Expression of alpha- and beta-globin genes occurs within different nuclear domains in haemopoietic cells.

The alpha- and beta-globin gene clusters have been extensively studied. Regulation of these genes ensures that proteins derived from both loci are produced in balanced amounts, and that expression is tissue-restricted and specific to developmental stages. Here we compare the subnuclear location of the endogenous alpha- and beta-globin loci in primary human cells in which the genes are either actively expressed or silent. In erythroblasts, the alpha- and beta-globin genes are localized in areas of the nucleus that are discrete from alpha-satellite-rich constitutive heterochromatin. However, in cycling lymphocytes, which do not express globin genes, the distribution of alpha- and beta-globin genes was markedly different. beta-globin loci, in common with several inactive genes studied here (human c-fms and SOX-1) and previously (mouse lambda5, CD4, CD8alpha, RAGs, TdT and Sox-1), were associated with pericentric heterochromatin in a high proportion of cycling lymphocytes. In contrast, alpha-globin genes were not associated with centromeric heterochromatin in the nucleus of normal human lymphocytes, in lymphocytes from patients with alpha-thalassaemia lacking the regulatory HS-40 element or entire upstream region of the alpha-globin locus, or in mouse erythroblasts and lymphocytes derived from human alpha-globin transgenic mice. These data show that the normal regulated expression of alpha- and beta-globin gene clusters occurs in different nuclear environments in primary haemopoietic cells.

Photorefractive keratectomy using a scanning-slit laser, rotary epithelial brush, and chilled balanced salt solution.

PURPOSE: To evaluate photorefractive keratectomy (PRK) using a scanning-slit excimer laser combined with removal of the epithelium using a rotary epithelial brush and prebrush and postoperative cooling of the cornea with chilled balanced salt solution (BSS(R)). SETTING: Johannesburg Laser Center, Johannesburg, South Africa. METHODS: In a prospective study, 500 consecutive eyes with myopia ranging from 1.00 to 12.75 diopters (D) and astigmatism up to 6.50 D were treated with PRK using a Nidek EC-5000 scanning-slit excimer laser, removal of the epithelium with a rotary epithelial brush, and prebrush and postlaser cooling of the cornea with chilled BSS (4 degrees C to 6 degrees C). The mean follow-up was 9.32 months (range 1 week to 39 months). Bilateral simultaneous PRK was performed in 238 patients (95.2% of eyes). RESULTS: After 1 week, uncorrected visual acuity was 20/20, 20/25, 20/30, 20/40, 20/60, and 20/80 in 9.80%, 38.60%, 68.20%, 89.40%, 97.80%, and 97.20% of eyes. After 6 months, in 405 eyes, it was 20/15, 20/20, 20/25, 20/30, and 20/40 in 9.38%, 69.88%, 91.11%, 94.81%, and 98.52%. After 12 months, in 222 eyes, it was 20/15, 20/20, 20/25, 20/30, and 20/40 in 6.76%, 68.92%, 83.78%, 91.89%, and 97.30%. After 18 months, in 95 eyes, it was 20/15, 20/20, 20/25, 20/30, and 20/40 in 6.32%, 69.47%, 88.42%, 91.58%, and 96.84%. Six eyes (1.20%) required retreatment. CONCLUSIONS: Scanning-slit laser PRK after rotary epithelial scrubbing and prescrub and postlaser cooling allows accurate correction of myopia and astigmatism with minimal regression.

Iatrogenic keratectasia after laser in situ keratomileusis for less than -4.0 to -7.0 diopters of myopia.

PURPOSE: To study 13 eyes with less than -4.0 to -7.0 diopters of myopia that developed central or inferior keratectasia after laser in situ keratomileusis (LASIK). METHODS: The progress of the ectasia was determined by a series of pre- and post-LASIK topographies and the case histories. RESULTS: Progressive ectasia developed from 1 week to 27 months after LASIK. This necessitated the wearing of hard contact lenses or penetrating keratoplasty. One eye improved for some months after photorefractive keratectomy retreatment. Two eyes in 1 patient and 1 eye in a second patient had latent keratoconus before surgery. CONCLUSION: Laser in situ keratomileusis can cause permanent weakening and ectasia of the cornea even in eyes with low myopia.

Using a Nidek excimer laser with a rotary epithelial brush and corneal chilling: clinical results.

PURPOSE: To perform a prospective study using a rotary epithelial scrubber, a prescrub, and postoperative cooling of the cornea with chilled balanced salt solution (BSS) (4 degrees C to 6 degrees C) and a Nidek EC-5000 excimer laser. SETTING: The Johannesburg Excimer Laser Eye Centre, South Africa. METHODS: The first 90 consecutive eyes with myopia from -1.00 to -10.50 diopters (D) and astigmatism up to 3.00 D were treated. Follow-up was from 9 to 22 months (mean 13.85 months). Bilateral photorefractive keratectomy was performed in 40 patients. RESULTS: Bilateral vision with a bandage lens on the day after surgery was 20/30, 20/40, and 20/60 in 20%, 60%, and 100% of patients. Uniocular vision was 20/20, 20/25, 20/40, 20/60, and 20/80 in 2.2%, 4.4%, 35.5%, 71.1%, and 93.3% of eyes, respectively. Uncorrected visual acuity (UCVA) on removal of the contact lens was 20/30, 20/40(-1), and 20/60 in 15.79%, 73.48%, and 100% of eyes. After 6 months (82 eyes), UCVA was 20/20, 20/25, and 20/40 in 75.6%, 93.9%, and 100%. After 12 months (36 eyes), it was 20/20 and 20/25 in 83.3% and 100%. No eye required retreatment. CONCLUSION: Scanning slit laser treatment after precise removal of the epithelium with a rotary scrubber, prescrub, and postlaser cooling allowed rapid, accurate correction of myopia and astigmatism.

Scanning electron microscopy comparison of corneal epithelial removal techniques before photorefractive keratectomy.

PURPOSE: To evaluate and compare the most common epithelial removal techniques by scanning electron microscopy. SETTINGS: Beckman Laser Institute, University of California, Irvine, California, USA. METHODS: The epithelium was removed in both eyes of 5 Dutch belted rabbits by 1 of 5 techniques: blunt mechanical debridement (with a blunt spatula), sharp mechanical debridement (with a sharp scalpel blade), application of topical alcohol, and transepithelial removal with the excimer laser and with the rotary epithelial scrubber. The animals were immediately killed and corneal specimens prepared for scanning electron microscopy. The degree of corneal trauma and the completeness of epithelial cell removal with the 5 techniques were evaluated by comparing the regularity and smoothness of the resulting stromal surfaces. RESULTS: Epithelial removal with alcohol, the excimer beam, and the rotary epithelial scrubber produced a smoother, more uniform anterior stromal surface than blunt and sharp mechanical debridement. CONCLUSIONS: The smooth and uniform anterior stromal surface produced with the rotary epithelial scrubber, alcohol, and the laser beam may be preferable prior to photorefractive keratectomy.

Acanthamoeba keratitis with live isolates treated with cryosurgery and fluconazole.

PURPOSE: To report live, active trophozoites in an eye with Acanthamoeba keratitis that resembled Acanthamoeba polyphagia in the anterior chamber fluid obtained by transcorneal tap. METHOD: After prediagnostic therapy had failed, we performed cryosurgery to break the corneal cell walls and treated the patient with oral fluconazole. RESULTS: The condition resolved after 8 weeks of oral fluconazole therapy. Residual leukoma was treated by corneal graft. CONCLUSION: Live, motile Acanthamoeba can be isolated from an anterior chamber tap; combination therapy with oral fluconazole after corneal cryosurgery may be effective.

Intraoperative keratometry with the oval comparator (astigmometer).

The Astigmometer is a simple accessory which is attached to a surgical microscope. It allows precise suturing of the cataract wound and reduced the amount of postoperative astigmatism at six weeks. This allowed rapid visual rehabilitation and more active patients. It obviated the removal of sutures in the postoperative period in most patients (90%). However, stable results after one year were obtained with selective suture cutting without the use of intraoperative keratometry. This was almost as good as in the astigmometer group, but the percentage of astigmatism less than 1 dioptre was reduced and that greater than 2 dioptres was increased.

Treatment of severe herpes keratitis with cryosurgery and immunotherapy.

The contrasting type of lesion produced in the first eye of non-immune and the second eye of the then immune rabbits using herpes simplex Type I virus is demonstrated. Cryosurgery may make the first eye worse but the second eye is healed. A large percentage of second eyes heal spontaneously, however, as circulating antibody titres are high. Artefacts may be mistaken for lesions in the immune eye but superficial viral growth has a characteristic plaque-like appearance. One hundred eyes with recurrent superficial, recurrent superficial stromal, disciform deep stomal, and metaherpes treated with cryosurgery and immunotherapy are discussed. An immediate cure was obtained in all cases. Seven cases recurred over the 10-year period studied, but these were all successfully re-treated. Corneal grafts were performed in twelve cases with failure in only one case.