Biomedical subjects

Berthold Seitz

Publications and source records attributed to Berthold Seitz.

At least 37 records · Page 2Linked to original sources

PubMed2005

Long-term outcome of excimer laser phototherapeutic keratectomy for treatment of Salzmann's nodular degeneration.

PURPOSE: To describe the technique and evaluate the long-term success of excimer laser phototherapeutic keratectomy (PTK) for treatment of Salzmann's nodular degeneration. SETTING: Department of Ophthalmology, University of Erlangen-Nürnberg, Erlangen, Germany. METHODS: This retrospective study comprised 22 eyes of 14 patients who consecutively had PTK for superficial corneal opacities in Salzmann's nodular degeneration between January 1990 and November 2003. In all cases, the nodules and as much pannus tissue as possible were removed with a hockey knife. Afterward, the laser ablation (MEL 60 or 70, Carl Zeiss-Meditec) was performed with repeated application of masking fluid to remove further scar tissue and smooth the surface. Intended depth of laser ablation ranged from 10 to 100 microm (mean: 41 microm +/- 43 [SD]). RESULTS: In 86% of eyes, visual acuity improved after PTK, from 0.4 +/- 0.2 preoperatively to 0.7 +/- 0.3 postoperatively. The mean myopic shift was 1.5 +/- 0.7 diopters [D]. Median refractive cylinder changed from 1.0 D preoperatively to 0.7 D postoperatively. The median surface regularity index/surface asymmetry index (SRI/SAI) of the TMS-1 topography analysis system (Tomey) decreased from 2.0/1.6 preoperatively to 1.2/1.2 postoperatively. In 4 (18%) of 22 eyes, a recurrence had to be treated by repeat PTK during a mean follow-up of 2.0 +/- 1.8 years. CONCLUSIONS: Results indicate that PTK is an effective and safe procedure for treatment of Salzmann's nodular degeneration. Laser ablation should be combined with prior mechanical removal of nodules and excessive pannus tissue.

Adult↗

PubMed2005

Delayed healing of corneal epithelium after phototherapeutic keratectomy for lattice dystrophy.

PURPOSE: To evaluate the time period necessary for complete epithelial healing after phototherapeutic keratectomy (o-PTK) carried out for various superficial corneal opacities. SUBJECTS AND METHOD: A total of 197 eyes were divided into 9 groups: group 1, Cogan dystrophy including recurrences (n = 15); group 2, Reis Bucklers dystrophy including recurrences (n = 12); group 3, granular dystrophy including recurrences (n = 63); group 4, lattice dystrophy including recurrences (n = 19); group 5, macular dystrophy including recurrences (n = 10); group 6, herpetic scars (n = 5); group 7, corneal scars of nonherpetic origin (including scrofulous, traumatic, central keratoconus, post-pterygium surgery) (n = 31); group 8, Salzmann nodular degeneration (n = 22); and group 9, miscellaneous (such as bullous keratopathy, acute chemical burn, corneal degeneration) (n = 20). After o-PTK, patients were examined daily at the slit lamp using fluorescein and blue light. The time period necessary for complete healing of the epithelial defect was compared among these groups. Delayed healing was considered where the epithelium was not closed after 7 days. RESULT: One hundred sixty-one eyes (95%) healed within 7 days. Overall, 63%, 80%, and 85% of epithelial defects were closed within 3, 4, and 5 days, respectively. Out of 9 eyes that had delayed healing, 6 eyes (67%) belonged to lattice dystrophy category. Mean time taken for healing in group 4 (8.6 +/- 8.4 days) was significantly longer than those in group 1 (3.0 +/- 1.5 days, P = 0.009), group 2 (3.7 +/- 3.1 days, P = 0.03), group 3 (3.1 +/- 1.5 days, P = 0.001), group 5 (2.7 +/- 0.8 days, P = 0.01), group 7 (3.6 +/- 2.4 days, P = 0.007), group 8 (3.3 +/- 1.3 days, P = 0.009), and group 9 (3.0 +/- 1.9 days, P = 0.011). CONCLUSION: Eyes with lattice corneal dystrophy suffered from delayed epithelial healing after o-PTK. In addition to adequate counseling, these patients should be followed up closely until complete closure of the epithelium to avoid ulceration, scarring, or even infection. These eyes might need additional treatment such as hyaluronic acid drops, autologous serum drops, simultaneous amniotic membrane patching, or even temporary lateral tarsorrhaphy.

Adolescent↗

PubMed2005

Salzmann's nodular degeneration of the cornea: a review and case series.

Salzmann's nodular degeneration is a rare, noninflammatory, slowly progressive, degenerative condition. Bluish-white nodules raised above the surface of the cornea characterize it. It has usually developed in corneas with a history of phlyctenulosis, trachoma, vernal keratoconjunctivitis, measles, scarlet fever, and various other viral diseases. However, today the majority of cases have been seen without recognized previous keratitis. It is composed of dense irregularly arranged collagen tissue with hyalinization between epithelium and Bowman's layer or beyond. Manual removal, phototherapeutic keratectomy (PTK) with or without the use of topical mitomycin-C, lamellar or penetrating keratoplasty have been used in the treatment of this disease. Salzmann's nodular degeneration does not seem to consist of one clinical entity. In some cases, elevated and pannus-like tissue can be separated easily from the corneal surface leaving Bowman's layer almost untouched. In these eyes, subsequent PTK may be necessary to smooth the surface. Recurrences are rare in these eyes. In contrast, some eyes (often with major peripheral vascularization) are left with deep defects in Bowman's layer and superficial stroma after difficult mechanical removal of nodules. In these eyes, multiple masking/laser ablation procedures are mandatory to acquire a homogenous surface. In our experience, the required laser ablation depth is significantly greater and the best-corrected visual acuity to be expected is reduced in contrast to the eyes with easy removal of the nodules. In these eyes recurrences seem to occur more frequently after treatment. Of 35 eyes documented to have Salzmann's nodular degeneration during the last 15 years in our department, 22 needed PTK treatment. Visual acuity increased from 0.4 to 0.7 on average. As a routine, laser ablation should be combined with previous conventional removal of nodules and excessive pannus tissue. By doing so, lamellar and penetrating keratoplasty techniques are hardly ever required in those eyes.

Cornea↗

PubMed2005

Systemic mycophenolate mofetil avoids immune reactions in penetrating high-risk keratoplasty: preliminary results of an ongoing prospectively randomized multicentre study.

Recently, in a monocentre study mycophenolate mofetil (MMF) was demonstrated to be efficacious and safe in penetrating high-risk keratoplasty. Here, preliminary results of a randomized multicentre trial are presented. To date, 86 of 140 scheduled patients undergoing high-risk penetrating keratoplasty have already been randomized into the two study groups: 48 into the MMF group and 38 into the control group. All 86 patients received fluocortolon 1 mg/kg body weight/day, tapered within 3 weeks, and topical prednisolone acetate 1% tapered within 5 months. MMF was administered at a daily oral dose of 2 x 1000 mg for the first 6 postoperative months. Thereafter, MMF was tapered within 2 weeks. The proportion of grafts with immune reactions and side-effects were the main outcome measures. Within an average follow up of 9.2 +/- 6.6 months two patients developed reversible endothelial immune reactions in the MMF group after cessation of MMF application. In the control group, five reversible and three irreversible immune reactions were observed within an average follow up of 10.1 +/- 7.6 months. According to Kaplan and Meier analysis, the ratio of grafts without immune reactions was estimated 89% 1 year postoperatively in the MMF group, in contrast to only 67% in the control group (P = 0.03; log-rank test). Fifteen patients experienced side-effects, especially gastroenterotoxicity, tachycardia, arthralgia or systemic infections. All attributable side-effects were reversible. Systemic MMF may be an effective and safe immune modulating drug in the prophylaxis of immune reactions after penetrating high-risk keratoplasty.

Adult↗

PubMed2005

Compensation of aniseikonia with toric intraocular lenses and spherocylindrical spectacles.

BACKGROUND AND PURPOSE: Magnification disparity between the two eyes (aniseikonia) is one of the major unresolved problems in modern cataract surgery, potentially degrading binocular visual function or causing diplopia. The purpose of this study is to describe a paraxial computing scheme using 4x4 system matrices to simulate a corrected pseudophakic 'optical system eye' with a meridional magnification that matches the magnification of a given contralateral eye. METHODS: Based on the definition of a centred optical system in the paraxial Gaussian space containing astigmatic surfaces using 4x4 refraction and translation matrices, we derived a methodology for calculating the refractive power and axis of toric intraocular lenses and spherocylindrical spectacle corrections for (i) fully correcting the optical system eye and (ii) realizing an arbitrary meridional magnification by solving a linear equation system. RESULTS: The capabilities of this computing scheme are demonstrated with two examples. In example 1 we calculate a toric lens and a spherocylindrical spectacle correction for compensation of a corneal astigmatism to realize a predefined iso-meridional magnification. In example 2 we first determine the meridional magnification of the contralateral eye, which has been treated with cataract surgery and toric lens implantation, and then we compute the appropriate combination of a fully correcting toric lens and spherocylindrical spectacle refraction, which exactly matches the meridional magnification of the contralateral eye. CONCLUSION: We presented an en bloc matrix based strategy for the calculation of an optical system eye containing an astigmatic cornea, a toric lens implant and a spherocylindrical spectacle correction, where the toric lens and the spherocylindrical spectacle correction are determined to fully correct the system and to realize an arbitrary meridional magnification i.e. to eliminate aniseikonia.

Aniseikonia↗

PubMed2005

Determination of pseudophakic accommodation with translation lenses using Purkinje image analysis.

PURPOSE: To determine pseudophakic accommodation of an accommodating posterior chamber intraocular lens (translation lens) using Purkinje image analysis and linear matrix methods in the paraxial space. METHODS: A 2 x 2 system matrix was defined for each Purkinje image I to IV using refraction, translation and mirror matrices. Image size (m) and axial image position (z) was determined as an example for an off-axis object (a 0.2 m off-axis object located 0.5 m in front of the cornea.). First, our method was applied to the phakic relaxed (emmetropic) and accommodated (6.96 D) Le Grand eye. Secondly, for demonstration of the applicability of the calculation scheme to the pseudophakic eye, we provide a clinical example where we determine the accommodation amplitude of the translation lens (1 CU, HumanOptics, Erlangen, Germany) from photographed Purkinje images in the relaxed and accommodated state. From the biometric data: axial length 23.7 mm, corneal power 43.5, corneal thickness 550 microns, implanted intraocular lens (IOL) with a refractive power of 20.5 D (shape equi-biconvex, refractive index 1.46), and refractive indices of the cornea, aqueous and vitreous from the Le Grand model eye, we calculated the refractive state and the sizes of Purkinje images I and III initiated from two off-axis light sources. RESULTS: For the Le Grand model eye, Purkinje image II (z/m = 3.5850 mm/0.0064) is slightly smaller than and directly in front of image I (z/m = 3.8698 mm/0.0077). Purkinje image III (z/m = 10.6097 mm/0.0151) is nearly double the size of image I and during accommodation it moves from the vitreous into the crystalline lens. Purkinje IV (z/m = 4.3244 mm/-0.0059) is inverted, three quarters the size of image I, lies in the crystalline lens and moves slightly towards the retina. For the pseudophakic eye, pseudophakic accommodation of 1.10 D was calculated from the proportion of distances between both Purkinje images I and III in the relaxed (3.04) and accommodated (2.75) state, which is in contrast to the total subjective accommodation of 2.875 D evaluated with an accommodometer. CONCLUSIONS: We present a straightforward mathematical strategy for calculation of the Purkinje images I-IV. Results of our model calculation resemble the values provided by Le Grand. In addition, this approach yields a simple en bloc scheme for determination of pseudophakic accommodation in pseudophakic eyes with accommodative lenses (translation lenses) using Purkinje image photography.

Accommodation, Ocular↗

PubMed2005

Impact of decentration of astigmatic intra-ocular lenses on the residual refraction after cataract surgery.

PURPOSE: The purpose of this study is to assess the impact of decentration of astigmatic intra-ocular lenses on the residual refraction after cataract surgery, using a computing scheme with 5 x 5 system matrices. METHODS: Based on the definition of an optical system in the paraxial Gaussian space containing astigmatic surfaces without restrictions to coaxiality, we derived a method (using 5 x 5 refraction and translation matrices) for calculating the residual refraction and the compensating prism in the spectacle plane after decentred implantation of thin and thick astigmatic intra-ocular lenses. The 'optical system eye' may contain astigmatic refractive surfaces with their axes at random. RESULTS: The capabilities of this computing scheme are demonstrated with two examples. In example 1 we calculate the residual refraction of a decentred 'thin astigmatic lens' for compensation of corneal astigmatism to achieve a spherical target refraction. In example 2 we compute the residual refraction after implantation of a 'thick astigmatic lens', where the spherical and cylindrical power as well as the implantation axis of the lens do not fully match the pre-operative recommendations and the lens is decentred relative to the optical axis. For both examples, we derive the residual prismatic effect in the spectacle plane and the lateral displacement of a ray exiting the spectacle correction when starting coaxially at the retina. CONCLUSIONS: We have presented an en bloc matrix-based strategy for the calculation of the residual spherocylindrical refraction at the spectacle plane after implantation of a decentred thin or thick astigmatic intra-ocular lens without restrictions to coaxiality. The resulting system matrix is written as a product of 5 x 5 refraction and translation matrices.

Astigmatism↗

PubMed2005

Intraocular lens power prediction for triple procedures in Fuchs' dystrophy using multiple regression analysis.

PURPOSE: To develop a correcting term for intraocular power (IOLP) prediction for penetrating keratoplasty combined with simultaneous extracapsular cataract extraction and posterior chamber lens implantation (triple procedure). METHODS: As part of a prospective clinical study, triple procedures were performed in 42 eyes with Fuchs' dystrophy. Only eyes with readable preoperative K-values were included in this study. Differences (DEV) between achieved and target refraction (TR) depending on the values of the theoretical-optical formula according to HAIGIS were investigated using multiple regression analysis in a linear anova model: DEV = a + b CP + c AL + d IOLP + e TR. CP represents central corneal power, AL represents axial length. RESULTS: Spherical equivalent after suture removal was - 1.39 +/- 2.86 D (TR: - 1.64 +/- 1.72 D). A multiple regression formula was developed for correction of conventionally calculated IOL power. CP (b = - 1.391, p = 0.028), AL (c = - 4.733, p = 0.007), IOLP (d = - 1.301, p = 0.009) and TR (e = - 1.804, p = 0.005) correlated significantly with DEV (a = 198.684). CONCLUSION: Proposed correcting multiple regression formula for IOL power prediction may help to improve the postoperative refractive outcome in patients undergoing triple procedures.

Adult↗

PubMed2004

Impact of phototherapeutic keratectomy on the outcome of subsequent penetrating keratoplasty in patients with stromal corneal dystrophies.

PURPOSE: To examine the impact of previous phototherapeutic keratectomy (PTK) on the outcome of subsequent penetrating keratoplasty (PK) in patients with stromal corneal dystrophies. DESIGN: Retrospective, cross-sectional, clinical single-center study. METHODS PATIENT POPULATION: Fifteen patients (21 eyes) age 39.9 +/- 11.4 years. INCLUSION CRITERIA: Primary homologous PK performed in phakic patients with granular or macular dystrophy; no use of combined surgical procedures; defined graft size and technique. The study group comprised eight eyes of five patients, PK performed 3.7 +/- 2.3 years after PTK. The control group (no previous PTK) comprised 13 eyes of 10 patients. In both groups, 38% had granular and 62% had macular dystrophy. Intervention Procedures: Phototherapeutic keratectomy was performed using a 193 nm excimer laser. All PKs were also performed using this laser, with trephination using a metal mask. Subjective refractometry (trial lenses), standard keratometry (Zeiss ophthalmometer), and corneal topography (Tomey TMS-1) were performed preoperatively, 6 months after PK, and after first and second suture removal (1.1 +/- 0.2 years; 1.6 +/- 0.2 years). MAIN OUTCOME MEASURES: Keratometric, topographic net astigmatism, and refractive cylinder; keratometric and topographic central power; best-corrected visual acuity (BCVA); surface regularity index (SRI), surface asymmetry index (SAI), potential visual acuity (PVA). RESULTS: Refractive power and astigmatism, BCVA, and PVA values did not differ significantly between the two groups at any time-point; SRI tended to be better in the study group after first suture removal (P =.05). CONCLUSION: Preceding PTK does not appear to impair the outcome of subsequent penetrating keratoplasty in stromal corneal dystrophy patients.

Adult↗

PubMed2004

Comparison of 6-month results of implantation of the 1CU accommodative intraocular lens with conventional intraocular lenses.

OBJECTIVE: To evaluate the clinical results of implantation of the new 1CU accommodative intraocular lens (IOL) in cataract patients and to compare results with those of conventional IOLs. DESIGN: Nonrandomized comparative trial. PARTICIPANTS: Twenty eyes of 20 patients (mean age = 65.8+/-13.3 years) in the 1CU group and 20 eyes of 20 patients (mean age = 67.4+/-11.6 years) in the control group. METHODS: All patients underwent phacoemulsification and IOL implantation. The 1CU accommodative lens was used in 20 eyes, and conventional IOLs (polymethyl methacrylate, hydrophilic or hydrophobic acrylate) were used in the control group. Patients were observed prospectively, and 6-month data were analyzed. MAIN OUTCOME MEASURES: Accommodative ranges determined by 3 different methods (near point, defocusing, and retinoscopy). Secondary outcome measures were (1) increase of anterior chamber depth after topical application of 1% cyclopentolate eyedrops and (2) distance-corrected near visual acuity with Birkhäuser reading charts at 35 cm. RESULTS: We observed a higher accommodative range with all 3 methods (mean = 1.83+/-0.49 vs. 1.16+/-0.27 diopters [D] [near point], 1.85+/-0.43 vs. 0.64+/-0.21 D [defocusing], and 0.98+/-0.55 vs. 0.17+/-0.22 D [retinoscopy]), a larger increase of anterior chamber depth after cyclopentolate eyedrops (mean = 0.42+/-0.18 vs. 0.11+/-0.06 mm), and better distance-corrected near visual acuity (median = 0.4 vs. 0.2) in the 1CU group relative to the control group. All differences between the 2 groups were statistically highly significant (P<0.001). CONCLUSIONS: In the present study, the 1CU accommodative IOL showed increased accommodative range and better near visual acuity than a control group with conventional IOLs. Further research is necessary to confirm these results in masked, randomized, prospective studies and to confirm further the accommodative power of this group of new IOLs.

Accommodation, Ocular↗

PubMed2004

Morphometric analysis of deposits in granular and lattice corneal dystrophy: histopathologic implications for phototherapeutic keratectomy.

OBJECTIVE: To quantify the distribution and size of deposits in granular and lattice corneal dystrophies and to estimate the impact of these findings on the potential benefit of phototherapeutic keratectomy (PTK) as primary treatment in these corneal disorders. METHODS: Central histologic sections of consecutive corneal buttons (34 granular dystrophy specimens of 27 patients (mean age 53 +/- 12 years) and 20 lattice dystrophy specimens of 20 patients (mean age 50 +/- 17 years) obtained from central penetrating keratoplasty were examined by light microscopy using Masson trichrome and Congo Red stains. Localization and anterioposterior diameter of the most superficial, the deepest, and the largest deposits were quantified in the central and the two peripheral thirds of the specimens. Bowman layer status and thickness of the epithelium were recorded. The clear central corneal zone size before and after a hypothetical superficial PTK (100-microm ablation) was calculated. RESULTS: Central deposits in granular dystrophy were mostly superficial (mean distance from the epithelium 28 +/- 19 microm) and associated with Bowman layer and epithelial changes. In lattice dystrophy, deposits were mostly midstromal (mean distance from the epithelium 79 +/- 54 microm, P < 0.001) with a larger scatter, showing minor superficial involvement. After a fictitious PTK, a significant increase in mean clear central zone was achieved (P = 0.004). This increase in mean clear central zone was more pronounced in granular (from 484 +/- 389 microm to 1451 +/- 1954 microm) than in lattice (from 258 +/- 183 microm to 846 +/- 784 microm) dystrophy (P = 0.004). Deposits were completely removed in 22% of the granular dystrophy samples. In both dystrophies, a clear central "pinhole" greater than 1 mm in diameter was achieved in around one third of corneas. CONCLUSION: According to the histopathologic corneal deposit size and distribution, PTK may be an effective treatment to increase visual acuity in patients with granular dystrophy more than in those with lattice dystrophy, to delay or even avoid penetrating keratoplasty.

Corneal Dystrophies, Hereditary↗

PubMed2004

Difficult lens power calculations.

PURPOSE OF REVIEW: Although cataract extraction seems to be feasible without major technical obstacles, the surgical technique has changed completely, and patients are no longer satisfied with good spectacle-corrected vision but anticipate complete visual rehabilitation after cataract surgery, without correction. To fulfill this desire, toric or accommodative intraocular lenses are of increasing popularity, and the intraocular lens power calculation after keratorefractive surgery has been improved. RECENT FINDINGS: In this review article, we provide an overview of different mathematical strategies of calculating the intraocular lens power with standard formulas and with new algorithms, such as paraxial or numeric ray-tracing. These enhanced techniques may improve the validity of lens power calculation due to reduction of the prediction error, especially in cases with high or excessive corneal astigmatism and after refractive laser surgery. Furthermore, a new calculation scheme for the determination of bitoric eikonic intraocular lenses allows a distortion-free imaging in astigmatic eyes. The biometric determinants for the different formulas and calculation schemes are discussed in detail. SUMMARY: In difficult cases, standard calculation schemes are overemployed and new mathematical algorithms are necessary to adequately address these problems. Ray-tracing algorithms and other complex mathematical computation schemes are of increasing interest and will more and more replace conventional calculation formulas for determination of intraocular lens power.

Accommodation, Ocular↗

PubMed2004

Frequency-doubling perimetry in patients following penetrating keratoplasty.

PURPOSE: Perimetry using a frequency-doubling technique (FDT perimetry) is becoming established as a new diagnostic tool to detect early visual field losses. The aim of this study was to evaluate the diagnostic usefulness of an FDT perimetry protocol (C-20-5) in patients after penetrating keratoplasty (PK) and to assess whether this method is influenced by postoperative corneal topographic changes. METHODS: Thirty-six patients (age 40 +/- 13, median 41 years) following PK and 68 age-matched controls were included in this study. The postoperative interval was 21 +/- 19, median 14 months. Patients with preexisting glaucoma or any postoperative intraocular pressure elevation were excluded. The indications for PK were keratoconus in 82%, Fuchs dystrophy in 15%, and secondary bullous keratopathy in 3%. In 19 patients keratoplasty was performed in 1 eye. FDT perimetry was evaluated in both eyes to judge intraindividual variability. FDT perimetry was done using the screening strategy, which begins testing at the normal 5% probability level. If a stimulus is not detected, further targets are presented. FDT viewfinder and statistics software were used for case-wise recalculation of all missed localized probability levels. RESULTS: Neither mean overall FDT score (0.8 +/- 1.9, median 0.0 versus 0.9 +/-1.0, median 0.0) nor total test time (44 +/- 4.7, median 44 versus 44 +/- 4.2, median 42 seconds) showed significant differences between patients after PK and controls (P = 0.5). There was also no significant difference of mean FDT score between eyes after keratoplasty (0.8 +/- 1.9, median 0.00) and nonoperated contralateral eyes (0.9 +/- 2.0, median 0.00, P = 0.8) in the same patient. No significant correlation between FDT score and visual acuity as well as corneal keratometric astigmatism could be found in patients after PK and in normals (r < 0.2, P = 0.3). In patients after PK, FDT score and examination time were statistically independent of keratometric astigmatism (P = 0.7), topographic astigmatism (P = 0.4), spherical equivalent (P = 0.5), central corneal thickness (P = 0.7), and interval of postoperative follow-up (P = 0.6). CONCLUSIONS: Perimetry using the FDT protocol (C-20-5) seems to be feasible in patients after PK and does not depend on postoperative topographic changes of the cornea. This method allows valid information on visual field abnormality in patients after PK The results indicate that this method may be helpful as a supplement to detect early glaucomatous damage in patients after PK.

Adult↗

PubMed2004

Evaluation of normal corneas using the scanning-slit topography/pachymetry system.

PURPOSE: To obtain anterior and posterior corneal shape, curvature, and thickness of normal human corneas. To provide a semiquantitative analysis of normal topography patterns of the anterior and posterior corneal surfaces. METHODS: Eighty-eight healthy corneas of 44 normal subjects were analyzed using the scanning-slit topography/pachymetry system. Anterior and posterior elevation and mean power (central and steepest spherical and cylindrical) values and pachymetry data were determined. Right eye values were submitted for primary analysis; however, a comparison between right and left eyes was made in addition to test the possible reliability of the system. RESULTS: There was no significant difference between right and left corneas in 28 evaluated parameters, except for anterior central cylindrical (P = 0.005) and steepest cylindrical (P = 0.017) mean power. The anterior central spherical mean power correlated inversely with the posterior central spherical mean power (r = -0.27, P = 0.04), and the anterior steepest spherical mean power value showed inverse correlation with the mean posterior steepest spherical value (r = -0.44, P = 0.001). The mean central thickness of the cornea was 593.7 +/- 54.19 microm at the center and was 578 +/- 50.53 microm at the thinnest point, which was localized in 41% (n = 18) of the cases in the inferotemporal quadrant. An oval-shaped pattern was the most characteristic feature of the anterior and posterior elevation, mean power, and pachymetry maps. CONCLUSION: Orbscan scanning-slit topography seems to be a reliable technique for the evaluation of normal corneas not only for anterior shape and curvature but also for a real pachymetry gradient recording.

Aged↗

PubMed2004

Consideration of the posterior corneal curvature for assessment of corneal power after myopic LASIK.

PURPOSE: To evaluate the effect of a separate measurement of the anterior and posterior corneal surface to calculate the total refractive power of the cornea after myopic laser in situ keratomileusis (LASIK). METHODS: A total of 39 eyes of 21 patients (aged 33 +/- 9 years) were included in this prospective, non-randomized, comparative study. These involved 19 myopic corrections (- 3.5 +/- 1.6 dioptres) and 23 refractive corrections of myopic astigmatism (sphere: - 3.7 +/- 1.6 D, cylinder: - 1.2 +/- 0.4 D). All procedures were accomplished with the Keratom II). Coherent-Schwind excimer laser and the Moria Model One) microkeratome (150 micro m head) at the Medical Education Centre, La Trinidad, Caracas, Venezuela. Subjective refractometry, Bausch & Lomb) keratometry and Orbscan) slit-scanning corneal topography analysis were performed before and 3 months after LASIK. Corneal power was assessed directly using keratometry (K1) and Orbscan videokeratography (T1). Corneal power was calculated using the preoperative keratometric (K2, 'gold standard', clinical history method) or topographic power (T2, clinical history method) and spherical equivalent change. A composite value was derived from the Orbscan anterior and posterior surface power and central pachymetry (T3). RESULTS: Three months postoperatively, corneal power ranged in a descending order from T1 (42.33 +/- 1.78 D), K1 (40.82 +/- 2.20 D), K2 (40.42 +/- 2.36 D), T2 (40.03 +/- 2.51 D) to T3 (38.78 +/- 2.23 D). On average, T1 exceeded the gold standard by 1.9 D and the gold standard exceeded T3 by 1.6 D. K2, T1, T2 and T3 correlated significantly with K1 (r = 0.975, p < 0.001; r = 0.909, p < 0.001; r = 0.963, p < 0.001; r = 0.853, p < 0.001, respectively). The differences T1-K2 (r = - 0.699, p < 0.001) and T3-K2 (r = - 0.499, p = 0.001) correlated highly inversely and K1-K2 correlated borderline inversely (r = - 0.325, p = 0.043) with the intended refractive correction. CONCLUSION: After myopic LASIK, refractive corneal power is overestimated by direct keratometric and especially videokeratoscopic measurements. The higher the intended refractive correction, the greater is this error. A separate measurement of both refractive surfaces of the cornea tends to underestimate but may enhance accuracy of the total refractive corneal power if the history of the patient is unknown.

Adult↗

PubMed2004

Pseudophakic accommodation with translation lenses--dual optic vs mono optic.

PURPOSE: To investigate the pseudophakic accommodation effect in dual and mono optic translation accommodative intraocular lenses (AIOL) using linear matrix methods in the paraxial space. METHODS: Dual (anterior optic of power +32 D linked to a compensatory posterior optic of negative power) and mono lens power was determined in the non-accommodated state using linear geometric optics based on the Gullstrand model eye. The position of the AIOL was calculated from a regression formula. Pseudophakic accommodation was assessed with three systems: (1) forward shift of the mono optic lens, (2) anterior translation of the anterior optic in the dual optic lens system with an unchanged position of the posterior minus lens and (3) symmetrical anterior and posterior translation of the anterior and posterior lens. The Gullstrand model eye was modified by changing the axial length (and proportionally changing the phakic anterior chamber depth) to investigate the accommodative effect in myopic and hyperopic eyes. RESULTS: The dual optic lens system (2) yields a nearly constant accommodation amplitude of 2.4-2.5 D mm(-1) movement over the total range of axial lengths. The mono optic lens (1) provides a higher accommodative effect only in extremely short eyes (high refractive power of the lens), whereas for normal eyes (1.4-1.5 D mm(-1) movement) and for long (myopic) eyes the accommodative effect is much less than the dual optic lens. The dual optic lens system under condition (3) yields less accommodation amplitude compared with the dual optic system under condition (2) over the total range of axial length but provides higher accommodation amplitude compared with the mono optic lens system (1) with axial lengths greater than 22.3 mm (lens power 25.5 D). In the accommodated state, with lens translation of 1 mm, the absolute value of the lateral magnification increases with the refractive power of the mono optic lens (1) and decreases in both dual optic lens systems (under conditions 2 and 3). CONCLUSIONS: A mathematical strategy is presented for calculation of the accommodative effect of mono-optic and dual optic AIOL. The dual optic lens yielded a nearly constant accommodation amplitude of about 2.4-2.5 D mm(-1) translation, whereas the mono optic lens yielded an accommodative response of <2 D mm(-1) translation in long myopic or normal eyes. Only in extremely short eyes is the accommodative amplitude of the mono-optic lens higher than the dual optic lens.

Accommodation, Ocular↗

PubMed2004

Matrix-based calculation scheme for toric intraocular lenses.

BACKGROUND AND PURPOSE: While a number of intraocular lens power prediction formulas are well established for determination of spherical lenses, no common strategy is published for the computation of toric intraocular lenses. The purpose of this study is to describe a paraxial computing scheme using 4 x 4 system matrices to describe the 'optical system eye' containing astigmatic refractive surfaces with their axes at random. METHODS: Based on the definition of a centred optical system in the paraxial Gaussian space containing astigmatic surfaces using 4 x 4 refraction and translation matrices, we derived a methodology for calculating the refractive power of thin and thick toric intraocular lenses by solving a linear equation system. In a second step, we derived a methodology for prediction of the residual spectacle refraction after implantation of any toric lens implant with any orientation. RESULTS: The capabilities of this computing scheme are demonstrated with three examples. In example 1 we calculate a 'thin toric lens' for compensation of a corneal astigmatism to achieve a spherical target refraction. In example 2 we compute a 'thick toric lens', which has to compensate for an oblique corneal astigmatism and rotate the spectacle cylinder to the 'against the rule' position to enhance near vision. In example 3 we predict the residual refraction at the corneal plane after implantation of a thick toric lens, when the cylinder of the lens implant is compensating the corneal cylinder in part and the axis of implantation is not fully aligned with the axis of the corneal astigmatism. CONCLUSION: We present an en bloc matrix-based strategy for the calculation of thick or thin toric intraocular lenses, with the flexibility of crossing an unlimited number of cylinders with restrictions to paraxial optics. The resulting system matrix S is written as a product of 4 x 4 refraction and translation matrices. Residual refraction at the corneal (contact lens) or spectacle plane can be derived by inverting the order of matrices for calculation of the system matrix.

Astigmatism↗

PubMed2004

Computerized calculation scheme for toric intraocular lenses.

BACKGROUND AND PURPOSE: While a number of intraocular lens (IOL) power prediction formulae are well established for determination of spherical lenses, no common strategy has been published for the computation of toric IOLs. The purpose of this study is to describe a paraxial computing scheme for tracing an axial pencil of rays through the 'optical system eye' containing astigmatic refractive surfaces with their axes at random. The capabilities of this computing scheme are demonstrated with clinical examples. METHODS: Based on a schematic model eye with spherocylindric surfaces, we use two alternative notations for description of vergences or prescriptions: (1) standard notation (refraction in both cardinal meridians and axis), and (2) component notation (spherical equivalent and cylindric component in 0 degrees and 45 degrees. Refractive surfaces are added to the vergence in component notation, whereas the transformation of the vergence through media is performed in the standard notation for both cardinal meridians. For calculation of the toric lens implant, a pencil of rays is traced through the spectacle and the cornea to the estimated lens position as well as backwards from the retina to the estimated lens position. For calculation of residual spectacle refraction, a pencil of rays is traced backwards from the retina through the toric lens implant and the cornea to the spectacle plane. RESULTS: In example 1 we calculate a 'thin toric lens' for compensation of a corneal astigmatism to achieve a spherical target refraction. In example 2 we compute a 'thick toric lens', which has to compensate for an oblique corneal astigmatism and rotate the spectacle cylinder to the against the rule position to enhance near vision. In example 3 we estimate the residual refraction at the corneal plane after implantation of a thick toric lens, when the cylinder of the lens implant is compensating the corneal cylinder in part and the axis of implantation is not fully aligned with the axis of the corneal astigmatism. CONCLUSION: This novel mathematical concept for computation of toric IOLs or prediction of the refractive outcome with a toric implant in place is a straightforward, computer-based approach, which may substitute for more or less empirical methods of determining toric IOL implants.

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