PRK) with the use of the excimer laser (193 nm) on 1519 myopic eyes during 1 year. From this group, we prospectively evaluated visual and refractive results of 202 (13%) consecutive myopic eyes that were followed for more than 1 year. Myopic eyes were divided into two groups according to the amount of myopia: group I, 135 eyes, 87 patients, less than -7.00 D, and group II, 67 eyes, 48 patients (-7.25 D to -13.50 D). The excimer laser system used was the ExciMed 200UV (Summit Technology, Inc, Waltham, Mass), the one-step computer program was fixed at a maximum ablation up to -6.00 D correction. Uncorrected visual acuity of 20/25 or better was achieved in 89.6% of eyes in group I and 47.8% in group II at 1 year. Best spectacle corrected visual acuity was equal to, or better than, the preoperative level in 93.8% of eyes. The difference between attempted and achieved refractive correction was within +/- 1.00 D in 91.4% in group I, and 51.7% in group II. The mean reduction of manifest (spherical equivalent) refraction in group II was 6.84 D at 1 year. Keratometric readings and central corneal thickness showed gradual changes until 6 months after surgery. Corneal haze disappeared in most of eyes at 1 year. The most common subjective complaint was glare and/or decreased vision at night or under dim light.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMedDate not supplied

Phototherapeutic keratectomy in nine eyes with superficial corneal diseases.

We performed phototherapeutic keratectomy (PTK) in seven patients (nine eyes) with superficial corneal disease such as band keratopathy (one patient), Reis-Bückler's dystrophy (one patient, two eyes), granular dystrophy (two patients, three eyes), recurrent granular dystrophy (one patient), postinfection scar (one patient), and corneal scarring after pterygium removal (one patient). All patients received PTK after topical anesthesia with Pontocaine 0.5% and underwent epithelial removal with a surgical blade. We used methylcellulose 1.0% as a surface modulator before laser ablation. Focal ablation of the central cornea with an ablation zone of 5 mm was performed routinely in most eyes and a smoothing technique was applied only in two eyes. All patients were followed for more than 9 months. Uncorrected and corrected visual acuity were significantly improved in six patients (8 eyes) and a mild hyperopic shift occurred in all eyes that received PTK centrally. Mild to moderate corneal haze appeared in these corneas during the first few months after surgery. Some patients avoided the need for keratoplasty. No significant complications occurred after PTK except recurrence of granular deposits in one case of granular dystrophy. We think that PTK with the 193-nanometer excimer laser is indicated in the treatment of some superficial corneal disorders.

Adult↗
PubMedDate not supplied

Excimer laser photorefractive keratectomy to correct residual myopia after radial keratotomy.

We performed excimer laser photorefractive keratectomy (PRK) on 10 undercorrected myopic eyes of nine patients with residual myopia, (N = 2, > -6.00 D, N = 8, -2.00 -5.75 D) after radial keratotomy. Patients' mean age was 32.1 years. The time interval between radial keratotomy and PRK ranged from 12 to 90 months (mean 35). All patients after PRK were followed 9 months or more. Nine months following PRK, uncorrected visual acuity ranged from 20/25 to 20/50 in all cases. Mean manifest refractive changed from -5.06 D preoperatively to -0.66 D after surgery, and the mean keratometric power changed from 41.40 +/- 1.56 D to 38.48 +/- 1.77 D. Persistent corneal haze (grade 1) was noted only in one eye at 9 months and no other significant complications occurred. Therefore, excimer laser PRK appears to be a good method to correct residual myopia after radial keratotomy.

Adult↗
PubMedDate not supplied

Clinical experience of two-step photorefractive keratectomy in 19 eyes with high myopia.

The maximum myopic correction with one-step ablation in excimer laser photorefractive keratectomy (PRK) using the ExciMed UV200 LA 193-nanometer excimer laser (Summit Technology, Inc, Waltham, Mass,) is only up to 6.00 D because of a fixed computer program. We performed a simultaneous two-step PRK procedure for nearly full correction on 19 eyes of 19 patients with myopia ranging from -8.00 to -13.50 D. We clinically evaluated the results of this modified technique at 6 months, or more, after surgery. In the two-step PRK procedure, we attempted in the first-step of a maximum correction of -6.00 D (including up to -7.50 D) with 4.5-millimeter ablation zone. The second step was performed immediately thereafter to correct the remaining myopia with a 5.0-millimeter diameter ablation. Mean preoperative manifest refraction was -9.77, D and mean postoperative manifest refraction was -1.09 D at 6 months after two-step PRK. Uncorrected visual acuity of 20/40 or better was achieved in 74% of 19 eyes (two were amblyopic eyes). Corneal subepithelial haze was trace or +1 in all cases at 3 months, but faded out after 3 months. Transient intraocular pressure elevation occurred in one case. No other significant complications developed. Long-term follow up will be required to evaluate the results of two-step PRK.

Adult↗
PubMedDate not supplied

Rotational autokeratoplasty in advanced lipid keratopathy.

1. Autokeratoplasty (AKP) has many advantages, such as having no immune reaction, providing easy postoperative care in younger patients, having susceptibility to amblyopia without delay, and demonstrating no vascularization of the autograft. 2. AKP does have its disadvantages, including limitations of patient selection and a high rate of postoperative astigmatism, anterior synechia, and glaucoma. 3. The largest problem inhibiting the widespread use of AKP is the limitations of patient selection.

Adult↗