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PubMed1981

Solution characterization of starch nicotinates with different degrees of esterification.

A series of starch-nicotinic acid copolymers with a degree of esterification ranging from about 15% to about 90% was prepared, and the stability in solution of two representative samples of the series was tested. The variation of some physico-chemical characteristics in the series was examined by solubility tests, viscometry and refractometry, and found to be not simply correlatable to the nicotinylation degree.

Esters↗
PubMed1982

Estimation of molecular weights of membrane proteins in the presence of SDS by low-angle laser light scattering combined with high-performance porous silica gel chromatography. Confirmation of the trimer structure of porin of the E. coli outer membrane.

An assessment study was carried out to evaluate the performance of the low-angle laser light-scattering technique combined with high-performance porous silica gel chromatography in the presence of sodium dodecyl sulfate and precision differential refractometry. It was found that the combined technique is highly promising as a reliable method for determining the molecular weight of a membrane protein solubilized by the surfactant. As a test, molecular weights of porin forming the permeability channel of the outer membrane of E. coli B in an oligomeric form were measured before and after heat treatment, which is known to cause dissociation. The results obtained indicate that the porin oligomer is a trimer with stoichiometric composition.

Chromatography, High Pressure Liquid↗
PubMed1983

Determination of molecular weight of membrane proteins by the use of low-angle laser light scattering combined with high-performance gel chromatography in the presence of a non-ionic surfactant.

An assessment study was carried out to evaluate the performance of the low-angle laser light scattering technique combined with high-performance gel chromatography in the presence of a nonionic surfactant, octaethyleneglycol n-dodecyl ether, precision differential refractometry and ultraviolet photometry. It was found that the combined technique is highly promising as a method for the determination of the molecular weight of a membrane protein solubilized by the surfactant. For trial, molecular weights of the following membrane proteins of Escherichia coli, both solubilized in oligomeric forms, were measured; porin that forms the transmembrane diffusion pore in the outer membrane, and lambda-receptor protein that facilitates the diffusion of maltose-maltodextrins across the outer membrane. The result obtained indicates that both porin and lambda-receptor protein exist as trimers in the surfactant solution.

Bacterial Outer Membrane Proteins↗
PubMed1986

A comparison of three methods for determining the concentration of rat urine.

The concentrations of 78 rat urines were compared using osmometry, refractometry and test strips for specific gravity. Test strip specific gravity values are a guide to urine concentration; where small changes of urine concentration are expected, the test strips should not be a replacement for more accurate methods such as osmometry.

Animals↗
PubMed1989

A field lab method to determine urine concentration in small mammals.

1. The concentrations of 136 urine samples from four species of small mammals were compared using osmometry, refractometry and a colorimetric test for urea concentration. 2. To obtain a wide range of concentrations (430-3950 mOsm/kg), urine samples were collected under normal and dehydration conditions. 3. Regression analyses of paired values indicate that measurements of total solids concentration (refractometric method) permit evaluations of urine osmolality and estimations of the concentration of urea with a high degree of confidence.

Animals↗
PubMed1981

Dilatometric, refractometric and viscometric study of lysozyme-cation interaction.

The interaction between hen egg-white lysozyme and Cu(II) or Co(II) cations has been studied by dilatometry, equilibrium dialysis-differential refractometry and viscometry at different metal cation concentrations. Delta V isotherms in copper and cobalt solutions have been obtained from dilatometry. Preferential adsorption parameters and specific viscosity have been determined from refractometric and viscosimetric measurements. It has been observed that this interaction produces structural alterations in lysozyme. The magnitude of these conformational changes depends on the metal ion and protein concentration. The results obtained using the three techniques are in good agreement.

Animals↗
PubMed1997

Assay of synovial fluid parameters: hyaluronan concentration as a potential marker for joint diseases.

Synovial fluids from the knees of patients with degenerative joint disease (n = 29), osteoarthritis (n = 16), diabetic arthropathy (n = 12), gout (n = 7) and acute inflammatory joint disease (n = 7) were investigated by high-performance size-exclusion chromatography combined with multiangle laser light scattering detection and differential refractometry. These data were compared with the viscosities of the same samples measured by rotation viscometry with one low shear rate, as well as with C reactive protein. The median value of the weight-average molecular weight of hyaluronan in synovial fluids, which differed less than the viscosity of these groups, varied between 1.09 x 10(6) g/mol (range 0.849-1.63 x 10(6) g/mol) (acute-inflammatory joint disease) and 1.91 x 10(6) g/mol (range 1.06-3.48 x 10(6) g/mol) (degenerative joint disease). The correlation between viscosity and hyaluronan concentration was much better than between viscosity and weight-average molecular weight. Changes in C reactive protein concentration were correlated with the disease activity. The concentration of hyaluronan was significantly higher in the cases of degenerative joint disease and diabetic arthropathy. These results suggest that synovial fluid concentration of hyaluronan is appropriate as a prognostic value in the evaluation of different kinds of joint diseases.

Biomarkers↗
PubMed1990

Water-soluble proteins do not bind octyl glucoside as judged by molecular sieve chromatographic techniques.

It is well known that the non-ionic detergent octyl glucoside (1-O-n-octyl-beta-D-glucopyranoside) solubilizes biological membrane components. It forms complexes with membrane-spanning proteins by hydrophobic interactions and it forms mixed micelles with membrane lipids. In contrast, non-ionic detergents usually do not bind to water-soluble proteins. According to a recent report, substantial and cooperative binding of octyl glucoside to several water-soluble proteins does occur near the critical micelle concentration. However, data have been obtained that contradict this report. No decrease was found in the elution volumes of five water-soluble proteins on molecular sieve chromatography on two Superose columns in tandem when 35 mM octyl glucoside was included in the eluent. No binding of the detergent to these proteins was observed at 20 or 22.5 mM octyl glucoside on molecular sieve chromatography on a TSK SW guard column as determined by differential refractometry and UV spectrophotometry of the proteins in the absence or presence of octyl glucoside. The experiments were done with the same buffer system and with six of the proteins used in the reported study. It is concluded that, as expected, there is no binding of octyl glucoside to water-soluble proteins above the detection limit (0.1 g detergent/g protein) of the refractometric method. The binding of, on average, 1.3 +/- 0.2 g of detergent per gram of water-soluble protein that was observed at 20 mM octyl glucoside in the reported study is not consistent with the present results.

Chromatography, Gel↗
PubMed2001

Posterior corneal curvature changes after myopic laser in situ keratomileusis.

OBJECTIVE: To assess the posterior corneal power and asphericity changes after myopic laser in situ keratomileusis (LASIK) and to correlate these changes with the amount of correction and the residual stromal bed thickness. DESIGN: Prospective nonrandomized (self-controlled) comparative study. PARTICIPANTS: Fifty-seven eyes of 14 women and 15 men, mean age at the time of surgery 33 +/- 9 (range, 19-53) years with a spherical equivalent (SEQ) of -1.00 to -15.50 (mean, -5.07 +/- 2.81) diopters (DI). INTERVENTION: All procedures were performed with the Keratom II Coherent-Schwind excimer laser and and the Moria Model One microkeratome (150-microm head). Subjective refractometry, Orbscan slit scanning corneal topography analysis and pachymetry were performed before and 3 months after LASIK for myopia (n=35, -1.00 to -15.50 D, mean -4.75 +/- -3.07 D) or myopic astigmatism (n=22, sphere 0.00 to -9.75 D, mean -4.75 +/- 2.36 D; cylinder -0.75 to -3.50 D, mean -1.68 +/- 0.86 D). Intended ablation depth ranged from 12 to 108 (mean, 48 +/- 22) microm. Topographic raw data were decomposed into a set of Zernike polynomials as published in detail previously, and parameters potentially indicative for detection of a "mild keratectasia" were derived. MAIN OUTCOME MEASURES: Posterior central corneal power and asphericity before and after LASIK were compared, and changes of these variables were correlated with the SEQ change (deltaSEQ)and the residual corneal bed thickness RBT). RESULTS: The mean RBT after LASIK was 280 +/- 42 microm. Overall, change of posterior power (-6.28 +/- 0.22 D/ -6.39 +/- 0.23 D, P=0.02) was statistically significant and change of asphericity (0.98 +/-0.07/1.14 +/- -.20, P<0.0001) was highly significant. In eyes with RBT < or =250 microm, the average change of posterior central power (-0.20 +/- 0.10 D vs. -0.08 +/- 0.18 D) was significantly greater than in eyes with RBT >250 microm (P=0.003). The change of posterior corneal power correlated significantly with deltaSEQ (P=0.004) and the RBT (P=0.002). CONCLUSIONS: Increased negative keratometric diopters and oblate asphericity of the posterior corneal curvature suggest that mild "keratectesia" of the cornea may be common early after LASIK. Further stuudies with longer follow-up are required to clarify whether this biomechanical deformation is progressive and whether a residual bed thickness of >250 microm can completely prevent it.

Adult↗
PubMed1997

Optic disc shape, corneal astigmatism, and amblyopia.

OBJECTIVE: The cornea and the optic disc form the anteroposterior opening of the sclera. This study evaluated whether an abnormal shape of the optic disc is associated with an abnormal configuration of the cornea measured as corneal astigmatism. DESIGN: The study design was a cross-sectional one. PARTICIPANTS: The study included 882 subjects (430 women, 452 men) with a mean age of 45.9 +/- 13.6 years (mean +/- standard deviation; range, 8-87 years) and a mean refractive error of -1.09 +/- 2.76 diopters (range, -21.0 diopters to +7.0 diopters). INTERVENTION: Corneal astigmatism was determined by keratometry, and the optic disc was analyzed morphometrically by planimetric evaluation of optic disc photographs. MAIN OUTCOME MEASURES: Corneal astigmatism, ratio of minimal-to-maximal disc diameter, and optic disc form factor were measured. RESULTS: The amount of corneal astigmatism was significantly (P < 0.001) correlated with an increasingly elongated optic disc shape. Corneal astigmatism was significantly (P < 0.01) higher in eyes with tilted discs. It was significantly (P = 0.006) smaller in eyes with an almost circular disc shape. Amblyopia was significantly (P < 0.05) associated with an elongated optic disc shape and high corneal astigmatism. The axis of corneal astigmatism was correlated with the orientation of the longest disc diameter. The optic disc was significantly (P < 0.05; chi-square test) more often horizontally oval in eyes with a steeper horizontal corneal meridian than in eyes with a steeper vertical corneal meridian. Correspondingly, the disc was significantly (P < 0.05) more often vertically oval in eyes with a steeper vertical corneal meridian than in eyes with a steeper horizontal corneal meridian. CONCLUSIONS: An abnormal optic disc shape is significantly correlated with corneal astigmatism. Especially in young children, if an abnormal optic disc shape is found on routine ophthalmoscopy, refractometry should be performed to rule out corneal astigmatism and to prevent amblyopia. The direction of the longest optic disc diameter can indicate the axis of corneal astigmatism.

Adolescent↗
PubMed1999

Underestimation of intraocular lens power for cataract surgery after myopic photorefractive keratectomy.

OBJECTIVE: To assess the validity of corneal power measurement and standard intraocular lens power (IOLP) calculation after photorefractive keratectomy (PRK). DESIGN: Nonrandomized, prospective, cross-sectional, clinical study. PARTICIPANTS: A total of 31 eyes of 21 females and 10 males with a mean age at the time of surgery of 32.3 +/- 6.6 years (range, 24.4-49.5 years). INTERVENTION: Subjective refractometry, standard keratometry, TMS-1 corneal topography analysis, and pachymetry were performed before and 15.8 +/- 10.4 months after PRK for myopia (n = 24, -1 .5 to -8.0 diopters [D], mean -5.4 +/- 1.9 D) or myopic astigmatism (n = 7, sphere -2.0 to -7.5 D, mean -4.4 +/- 1.9 D; cylinder -1.0 to -3.0 D, mean -1.9 +/- 0.7 D). The IOLP calculations were done using two different formulas (SRK/T and HAIGIS). MAIN OUTCOME MEASURES: Keratometric power (K) and topographic simulated keratometric power (TOPO) as measured (Kmeas, TOPOmeas) and as calculated according to the change of power of the anterior corneal surface or according to the spherical equivalent change after PRK (Kcalc, TOPOcalc), IOLP for emmetropia, and postoperative ametropia for calculated corneal powers were assessed in a model. RESULTS: After PRK, mean Kmeas and TOPOmeas were significantly greater (0.4-1.4 D, maximum 3.3 D) than mean KRcalc and TOPOcalc (P < 0.0001). On average, the relative flattening of the cornea after PRK was underestimated by 14% to 30% (maximum, 83%) depending on the method of calculation. The mean theoretical IOLP after PRK ranged from + 17.4 D (SRK/T, TOPOmeas) to +20.9 D (HAIGIS, Kcalc) depending on the calculation method for corneal power and IOLP calculation formula used. For both formulas, IOLP values using keratometric readings were significantly higher (>1 D) than IOLP values using topographic readings (P < 0.0001). The theoretically induced mean refractive error after cataract surgery ranged from +0.4 to +1.4 (maximum, +3.1) D. Corneal power overestimation and IOLP underestimation correlated significantly with the spherical equivalent change after PRK (P = 0.001) and the intended ablation depth during PRK (P = 0.004). CONCLUSIONS: To avoid underestimation of IOLP and hyperopia after cataract surgery following PRK, measured corneal power values must be corrected. The calculation method using spherical equivalent change of refraction at the corneal plane seems to be the most appropriate method. In comparison with this method, direct power measurements underestimate corneal flattening after PRK by 24% on average. Use of conventional topography analysis seems to increase the risk of error. However, because this study is retrospective and theoretical, there is still a need for a large prospective investigation to validate the authors' findings.

Adult↗
PubMed1999

Nonmechanical corneal trephination with the excimer laser improves outcome after penetrating keratoplasty.

OBJECTIVE: To assess the impact of nonmechanical trephination on the outcome after penetrating keratoplasty (PK). DESIGN: Prospective, randomized, cross-sectional, clinical, single-center study. PATIENTS: A total of 179 eyes of 76 females and 103 males, mean age at the time of surgery 50.6 +/- 18.5 (range, 15-83) years. Inclusion criteria were (1) time interval from October 1992 to December 1997; (2) one surgeon (GOHN); (3) primary central PK; (4) Fuchs dystrophy (diameter, 7.5 mm) or keratoconus (diameter, 8.0 mm); (5) graft oversize, 0.1 mm; (6) no previous intraocular surgery; and (7) 16-bite double-running diagonal suture. INTERVENTION: In a randomized fashion, eyes were assigned either to trephination with the 193-nm Meditec excimer laser (manually guided beam in patients, automated rotation device of artificial anterior chamber in donors) along metal masks with eight orientation teeth/notches (EXCIMER: 53 keratoconus, 35 Fuchs dystrophy; mean follow-up, 37 +/- 16 months) or with a hand-held motor trephine (Microkeratron; Geuder) ( CONTROL: 53 keratoconus, 38 Fuchs dystrophy; mean follow-up, 38 +/- 14 months). Subjective refractometry (trial glasses), standard keratometry (Zeiss), and corneal topography analysis (TMS-1; Tomey) were performed before surgery, before removal of the first suture (15.2 +/- 4.2 months), and after removal of the second suture (21.4 +/- 5.6 months). MAIN OUTCOME MEASURES: Keratometric and topographic net astigmatism as well as refractive cylinder; keratometric and topographic central power; best-corrected visual acuity (VA); surface regularity index (SRI), surface asymmetry index (SAI), and potential visual acuity (PVA) of the TMS-1. RESULTS: Before suture removal, mean refractive/keratometric/topographic astigmatism did not differ significantly between EXCIMER (2.5 +/- 1.8 diopters [D]/3.4 +/- 2.8 D/4.7 +/- 3.1 D) and CONTROL groups (3.0 +/- 1.8 D/3.7 +/- 2.4 D/4.3 +/- 2.1 D). After suture removal, respective values were significantly lower in the EXCIMER group (2.8 +/- 2.0 D/3.0 +/- 2.1 D/3.8 +/- 2.6 D) than in the CONTROL group (4.2 +/- 2.4 D/6.1 +/- 2.7 D/6.7 +/- 3.1 D) (P < 0.0009). In the EXCIMER versus CONTROL group, mean VA increased from 20/100 versus 20/111 (P > 0.05) before surgery, to 20/31 versus 20/38 before (P = 0.001) and to 20/28 versus 20/39 (P < 0.00001) after suture removal. Mean spherical equivalent was significantly less myopic in the EXCIMER group before (-0.9 +/- 3.6 D vs. -2.6 +/- 3.4 D) (P = 0.01) and after suture removal (-1.4 +/- 3.1 D vs. -2.4 +/- 3.5 D) (P = 0.02). Mean SRI (P = 0.04) and PVA (P = 0.007) were significantly more favorable in the EXCIMER versus CONTROL group after suture removal (0.91 +/- 0.45 and 0.82 +/- 0.15 vs. 1.05 +/- 0.46 and 0.73 +/- 0.18). CONCLUSIONS: Postkeratoplasty results seem to be superior using nonmechanical excimer laser trephination. Thus, this methodology is recommended as the procedure of first choice in avascular corneal pathologies requiring PK.

Adolescent↗
PubMed1999

Nonvitrectomizing vitreous surgery: a strategy to prevent postoperative nuclear sclerosis.

OBJECTIVE: The development or progression of postoperative nuclear sclerosis is the most common complication of successful vitrectomy in elderly patients. The authors treated idiopathic epimacular proliferation (EMP) with nonvitrectomizing vitreous surgery in an attempt to prevent postoperative nuclear sclerosis. DESIGN: Prospective, nonrandomized, comparative case series. PARTICIPANTS: The authors surgically removed membranes from the sensory retina in 21 eyes of 21 patients with EMP. INTERVENTION: Neither intravitreal infusion nor vitrectomy of any kind was performed during the procedure. The peeled membrane was left floating in the vitreous cavity in 11 (group 1) eyes and removed in 10 eyes (group 2). Nonoperated fellow eyes served as controls. MAIN OUTCOME MEASURES: Visual acuity, slit-lamp and/or Scheimpflug photography, and refractometry were performed pre- and postoperatively to evaluate changes in the degree of lenticular opacity. RESULTS: There was no difference in the rate of development or progression of nuclear sclerosis or the degree of myopic shift between operated and control eyes during the postoperative follow-up period (mean, 9.7 months). No serious complications were noted. There was no difference in postoperative course between patients in the two operative groups. CONCLUSIONS: Although interpretation of the results of this study is limited due to its small size and short follow-up, nonvitrectomizing vitreous surgery seems to decrease the postoperative development or progression of nuclear sclerosis in patients with idiopathic EMP.

Aged↗
PubMed1984

Macroscale high-performance liquid chromatographic separation and instrumental identification of components of diethylaminoethyl murine epidermal growth factor.

Murine epidermal growth factor (m-EGF), a polypeptide produced as a chromatographically homogeneous peak on diethylaminoethyl (DEAE) cellulose by the method of Savage and co-workers, and characterised as a single compound, has been shown by ourselves and several other groups to be a mixture. The present contribution extends our previously reported work and discusses the separation of this material, termed DEAE-m-EGF, into its components by preparative ion-pair reversed-phase high-performance liquid chromatography (RP-HPLC) on C18 mu Bondapak in quantities up to 50 mg per run. Isocratic elution was used and the mobile phase was acetonitrile-water (26:74, v/v, 0.04 M in triethylamine acetate); pH was 5.6, temperature 40 degrees C, and detection was by ultraviolet absorption at 254 nm, and (for some runs) by differential refractometry. Seven significant peaks, four major, three minor, were detected. Of the major peaks, two designated alpha- and beta-EGF, constituted 70% of the total mass and were the most important to our work. Each of the eluted peaks was recovered by lyophilisation, and this product checked for homogeneity by ion-pair RP-HPLC on a C18 mu Bondapak analytical column, with ultraviolet detection as before. All recovered peaks were found to be homogeneous by this criterion. These chromatographically homogeneous compounds were investigated by modern physicochemical instrumentation to determine their structure. The molecular weight of each of the species was determined by fast atom bombardment mass spectrometry. High-field proton magnetic resonance at 270 MHz provided structural and conformational information. Polarimetry and ultraviolet absorption were also used to characterise the compound. alpha-EGF, for example, had a molecular weight of 6040 corresponding to the 53 amino acid residue peptide previously designated EGF; beta-EGF had a molecular weight of 5930. This molecular weight differential of 110 suggested the hypothesis that beta-EGF was a 52 residue peptide corresponding to alpha-EGF minus the terminal asparagine at position 1. Proton magnetic resonance difference spectroscopy (beta spectrum subtracted from alpha) provided powerful confirmatory evidence for this hypothesis. All materials recovered from RP-HPLC were tested in the sheep and found to retain their biological activity.

Animals↗
PubMed1978

Interaction of ribonuclease A with aqueous 2-methyl-2,4-pentanediol at pH 5.8.

The interactions between ribonuclease A and solvent components in aqueous 2-methyl-2,4-pentanediol (MPD) have been investigated by differential refractometry and light scattering at pH 5.8, i.e., conditions similar to those used to crystallize the protein from this solvent system. Application of multicomponent thermodynamic theory shows that, at all solvent compositions up to 50% (v/v) MPD, the protein is preferentially hydrated; i.e., addition of ribonuclease to the mixed solvent leads to an increase in the chemical potential of MPD. This unfavorable thermodynamic interaction leads to phase separation, probably caused by local salting out of the MPD by the charges on the surface of the protein molecule. A parallel examination by circular dichroism (CD) has shown that the CD spectrum of ribonuclease in 50% MPD is indistinguishable from that in dilute buffer.

Animals↗
PubMed1976

Proton-dependent dissociation equilibrium of hemoglobin. 1. A 700-nanometer light-scattering study on horse methemoglobin in the pH range 4.8 to 7.2.

The effect of proton concentration upon the subunit dissociation of horse methemoglobin has been investigated at two ionic strengths by light scattering photometry at 700 nm. Differential refractometry revealed a slight but systematic decrease of the specific refractive index increment with decreasing protein concentration for solutions in dialytic equilibrium with the solvent. In the pH range 4.8-7.2 the dissociation can be described by a simple equilibrium between tetramers and dimers. The dissociation constant Kd of the met derivative is found to be very similar to those of the O2- and CO-ligated states. From the slope of a plot of log Kd vs. pH, the number of protons bound is n = 1.3 +/- 0.1 resulting from an increase in the pK values of two groups upon dissociation. These two groups must be identical because the dissociation is symmetrical.

Animals↗
PubMed2002

Refractive change during hyperbaric oxygen therapy. A clinical trial including ultrasound oculometry.

PURPOSE: To record changes in refraction and refractive parameters associated with a standard hyperbaric oxygen treatment protocol consisting of a 95 min session at > 95% oxygen at 2.5 atmospheres (ATA) given daily Monday to Friday, to a total of 30 sessions. PATIENTS AND METHODS: Seventeen of the 26 patients included were able to attend for ophthalmic assessment at time zero (to) and after 20 treatments (t20). Thirteen patients also had a post-treatment follow-up. Most patients were being treated for osteoradionecrosis after radiotherapy of ENT cancers, and drop-outs for the eye exam were common. Refraction was determined subjectively and by refractometry, before and after tropicamide 1% eyedrops. Refractive parameters were assessed by keratometry and by A-scan axial ultrasound measurement. RESULTS: Results are given for the 17 patients with to and t20 assessments. The induced refractive change ranged from 0 to 1.5 D. When observed, refractive changes were myopic in nature. The shift averaged 0.58 D according to the refractometer and 0.49 D as subjectively assessed, with corresponding median change values being 0.62 and 0.39 D. The differences between 0 D and these values, although small, were statistically highly significant. CONCLUSIONS: The refractive changes associated with hyperbaric oxygen therapy were smaller than the literature had led us to expect. No significant change in axial eye length measurements was found, and keratometry readings reflected only minimal change, although this was statistically significant on a 0.05 level. Therefore it is most likely that lens changes, whether in internal refractive indices or curvatures, accounted for the transitory shift towards more myopic/less hyperopic values.

Adult↗
PubMed2001

[Effect of pupil size on longitudinal focal distribution after photorefractive keratectomy ].

BACKGROUND: Optical aberrations induced by the transition zone of a myopic photorefractive keratectomy (PRK) may degrade the image quality. The subjectively evaluated visual acuity and contrast sensitivity may be reduced significantly especially with mydriasis. The purpose of this study was to calculate the image forming properties of the eye using raytracing techniques of a spot light source based on topographic height data of a scanning slit videokeratoscope. METHODS: Refractive surfaces were calculated from raw height data sets of the anterior and posterior corneal surface measurements (Orbscan, Orbtec, USA). The characteristics of the residual refractive surfaces were derived from Navarro's eye model. The focal distance was calculated using the exact raytracing calculation. Point spread function was determined at the focal plane and at 5 (delta = 0.2 mm) parafocal planes in front of and behind the focal distance in accordance to the pupil diameter (2, 3 and 6 mm). The algorithm was applied to 11 selected eyes (6 left, 5 right) of 8 patients before and after PRK with myopia (n = 6) and myopic astigmatism (n = 5). RESULTS: Before PRK the focal distance did not decrease significantly with increasing pupil size (2 to 6 mm), but decreased significantly after PRK (-0.41 +/- 0.12 mm, p = 0.02). Preoperatively, the variance of the point spread function did not differ significantly between a 2 mm (0.046 +/- 0.015 mm) and a 6 mm (0.055 +/- 0.021 mm) pupil size but was affected significantly by the pupil size postoperatively (2 mm: 0.049 +/- 0.018 mm, 6 mm: 0.096 +/- 0.045 mm, p = 0.04). CONCLUSIONS: Raytracing of corneal topography height data based on refined eye models with the option of calculation of the focus has the potential of tracing the optical resolution of the eye as a function of the pupil size. Due to of the altered surface geometry of the cornea after myopic PRK, both the variance of the point-spread function and the depth of focus increase with pupil size. This may be an explanation for impaired subjective refractometry and reduced contrast sensitivity of the patient after conventional keratorefractive surgery.

Adult↗