Biomedical subjects
Publications and source records attributed to B Tengroth.
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BACKGROUND: Our aim was to assess visual acuity using standardized charts and illumination conditions after photorefractive keratectomy. METHODS: High and low contrast visual acuity were measured on Bailey-Lovie logarithm of the minimum angle of resolution (LogMAR) charts under high and low illumination conditions on 105 photorefractive keratectomy patients who had been treated with the Summit (N = 60) or the VISX (N = 45) excimer laser. RESULTS: Best corrected visual acuity was reduced in the treated eye compared with the untreated control eye under all test conditions, with the greatest differences under conditions of low contrast and low illumination. Reduction of acuity under low contrast and low illumination was related to small optic zone sizes and steep ablation edge profiles found in Summit-treated eyes. In the VISX-treated eyes, high contrast acuity was reduced in the presence of central topographical irregularities, subepithelial haze, and higher myopic corrections. CONCLUSIONS: Testing conditions such as those described here may be useful in quantifying vision degradation in suboptimal viewing conditions and among patients with vague complaints.
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PURPOSE: To determine the effect of patient age, postoperative time, ablation zone diameter and depth, attempted correction, and corneal topography on postoperative corneal epithelial thickness after photorefractive keratectomy (PRK). SETTING: Private clinic and university hospital, Stockholm, Sweden. METHODS: This retrospective, unmasked study comprised 136 myopic patients treated unilaterally with PRK. Seventy eyes had been treated with the Summit excimer laser 27 months +/- 7 (SD) earlier using ablation zone diameters of 4.1 to 5.0 mm. Sixty-six eyes had been treated with the VISX excimer laser 6 +/- 3 months earlier using a 6.0 mm zone diameter. The untreated fellow eyes served as controls. Epithelial thickness was measured at a standardized central corneal area with a modified optical pachymeter, and corneal topography was determined using computerized videokeratoscopy. RESULTS: In the Summit group, the epithelial layer in the PRK eyes was 12.0 microns (21%) thicker than in the control eyes (P < .001; 95% confidence interval [CI] 9.35 to 14.3 microns). This thickness differential correlated significantly with increased ablation depth and attempted correction. In the VISX group, the epithelium in the treated eyes was 7.0 microns (7%) thinner (P = .0009; 95% CI -1.9 to -6.7 microns) and thickness did not correlate with ablation depth or attempted correction. There was no correlation between epithelial hyperplasia and patient age or postoperative follow-up. With the laser groups combined, epithelial hyperplasia was greater with smaller zone sizes and a greater rate of change in power at the edge of the ablation zone. CONCLUSION: The factors associated with an increase in epithelial thickness were small ablation zones, greater attempted corrections, and deeper ablations. Larger, smoother ablation profiles may result in less epithelial hyperplasia.
In order to determine the risk for bilateral blindness from glaucoma and to which extent other diseases are responsible for the disability, the registers of low vision clinics were surveyed. All registered patients still alive in 1991 with the diagnosis of glaucoma were included. Eighteen hundred and ninety-five patients fulfilled these criteria. Blindness was defined as bilateral visual acuity < or = 0.1. The majority of the patients (68%) had a visual acuity better than 0.1. The remaining 590 patients had a visual acuity < or = 0.1. In this latter group glaucoma was the reason for the low visual acuity in 20%, glaucoma in combination with other eye diseases in 35% and other eye diseases in 44%. Macular degeneration and cataracts were the main causes of the low vision in the latter group. The prevalence of glaucoma blindness in the Stockholm region was found to be 0.007% for glaucoma and 0.020% for glaucoma in combination with other eye diseases.
The study was designed to determine whether dopaminergic neurotransmission in the retina can operate via volume transmission. In double immunolabelling experiments, a mismatch as well as a match was demonstrated in the rat retina between tyrosine hydroxylase (TH) and dopamine (DA) immunoreactive (ir) terminals and cell bodies and dopamine D2 receptor-like ir cell bodies and processes. The match regions were located in the inner nuclear and plexiform layers (D2 ir cell bodies plus processes). The mismatch regions were located in the ganglion cell layer, the outer plexiform layer, and the outer segment of the photoreceptor layer, where very few TH ir terminals can be found in relation to the D2 like ir processes. In similar experiments analyzing D1 receptor like ir processes versus TH ir nerve terminals, mainly a mismatch in their distribution could be demonstrated, with the D1 like ir processes present in the outer plexiform layer and the outer segment where a mismatch in D2 like receptors also exists. The demonstration of a mismatch between the localization of the TH terminal plexus and the dopamine D2 and D1 receptor subtypes in the outer plexiform layer, the outer segment and the ganglion cell layer (only D2 immunoreactivity (IR)) suggests that dopamine, mainly from the inner plexiform layer, may reach the D2 and D1 mismatch receptors via diffusion in the extracellular space. After injecting dopamine into the corpus vitreum, dopamine diffuses through the retina, and strong catecholamine (CA) fluorescence appears in the entire inner plexiform layer and the entire outer plexiform layer, representing the match and mismatch DA receptor areas, respectively. The DA is probably bound to D1 and D2 receptors in both plexiform layers, since the DA receptor antagonist chlorpromazine fully blocks the appearance of the DA fluorescence, while only a partial blockade is found after haloperidol treatment which mainly blocks D2 receptors. These results indicate that the amacrine and/or interplexiform DA cells, with sparse branches in the outer plexiform layer, can operate via volume transmission in the rat retina to influence the outer plexiform layer and the outer segment, as well as other layers of the rat retina such as the ganglion cell layer.
Epithelial hyperplasia has been found to occur after photorefractive keratectomy in eyes treated with small (5 mm or less) ablation zone diameters with the Summit laser, but not with large zones (6 mm) with the VISX laser (Gauthier et al. 1995a). The aim of this study was to further investigate the effect of surgical parameters on epithelial hyperplasia by comparing eyes treated with the same zone diameter but two different lasers. We examined 11 subjects who had photorefractive keratectomy for myopia performed with 5 mm ablation zones with the Summit excimer laser in one eye and the VISX 20/20 laser in the fellow eye an average of 21 months previously. Epithelial thickness and corneal topography were measured. The mean epithelial thickness was not statistically different (p = 0.083) between the eyes treated with the Summit (66 +/- 12 microns) and VISX (60 +/- 14 microns) lasers. Postoperative corneal dioptric power showed a similar profile between the two eyes at the edge of the zone, with the VISX-treated corneas being more shallow centrally. There was a trend towards greater epithelial thickness with deeper ablations. This study supports the hypothesis that epithelial hyperplasia is dependent on ablation zone diameter and ablation depth.
AIM: To determine the relation between epithelial hyperplasia and regression of effect after photorefractive keratectomy (PRK). METHODS: Seventy unilaterally treated patients with PRK were examined. All eyes had been treated with the Summit excimer laser 27 (SD 7) months previously with zone diameters of 4.1 to 5.0 mm. The untreated fellow eyes served as controls. Epithelial thickness was measured centrally with a thin slit optical pachometer and manifest subjective refraction was performed. RESULTS: The epithelium was 21% thicker in the treated eye (p < 0.0001). The relation between refractive regression and epithelial hyperplasia was significant (r = 0.41; p < 0.001). CONCLUSIONS: Epithelial hyperplasia after PRK correlated with the myopic shift (including hyperopia reduction) after treatment with the Summit laser. A model is proposed suggesting that both subepithelial and epithelial layers contribute to regression in the Summit treated eyes with 18 microns of epithelial hyperplasia contributing each dioptre of regression.
BACKGROUND AND OBJECTIVE: The aim of the study was to evaluate the refractive outcome 36 months following excimer laser photorefractive keratectomy (PRK) performed on myopic eyes. We analyzed the refractive stability between 24 and 36 months. PATIENTS AND METHODS: PRK was performed on 457 eyes with a pre-operative refraction ranging from -1.25 to -7.50 diopters (D). Ablation zone diameters of 4.3 to 4.5 mm were used. The follow up time was 36 months. RESULTS: The mean refraction 36 months following surgery was -0.22 to 0.75 D for the whole group, which was not significantly different from the mean at 24 months (-0.27 +0.74D). If we analyze the subgroups at 36 months, we find a significantly better refractive outcome in the low myopia group (up to -2.90D) compared with those with higher myopia. At 36 months, 91% of the 456 eyes had an uncorrected visual acuity of at least 20/40, and 88% of the eyes were within 1.00 D of emmetropia. CONCLUSION: These results show stability between 24 and 36 months.
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The time needed to recover optokinetic nystagmus or electroretinography complexes after a glare inducing flash was measured to study the receptor and neural visual readaptation. Electroretinographs and optokinetic nystagmus were evoked with low intensity stimuli. The light from a flash tube was filtered with an interference filter (Tmax = 536 or 622 nm) and evenly distributed into a Goldmann hemisphere observed by the subject. The Recovery of the amplitude of the a-wave of the electroretinography is quicker than the recovery of optokinetic nystagmus after a low intensity glare inducing flash. The recovery time was shorter for a red than for a green flash of equivalent dose for both recovery modalities. The time difference between electroretinography a-wave and optokinetic nystagmus recovery was the same and independent of glare inducing flash wavelength. The recovery of the amplitude of the a-wave of the electroretinography was quicker than the recovery of optokinetic nystagmus after a low intensity glare inducing flash. This time difference between the recovery modalities may in part be due to the difference between the physiological stimuli used, but it is believed that most of the time difference is because the recovery of optokinetic nystagmus monitors more of the afferent visual pathway with complex post receptor neural mechanisms than the recovery of the a-wave.
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Regression of effect is a well-established complication of excimer laser photorefractive keratectomy for the correction of myopia. In 17 eyes retreated with excimer photorefractive keratectomy, minimum follow-up time was six months. Mean (+/- SD) refraction at six months postoperatively was -0.97 +/- 2.10 diopters, significantly different (P < .01) from the pre-retreatment mean of -2.91 +/- 0.86 diopters. The 11 best eyes (six-month refraction < -1.00 diopter) had a mean refraction of +0.32 +/- 0.67 diopter. At six months after retreatment, 64.7% had an uncorrected visual acuity greater than or equal to 20/40, and 58.8% were within 1.00 diopter of emmetropia. Two eyes showed a loss of one to two Snellen lines at six months. There was no significant increase in mean haze after retreatment. While the percentage of eyes with uncorrected visual acuity greater than or equal to 20/40 and the percentage of eyes within 1.00 diopter of emmetropia were lower than in eyes which did not require retreatment, the results of this study indicate that the majority of photorefractive keratectomy regressions can be successfully retreated.
PURPOSE: To evaluate the 24-month refractive outcome of excimer laser photorefractive keratectomy (PRK) performed on normal, sighted myopic eyes; and to assess the evolution of postoperative refraction, the accuracy of predicted correction, and the results in terms of uncorrected visual acuity. METHODS: Photorefractive keratectomy was performed on 495 eyes, with a preoperative refraction ranging from -1.25 to -7.50 diopters (D). Ablation zone diameters of 4.3 and 4.5 mm were used. All patients were treated with a standard topical steroid regimen postoperatively. Minimum follow-up time was 24 months. RESULTS: Mean refraction (spherical equivalent +/- standard deviation) at 24 months was -0.27 +/- 0.74 D, which was significantly (P < 0.01) different from the mean at 12 months (0.01 +/- 0.78 D). There was also a significant (P = 0.01) difference between the 12- and 18-month (-0.15 +/- 0.82 D) mean refractions. But there was no significant difference between the means at 18 and 24 months postoperatively. Subgroup analysis at 24 months showed that patients with low to moderate myopia (up to -3.90 D) had significantly better refractive outcomes than those with higher myopia. Also at 24 months, 91% of the eyes had an uncorrected visual acuity of at least 20/40, and 81.5% had an uncorrected visual acuity of at least 20/30. Correspondingly, 87.5% of the eyes were within 1.00 D of emmetropia, and 71.7% were within 0.50 D. Only 0.4% lost one line of best-corrected visual acuity, no eye lost two lines or more. CONCLUSIONS: Refraction after PRK is slow to stabilize, but appears to reach stability by 18 to 24 months after surgery. The refractive results are reasonably predictable and compare well with those achieved with radial keratotomy.
To assess the role of topical steroids following excimer laser photorefractive keratectomy (PRK) for myopia, we compared the refractive outcome in 100 eyes that did not receive steroids in the immediate postoperative period (untreated eyes) with 100 eyes that were treated with topical dexamethasone for three months postoperatively. Photorefractive keratectomy was performed with the Summit laser, using 4.3 mm and 4.5 mm ablation zones. At three months after surgery, the untreated eyes had a mean refraction of -0.97 +/- 1.15 diopters (D), significantly different (P < .01) from the mean refraction (+0.46 +/- 0.74 D) of the steroid-treated eyes. By six months postoperatively, 86% of the untreated eyes had regressed to a myopia of at least 0.50 D, whereas only 23% of the steroid-treated eyes had regressed. In a second study, we compared the results in 25 patients whose first PRK eye was treated with steroids after surgery but whose second eye was not. At three months postoperatively, mean refraction in the steroid-treated eyes was +1.23 +/- 0.71 D, significantly different (P < .01) from the mean of -0.45 +/- 1.29 D in the untreated eyes. The refractive results in PRK eyes treated with the Summit unit and with relatively small ablation zone diameters showed that eyes that received dexamethasone postoperatively were less likely to regress to myopia.
The aim of the study was to evaluate the algorithm and surgical performance of two excimer lasers, the Summit Excimed 200 LA and the VISX 20/20, by assessing visual outcome parameters such as visual acuity and contrast sensitivity, and subjectively estimating dark vision performance. Furthermore, refractive results and centration of the surgically ablated area were assessed. Twenty patients were included in each group. The indications were myopia between -2 to -5 diopters allowing up to -0.75 diopters astigmatism. The treatment diameter was 5 mm. The postoperative treatment was topical dexamethasone for 3 months. The follow-up time was 12 months. The results showed a median refraction +/- 0.0 D in the Summit group and -0.5 D in the VISX group 12 months postoperatively. The uncorrected visual acuity was 0.5 (20/40) or better for 100% of the Summit treated eyes, whereas 85% of the VISX treated eyes achieved 0.5 (20/40) or better. The other visual qualities as contrast sensitivity, dark vision and centration of the ablation zone were the same in both groups. The slightly more myopic outcome of the VISX laser explains the poorer average uncorrected visual acuity in this group. We have, as a result of the refractive results, changed our algorithm in the VISX machine to achieve emmetropia. It is our experience that one should try to reach emmetropia in this young population.
Seventy-six patients with recurrent corneal erosions resistant to conventional therapy with ointment, abrasion or contact lenses were treated with the excimer laser. The patients were treated in 3 different ways; ablation of 3 or 5 microns after epithelial removal, or ablation of 20 microns directly on the epithelium. Twenty out of the 76 treated eyes showed recurrences. Thirty-five of the patients had no symptoms after treatment and 21 patients had minor symptoms. The 3 different treatment modes were equally successful in the present study.