(1/1261) Streptococcal keratitis after myopic laser in situ keratomileusis.
A 24-year-old healthy male underwent uncomplicated laser in situ keratomileusis (LASIK) in left eye. One day after the surgery, he complained of ocular pain and multiple corneal stromal infiltrates had developed in left eye. Immediately, the corneal interface and stromal bed were cleared, and maximal antibiotic treatments with fortified tobramycin (1.2%) and cefazolin (5%) were given topically. The causative organism was identified as 'Streptococcus viridans' both on smear and culture. Two days after antibiotic therapy was initiated, the ocular inflammation and corneal infiltrates had regressed and ocular pain was relieved. One month later, the patient's best corrected visual acuity had returned to 20/20 with -0.75 -1.00 x 10 degrees, however minimal stromal scarring still remained. This case demonstrates that microbial keratitis after LASIK, if treated promptly, does not lead to a permanent reduction in visual acuity. (+info)
(2/1261) Tonic accommodation, age, and refractive error in children.
PURPOSE: An association between tonic accommodation, the resting accommodative position of the eye in the absence of a visually compelling stimulus, and refractive error has been reported in adults and children. In general, myopes have the lowest (or least myopic) levels of tonic accommodation. The purpose in assessing tonic accommodation was to evaluate it as a predictor of onset of myopia. METHODS: Tonic accommodation was measured in children enrolled in the Orinda Longitudinal Study of Myopia using an infrared autorefractor (model R-1; Canon, Lake Success, NY) while children viewed an empty lit field or a dark field with a fixation spot projected in Maxwellian view. Children aged 6 to 15 years were measured from 1991 through 1994 (n = 714, 766, 771, and 790 during the 4 years, successively). Autorefraction provided refractive error and tonic accommodation data, and videophakometry measured crystalline lens curvatures. RESULTS: Comparison of the two methods for measuring tonic accommodation shows a significant effect of age across all years of testing, with the lit empty-field test condition yielding higher levels of tonic accommodation compared with the dark-field test condition in children aged 6 through 11 years. For data collected in 1994, mean (+/-SD) tonic accommodation values for the lit empty-field condition were significantly lower in myopes, intermediate in emmetropes, and highest in hyperopes (1.02 +/- 1.18 D, 1.92 +/- 1.59 D, and 2.25 +/- 1.78 D, respectively; Kruskal-Wallis test, P < 0.001; between-group testing shows each group is different from the other two). Age, refractive error, and Gullstrand lens power were significant terms in a multiple regression model of tonic accommodation (R2 = 0.18 for 1994 data). Lower levels of tonic accommodation for children entering the study in the first or third grades were not associated with an increased risk of the onset of myopia, whether measured in the lit empty-field test condition (relative risk = 0.90; 95% confidence interval = 0.75, 1.08), or the dark-field test condition (relative risk = 0.83; 95% confidence interval = 0.60, 1.14). CONCLUSIONS: This is the first study to document an association between age and tonic accommodation. The known association between tonic accommodation and refractive error was confirmed and it was shown that an ocular component, Gullstrand lens power, also contributed to the tonic accommodation level. There does not seem to be an increased risk of onset of juvenile myopia associated with tonic accommodation. (+info)
(3/1261) Colchicine causes excessive ocular growth and myopia in chicks.
Colchicine has been reported to destroy ganglion cells (GCs) in the retina of hatchling chicks. We tested whether colchicine influences normal ocular growth and form-deprivation myopia, and whether it affects cells other than GCs. Colchicine greatly increased axial length, equatorial diameter, eye weight, and myopic refractive error, while reducing corneal curvature. Colchicine caused DNA fragmentation in many GCs and some amacrine cells and photoreceptors, ultimately leading to the destruction of most GCs and particular sub-sets of amacrine cells. Colchicine-induced ocular growth may result from the destruction of amacrine cells that normally suppress ocular growth, and corneal flattening may result from the destruction of GCs whose central pathway normally plays a role in shaping the cornea. (+info)
(4/1261) The growing eye: an autofocus system that works on very poor images.
It is unknown which retinal image features are analyzed to control axial eye growth and refractive development. On the other hand, identification of these features is fundamental for the understanding of visually acquired refractive errors. Cyclopleged chicks were individually kept in the center of a drum with only one viewing distance possible. Defocusing spectacle lenses were used to stimulate the retina with defined defocus of similar magnitude but different sign. If spatial frequency content and contrast were the only cues analyzed by the retina, all chicks should have become myopic. However, compensatory eye growth was still always in the right direction. The most likely cues for emmetropization, spatial frequency content and image contrast, do therefore not correlate with the elongation of the eye. Rather, the sign of defocus was extracted even from very poor images. (+info)
(5/1261) Naturally occurring vitreous chamber-based myopia in the Labrador retriever.
PURPOSE: To investigate whether myopia is present in a breed of domestic dog, the Labrador retriever, and how the ocular components are related to refractive error in this breed. METHODS: Cycloplegic refractive error was measured in 75 Labrador retrievers by retinoscopy. Corneal and crystalline lens radii of curvature were measured in the right eyes of 57 of these dogs using a video-based keratophakometer, with axial ocular dimensions measured using A-scan ultrasonography. RESULTS: Of the 75 dogs tested, 11 (14.7%) were myopic by at least -0.50 D in one eye, and 6 (8.0%) were myopic in both eyes (full range of refractive errors, +3.50 D to -5.00 D). Of the 57 dogs with ocular component measurements, seven (12.3%) were myopic by at least -0.50 D in the right eye. There was a significant negative correlation between refractive error and vitreous chamber depth (Spearman r = -0.42; P < 0.001). Myopic eyes had an elongated vitreous chamber depth (10.87+/-0.34 mm for myopic dogs, 10.02+/-0.40 mm for nonmyopic dogs; P < 0.0001, Kruskal-Wallis test). There was also a significant quadratic association between lens thickness and vitreous chamber depth (P < 0.005; R2 = 0. 11), indicating that thinner lenses occurred at both shorter and longer vitreous chamber depths. CONCLUSIONS: Myopia in the Labrador retriever is analogous to human myopia in that it is caused by an elongated vitreous chamber. Thinner crystalline lenses found at longer vitreous chamber depths may be analogous to lens thinning documented in human ocular development. The Labrador retriever warrants investigation as a potential model of myopia that is naturally occurring rather than experimentally induced. (+info)
(6/1261) Spherical and aspherical photorefractive keratectomy and laser in-situ keratomileusis for moderate to high myopia: two prospective, randomized clinical trials. Summit technology PRK-LASIK study group.
OBJECTIVE: Determine the outcomes of single-zone photorefractive keratectomy (SZPRK), aspherical photorefractive keratectomy (ASPRK), and laser in-situ keratomileusis (LASIK) for the correction of myopia between -6 and -12 diopters. DESIGN: Two simultaneous prospective, randomized, multi-center clinical trials. PARTICIPANTS: 286 first-treated eyes of 286 patients enrolled in one of two studies. In Study I, 134 eyes were randomized to SZPRK (58 eyes) or ASPRK (76 eyes). In Study II, 152 eyes were randomized to ASPRK (76 eyes) or to LASIK (76 eyes). INTERVENTION: All eyes received spherical one-pass excimer laser ablation as part of PRK or LASIK performed with the Summit Technologies Apex laser under an investigational device exemption, with attempted corrections between -6 and -12 diopters. MAIN OUTCOME MEASURES: Data on uncorrected and best spectacle-corrected visual acuity, predictability and stability of refraction, and complications were analyzed. Follow-up was 12 months. RESULTS: At 1 month postoperatively, more eyes in the LASIK group achieved 20/20 and 20/25 or better uncorrected visual acuity than PRK-treated eyes; at the 20/25 or better level, the difference was significant for LASIK (29/76 eyes, 38%) over SZPRK (10/58 eyes, 17%) (P = .0064). At all subsequent postoperative intervals, no difference was seen between treatment groups. Similarly, best corrected visual acuities were better for LASIK than all PRK eyes at 1 month postoperatively, and LASIK was better than SZPRK at 3 months follow-up (e.g., for 20/20 or better at 1 month, LASIK 50/76 eyes (66%) versus SZPRK 24/57 eyes (42%), P = .0066). PRK eyes had a mean loss of BCVA through 6 months, while LASIK eyes had a slight gain of mean BCVA through month 6; at 12 months, both ASPRK groups but not SZPRK continued to have a small mean loss of BCVA (e.g., compared to preoperative, mean BCVA at 12 months for SZPRK was + 0.3, LASIK was +.21, ASPRK I was -0.11, and ASPRK II -0.31 (SZPRK versus ASPRK II, P = .0116). Predictability was better for PRK than LASIK at all follow-up intervals (e.g., for manifest refraction spherical equivalent +/- 1.0 diopters at 6 months, ASPRK I 42/62 eyes (68%) versus LASIK 29/72 eyes (40%), P = .0014%). Stability was slightly but insignificantly less in the LASIK eyes compared to PRK eyes. All visual outcome measures were better for eyes with preoperative myopia between -6 and -8.9 D compared with eyes with myopia between -9 and -12 D. No consistent differences in refractive outcomes or postoperative corneal haze were seen between aspherical and single-zone ablations; haze diminished over 12 months and was judged to be vision-impairing in only one ASPRK eye. Microkeratome and flap complications occurred in 4 eyes, resulting in delay of completion of the procedure in 3 eyes but not causing long-term impairment. CONCLUSIONS: Improvement in uncorrected visual acuity and return of best corrected visual acuity was more rapid for LASIK than PRK, but efficacy outcomes in the longer term through 12 months were similar for all treatment groups. LASIK eyes tended toward undercorrection with the nomogram employed in this study compared to PRK, but the scatter was similar, suggesting little difference between these procedures for most patients by 6 months and thereafter. No consistent advantage was demonstrated between aspherical and single-zone ablation patterns. Predictability was much better for all procedures for corrections of -6 to -8.9 D compared with -9 to -12 D. Sporadic loss of best corrected vision in the PRK eyes not found in the LASIK eyes and other measures of visual function require further study. (+info)
(7/1261) Enhancement ablation for the treatment of undercorrection after excimer laser in situ keratomileusis for correcting myopia.
OBJECTIVE: To evaluate the treatment of undercorrection after the excimer laser in situ keratomileusis (LASIK) for correcting moderate and high myopia. METHODS: An enhancement ablation was performed in 48 eyes of 39 patients who had undergone LASIK but remained in undercorrection. Four procedures were performed within 1 month postoperatively, and the others performed between 3 and 10 months. The surgical technique includes the re-invert of the corneal cap from the temporal side, the excimer laser ablation, and the re-position of the cap. RESULTS: The undercorrection (spherical equivalent) ranged from -2.00 to -11.00 D, with a mean of -4.34D +/- 1.95 D. Following up after enhancement ablation was done after 4 to 12 months, the refractions in the 42 eyes were found to be within +/- 1.00 D. Undercorrection of -2.50 D to -5.00 D recurred in 6 eyes. Uncorrected visual acuity equals to the preoperative spectacle corrected visual acuity in 39 of 48 eyes (81.3%). Five eyes gained 1 line, 1 eye gained 2 lines and 4 eyes lost 1 line. No eyes had haze. CONCLUSION: Undercorrection after LASIK can be corrected by an enhancement ablation of the stroma under the primary corneal cap with a 193 nm ArF excimer laser, and the time for the enhancement of ablation is at 3 months postoperatively. (+info)
(8/1261) Long-term changes in retinal contrast sensitivity in chicks from frosted occluders and drugs: relations to myopia?
Experiments in animal models have shown that the retinal analyzes the image to identify the position of the plane of focus and fine-tunes the growth of the underlying sclera. It is fundamental to the understanding of the development of refractive errors to know which image features are processed. Since the position of the image plane fluctuates continuously with accommodative status and viewing distance, a meaningful control of refractive development can only occur by an averaging procedure with a long time constant. As a candidate for a retinal signal for enhanced eye growth and myopia we propose the level of contrast adaptation which varies with the average amount of defocus. Using a behavioural paradigm, we have found in chickens (1) that contrast adaptation (CA, here referred to as an increase in contrast sensitivity) occurs at low spatial frequencies (0.2 cyc/deg) already after 1.5 h of wearing frosted goggles which cause deprivation myopia, (2) that CA also occurs with negative lenses (-7.4D) and positive lenses (+6.9D) after 1.5 h, at least if accommodation is paralyzed and, (3) that CA occurs at a retinal level or has, at least, a retinal component. Furthermore, we have studied the effects of atropine and reserpine, which both suppress myopia development, on CA. Quisqualate, which causes retinal degeneration but leaves emmetropization functional, was also tested. We found that both atropine and reserpine increase contrast sensitivity to a level where no further CA could be induced by frosted goggles. Quisqualate increased only the variability of refractive development and of contrast sensitivity. Taken together, CA occurring during extended periods of defocus is a possible candidate for a retinal error signal for myopia development. However, the situation is complicated by the fact that there must be a second image processing mode generating a powerful inhibitory growth signal if the image is in front of the retina, even with poor images (Diether, S., & Schaeffel, F. (1999). (+info)