Outcome of Bleb Revision With Autologous Conjunctival Graft Alone or Combined With Donor Scleral Graft for Late-onset Bleb Leakage With Hypotony After Standard Trabeculectomy With Mitomycin C.

PRCIS: Treatment of leakage with ocular hypotony after trabeculectomy with mitomycin C (MMC) can be safely achieved through conjunctival patch alone or combined with donor scleral graft in cases of melted underlying sclera. PURPOSE: To report outcomes of 2 surgical approaches for treating ocular hypotony in eyes with blebs with late-onset leakage after standard trabeculectomy with MMC. METHODS: Thirty consecutive cases with bleb leakage and hypotony underwent bleb revision surgery between 2009 and 2014 by the same surgeon (J.W.) at the Department of Ophthalmology of the Mainz University Medical Center, Germany. In 18 patients, an autologous conjunctival patch graft was applied. In 12 patients, the underlying sclera was found melted and an additional scleral donor graft was sutured in place. The authors analyzed intraocular pressure, visual acuity, and optical coherence tomography of the macula preoperatively at 1 day, 1 week, 4 weeks, and 6 months after surgery. RESULTS: The mean IOP was 6.2±3.5 mm Hg preoperatively and 21.7±16.4 mm Hg at 1 day, 13.7±6.7 at 1 week, 13.1±5.1 mm Hg at 4 weeks, and 12.1±4.7 mm Hg at 6 months after surgery. Visual acuity (logMar) increased from 0.57±0.49 preoperatively to 0.49±0.40 at 6 months. Optical coherence tomography showed flattening of macular folds that were present before treatment. No serious adverse event was reported. CONCLUSIONS: This revision technique with conjunctival patch and/or additional donor scleral graft is an effective and safe method for treating late bleb leakage and hypotony maculopathy after trabeculectomy with MMC.

Suture Removal After Trabeculectomy With Fornix-based Conjunctival Flap Leads to Faster Visual Recovery but Not Reduced Astigmatism.

PRéCIS:: The closing limbal suture after trabeculectomy with a fornix-based conjunctival flap plays no critical role in the development of corneal astigmatism and intraocular pressure (IOP). A standard removal is not recommended. PURPOSE: To investigate the effect of removal of the conjunctival suture after trabeculectomy with fornix-based conjunctival flap on corneal astigmatism, visual acuity, and IOP. METHODS: Eighty-seven cases of trabeculectomy with mitomycin C with a fornix-based conjunctival flap performed in the eyes of 82 patients (5 patients underwent bilateral trabeculectomy) were enrolled in a prospective randomized study. All surgeries were conducted by the same surgeon (J.W.) in the Ophthalmology Department of the University Medical Center of Mainz, Germany. All eyes received a corneal-conjunctival, continuous, mattress, interlocked suture for closing the conjunctiva at the limbus. After randomization, in 46 cases the suture was removed 6 weeks postoperatively; in 41 patients, the suture was left in place. All patients were examined preoperatively, and at 6 weeks, 3 months, 6 months, and 12 months after surgery. Astigmatism was measured using objective refraction and corneal topography, IOP and visual acuity were also assessed. Results were compared using a Wilcoxon test or Mann-Whitney U test for single time-points. RESULTS: During follow-up, no significant differences between the 2 study groups regarding refractive or topographic values were found. Patients in the suture removal group had a significantly higher visual acuity than controls at 3 months, 6 months, and 1 year after surgery. IOP was similar in both groups throughout the study. CONCLUSIONS: Removal of the conjunctival suture in trabeculectomy with a fornix-based conjunctival flap leads to a faster rehabilitation of visual acuity but does not significantly affect corneal astigmatism or IOP.

The Evonik-Mainz Eye Care-Study (EMECS): Development of an Expert System for Glaucoma Risk Detection in a Working Population.

PURPOSE: To develop an expert system for glaucoma screening in a working population based on a human expert procedure using images of optic nerve head (ONH), visual field (frequency doubling technology, FDT) and intraocular pressure (IOP). METHODS: 4167 of 13037 (32%) employees between 40 and 65 years of Evonik Industries were screened. An experienced glaucoma expert (JW) assessed papilla parameters and evaluated all individual screening results. His classification into "no glaucoma", "possible glaucoma" and "probable glaucoma" was defined as "gold standard". A screening model was developed which was tested versus the gold-standard. This model took into account the assessment of the ONH. Values and relationships of CDR and IOP and the FDT were considered additionally and a glaucoma score was generated. The structure of the screening model was specified a priori whereas values of the parameters were chosen post-hoc to optimize sensitivity and specificity of the algorithm. Simple screening models based on IOP and / or FDT were investigated for comparison. RESULTS: 111 persons (2.66%) were classified as glaucoma suspects, thereof 13 (0.31%) as probable and 98 (2.35%) as possible glaucoma suspects by the expert. Re-evaluation by the screening model revealed a sensitivity of 83.8% and a specificity of 99.6% for all glaucoma suspects. The positive predictive value of the model was 80.2%, the negative predictive value 99.6%. Simple screening models showed insufficient diagnostic accuracy. CONCLUSION: Adjustment of ONH and symmetry parameters with respect to excavation and IOP in an expert system produced sufficiently satisfying diagnostic accuracy. This screening model seems to be applicable in such a working population with relatively low age and low glaucoma prevalence. Different experts should validate the model in different populations.

Impact of Posterior Corneal Surface on Toric Intraocular Lens (IOL) Calculation.

PURPOSE: To quantify the impact of posterior cornea on toric IOL calculation accuracy using Placido-topography of anterior corneal surface and Scheimpflug measurements of corneal thickness. MATERIALS AND METHODS: Three-hundred seventy-nine non-selected eyes undergoing cataract surgery with non-toric intraocular lens (IOL) implantation were measured with TMS-5 (Tomey, Japan), IOLMaster (Zeiss, Germany) and Lenstar (Haag-Streit, Switzerland). Anterior, posterior and total measured corneal astigmatisms were compared with astigmatisms from postoperative refraction by calculating vector differences. RESULTS: The average absolute vector difference between anterior astigmatism and total astigmatism combining the measurements of anterior and posterior cornea was only 0.3 ± 0.2 D, with a median of only 0.27 D, but a maximum of 1.5 D. Measurements of anterior cornea alone show a systematic difference from refractive cylinder of 0.3-6 D at 90, 0.38 D at 89° and 0.28 D at 91° (IOLMaster, Lenstar and anterior TMS5), whereas the total TMS5 cylinder differs on average by only 0.14D at 81° from the refractive cylinder. With-the-rule (WTR) corneal astigmatism is slightly reduced and against-the-rule (ATR) astigmatism slightly increased on average when posterior corneal surface is taken into account additionally. This could also be confirmed by the calculation of an average pachymetry of all eyes in which the thinnest central part shows an ellipsoidal shape with horizontally long axis. CONCLUSION: Measurements of posterior cornea have on average only a small but significant impact on the outcome of toric IOL calculation, however, they are nevertheless recommended to detect outliers in which corneal irregularities (e.g. beginning keratokonus) may be overlooked.

The Evonik-Mainz-Eye-Care-Study (EMECS): design and execution of the screening investigation.

PURPOSE: To determine if screening for major ophthalmological diseases is feasible within the frame of routine occupational medicine examinations in a large working population. METHODS: 13037 employees of Evonik Industries aged 40 to 65 years were invited to be screened for major ophthalmological diseases (glaucoma, age related macular degeneration and diabetic retinopathy between June 2007 and March 2008 within an extended setting of occupational medicine. Ophthalmological examinations consisted of visual acuity, objective refraction, pachymetry, tonometry, perimetry (frequency doubling technology), confocal scanning laser ophthalmoscopy and digital fundus photography. Participants responded to a questionnaire addressing history of ocular and general diseases and social history. RESULTS: 4183 participants (961 female and 3222 male) were examined at 13 different sites. Response rates for eligible persons at those sites ranged from 17.9 to 60.5% but were in part limited by availability of examination slots. Average age of participants was 48.4 ± 5.4 years (mean ± SD). 4147 out of 4183 subjects (99.1%) had a visual acuity ≥ 0.5 in the better eye and 3665 out of 4183 (87.6%) subjects had a visual acuity ≥ 0.8 in the better eye. 1629 participants (38.9%) had previously not been seen by an ophthalmologist at all or not within the last three years. CONCLUSION: This article describes the study design and basic characteristics of study participants within a large occupational medicine based screening study for ophthalmological diseases. Response rates exceeded expectations and were limiting examination capacity. Meaningful data could be obtained for almost all participants. We reached participants who previously had not received ophthalmic care. Thus, ophthalmological screening appears to be feasible within the frame of routine occupational medicine examinations.

Neuroprotection of medical IOP-lowering therapy.

Intraocular pressure (IOP)-lowering therapy has been shown to arrest or retard the progression of optic neuropathy typical for glaucoma and can, thus, be described as neuroprotective. At present, six classes of medical therapy are employed, namely parasympathomimetics, alpha/beta-sympathomimetics, ß-blockers, carbonic anhydrase inhibitors, α2-adrenergic receptor agonists and prostaglandin analogues. For several of these substances, some experimental evidence exists of a possible neuroprotective mechanism, beyond their IOP-lowering activity. ß-Blockers are involved in the up-regulation of brain-derived neurotrophic factor (BDNF) and can decrease glutamate-mediated NMDA receptor activation. Not only systemic but also topical carbonic anhydrase inhibitors are able to increase retinal blood flow. α2-Adrenergic receptor agonists can up-regulate the formation of BDNF and anti-apoptotic factors. Prostaglandin analogues increase blood flow to the eye, possibly including the retina. To date, evidence for a neuroprotective effect independent of IOP regulation in human glaucoma is scarce and has only been shown to be likely for the α2-adrenergic receptor agonist, brimonidine.

A ray tracing approach to calculate toric intraocular lenses.

PURPOSE: To quantify the precision of astigmatic correction in routine cataract surgery with toric intraocular lenses (IOLs) and to evaluate the predictability of keratometric and anterior/posterior topographic measurement for the improvement of the overall accuracy. METHODS: Seventy-eight eyes of 56 patients were implanted with toric IOLs. Data acquired by the Lenstar optical biometer (Haag-Streit, Bern, Switzerland) and TMS5 topography (Tomey, Nagoya, Japan) were processed with the ray tracing software Okulix (Tedics, Dortmund, Germany) to predict the residual refraction. Four different inputs were examined: keratometry only, anterior topography, anterior and posterior topography/ tomography, and combination of keratometry only and anterior and posterior topography/tomography. Four weeks postoperatively, the spherical prediction error and the cylindrical prediction error (difference vector between predicted and achieved cylindrical refraction) were determined. RESULTS: Mean absolute error of spherical prediction error was 0.27 diopter (D). Cylindrical prediction errors were 0.57 D (keratometry only), 0.56 D (anterior topography), 0.56 D (anterior and posterior topography/ tomography), and 0.50 D (combination of keratometry only and anterior and posterior topography/tomography). Differences between intraocular lens groups were statistically significant (Friedman test, P < .05). CONCLUSION: The combination of keratometry and anterior and posterior topography/tomography of anterior and posterior surface yielded the best results for toric IOL power calculations.

Accuracy of intraocular lens calculation with ray tracing.

PURPOSE: To quantify the current accuracy limits of ray tracing for intraocular lens (IOL) calculations, compare results for spherical vs aspheric IOLs, and determine the value of using crystalline lens thickness in IOL calculations. METHODS: Of 591 eyes, 363 eyes were implanted with spherical IOLs (320 SA60AT [Alcon Laboratories Inc] and 43 Y-60H [Hoya Corp]) and 228 eyes had aspheric, aberration-correcting IOLs (57 SN60WF [Alcon Laboratories Inc], 112 Tecnis ZCB00 [Abbott Medical Optics], 21 CTAsphina404 [Carl Zeiss Meditec], and 38 iMics1 [Hoya Corp]), all calculated with OKULIX ray tracing (Tedics), based on Lenstar (Haag-Streit) measurements of axial length, corneal radii, and position and thickness of the crystalline lens. The measure of accuracy was the prediction error, ie, the difference between calculated refraction and manifest refraction (spherical equivalent) 1 month after surgery calculated as mean absolute error (MAE). RESULTS: The prediction error with aspheric IOLs was lower than that with spherical IOLs (MAE 0.27 vs 0.36 D) and was lower for patients with corrected distance visual acuity (CDVA) ⩾1.0 compared to CDVA <1.0 (MAE 0.26 vs 0.38 D). For aspheric IOLs and CDVA ⩾1.0, MAE differed by a factor of two compared to spherical IOLs and CDVA <1.0 (MAE 0.21 vs 0.42 D). Taking the crystalline lens position and thickness into account improved the prediction error by ∼9% overall (MAE 0.33 vs 0.36 D) and was most beneficial in patients with aspheric lenses and CDVA ⩾1.0 (MAE improved from 0.26 to 0.21 D). All differences between the investigated subgroups were statistically significant (P<.05). CONCLUSIONS: Ray tracing for IOL calculation is particularly beneficial with aspheric IOLs and in eyes with good (20/20 or better) postoperative visual acuity.

Flap suture--a simple technique for the revision of hypotony maculopathy following trabeculectomy with mitomycin C.

BACKGROUND: A serious complication following trabeculectomy with mitomycin C (MMC) is intraocular hypotony with hypotony maculopathy, papilledema, flattening of the anterior chamber, corneal decompensation and a decrease in visual acuity. We describe a new simple surgical technique for the treatment of hypotony maculopathy following trabeculectomy with MMC. METHODS: In a prospective consecutive case study, 16 patients with hypotony maculopathy following trabeculectomy with MMC were included. Through the intact conjunctiva, additional 10.0 nylon sutures were placed through the scleral flaps into the adjacent sclera. Assessment of visual acuity, intraocular pressure (IOP) measurement and fundoscopy were performed on the 1st and 7th day postoperatively and 1, 3 and 6 months postoperatively. Photography of the bleb and the posterior pole and optical coherence tomography imaging of the posterior pole were performed. RESULTS: Before surgery (flap suture), the mean IOP was 2.8 mmHg (+/-1.1; range from 1 to 4 mmHg). It was 24.9 +/- 11.7 mmHg (range; 9-48 mmHg) on the 1st postoperative day, 15.7 +/-8.1 mmHg (range; 5-35 mmHg) on day 7, 11.1 +/-4.1 mmHg (range; 5-20 mmHg) 1 month after surgery, 9.3 +/-3.9 mmHg (range; 2-20 mmHg) after 3 months, and 9.6 +/-4.2 mmHg (range; 2-20 mmHg) after 6 months. The best corrected mean visual acuity was 20/50 before trabeculectomy and 20/160 before flap suture. It improved to 20/63 at 6 months postoperatively. Clinical signs of hypotony maculopathy disappeared in all patients. No bleb leakage was observed in any patient during follow-up. CONCLUSION: Resuturing the scleral flap through the intact conjunctiva is an effective and minimally invasive method to treat hypotony maculopathy following trabeculectomy with MMC. Thus, opening the conjunctiva can be avoided.

Topography-based intraocular lens power selection.

PURPOSE: To provide mathematical tools for selecting intraocular lens (IOL) power for normal eyes and for "odd" eyes, particularly after corneal refractive surgery. SETTING: Universitats-Augenklinik, Mainz, Germany. METHODS: First, IOL power is selected based on the radii and numerical eccentricity of the cornea, extracted from corneal topography in a consistent numerical model of the cornea. To fine-tune the result, the visual impression is simulated by blurred Landolt rings superimposed on the retinal receptor grid. The calculation uses numerical ray tracing of the whole pseudophakic eye comprising all monochromatic errors. The error contributions of the influencing parameters, such as anterior and posterior corneal shape and corneal thickness, are quantified in detail. The method is verified in IOL power selection for normal eyes and for eyes after corneal refractive surgery. RESULTS: The main difference between normal corneas and corneas after refractive surgery results from different asphericities. Normal corneas are prolate, with typical numerical eccentricities of 0.5, whereas corneas after laser surgery for myopia are oblate. This causes the main difference (hyperopic shift up to 2.0 diopters) in IOL power selection. Shifts in the posterior corneal radius and corneal thickness are of minor importance. CONCLUSION: Intraocular power selection after corneal refractive surgery should be based on all the information corneal topography provides.

Predicting postoperative intraocular lens position and refraction.

PURPOSE: To predict the postoperative IOL position and refraction as accurately as possible independent of individualization of the parameters. SETTING: Universitats-Augenklinik, Mainz, Germany, and Vienna, Austria. METHODS: One patient cohort (189 eyes, Vienna) was used to calibrate the prediction method, which was then applied to a second cohort (65 eyes, Mainz). All calculations were based on consistent numerical ray tracing of the pseudophakic eye using the original manufacturer's intraocular lens (IOL) data (radii, thickness, refractive index). A new algorithm to predict IOL position was developed. Ultrasound (US) axial lengths were calibrated relative to partial coherence interferometry (PCI). Corneal radii extracted from topography were checked against radii measured with the IOLMaster (Zeiss) and by Littmann keratometry. RESULTS: Zero mean prediction errors for IOL position and refraction were obtained without adjusting the parameters and with PCI lengths or US lengths calibrated relative to the PCI values. There was no significant loss of accuracy of US data compared to PCI data. Corneal radii extracted from topography were slightly but statistically significantly different from the Littmann values, and they were more accurate than the latter with respect to prediction error. The measured mean central IOL position (distance from posterior corneal surface) for all IOL types was 4.580 mm, a value very close to the mean recalculated from A-constants (4.587 mm). The difference in the individual central IOL position relative to the mean value depended only linearly (ie, no higher orders such as square or cubic are needed) on axial length, with the mean central IOL position as a free parameter. This parameter should be 4.6 +/- 0.2 mm (the same value as independently measured or recalculated) to obtain zero steepness of the prediction error as a function of axial length, producing zero bias for long and short eyes. CONCLUSIONS: Calculation errors from formulas and confusing adjusting parameters can be avoided if calculations and measurements are performed on a clear and simple physical basis. Nevertheless, an individual prediction error, typically 0.5 to 1.0 diopter, seems to be unavoidable.

Determining postoperative anterior chamber depth.

PURPOSE: To compare measured and calculated postoperative anterior chamber depths (ACDs). SETTING: Department of Ophthalmology and Institute of Medical Physics, University of Vienna, Vienna, Austria, and Department of Ophthalmology, University of Mainz, Mainz, Germany. METHODS: The postoperative ACD was measured in 189 pseudophakic eyes using a laboratory prototype of partial coherence interferometry (PCI). In 6 intraocular lens (IOL) groups, the mean ACD was calculated by ray tracing based on the best-known A-constants of the SRK formulas. In addition, for each IOL type, each measured ACD was compared with a value calculated using the individual spherical equivalent of the postoperative refraction. RESULTS: The measured and the calculated ACD values were close and did not show systematic differences. The ACD values obtained in the study, however, differed significantly from the values published by the IOL manufacturers. A comparison of the PCI-assessed ACDs and the calculated values using the postoperative refraction showed more scattered results for the refraction-based data, which was probably the result of higher measurement errors with the autorefractometer than with PCI. CONCLUSIONS: High-precision interferometry measurements and ray-tracing calculations confirmed each other. The resulting mean ACD values should be used instead of the manufacturers' values. The refractive outcome of cataract surgery can be improved by combining preoperative high-precision PCI biometry and numerical ray tracing for IOL power calculations.

Simplified mathematics for customized refractive surgery.

PURPOSE: To describe a simple mathematical approach to customized corneal refractive surgery or customized intraocular lens (IOL) design that allows "hypervision" and to investigate the accuracy limits. SETTING: University eye hospital, Mainz, Germany. METHODS: Corneal shape and at least 1 IOL surface are approximated by the well-known Cartesian conic section curves (ellipsoid, paraboloid, or hyperboloid). They are characterized by only 2 parameters, the vertex radius and the numerical eccentricity. Residual refraction errors for this approximation are calculated by numerical ray tracing. These errors can be displayed as a 2-dimensional refraction map across the pupil or by blurring the image of a Landolt ring superimposed on the retinal receptor grid, giving an overall impression of the visual outcome. RESULTS: If the eye is made emmetropic for paraxial rays and if the numerical eccentricities of the cornea and lens are appropriately fitted to each other, the residual refractive errors are small enough to allow hypervision. Visual acuity of at least 2.0 (20/10) appears to be possible, particularly for mesopic pupil diameters. However, customized optics may have limited application due to their sensitivity to misalignment errors such as decentrations or rotations. CONCLUSIONS: The mathematical approach described by Descartes 350 years ago is adequate to calculate hypervision optics for the human eye. The availability of suitable mathematical tools should, however, not be viewed with too much optimism as long as the accuracy of the implementation in surgical procedures is limited.

Corneal model.

PURPOSE: To describe the optical region of the cornea with as few parameters as possible and to compare this approach to commonly used mathematical models for the cornea. SETTING: University eye hospital, Mainz, Germany. METHODS: Corneal surface is approximated by a simple model (SM) that is defined by 2 perpendicular vertex radii, their angle to the horizontal, and a unique numerical eccentricity. These parameters, together with a parameter quantifying the decentration of the recording, are obtained in a consistent fit of corneal topographic data. The SM is compared to Zernike polynomial approximations of the 4th (Z4 model) and 8th (Z8 model) radial orders. Residual refraction errors for these approximations are calculated by numerical ray tracing, allowing a comparison of the different approaches. The statistical evaluation was carried out in 100 healthy eyes. RESULTS: The model approximation accuracy for the SM was at least as high as the reproducibility of the topographic measurements. For small optical zones up to 4.0 mm in diameter, the SM was on average more accurate than the Z4 model. CONCLUSIONS: The parameters of the SM, which are closely related to conventional parameters of the cornea, provided a highly accurate basis for following refractive interventions (customized corneal or cataract surgery). Zernike polynomials tend to improve peripheral optical quality at the expense of the central quality. Except in cases of technical optics, this is an unwanted effect in the human eye.

Ray tracing for intraocular lens calculation.

PURPOSE: To improve accuracy in intraocular lens (IOL) calculations and clarify the effect of various errors. SETTING: University eye hospitals, Mainz, Germany, and Vienna, Austria. METHODS: A numerical ray-tracing calculation has been developed for the pseudophakic eye. Individual rays are calculated and then undergo refractions on all surfaces of the IOL and cornea. The calculations do not use approximations; ie, the refractions are calculated exactly using Snell's law. Rays can be calculated for any distance from the optical axis and for other parameter variations. The effects of aspheric surfaces can also be investigated. Instead of IOL powers, manufacturers' IOL data (radii, refractive index, thickness) are used in the calculations for different IOL types. The resulting optical quality is visualized by using Landolt rings superimposed on the grid of retinal receptors. RESULTS: Intraocular lens design, corneal asphericity, and specific spherical aberration influence the visual quality of the pseudophakic eye significantly. The IOL refractive power is an ambiguous parameter that cannot characterize the visual outcome sufficiently accurately for an IOL implanted at a given position. The effects can be calculated only in numerical ray tracing, not in Gaussian optics. The accuracy of numerical ray tracing is independent of axial length. Therefore, very long or very short eyes gain the most from the higher accuracy of this approach. For average-size eyes, however, the results are the same as with SRK calculations. CONCLUSION: Calculations in Gaussian optics should be replaced by state-of-the-art numerical methods, which can be run on any standard personal computer.