The extracellular matrix in colorectal cancer and its metastatic settling - Alterations and biological implications.

Colorectal cancer (CRC) remains one of the most common cancers worldwide. Metastatic disease is ultimately fatal when incurable. Cancer research has evolved to take the importance of the tumour microenvironment (TME) into account. The extracellular matrix (ECM) has been viewed merely as a structural scaffold, but it is now evident that the ECM is a highly active part of the TME and affects tumour cell behaviour and metastatic capability. The ECM context and composition are linked to patient outcome and the response to surgical and oncological therapy in CRC patients and may be an area for developing novel biomarkers and targeted therapy. In this review we focus on the components of the ECM in human primary and metastatic CRC. We discuss future aspects of the ECM for targeted therapy, as a source of novel biomarkers, current knowledge of the area and important considerations when studying the ECM in human CRC.

A beam model for focused proton pencil beams.

INTRODUCTION: We present a beam model for Monte Carlo simulations of the IBA pencil beam scanning dedicated nozzle installed at the Skandion Clinic. Within the nozzle, apart from entrance and exit windows and the two ion chambers, the beam traverses vacuum, allowing for a beam that is convergent downstream of the nozzle exit. MATERIALS AND METHODS: We model the angular, spatial and energy distributions of the beam phase space at the nozzle exit with single Gaussians, controlled by seven energy dependent parameters. The parameters were determined from measured profiles and depth dose distributions. Verification of the beam model was done by comparing measured and GATE acquired relative dose distributions, using plan specific log files from the machine to specify beam spot positions and energy. RESULTS: GATE-based simulations with the acquired beam model could accurately reproduce the measured data. The gamma index analysis comparing simulated and measured dose distributions resulted in >95% global gamma index pass rates (3%/2 mm) for all depths. CONCLUSION: The developed beam model was found to be sufficiently accurate for use with GATE e.g. for applications in quality assurance (QA) or patient motion studies with the IBA pencil beam scanning dedicated nozzles.

A mechanistic linkage between oral lichen planus and autoimmune thyroid disease.

OBJECTIVE: To determine the levels of antithyroid antibodies and thyroid hormones in the sera of patients with oral lichen planus (OLP), and to quantify the expression of thyroid proteins in OLP lesions. SUBJECTS AND METHODS: Venous blood samples were drawn from 110 patients with OLP who had no history of thyroid disease or levothyroxine supplementation (OLP+/LT4 -). A random population sample of 657 healthy subjects was used as the control group. Two additional groups were used as comparators. Immunohistochemical and qPCR analyses were performed on tissue specimens collected from the patients with OLP and thyroid disease and healthy subjects. RESULTS: No association was found between the presence of antithyroid antibodies and OLP. More patients in the OLP+/LT4 - group showed high levels of thyroid-stimulating hormone and low levels of free thyroxine than were seen in the control group. Thyroid-stimulating hormone receptor was more highly expressed in the OLP lesions of patients with thyroid disease than in the healthy oral mucosa. CONCLUSIONS: A significant number of patients with OLP who are not previously diagnosed with thyroid disease have thyroid parameters that are compatible with hypothyroidism. The expression of thyroid-stimulating hormone receptor in OLP lesions suggests that mechanisms related to autoimmune thyroid disease are involved in the aetiology of OLP.

A Paleolithic-type diet results in iodine deficiency: a 2-year randomized trial in postmenopausal obese women.

BACKGROUND/OBJECTIVES: Different diets are used for weight loss. A Paleolithic-type diet (PD) has beneficial metabolic effects, but two of the largest iodine sources, table salt and dairy products, are excluded. The objectives of this study were to compare 24-h urinary iodine concentration (24-UIC) in subjects on PD with 24-UIC in subjects on a diet according to the Nordic Nutrition Recommendations (NNR) and to study if PD results in a higher risk of developing iodine deficiency (ID), than NNR diet. SUBJECTS/METHODS: A 2-year prospective randomized trial in a tertiary referral center where healthy postmenopausal overweight or obese women were randomized to either PD (n=35) or NNR diet (n=35). Dietary iodine intake, 24-UIC, 24-h urinary iodine excretion (24-UIE), free thyroxin (FT4), free triiodothyronine (FT3) and thyrotropin (TSH) were measured at baseline, 6 and 24 months. Completeness of urine sampling was monitored by para-aminobenzoic acid and salt intake by urinary sodium. RESULTS: At baseline, median 24-UIC (71.0 µg/l) and 24-UIE (134.0 µg/d) were similar in the PD and NNR groups. After 6 months, 24-UIC had decreased to 36.0 µg/l (P=0.001) and 24-UIE to 77.0 µg/d (P=0.001) in the PD group; in the NNR group, levels were unaltered. FT4, TSH and FT3 were similar in both groups, except for FT3 at 6 months being lower in PD than in NNR group. CONCLUSIONS: A PD results in a higher risk of developing ID, than a diet according to the NNR. Therefore, we suggest iodine supplementation should be considered when on a PD.

Hypoxia-inducible factor 1α predicts recurrence in high-grade soft tissue sarcoma of extremities and trunk wall.

BACKGROUND AND AIM: Sarcomas are of mesenchymal origin and typically show abundant tumour stroma and presence of necrosis. In search for novel biomarkers for personalised therapy, we determined the prognostic impact of stromal markers, hypoxia and neovascularity in high-grade soft tissue leiomyosarcoma and pleomorphic undifferentiated sarcoma. METHOD: We evaluated CD163, colony-stimulating factor (CSF)-1, CD16 and hypoxia-inducible factor 1 (HIF-1)α using immunohistochemical staining and assessed microvessel density using CD31 in 73 high-grade leiomyosarcomas and undifferentiated pleomorphic sarcomas of the extremities and the trunk wall. The results were correlated to metastasis-free and overall survival. RESULTS: Expression of HIF-1α was associated with the presence of necrosis and independently predicted shorter metastasis-free survival (HR 3.2, CI 1.4 to 7.0, p=0.004), whereas neither expression of the stromal markers CD163, CD16 and CSF-1 nor microvessel density was prognostically relevant in this series. CONCLUSIONS: There is increasing evidence for the prognostic role of hypoxia in high-grade soft tissue sarcoma, and these data suggest that HIF-1α expression represents a candidate prognostic biomarker for clinical application in high-grade leiomyosarcoma and undifferentiated pleomorphic sarcoma.

Does a too risk-averse approach to the implementation of new radiotherapy technologies delay their clinical use?

Radiotherapy is a generally safe treatment modality in practice; nevertheless, recent well-reported accidents also confirm its potential risks. However, this may obstruct or delay the introduction of new technologies and treatment strategies/techniques into clinical practice. Risks must be addressed and judged in a realistic context: risks must be assessed realistically. Introducing new technology may introduce new possibilities of errors. However, delaying the introduction of such new technology therefore means that patients are denied the potentially better treatment opportunities. Despite the difficulty in quantitatively assessing the risks on both sides of the possible choice of actions, including the "lost opportunity", the best estimates should be included in the overall risk-benefit and cost-benefit analysis. Radiotherapy requires a sufficiently high level of support for the safety, precision and accuracy required: radiotherapy development and implementation is exciting. However, it has been anxious with a constant awareness of the consequences of mistakes or misunderstandings. Recent history can be used to show that for introduction of advanced radiotherapy, the risk-averse medical physicist can act as an electrical fuse in a complex circuit. The lack of sufficient medical physics resource or expertise can short out this fuse and leave systems unsafe. Future technological developments will continue to present further safety and risk challenges. The important evolution of radiotherapy brings different management opinions and strategies. Advanced radiotherapy technologies can and should be safely implemented in as timely a manner as possible for the patient groups where clinical benefit is indicated.

Type IV collagen as a tumour marker for colorectal liver metastases.

BACKGROUND: About 50% of patients with primary colorectal cancer (CRC) will develop liver metastases (CLM). Currently, carcinoembryonic antigen (CEA) is the most common tumour marker for CRC and CLM. However, the sensitivity and specificity of this marker is not optimal, as almost 50% of patients have tumours that do not produce CEA. Therefore there is a need for better markers for CRC and CLM. METHODS: The circulating levels of type IV collagen were measured in patients with CLM, primary CRC and in healthy controls. The expression pattern of type IV collagen was studied by immunofluorescence in CLM and normal liver tissue. The metastatic volume of CLM in the liver was estimated from CT. RESULTS: In CLM tissue type IV collagen is highly expressed in the areas of desmoplasia. Patients with primary CRC (Dukes' A-C) did not show any increase in circulating type IV collagen compared to healthy controls. However, patients with CLM have significantly elevated levels of circulating type IV collagen when compared to patients with primary CRC and healthy controls. The levels of type IV collagen decreased during chemotherapy and increased at the time of disease progression. The circulating levels of type IV collagen seem to reflect the tumour burden in the liver. CONCLUSIONS: Type IV collagen has the potential to be used as tumour associated biomarker for CLM. These results indicate the importance of interaction between cancer cells and the stroma in the tumour microenvironment.

Thyroid volume in Swedish school children: a national, stratified, population-based survey.

BACKGROUND/OBJECTIVES: Sweden has had a salt iodination program since 1936. This first national surveillance study on iodine nutrition infers an adequate level of urinary iodine concentration (UIC 125 µg/l) and the aim is now to evaluate thyroid volume (Tvol) in the same national sample. SUBJECTS/METHODS: A stratified probability proportionate to size cluster sampling was used to obtain a representative national sample of Swedish children aged 6-12 years. Median Tvol obtained ultrasonographically and the prevalence of enlarged thyroid glands were compared with an international reference standard. Regional differences were evaluated through comparisons of Tvol between coastal and inland areas, urban and rural regions, and former goitre and non-goitre regions. RESULTS: Tvol was correlated with age, body surface area (BSA), weight, height and body mass index for both sexes (P<0.0001) but not with UIC. The most important predictors for Tvol were age (girls: P<0.0001, boys: P=0.001) and BSA (girls: P<0.0001, boys: P<0.01). Median Tvol was higher in Sweden than in the reference study (P<0.0001). The prevalence of goitre was higher in Sweden (correlated to age 22.3%, BSA 15.7%, weight 17.6%, height 12.9%) than in the international reference (correlated to age 2.5%, BSA 2.5%, weight 2.5%, height 2.5%) (P<0.0001). Thyroids were larger in boys from urban and former non-goitre areas. CONCLUSIONS: Tvols were higher in Swedish school children than in the international reference study although iodine intake is considered optimal in Sweden. These findings underline the importance of regular monitoring of iodine intake, especially with regard to the decreased intake of table salt that is likely to follow initiation of health campaigns.

Perfusion of the human placenta with red blood cells and xanthine oxidase mimics preeclampsia in-vitro.

BACKGROUND AND PURPOSE: Preeclampsia is a major obstetric problem of unknown etiology. The fact that removal of the placenta is the only cure for preeclampsia, has led to the well-established hypothesis, that the placenta is central in the etiology. Gene profiling and proteomics studies have suggested oxidative stress caused by reperfusion and free oxygen radicals as a potential pathophysiological mechanism in preeclampsia. In this study, the dual placental perfusion model was used in order to evaluate the damaging effects of oxidative stress induced by xanthine/xanthine oxides and free hemoglobin. MATERIAL AND METHODS: The dual placenta perfusion model is a well-established in vitro model for functional placental studies. Placentas were perfused with medium containing either xanthine/xanthine oxidase or erythrocytes as a source of free hemoglobin. Concentration of free hemoglobin in the medium was measured by means of ELISA. Whole genome microarray technique and bioinformatics were used to evaluate the gene expression profile in the two groups. RESULTS: Substantial levels of free adult hemoglobin were detected in the perfusions. A total of 58 genes showed altered gene expression, the most altered were hemoglobin alpha, beta and gamma, tissue factor pathway inhibitor 2 and superoxide dismutase 2. Bioinformatics revealed that biological processes related to oxidative stress, anti-apoptosis and iron ion binding were significantly altered. CONCLUSIONS: The results suggest that perfusion with xanthine/xanthine oxidase and free hemoglobin induce changes in gene expression similar to what has been described for the preeclamptic placenta.

Cardiac concentric remodelling induced by non-aromatizable (dihydro-)testosterone is antagonized by oestradiol in ovariectomized rats.

Previous studies on the cardiovascular effects of androgens in females, most of them using testosterone treatment, have yielded conflicting results. Testosterone is metabolized into oestradiol (E2) and dihydrotestosterone (DHT) within cardiovascular tissues. The aim of the present study was to explore the cardiovascular effects exerted by E2 and the non-aromatizable androgen DHT and to study possible interactions between these in female rats. Ovariectomized rats were treated with DHT, E2, or DHT+E2 for 6 weeks. DHT increased left-ventricular posterior wall thickness, assessed by echocardiography, whereas left-ventricular dimension, as well as total heart weight and calculated left-ventricular mass, were unchanged. DHT also increased the levels of insulin-like growth factor-I mRNA in the left ventricle. E2 abolished the effect of DHT on left-ventricular remodelling and insulin-like growth factor-I mRNA when the two treatments were given in combination. E2 also reduced androgen receptor mRNA levels in the heart. Neither E2 nor DHT changed blood pressure measured by telemetry. In conclusion, treatment with the endogenous non-aromatizable androgen DHT causes cardiac concentric remodelling in ovariectomized rats, possibly mediated by increased local levels of insulin-like growth factor-I. The effect of DHT on cardiac wall thickness was antagonized by E2, possibly through downregulation of cardiac androgen receptors. These mechanisms may be of importance for the concentric left-ventricular geometric pattern developing in women after menopause.

Reduced sympathetic responsiveness as well as plasma and tissue noradrenaline concentration in growth hormone transgenic mice.

AIMS: Acromegaly [overproduction of growth hormone (GH)] and GH deficiency have both been associated with alterations in autonomic nervous system function. The aim of this study was to investigate autonomic nervous system influence on heart rate (HR) in transgenic mice overexpressing bovine GH (bGH). METHODS: HR and HR variability (HRV) were measured in conscious young (8-13 weeks) and old (5-6 months) female bGH and control mice using telemetry. HR control was studied using antagonists and an agonist of adrenergic and muscarinic receptors. Noradrenaline was measured in plasma, heart and kidney using high performance liquid chromatography. RESULTS: Average 24 h resting HR did not differ between bGH and control mice. After saline injection and after muscarinic blockade with methylscopolamine HR increase was blunted (in old) or absent (in young) bGH mice compared with control mice (P < 0.05). Phenylephrine caused a baroreflex mediated decrease in HR from around 550 to 300-350 beats min(-1), not different between bGH and control mice. Time- and frequency-domain measures of HRV were reduced in old bGH compared with control mice (P < 0.05). Noradrenaline concentrations were reduced by 25-49% in plasma and tissue of bGH compared with control mice (P < 0.05). CONCLUSION: The current study suggests reduced autonomic modulation of HR in bGH transgenic mice. Thus, GH appears to have marked effects on autonomic tone, reducing sympathetic nervous system function possibly via reduced noradrenaline stores.

Neurohormonal influences on maintenance and reversal of two-kidney one-clip renal hypertension.

The factors involved in maintenance and reversal of mean arterial blood pressure (MAP) in the chronic two-kidney one-clip hypertensive rat (2K1C-RHR) are still debated. The reduction in MAP after reversal of 2K1C hypertension has been ascribed either to release of a renal medullary depressor hormone (RMDH) or suppression of the renin-angiotensin and/or sympathetic nervous system. We studied in conscious rats: (i) The effects of angiotensin II receptor blockade (ARB; candesartan), sympathetic blockade (propranolol and phentolamine) or a combination on MAP in 6-week long 2K1C-RHR; (ii) The effects of reversal of 2K1C hypertension by removal of the constricting clip (unclipping, UC) or nephrectomy (Nx) on MAP, plasma renin activity (PRA) and noradrenaline (NA) spillover rates. The results show that: (i) MAP in the 2K1C-RHR was almost normalized by ARB but not significantly affected by the sympathetic blockade. The combination was not more effective than ARB alone; (ii) UC and Nx reduced MAP in 2K1C to similar levels as ARB. No significant changes in PRA or catecholamines could be detected in UC and Nx groups. We conclude that hypertension in 2K1C-RHR is maintained by the renin-angiotensin system without much contribution from the sympathetic nervous system. Furthermore, we found no evidence that UC of our model of 2K1C was associated with a generalized decrease in sympathetic tone or substantial release of RMDH from the unclipped kidney. Thus, we conclude that in the present model of 2K1C, both maintenance and reversal of hypertension are controlled by the renin-angiotensin system.

Cellular proliferation and leukocyte infiltration in the rabbit cornea after photorefractive keratectomy.

PURPOSE: To map the proliferative activity of corneal cells during wound healing following photorefractive keratectomy (PRK) and to compare two markers for proliferation. METHODS: PRK, 5- mm in diameter with a -6 D setting, was performed in one eye of 28 New Zealand White Rabbits. The rabbits were sacrificed at time points between 12 hours and three months after surgery. The treated and fellow corneas were fixed in 10% formaldehyde, paraffin embedded, and immunohistochemically stained for proliferate cell nuclear antigen (PCNA) and at one time point, 1 week, also for Ki-67. RESULTS: Following initial sliding of the epithelial cells, the proliferative activity in the wound area starts in the leading edge (24 hours) and is spread towards the periphery. The proliferative activity peaks after one week and subsides during the following two weeks. Early (24 hours) proliferative activity is also seen in the limbal epithelium which peaks after three days. The keratocytes express PCNA in the peripheral stroma 48 hours after injury. They then also migrate to repopulate the stroma under the wound area. The expression period lasts 1 week and subsides the following week. Leukocytes are found in the wound as early as 12 hours after injury. The cells disappear around the time of epithelial wound closure, i.e. after 3 days. The two proliferative markers PCNA and KI 67 show a similar distribution after surgery. CONCLUSION: Epithelial proliferative activity starts earlier after injury, and is preceded by leukocyte presence in the wound. The PCNA expression starts later in the keratocytes but lasts somewhat longer (3 weeks). PCNA expression appears more efficient than Ki-67 to show proliferative activity of slow cycling cells in the cornea

Photorefractive keratectomy for hyperopia in 800 eyes with the Meditec MEL 60 laser.

PURPOSE: To evaluate the refractive results of 800 hyperopic eyes undergoing PRK treatment. METHODS: Eight hundred hyperopic eyes were treated with PRK. An Aesculap-Meditec MEL 60 scanning ArF excimer laser used. Treatment Group 1 consisted of eyes with a preoperative refractive error of +3.50 D or less (n = 482) and Group 2, of +3.75 D or more (n = 318). RESULTS: Preoperatively, Group 1 required an average correction of +2.88+/-1.34 D and Group 2 required +5.64+/-2.96 D. One year after PRK, average residual correction was +1.26+/-1.24 D in Group 1, and in Group 2, +2.46+/-1.84 D. In Group 1, uncorrected visual acuity (UCVA) was 20/40 or better in 88.4% (426/482); 20/20 or better in 75.7% (365); 2.1% (10/482) of eyes lost 2 lines, 2.1% (10/482) gained 2 lines; 3.1% (15/482) gained 2 or more lines of BSCVA; 74.4% (359/482) of eyes were within +/-0.50 D of target correction and 84.8% (408/482) were within +/-1.00 D. In Group 2, 47.5% (151/318) had UCVA of 20/40 or better; 34.2% (109/318) saw 20/20 or better uncorrected; 19.1% (61/318) lost 2 lines; 11.6% (37/318) lost 3 lines; none of the eyes gained 2 or more lines of BSCVA; 22.3% (71/318) were within +/-0.50 D and 46.8% (149/318) were within +/-1.00 D of target correction. Refractive stability was achieved after 6 months; a slight regression after 6 months was still observed. In Group 1, 10.5% (42/482) and in Group 2, 21.6% (69/318) complained of problems with daytime vision (glare and ghost image); during night-driving in Group 1, 17.6% (85/482) and in Group 2, 40.5% (129/318) had problems. CONCLUSION: PRK with the Aesculap-Meditec MEL 60 scanning ArF excimer laser offered the best long-term results with +3.50 D or less preoperative refractive error. With higher corrections, regression, decrease in BSCVA, and daytime visual problems were encountered.

Effects of the ET(A)/ET(B) antagonist, TAK-044, on blood pressure and renal excretory function after unclipping of conscious one-kidney-one-clip hypertensive rats.

BACKGROUND: Restoring renal perfusion pressure (unclipping) of one-kidney-one-clip renal hypertensive (1 K1C) rats normalizes mean arterial pressure (MAP) rapidly. This has been attributed to salt/volume losses or release of the putative renal medullary depressor hormone (RMDH). OBJECTIVE: To investigate the effects of endothelin receptor A and B (ET(A)/ET(B)) antagonism on unclipping. DESIGN AND METHODS: Telemetric devices were implanted in male Wistar 1K1C rats for measurement of conscious MAP. Hypertension was reversed by unclipping with the animal under brief anaesthesia. Seven rats were treated with the ET(A)/ET(B) antagonist, TAK-044 (two doses of 10 mg/kg intraperitoneally in 24 h), and eight rats received its vehicle. In order to investigate whether endothelin receptor antagonism could release RMDH under resting conditions, TAK-044 was administered to telemetered non-clipped intact and chemically renal medullectomized rats (BEA treatment). RESULTS: TAK-044 did not affect resting MAP, urine flow or sodium excretion in 1K1C rats. However, after unclipping, the TAK-044-treated group showed a more marked reduction in MAP during the first 24 h after unclipping (P< 0.01). TAK-044 also reduced urine flow and sodium excretion during the first 8 h after unclipping (P< 0.05). TAK-044 reduced resting MAP (P< 0.05) to a similar extent in intact and BEA rats. CONCLUSIONS: TAK-044 potentiated the reduction in MAP after unclipping, independently of changes in urine flow and sodium excretion. It also reduced MAP in normotensive rats--an effect that was not dependent on an intact renal medulla. Potentiation of the depressor response to unclipping by TAK-044 could be the result of an interaction of endogenous endothelin receptors with renal depressor mechanisms--possibly, the release, actions, or both, of the putative RMDH.

A comparative description of three multipurpose phantoms (MPP) for external audits of photon beams in radiotherapy: the water MPP, the Umeå MPP and the EC MPP.

AIM: To present a technical description and intercomparison of three multipurpose phantoms (MPP) developed for mailed dosimetry checks of therapeutic photon beams in reference and non-reference conditions. MATERIALS: The W-MPP is a water MPP, whereas the Umeâ-MPP, made of perspex (PMMA, Plexiglas), and the EC-MPP, made of polystyrene, are solid MPPs. The W-MPP uses only thermoluminescent dosimeters (TLD) for dosimetry checks, the EC MPP uses film and TLD; the Umeâ phantom uses film and TLD, and offers in addition the possibility for ionization chamber measurements. Either using TLD or films, the MPPs have been designed to check on-axis and off-axis the following irradiation conditions: square and rectangular fields, asymmetric fields, wedged beams, oblique incidence and, for the solid MPPs, also the influence of inhomogeneities. RESULTS AND DISCUSSION: The MPPs have been compared for different aspects going from their dosimetric performance (number of dosimetric parameters that can be checked) to some practical consideration in the use of the different MPPs (set-up time, stability, instruction sheets, etc.). From a comparison between the solid multi-purpose phantoms, it turns out that the EC-MPP is capable of checking the largest number of dosimetric parameters per beam, but has the longest set-up time ( approximately 2 h) per beam according to the users. The Umeå-MPP has a smaller number of set-ups (hence a smaller average time) and also includes some parameters not checked with the EC-MPP (e.g. SSD accuracy). The major drawback however of the Umeå-MPP is considered to be its high density (>1.1 g/cm(3)) which increases the difficulty of the analysis with the treatment planning system. The W-MPP checks the smallest number of parameters, but is the fastest in set-up time, the easiest for mailing, and is water equivalent, which is advantageous for the TPS checks. The major drawback of this MPP is however the inability to check complete dose distribution (film) or inhomogeneities.

Computer-supported identification and intervention for diabetic patients at risk for amputation.

We used the fully automated medical record system at Kaiser Permanente of Ohio to direct appropriate interventions to diabetic patients at risk for amputation. The computer identified all patients with a diagnosis of diabetes, reminded physicians, at the moment of care, of the need to enter the patient's risk status for amputation, and kept track of patients at medium or high risk for amputation who were due for an evaluation with education in the podiatry department. Two years and four months after activation of this reminder system, the risk level had been determined for 76% of the diabetic population (n = 10,000), and two thirds of those at medium or high risk had received the appropriate intervention. In patients in the medium and high risk groups, the risk ratio for amputation was 17.5.

Assessment of high and low contrast visual acuity after photorefractive keratectomy for myopia.

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.

The outcome of reoperation following photorefractive keratectomy.

PURPOSE: The aim of this study was to assess the outcome of reoperation following photorefractive keratectomy related to different techniques. MATERIAL AND METHODS: 265 retreated eyes were divided into 5 groups; low to moderate myopia, high myopia, enlargement, abrasion, and non-compliance. The low to moderate group was further subdivided into 5 categories based on the surgical approach of the reoperation. Outcomes were compared at 12 months after reoperation. RESULTS: There was no statistically significant difference in the median refraction prior to initial PRK, before reoperation, and after reoperation between the 5 categories 66%, of all reoperated patients achieved an uncorrected visual acuity of 0.5 or better after 12 months. 72% had a postoperative refraction between +/- 1 diopter. The other 4 groups were not statistically analyzed due to the wide variety of patients included and non-compliance. CONCLUSION: In low to moderate myopes, approximately 97% achieve uncorrected visual acuity of 0.5 or better following PRK, including one reoperation.