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At least 1,351 records · Page 75Linked to original sources
PubMed2003

[Laser-assisted subepithelial keratectomy (LasEk). Review of the current state of knowledge].

This article offers an overview of the current state of knowledge on the results and techniques of the evolving refractive procedure called laser-assisted subepithelial keratectomy (LasEk). A few peer-reviewed published clinical and experimental studies on this new technique are critically debated. Furthermore we discuss the indications for this procedure in comparison to photorefractive keratectomy (PRK) and laser in situ keratomileusis (Lasik) based on the current body of literature and the first author's clinical and scientific personal experience.

Epithelium, Corneal↗
PubMed2004

[Phakic intraocular lenses. Current status and limitations].

Phakic intraocular lenses (PIOLs), which are located closer to the eye's nodal points than the anterior corneal surface, can provide superior optical quality for higher corrections because of retention of normal prolate corneal asphericity and larger effective optical zones. Improvements in the material and design of phakic intraocular lenses and their insertion devices combined with advances in the understanding of the anatomical and physiological interactions of the PIOLs with intraocular structures, have increased safety and efficacy. Safety of these implants over the long term remains a concern, but in several situations PIOLs are the refractive correction of choice. The purpose of this review is to compare the different types of PIOLs regarding outcome and complications. Improvements in imaging technologies should improve the accuracy of ICL sizing and allow more precise prediction of effective lens position with more accurate power calculation. It is important to inform patients that phakic lens surgery only corrects the refractive aspect, and that the refractive error itself as well as the changes by surgery still has the potential for serious complications.

Adolescent↗
PubMed2005

[Corneal wound healing after hyperopic PRK and LASIK].

BACKGROUND: The purpose of this study was to investigate the influence of different postoperative treatments on the wound healing reaction in the anterior stroma after PRK and in the interface area after LASIK. METHODS: Seventy-two corneal buttons of refractively treated rabbit eyes underwent different postoperative eyedrop regimens with antibiotics and/or steroids or additional UV-B irradiation. Morphological and immunohistological investigations were performed 6 months postoperatively by light and transmission electron microscopy. RESULTS: PRK eyes showed interdigitations between the epithelia and the anterior stroma. LASIK-treated eyes showed only minor changes between epithelia and stroma in the incisional region. Only a slight increase in deposits of fibrillar extracellular matrix components were detectable in the interface region. CONCLUSIONS: The clinically important problem of haze after PRK is caused by the interdigitations between epithelia and anterior stroma. The delicate wound healing reactions in the interface region in LASIK eyes corresponded to the clinically visible minor changes in these corneas.

Adrenal Cortex Hormones↗
PubMed2005

[Transient visual decrease after photodynamic therapy].

BACKGROUND: After photodynamic therapy (PDT) some patients complain about a transient decrease of visual acuity during the first postoperative week. PATIENTS AND METHODS: Prior to and at 2 days and 1 week after PDT the following parameters were measured: (1) best corrected visual acuity (VA), (2) changes in refraction, and (3) A scan ultrasound biometry was carried out. Linear and 3-D optical coherence tomography was performed in three cases. A total of 53 PDT treatments were followed-up in 24 patients. RESULTS: Comparison of the pre- and postoperative refraction demonstrated a mean hyperopic shift of +0.35 diopters (dpt) in 43% of treatments (23/53) on the second postoperative day. The hyperopic shift reduced to +0.07 dpt after 1 week. The best corrected VA remained stable or was even better in 68% (36/53) on the second postoperative day. A decrease in VA could be noticed in 32% (17/53) at this time which declined to 23% (12/53) after 1 week. Measurement of the cornea-retina distance using A-scan ultrasound biometry disclosed a mean axial reduction of 0,13 mm at the second postoperative day. This correlates closely with an average hyperopic shift of 0,35 dpt. OCT examination disclosed a transient macular edema in the treated retinal areas. CONCLUSIONS: A transient hyperopic shift can be measured in 43% on the second postoperative day. The subjective decrease in visual acuity measured over the postoperative days was mainly due to a transient hyperopic shift in our patients. OCT findings disclosed a transient macular edema of the retina treated with PDT, which may relate to a hyperopic shift.

Aged↗
PubMed1997

[Does the fundus perimetry determined edge of the blind spot depend on the superficial form of the papilla?].

BACKGROUND: We wanted to find out whether the borders of the blind spot depend on the surface topography of the optic disc and its surrounding area. PATIENTS AND METHODS: We therefore examined ten eyes with parapapillary atrophy adjacent to the temporal side of the disc. Fundus perimetry was performed under direct fundus control using a Rodenstock scanning laser ophthalmoscope. We examined the horizontal meridian of the optic discs in 0.5 degree steps using Goldmann IV-stimuli with 10 different degrees of brightness and the Goldmann stimulus 1, 0 dB (greatest luminance). Six eyes with symmetric, "normal" excavation served as controls. Optic disc topography was measured with the Heidelberg Retina Tomograph (HRT). RESULTS: Stimuli with a large luminance power (Goldmann IV, 4 dB) were seen up to 0.8 degree centrally (i.e., towards the optic disc center) from the temporal edge of the parapapillary atrophy, but up to 1.9 degrees centrally from the nasal optic disc border (P < 0.01). Horizontal HRT section profiles of the optic disc consistently showed prominent nasal disc borders contrasting with a shallow excavation within the temporal parapapillary atrophy. In all six subjects with a normally shaped disc there was no such "nasotemporal asymmetry." CONCLUSIONS: The size of scotomas depends on the surface topography of the tested area. The prominent nasal part of the optic disc appears less "blind" than the shallow temporal part, probably due to more intensive light scattering by the prominent nasal part of the disc.

Adult↗
PubMed2000

[Bilateral simultaneous LASIK. Pro and contra].

Until recently simultaneous bilateral laser in situ keratomileusis (LASIK) was regarded as contraindicated in Germany. However, the procedure was sporadically performed, because it offers patient comfort and is more cost effective than sequential LASIK. Even though the complication rate is below the calculated rate of 0.01%, bilateral complications may have catastrophic effects on the patient. In addition, there is the theoretical disadvantage that the results from the first eye cannot be used for the second eye. However, this effect has yet to be clinically proven.

Adult↗
PubMed1999

Effects of retinal dopamine depletion on the growth of the fish eye.

We investigated the suitability of fishes as animal models to study the involvement of the retinal dopaminergic system in the visually guided control of eye growth (emmetropization). Advantages of such a model system are (i) that all dopaminergic cells in the retina can be destroyed without apparent damage to other neurons, (ii) simple optical design and short depth of field of the eye, and (iii) continuous growth throughout life. Depleting the retina of dopamine in Aequidens pulcher (Cichlidae) had no apparent effect on refractive state, since size and focal length of the eye were reduced by the same amount. Furthermore, imposed defocus was compensated at a normal rate in spite of the absence of retinal dopamine. In A. pulcher, the dopaminergic system of the retina trus appears not to have an essential role in emmetropization. Our results furthermore suggest that in eyes of more complicated optical design, manipulation of the retinal dopaminergic system may lead to unrelated effects indistinguishable from direct interference with emmetropization. A major disadvantage of the fish model was that refractive state of the eye could not be measured accurately in vivo with standard methods.

Animals↗
PubMed2005

The effect of digital measurement software on photodynamic therapy.

BACKGROUND: To investigate the effect of refraction-corrected digital measurement software on photodynamic therapy (PDT) treatment spot size. METHODS: Experimental study using a calibrated Gullstrand-type model eye. The axial length of the model eye was set to different values, ranging from 20 to 31 mm, and the PDT treatment spot sizes obtained from refraction-corrected digital measurement software and manual measurement with a fixed-magnification factor, as well as four different indirect contact laser lenses, were calculated and compared for a treatment spot with a diameter of 4 mm. RESULTS: The maximum deviation from the treating laser spot was +39.6% under myopic and +17.4% under hyperopic conditions when the refraction-corrected digital measurement software was used. The maximum deviation was +14.2% under myopic and +13.3% under hyperopic conditions when the manual measurement with the fixed-magnification factor was used. CONCLUSIONS: The use of refraction-corrected digital measurement software produces a larger deviation from treating laser spot than the use of manual measurement with a fixed-magnification factor. Therefore, refraction-corrected digital measurement software might not be suitable for calculating the recommended PDT treatment spot size in eyes with high refractive errors.

Choroidal Neovascularization↗
PubMed2005

An objective technique to measure the depth-of-focus in free space.

BACKGROUND: Determining the depth-of-focus (DOF) objectively in free space is important, as this provides information regarding the range of clear vision under more natural viewing conditions in which target blur, size, and proximal information, as well as other monocular depth cues, are present. METHODS: The DOF was assessed objectively in free space in young adults [n=20, ages 24.9+/-3.1years: myopes (n=14), emmetropes (n=5), hyperope (n=1)] by monitoring accommodation continuously using the commercially available Power Refractor II (PR II) under monocular viewing conditions. A high-contrast target ( approximately 83%) subtending a mean visual angle of 2.3 deg was placed on an optical bench at 25 cm (4 D) along the line-of-sight of the viewing right eye and was displaced slowly ( approximately 0.1-0.15 D/s) proximally and distally. This target provided blur, size, and proximal information, and other depth cues, as normally found in free space. The first consistent change in steady-state accommodative baseline level reflected one edge of the DOF. The mean dioptric difference between these distal and proximal endpoints was averaged, and this represented the total objective DOF. RESULTS: The group mean total objective DOF (n=20) was +/-0.61+/-0.09 D, with a range from +/-0.46 D to +/-0.81 D. Repeatability was excellent. CONCLUSION: A technique was developed and tested to measure the DOF in free space objectively. Further development of this technique will allow the assessment of blur perception under more complex natural viewing conditions simulating the everyday environment.

Accommodation, Ocular↗
PubMed2006

Online optical coherence pachymetry to evaluate intraoperative ablation parameters in LASIK.

PURPOSE: The ablation of corneal tissue with the excimer laser can be variable and can lead to miscorrections. The purpose of this study was to evaluate intraoperative ablation parameters during laser-assisted in-situ keratomileusis (LASIK) with online optical coherence pachymetry (OCP). METHODS: In a prospective, nonrandomized, comparative clinical study, the ablation parameters were continuously assessed intraoperatively with online OCP (Heidelberg Engineering, Lübeck, Germany) in 45 myopic and 10 hyperopic LASIK treatments. The central intraoperative ablation values were compared with the calculated values of the excimer laser (ESIRIS, Schwind, Germany) and the postoperative refraction. The ablation process and the ablation rate in mum per layer, time, and dioptric correction were evaluated in myopic corrections. RESULTS: In myopic LASIK treatments, a linear ablation process was measured with a mean correlation coefficient of -0.968 +/- 0.04. The intraoperative ablation rate was, on average, 0.59 +/- 0.17 microm per layer, 1.45 +/- 0.48 microm per second, and 24.63 +/- 7.81 microm per corrected diopter. These values were 28.7% to 29.6% higher (P < 0.001) than the calculated values. There was a significant correlation (P < 0.001) for the ablation rate per layer (r = 0.823), per second (r = 0.869), and corrected diopter (r = 0.892), but no correlation (r = 0.21, P = 0.239) between the measured linear ablation process and the postoperative refraction. During hyperopic LASIK treatments, without ablation of the corneal center, there was a significant decrease (P = 0.005) of the stromal thickness by 18.34 +/- 14.13 microm, which corresponded to a mean corneal dehydration rate of 0.27 microm per second. CONCLUSIONS: Online OCP allowed a clinical evaluation of intraoperative ablation parameters in LASIK. Further studies are needed to assess a possible active control of the excimer laser ablation from these continuous values, which could possibly improve current ablation nomograms.

Adult↗
PubMed2001

Influence of refractive correction on peripheral visual field in static perimetry.

PURPOSE: To determine the influence of refractive errors on peripheral visual field thresholds in automated static perimetry. METHODS: In 47 subjects (age 16-49 years), the difference of perimetric thresholds was tested in the peripheral visual field without and with contact lens correction, using a custom-made program (Goldmann stimulus size III) with the automated perimeter Octopus 2000 R. Refractive errors ranged from -16.75 to +12.5 diopters. Sixty-four test locations on three concentric rings between 30 degrees and 50 degrees in 19 hyperopic and 28 myopic eyes were tested. RESULTS: All rings in myopic eyes revealed a significant influence of refraction on the differential light sensitivity in the peripheral visual field. In hyperopic eyes only the inner ring showed a significant influence of refraction. The decrease in sensitivity, measured in dB/diopter, for the myopic inner ring was 0.75; for the myopic middle ring it was 0.46; for the myopic outer ring it was 0.22; and for the hyperopic inner ring it was 0.40. CONCLUSIONS: A significant association between refractive errors and differential light sensitivity exists in the peripheral visual field of myopic eyes. Therefore, contact lens wear is recommended when performing automated perimetry of the peripheral visual field of myopic patients with higher refractive errors.

Adolescent↗
PubMedDate not supplied

Relationship between corneal aberrations and contrast sensitivity after hyperopic laser in situ keratomileusis.

PURPOSE: To evaluate the relationship between corneal aberrations and contrast sensitivity (CS) after hyperopic laser in situ keratomileusis (H-LASIK). METHODS: In 13 patients (13 eyes) who underwent H-LASIK, we measured CS and corneal topography preoperatively and at 1 year postoperatively. Photopic and scotopic CS values were measured at 3, 6, and 12 cycles/degree (cpd) using an MCT-8000 contrast tester. Corneal aberrations were determined from the data on corneal topography using CTView. The corneal high-order aberrations were defined as the sum of the third- and fourth-order aberrations in the 4-mm zone and the sum of the third- to sixth-order aberrations in the 6-mm-zone. RESULTS: Under scotopic conditions at 12 cpd, the changes in CS significantly correlated with changes in the corneal aberrations. Scotopic CS was significantly deteriorated by glare, but photopic CS was not significantly changed. H-LASIK induced a significant increase in corneal aberrations that positively correlated with the amount of correction, regardless of the improvement in logMAR corrected visual acuity. LogMAR corrected visual acuity did not significantly correlate with corneal aberrations. Furthermore, decentration significantly correlated with the changes in the 6-mm zone corneal aberrations. CONCLUSIONS: In eyes after H-LASIK, the changes in scotopic CS significantly correlated with those in the corneal aberrations, which might have resulted from decentration or ablation profiles in H-LASIK and a relatively small optical zone. Further studies will be needed to validate this relationship.

Adult↗