Thomas Kohnen

Retrospective comparison of techniques to prevent secondary cataract formation after posterior chamber intraocular lens implantation in infants and children

Purpose: To determine the effect of various methods of managing the posterior capsule and anterior vitreous on the rate of posterior capsule opacification in pediatric eyes implanted with posterior chamber intraocular lenses (PC IOLs). Setting: Cullen Eye Institute, Baylor College of Medicine, Houston, Texas, USA. Methods: We reviewed the charts of 20 eyes of 15 children (aged 1.5 to 2 years) who had primary cataract surgery with PC IOL implantation during the past 5 years. The posterior capsule and anterior vitreous were managed in a variety of ways: In 5 eyes, the posterior capsule was left intact; in 15 eyes, a posterior continuous curvilinear capsulorhexis (PCCC) was performed‐6 with and 9 without anterior vitrectomy; in 8 eyes, posterior optic capture was performed‐3 with and 5 without vitrectomy. The follow‐up ranged from 1 to 4.5 years (mean 2 years). Results: Visually significant secondary cataract developed in the five eyes with intact posterior capsules and in the four eyes that had PCCC without vitrectomy and without posterior optic capture (i.e., the optic was left in the capsular bag). The optical axis remained clear in the six eyes that had PC IOL implantation with vitrectomy (with or without posterior optic capture). Initially, all eyes that had optic capture without vitrectomy also remained clear, but after 6 months, four of five developed opacification. Conclusion: In this series, PCCC with anterior vitrectomy was the only effective method of preventing or delaying secondary cataract formation in infants and children.

Corneal architecture of femtosecond laser and microkeratome flaps imaged by anterior segment optical coherence tomography

PURPOSE: To assess and compare the morphology of laser in situ keratomileusis flaps (LASIK) created by a 60 kHz femtosecond laser and a mechanical microkeratome. SETTING: Department of Ophthalmology, Johann Wolfgang Goethe‐University, Frankfurt am Main, Germany. METHODS: Anterior segment optical coherence tomography (AS‐OCT) (Visante) was used to assess 1 week postoperatively the morphology of 20 LASIK flaps created with the IntraLase femtosecond laser or the Zyoptix XP microkeratome. The flap diameter and flap thickness were assessed at 20 measuring points across each flap. First, the repeatability of the AS‐OCT flap measurement was evaluated. On this basis, the dimensions of femtosecond laser flaps and microkeratome flaps were tested and their regularity, reproducibility, and accuracy compared. RESULTS: The method was approved with a repeatability of maximum 8.9 μm. The femtosecond laser flaps were more regular than the microkeratome flaps (P = .02). The reproducibility of flap morphology was not different in the central 1.0 mm radius area (P = .26); however, the femtosecond laser was significantly more precise than the microkeratome in the peripheral area (P = .001). The mean thickness of the femtosecond laser flap was significantly more accurate than the mean thickness of the microkeratome flap (P = .01), with a mean deviation of +16.9 μm and 40.8 μm, respectively. CONCLUSIONS: The flap architecture created with the femtosecond laser was more regular and accurate than the flap architecture created with the microkeratome.

Detection of Subclinical Keratoconus by Using Corneal Anterior and Posterior Surface Aberrations and Thickness Spatial Profiles

PURPOSE. To assess the suitability of corneal anterior and posterior surface aberrations and thickness profile data for discrimination between eyes with early keratoconus (KC), fellow eyes of eyes with early KC, and normal eyes. METHODS. Thirty-two eyes (group 1) of 25 patients were newly diagnosed with KC; 17 eyes of 17 patients (group 2) were asymptomatic fellow eyes without clinical signs of KC. One hundred twenty-three healthy eyes of 69 patients were negative control eyes (group 3). Zernike coefficients from anterior and posterior surfaces, data from corneal thickness spatial profiles, and output values of discriminant functions based on wavefront and pachymetry data were assessed by receiver operating characteristic (ROC) curve analysis for their usefulness in discriminating between KC (groups 1, 2) eyes and control eyes. RESULTS. Vertical coma (C(3)(-1)) from the anterior surface was the coefficient with the highest ability to discriminate between groups 2 and 3 (area under the ROC curve [A(z)ROC] = 0.980; cutoff, -0.2 microm). For posterior wavefront coefficients and pachymetry data, A(z)ROC values were lower. Constructing discriminant functions from Zernike coefficients increased A(z)ROC values. The function containing first-surface data reached an A(z)ROC of 0.993; the functions containing posterior surface or pachymetry data had lower A(z)ROC values (0.932 and 0.903, respectively). The function with anterior, posterior, and pachymetry data reached an A(z)ROC of 1.0. CONCLUSIONS. Corneal wavefront and pachymetry data enabled highly accurate distinction of eyes with subclinical keratoconus from normal eyes. Posterior aberrations and thickness spatial profile data did not markedly improve discriminative ability over that of anterior wavefront data alone.

Optic neuropathy associated with laser in situ keratomileusis

Purpose: To report 4 cases of optic neuropathy following laser in situ keratomileusis (LASIK). Setting: Tertiary care ophthalmic practices. Methods: In this retrospective observational case series, 4 patients who developed acute visual loss following LASIK are reported. All had clinical evidence of optic neuropathy. Two had optic disc edema and 2 had normal appearing optic discs initially. None of the patients experienced significant visual recovery, and all developed optic atrophy in the affected eye. Results: All patients had evaluations for alternative etiologies of their optic neuropathy, with negative results. All patients were therefore presumed to have experienced an ischemic optic neuropathy following LASIK. Conclusions: Patients who have LASIK may experience an acute anterior or retrobulbar optic neuropathy. The etiology is unknown but may be related to the marked increase in intraocular pressure that occurs during a portion of the procedure.

Evaluation of intraocular pressure with Healon and Healon GV in sutureless cataract surgery with foldable lens implantation

Purpose: To evaluate transient increases in intraocular pressure (IOP) after use of high‐viscosity viscoelastic agents in cataract surgery. Setting: Military Hospital, Ulm, Germany. Methods: In a prospective, randomized study, we evaluated IOP following cataract surgery using two different viscoelastic substances (Healon®, Healon® GV). The viscosity of Healon GV is 10 times higher than that of Healon because of higher concentration and molecular weight. Patients having identical phacoemulsification procedures (sutureless clear corneal tunnel incision with foldable silicone lens implantation) (N = 60) and identical viscoelastic removal were assigned to groups of 15 based on viscoelastic used and removal time (20 or 40 seconds). Intraocular pressure was measured preoperatively and at 6, 24, 36, and 48 hours and 1 month postoperatively. Results: The highest mean IOP elevations in both viscoelastic groups were obtained at 24 hours postoperatively (2.9 mm Hg ± 4.3 [SD] with Healon and 3.3 ± 6.3 mm Hg with Healon GV). There were no statistically significant differences between the two viscoelastics and the two removal times during the entire follow‐up period (unpaired t‐test), but standard deviations were higher in the Healon GV groups at 6 and 24 hours. Two patients in the Healon groups and three in the Healon GV groups required medical treatment for IOP within the first 24 postoperative hours; however, all five patients had an IOP lower than 22 mm Hg on the second postoperative day. Conclusions: Based on postoperative IOP, both viscoelastics can be equally well removed from the anterior chamber. Incidence of high IOP using high‐viscosity hyaluronic acid is minimized by the described removal technique.

Tilt and decentration of spherical and aspheric intraocular lenses: effect on higher-order aberrations.

PURPOSE: To determine the impact of spherical and aspheric foldable intraocular lens (IOL) tilt and decentration on optical quality after cataract surgery in an intraindividual comparative study. SETTING: Department of Ophthalmology, Goethe‐University, Frankfurt am Main, Germany. METHODS: Randomized implantation of a spherical IOL (Sensar AR40e) was performed in 1 eye and of an aspheric IOL with negative spherical aberration (Tecnis Z9000) in the contralateral eye. Three to 4 months postoperatively, the wavefront was measured and higher‐order aberrations (HOAs) were calculated for virtual pupil diameters of 3.5 mm and 6.0 mm. Tilt and decentration of the IOLs were measured using Scheimpflug photography. The tilt and decentration, HOAs, and best corrected visual Strehl ratio of the optical transfer function (BCVSOTF) calculated from the wavefront aberration were compared. The effect of tilt and decentration on HOAs and optical quality was assessed using multiple regression analysis. RESULTS: The mean optic tilt was 2.89 degrees ± 1.46 (SD) for the spherical IOL and 2.85 ± 1.36 degrees for the aspheric IOL. The mean optic decentration was 0.19 ± 0.12 mm and 0.27 ± 0.16 mm, respectively. No significant intergroup differences in IOL tilt or decentration were found. Tilt and decentration did not significantly affect the BCVSOTF with either IOL. CONCLUSIONS: The amounts of tilt and decentration of both IOLs were not large enough to cause deterioration of optical quality. Thus, when IOL tilt and decentration are within normal limits, they do not compromise the correction of spherical aberration by the aspheric IOL.

Effect of Intraocular Lens Asphericity on Quality of Vision after Cataract Removal: An Intraindividual Comparison

PURPOSE To determine the effect of intraocular lens (IOL) asphericity on quality of vision after cataract removal. DESIGN Intraindividual, prospective, randomized clinical trial. PARTICIPANTS Twenty-six cataract patients received 2, one-piece, blue-light-filtering hydrophobic acrylic IOLs each. METHODS One eye was implanted with a spherical (SN60AT, Alcon) and the contralateral eye with an aspheric (SN60WF, Alcon) IOL with -0.2 mum spherical aberration (SA). All trial-specific measurements (corneal topography, wavefront sensing, high-contrast visual acuity [HCVA], contrast sensitivity [CS]) were performed 6 months after surgery. A paired Student t-test or Wilcoxon test was used to check intergroup differences. MAIN OUTCOME MEASURES Absolute values and intraindividual differences (Delta(i)) of corneal and ocular higher order aberrations and best-corrected visual Strehl ratio based on the optical transfer function (BCVSOTF) values for virtual pupil diameters of 3, 4, 5, and 6 mm were computed. Photopic and mesopic HCVA, photopic, and high-mesopic CS as well as high-mesopic disability glare (DG) were measured using the Frankfurt-Freiburg Contrast and Acuity Test System. RESULTS No intergroup difference of demographic data, pupillometry, and corneal aberrations were observed. Coma and trefoil root mean square and SA were significantly lower in the aspheric group resulting in higher BCVSOTF, mesopic HCVA, and photopic and high mesopic CS. All Delta(i) values with exception of photopic HCVA and DG indicated significantly better performance of the aspheric IOL. CONCLUSIONS An aspheric IOL with -0.2 microm SA provide higher quality of vision than spherical IOL in terms of retinal image quality, mesopic HCVA and CS. FINANCIAL DISCLOSURE(S) Proprietary or commercial disclosures may be found after the references.

Comparison of changes in manifest refraction and corneal power after photorefractive keratectomy

PURPOSE To determine which corneal curvature values most closely correlate to change in manifest refraction after excimer laser photorefractive keratectomy. METHODS In a prospective study at the Cullen Eye Institute, excimer laser photorefractive keratectomy was performed on 27 eyes of 27 patients (mean age, 38.07+/-6.65 years). Preoperative refractive errors ranged from -2.25 diopters to -8.75 diopters (mean, -5.74+/-2.09 diopters). Preoperatively and 1 month postoperatively, we determined the spherical equivalent of the subjective manifest refraction (corrected for a 12-mm vertex distance) and measured corneal power using standard keratometry (Bausch & Lomb Keratometer; Rochester, New York) and computerized videokeratography (EyeSys Corneal Analysis System; Premier Laser Systems Inc, Houston, Texas). We collected 15 corneal values: standard keratometry and 14 computerized videokeratography values calculated using the axial, instantaneous, and refractive formulas. All calculations were performed with 1.3375 and 1.376 for the refractive index of the cornea. For each of the corneal values, we subtracted the change in corneal power from the change in manifest refraction and calculated for this difference the means, SDs, correlations, and regressions. RESULTS Mean differences between change in refraction and change in corneal power were lower when for a refractive index of 1.376 than for 1.3375, were lowest for the most central measurement points, and displayed a high SD. A value of 1.408 for the refractive index would be required to optimize the correlation between change in manifest refraction and effective refractive power of the central 3 mm of the cornea. CONCLUSIONS For individual patients who have undergone photorefractive keratectomy, changes in corneal values determined by computerized videokeratography or by standard keratometry do not reliably predict change in manifest refraction.

Hyperopia correction by noncontact holmium : YAG laser thermal keratoplasty. U.S. phase IIA clinical study with 2-year follow-up

PURPOSE This study was performed to determine the long-term efficacy, safety, and stability of noncontact holmium:yttrium aluminum garnet (Ho:YAG) laser thermal keratoplasty (LTK) for correction of low-to-moderate hyperopia. METHODS The authors treated 1 eye each of 28 patients for correction of low-to-moderate hyperopia (up to +3.88 diopters [D] refractive error) using the Sun 1000 Corneal Shaping System (Sunrise Technologies, Inc., Fremont, CA). Treatments were performed with one or two rings of eight spots per ring with centerline diameters of 6 mm (one ring) or 6 and 7 mm (two rings), ten pulses of laser light at 5-Hz pulse repetition frequency, and pulse energies ranging from 208 to 242 mJ. Follow-up was 2 years. RESULTS At 2 years after surgery, uncorrected distance visual acuity was improved by 1 or more lines of Snellen visual acuity in 19 (73%) of 26 of the treated eyes. The mean lines gained was 2.5 +/- 2.2/3.3 +/- 2.7 for one- and two-ring treatment groups, respectively. The mean change in spherical equivalent of the subjective manifest refraction was -0.53 +/- 0.33 D/-1.48 +/- 0.58 D for one- and two-ring treatment groups. Regression between 1 and 2 years was 0.01 D and 0.16 D, respectively. In the one-ring treatment group (18 eyes), 13 eyes (72%) had refractive corrections (range, -0.38 to -1.13 D), and 5 eyes (29%) were unchanged (within +0.25 D) relative to their preoperative measurements. In the two-ring treatment group, all eight eyes (100%) had reductions in their hyperopia (range of corrections, -0.38 to -2.25 D). None of the eyes lost two or more lines of spectacle-corrected distance visual acuity. There were no sight-threatening complications. CONCLUSIONS This initial U.S. clinical study indicates that noncontact laser thermal keratoplasty treatment of low hyperopia is safe and produces modest but persistent corrections with 2-year follow-up. Expanded studies of this treatment method are warranted.

Hyperopia Correction by Noncontact Holmium.YAG Laser Thermal Keratoplasty:Clinical Study with Two-year Follow-up

BACKGROUND Thermal keratoplasty to correct hyperopia has been attempted with nonlaser and laser devices. Problems have included long-term regression and irregular induced astigmatism. The present clinical study was performed to investigate the safety, efficacy, and stability of a noncontact mode of holmium: YAG laser energy delivery and a modified laser thermal keratoplasty treatment procedure for correction of low hyperopia. METHODS Seventeen patients underwent noncontact holmium: YAG laser thermal keratoplasty in their nondominant eyes for correction of hyperopia of up to 3.00 diopters. Treatment parameters included simultaneous delivery of eight holmium: YAG laser spots in a symmetrical octagonal array with a centerline diameter of 6mm, 10 pulses of laser light at 5-Hz pulse repetition frequency, and pulse energies of 159 to 199mJ. Follow-up was 2 years in 15 of 17 patients. RESULTS In the 15 eyes examined at 2 years after surgery, mean uncorrected distance Snellen visual acuity improved from 20/125-1 to 20/50-2. The mean change in spherical equivalent of subjective manifest refraction was -0.79 diopter. Eleven of these 15 eyes (73%) had a mean refractive correction of -1.1 diopters (range, -0.38 to -2.63 diopters); regression between 14 days and 2 years was 0.2 diopter. Four eyes (27%) had no persistent refractive correction (within +/- 0.25 diopter). Mean induced refractive astigmatism was 0.18 diopter. None of the eyes lost two or more lines of spectacle-corrected distance vision. The amount of refractive correction at 2 years after surgery was correlated to the treatment pulse energy and the volume of the opacified corneal tissue observed immediately after treatment. CONCLUSIONS This technique of noncontact laser thermal keratoplasty produced safe, effective, and persistent corrections of low hyperopia in the majority of treated eyes.