ALT (allogeneic limbal transplantation): a new surgical technique for limbal stem cell deficiency.

PURPOSE: Limbal stem cell deficiency (LSCD) is a rare but extremely relevant disease of the eye. LSCD patients often require a variety of surgical procedures, including keratoplasty in some cases. However, the outcome of these surgeries, including opacification and revascularization, is often frustrating due to LSCD relapse. METHODS: We developed a new surgical technique for the treatment of LSCD in which partial allogenic limbal transplantation (ALT) is carried out as part of penetrating keratoplasty (PK). After the PK, 1-8 slices from the limbal tissue of the donor graft are prepared and placed under the double running sutures attaching the corneal graft. This procedure was performed on 14 patients with LSCD, caused by severe ocular burn in 5 cases and by infection in 9. Between one and eight limbal transplants were used depending on the extension of the LSCD. RESULTS: All 14 patients showed stable or increased visual acuity after the ALT surgery compared to their preoperative visual acuity. All of the grafts were integrated into the superficial corneal layers without progression of corneal vascularization beyond the limbal grafts. The median follow-up period was 12 months on average. CONCLUSION: The ALT method seems to be a promising surgical procedure for the treatment of patients with LSCD. It can be properly carried out in the context of keratoplasty and does not require a separate donor tissue. The ALT grafts may offer the possibility of constructing a new limbal region, resulting in stable or even increased visual acuity and the absence of corneal vascularization.

Sclerocorneal graft and sequential removal of melted cornea after severe corneal burn with perforation.

Corneal burn grade IV usually leads to blindness. Several different surgical techniques remain challenging owing to the extensive tissue damage. Here, we introduce a novel technique with a 15 mm corneoscleral and limbal homologous graft combined with sequential autologous corneal removal ab interno, with a vitrectomy probe to save the anterior chamber angle. In vivo anatomy with optical coherence tomography is the surgical key. A large 15 mm sclerocorneal graft is sutured on top of the remainder of the destroyed cornea and sclera after removal of the epithelium and conjunctiva, with anterior synechiolysis if necessary, peripheral iridectomy and conjunctivoplasty. The recipient central corneal stroma is not removed, primarily to protect the anterior chamber angle. After three weeks, the collagenolytic central recipient corneal stroma can be removed with a small 23 g vitrectomy probe, respecting the lens and scleral spur. The corneoscleral graft remains clear under systemic and local immunosuppression. Intraocular pressure is well controlled because the anterior chamber angle is respected. Recurrent corneal erosions need close follow-up. Therapeutic soft contact lenses can support topical therapy. In cases of sclercorneal graft decompensation or rejection after 3-5 years, a new sclerocorneal graft (with limbal donation) seems to be superior to perforating keratoplasty without limbal stem cell transplantation. Repeated sclerocorneal grafts after severe corneal burn with limbal transplantation and maintenance of the complete anterior angle structure are a successful option for preventing blindness and achieving good visual acuity. Clin. Anat. 31:39-42, 2018. © 2017 Wiley Periodicals, Inc.

Epithelial invasion after open globe injury.

Epithelial invasion after open globe injury is a rare complication. Wrong treatment (laser opening of the cyst) or no treatment can lead to painful blindness. Forty percent (25/62) of patients with block excision with epithelial downgrowth had a history of open globe injury. Four of them were female. Their mean age was 45 ±21 years. A tectonic keratoplasty with block excision was performed on 25 patients. Seven of them had simultaneously undergone cataract surgery. The mean extension of epithelial invasion was 3.0 ± 1.3 clock hours. Laser cystotomy was contraindicated. The diameter of the block excision was 8.2 ± 1.5 mm. Histological examination revealed diffuse epithelial invasion in three eyes and cystic epithelial downgrowth in 22 eyes. Mean pre- and post-operative visual acuity (20/60) did not differ significantly. The intraocular pressure was 16 ± 7 mm Hg before and 14 ± 7 mm Hg after the surgery. Only one eye (4%) developed ocular hypotony after block excision. Epithelial invasion can become manifest many years after an open globe injury. En block excision for cystic epithelial downgrowth with an extension less than 150 degrees is the therapy of choice. Opening of the cyst by laser or surgically is not recommended: It can induce transformation of cystic into diffuse epithelial invasion, and the succeeding secondary glaucoma can be refractory to therapy and lead to blindness. Clin. Anat. 31:68-71, 2018. © 2017 Wiley Periodicals, Inc.

Traumatic globe rupture after deep anterior lamellar keratoplasty-A novel management technique.

A traumatic wound dehiscence can occur many years after surgery in 2-6% of all keratoplasties. Intraocular tissue prolapse can lead to severe visual loss. Deep anterior lamellar keratoplasty (DALK) leads to higher wound stability because of the intact Descemet membrane. We report a case of a novel management of wound dehiscence following DALK. A 59-year-old patient underwent uncomplicated DALK for advanced keratoconus. Eighteen months later he experienced a traumatic wound dehiscence (globe rupture) after a fall. Visual acuity decreased to light perception on the affected eye, the iris and prolapsed vitreous were incarcerated, and no retinal details were recognizable. The corneal graft was dehiscent over eight clock hours, the Descemet membrane was ruptured, and the stroma dissolved over 30% of its surface in a bell shape. Primary wound closure was performed with nylon 10-0 single interrupted corneal sutures. One day after emergency treatment, a 23-gauge pars-plana-vitrectomy for vitreous hemorrhage was conducted and a retinal tear was treated with laser photocoagulation. The Descemet membrane was repositioned using a 23 g vitrectomy probe under air and the globe was filled with SF6 gas. Postoperatively, visual acuity increased to 6/15 and the cornea cleared up. Corneal graft and Descemet membrane repositioning after trauma can avoid a further keratoplasty and the risk of immunological rejection of donor endothelial cells. Clin. Anat. 31:56-59, 2018. © 2017 Wiley Periodicals, Inc.

Methods of fixation of intraocular lenses according to the anatomical structures in trauma eyes.

Ocular trauma can lead to severe visual impairment and morbidity, depending on the anatomical structures affected. The main causes of ocular trauma include foreign bodies, impact by an object, falls, and chemicals. Most ocular traumas occur in children or young male adults. A meticulous slit lamp examination is crucial for assessing all anatomical structures. Trauma to the crystalline lens can result in dislocation, an intralenticular foreign body, cataract, fragmentation, and capsular breach. An intraocular lens (IOL) can endure subluxation or luxation under the conjunctiva, into the anterior chamber or the vitreous, or can be extruded. The surgical approach depends on the condition and morphology of the lens and the anatomical structures surrounding it. If there is capsular bag support, a secondary IOL can be placed in the sulcus using remnants of the damaged capsule. If there is no capsular bag support, a secondary IOL can be fixated to the anterior chamber angle, to the iris, or to the sclera. A detailed history of injury cannot always be obtained in trauma settings. Proper education, supervision, and certified safety eye protectors could prevent up to 90% of ocular injuries. Lens trauma can be treated with various surgical procedures and fixation techniques, which nevertheless require advanced surgical skills owing to the fine anatomical structure of the anterior segment. A careful surgical strategy should be established for a globe reconstruction after trauma with secondary lens implantation. Clin. Anat. 31:6-15, 2018. © 2017 Wiley Periodicals, Inc.

Clinical anatomy of the anterior chamber angle in congenital aniridia and consequences for trabeculotomy/cyclophotocoagulation.

Intraocular pressure lowering surgery in congenital aniridia glaucoma (CAG) can be complicated by dysgenesis of the limbal region, anterior chamber angle, iris, and lens. The anterior segments of 23 eyes (17 patients) with congenital aniridia were investigated under general anesthesia using ultrasound biomicroscopy (UBM). The structures of the anterior segment were examined: distance of ciliary body processes from the anterior chamber angle and positioning of Schlemm's canal. A surgical plan was created on the basis of these data. Schlemm's canal was detected in 21 of the 23 examined eyes. The mean distance from the anterior chamber angle was 1.3 ± 0.4 mm (range: 0.5-to 2.1 mm). The mean distance between the anterior chamber angle and the ciliary body was 561 ± 301 µm (range: 270-1,300 µm). The mean prominence of the ciliary body towards the lens was 799 ± 352 µm (range: 210-1,660 µm). This resulted in a precise UBM-based trabeculotomy. In addition, the ciliary body was detected and coagulated ab externo with a diode laser probe (810 nm) using diaphanoscopy and UBM. An initial UBM examination of the anterior segment is essential in eyes with CAG scheduled for trabeculotomy or cyclophotocoagulation. Clin. Anat. 31:64-67, 2018. © 2017 Wiley Periodicals, Inc.

Anatomic landmarks in lacrimal surgery from an ophthalmologist's point of view: Clinical findings of external dacryocystorhinostomy and dacryoendoscopy.

Epiphora is a common clinical symptom of nasolacrimal duct obstruction. However, it is present in several pathologies and can lead to decreased quality of life for patients. A careful clinical examination including a detailed patient's history and diagnostic tests such as the fluorescein dye disappearance test and diagnostic syringing of the lacrimal duct are essential. Depending on the time of presentation (congenital, primary, or secondary acquired), grade (subtotal or total) and location of the stenosis, different surgical approaches can be considered. These are subdivided into minimally invasive (transcanalicular) and anastomosing (dacryocystorhinostomy) procedures. Furthermore, the anatomical landmarks and the site of surgical intervention differentiate the surgical techniques into endoscopic or transcutaneous. Modern intubation techniques offer a large spectrum of therapeutic possibilities enabling patient care to be customized and individualized. Knowledge of the topographical anatomy is crucial for achieving greater success and a lower complication rate. Clin. Anat. 30:1034-1042, 2017. © 2017 Wiley Periodicals, Inc.

[The Effect of Non-Depolarising Muscle Relaxants on Ocular Pulse Amplitude and Intraocular Pressure]. / Beeinflussung der okulären Pulsamplitude und des Intraokulardrucks durch nicht depolarisierende Muskelrelaxanzien.

AIM: In general anaesthesia (GA) for ocular surgery the chosen non-depolarising muscle relaxant has a high influence on the fluctuations of intraocular pressure (IOP) and ocular pulse amplitude (OPA). PATIENTS AND METHODS: In 229 patients, who needed GA for their ophthalmic surgery, OPA and IOP were measured with the dynamic contour tonometer (DCT) before and 5 minutes after intubation. For GA, three groups of non-depolarising muscle relaxants, namely, mivacurium (n = 71), atracurium (n = 91) and rocuronium (n = 67) were used. RESULTS: The IOP decreased by about 4.0 ± 2.3 mmHg using mivacurium in GA, by about 6.1 ± 2.2 mmHg using atracurium and by about 7.4 ± 1.7 mmHg using rocuronium (p < 0.001). The relative decrease of the IOP was 20% for mivacurium, 31% for atracurium and 37% for rocuronium. For mivacurium the OPA decreased from 3.4 ± 1.5 mmHg to 2.2 ± 1.1 mmHg (p < 0.001) in contrast to atracurium (decrease from 3.6 ± 1.5 mmHg to 1.8 ± 0.8 mmHg; p < 0.001) and rocuronium (decrease from 3.1 ± 1.6 mmHg to 1.7 ± 0.9 mmHg; p < 0.001). Mean OPA reduction was lowest with mivacurium (1.3 mmHg) and the highest with atracurium (1.7 mmHg). The mean relative decrease of the OPA was 34% with mivacurium, 46% with atracurium and 43% with rocuronium (p < 0.001). There was no linear correlation between the relative OPA decrease and the relative IOP decrease. CONCLUSION: Risks for ophthalmic surgery may be minimised by avoiding mivacurium in general anaesthesia. Due to its negative effects on IOP and OPA mivacurium does not seem to be suitable for operations with a large opening in the eye such as penetrating keratoplasty and block excision. Rocuronium can be used because it induces a favourised intraoperative decrease of the IOP.

The Alteration of Intraocular Pressure and Ocular Pulse Amplitude by Retrobulbar Anaesthesia-A Search for Risk Factors for Serious Complications Due to Retrobulbar Anaesthesia.

Our goal was to assess the impact of retrobulbar anaesthesia on ocular pressure and perfusion development and to find out if there were systemic or biometric parameters of patients affecting them in order to understand the effect of retrobulbar anaesthesia better. Methods: Changes in intraocular pressure (IOP) and ocular pulse amplitude (OPA) using a dynamic contour tonometer (DCT) were noted before and after retrobulbar anaesthesia (RBA) in combination with five minutes of oculopression at 40 mmHg in 134 patients. Only results with a quality Q 1-3 were considered for further statistical analysis. Systemic and ophthalmic parameters were noted and their impact was tested using linear regression. Results: IOP decreased from 18.9 ± 7.2 mmHg to 15.4 ± 6.3 mmHg (n = 71, p = 0.001) after first RBA. The dosage of midazolam administered during premedication was found to increase IOP significantly after first RBA (B = 3.75; R2 = 0.38). Ocular pulse amplitude decreased significantly from 3.8 ± 1.7 mmHg to 3.0 ± 1.9 mmHg after first RBA (n = 72, p < 0.001). This change was found to be dependent on the presence of diabetes mellitus (n = 68, p = 0.048). Conclusions: IOP and OPA decrease after RBA and oculopression. Caution is needed with midazolam premedication due to potential IOP increase. Patients with diabetes and pre-existing retinal or optic nerve damage should consider alternative anaesthesia methods, such as eye drops or general anaesthesia, due to the observed decrease in OPA after RBA and oculopression.

Simultaneous Muraine Sutures and Excimer Laser-Assisted Penetrating Keratoplasty for Acute Keratoconus.

Background: Acute keratoconus (acute KC), which affects approximately 1.6-2.8% of keratoconus (KC) patients, is a pathological condition of the cornea characterized by stromal edema due to entry of aqueous humor through a tear in Descemet's membrane. Methods: We present a novel combination of surgical procedures that allows swifter visual recovery in a consecutive, retrospective case series. The new surgical procedure for acute KC consists of a combination of Muraine corneal sutures to smooth the corneal curvature and Excimer laser-assisted penetrating keratoplasty and was performed in six acute KC patients from 2019 to 2022 at the Department of Ophthalmology, University Hospital of Martin-Luther-University Halle-Wittenberg (UMH), Germany. We monitored data on preoperative status, operative details, intraoperative and postoperative complications and visual outcomes were analyzed. Results: The mean age was 41.5 ± 13.5 years (3 OD, 3 OS). Neurodermatitis was present in 3 patients (50%). All patients received significant visual benefits from the procedure. Preoperative BCVA was hand motion (logMAR 3.0) in all patients; postoperatively, BCVA improved significantly logMAR 0.03 ± 0.09 [range: 0.2-0.4; p < 0.001, FUP 20+/-10 months). Visual acuity remained stable throughout the roughly biannual follow-ups. One patient developed endothelial graft rejection after 2 years. During the last examination, all eyes had clear grafts and stable curvatures, K1 and K2 being 42.43 ± 4.17 D and 44.95 ± 4.07 D, respectively, and mean corneal astigmatism was 2.61 ± 1.74 D. The thinnest corneal thickness was 519 ± 31 µm. A graft size of 8.0 × 8.1 mm was the most beneficial. Conclusions: in patients with acute KC and hydrops, a penetrating keratoplasty with Muraine corneal sutures is successful in terms of graft clarity and visual outcome. Combining the procedures allows quicker visual recovery. Patients with a history of neurodermatitis should have preoperative and postoperative dermatologic treatment and close follow-up for possible complications.

Evaluation of the Possible Influence of Povidone Iodine (PVI) Solution and Polyhexanide (PHMB) on Wound Healing in Corneal Epithelial Regeneration.

This study investigates the possible toxic effects of the preoperative antiseptic substances povidone iodine (PVI) and polyhexanide (PHMB; Serasept® 2) on wound healing in ophthalmology. To assess this impact, human telomerase-immortalized corneal epithelial (hTCEpi) cells and human telomerase-immortalized conjunctival epithelial (hCjE) cells were exposed to 1% and 5% PVI or 0.04% PHMB for different periods to evaluate the cytotoxicity of these two antiseptics. Furthermore, the toxicity of these antiseptics was investigated in a human tissue-specific corneal epithelial construct and porcine eye culture model. The results reveal the high cytotoxicity of PVI and PHMB in the hTCEpi and hCjE in monolayer cell culture models, independent of the incubation time and concentration of these substances. However, after hTCEpi cell differentiation into a tissue-specific corneal epithelial construct, contact with these antiseptics for the relevant preoperative time did not alter cPARP1 or Ki67 expression. Furthermore, the wound-healing process in the porcine cornea was not significantly influenced after incubation with these antiseptics. In summary, corneal and conjunctival epithelial cell lines are very sensitive to PVI and PHMB, whereas no significant alterations were found in intact tissue-specific corneal epithelial constructs or porcine corneas. Therefore, we could not identify PVI and PHMB as reasons for postoperative eye irritation.

Intraocular Epithelial Ingrowth after Traumatic and Surgical Corneal Injuries.

Intraocular epithelial ingrowth is a rare but serious complication of eye surgery or trauma. The diagnosis is challenging but can be aided by techniques such as anterior optical coherence tomography (AS-OCT). This study aimed to compare clinical and histopathological diagnostic data to evaluate the accuracy of AS-OCT. This retrospective analysis focused on patients presenting with suspected epithelial invasion between 2017 and 2022. Clinical data and histopathological findings were analyzed for diagnostic confirmation. Immunohistochemistry using the corneal-specific marker cytokeratin 3 and the conjunctival-specific marker cytokeratin 13 helped to identify the type of invading epithelial cells. Statistical analysis was used to evaluate the effectiveness of AS-OCT for diagnosis. This study included 51 patients who underwent keratoplasty or enucleation. Sixteen cases (31%) of epithelial ingrowth were histologically confirmed. The most common type was the cystic form (82%). Enucleation was required in 25% of patients, mainly due to diffuse epithelial invasion. Immunohistochemistry revealed a conjunctival origin in 82% of the infiltrated cells. AS-OCT showed a sensitivity of 78% and a specificity of 26% in detecting hyperreflective structures associated with epithelial invasion. This study highlights the diverse manifestations of epithelial ingrowth and the need for improved diagnostic techniques, with AS-OCT showing promising results but requiring further validation to avoid misdiagnosis.

Allogeneic Limbal Transplants Integrate into the Corneal Surface and Lead to an Improved Visual Acuity.

Limbal stem cell deficiency (LSCD) severely impairs vision and can lead to blindness. LSCD causes include chemical burns, infections, multiple previous operations and congenital malformations. Allogeneic limbal transplantation is a procedure for treating LSCD where prepared limbal tissue is attached using a double running suture during allogeneic penetrating keratoplasty (PKP). A total of 22 patients underwent ALT surgery between February 2019 and June 2022 at the University Hospital Halle (Saale). Regular follow-up was performed postoperatively every three months and included visual acuity testing, pressure measurement, slit lamp microscopic examination, fundoscopy, corneal topography and anterior segment optical coherence tomography (AS-OCT). The mean patient age was 69.5 years, and the mean follow-up was 19 months. All included patients had LSCD and multiple previous surgeries. Patient LSCD etiology was 59% infectious and 41% traumatic. ALTs integrated into corneal surfaces in all patients, demonstrated on AS-OCT. Since most patients initially received allogeneic limbal transplants, none of the operated eyes had surgical complications. Overall, visual acuity improved postoperatively from an initial 2.06 to 1.44 logarithm of the minimum angle of resolution (logMAR). Allogeneic limbal transplantation can be used to treat LSCD and its integration into the surrounding corneal tissue can be observed on AS-OCT.

[Intraocular pressure elevation after vitrectomy-Goldmann applanation tonometry measures lower intraocular pressure than dynamic contour tonometry]. / Intraokularer Druckanstieg nach Vitrektomie ­ Applanationstonometrie nach Goldmann misst niedriger als dynamische Konturtonometrie.

BACKGROUND: The dynamic contour tonometer PASCAL (DCT) is a direct noninvasive digital tonometer matching the corneal contour. We compared the DCT with the Goldmann applanation tonometer (GAT). METHODS: A total of 100 eyes were included in this prospective comparative clinical investigation and intraocular pressure (IOP) was measured with GAT and DCT before and after pars plana vitrectomy (ppV). Different intraocular endotamponades, such as gas and silicone oil were used. Preoperative IOP, changes in IOP postoperatively and intertonometer differences were measured. RESULTS: The preoperative mean IOP was 15.8 ± 5.2 mm Hg measured with the GAT and 17.5 ± 5.9 mm Hg with DCT. On the first postoperative day, in eyes with gas endotamponade the mean IOP rise was 2.5 mm Hg (p = 0.035) and 18 eyes were measured with an IOP of ≥ 25 mm Hg (19.1%; DCT). Postoperative IOP measured by GAT was 2.5 mm Hg lower and in eyes with gas endotamponade the GAT measured the IOP 3.0 mm Hg lower than the DCT. In eyes with a postoperative IOP above 20 mm Hg, the GAT measured the IOP 4.7 mm Hg lower compared to the DCT. Out of 18 eyes 10 with IOP ≥ 25 mm Hg were not recognized as hypertensive (≥ 25 mm Hg) by GAT. In 13% of the eyes the DCT measured at least 6 mm Hg higher IOP levels than GAT on the first postoperative day. In one extreme case with gas endotamponade, GAT underestimated the IOP by 12 mm Hg compared to the DCT. CONCLUSION: The IOP spikes after ppV are a feared complication and can lead to irreversible visual loss. Depending on the endotamponade, GAT measures lower IOP than DCT, especially in IOP spikes caused by expansive gas endotamponade. Postoperative IOP measurement is important and readings between GAT and DCT can differ.

New Safety Aspects in Corneal Donation-Studies on SARS-CoV-2-Positive Corneal Donors.

In the tissue donation field, to prevent pathogen transmission, all donors are screened by postmortem swabs for SARS-CoV-2 using qRT-PCR. Corneas from donors who tested positive for SARS-CoV-2 were subjected to further investigations. Corneal transplants and culture medium from positive donors were cultured under appropriate safety conditions for further analyses. Cornea tissue samples, including sclera/limbus/cornea, and culture media were taken at different time points for testing for SARS-CoV-2 using qRT-PCR, immunohistochemistry (IHC) and subgenomic RNA (sgRNA) analysis. Between January and May 2021, in four donors with initial negative premortem rapid tests, SARS-CoV-2 was detected post-mortem using qRT-PCR. In these cases, SARS-CoV-2 was observed at the beginning of cultivation in both tissue and culture medium using qRT-PCR and IHC. The virus was mainly localized in the limbus epithelial cells, with a stable detection level. Premortem rapid tests are potentially insufficient to exclude SARS-CoV-2 infection in corneal donors. While, for SARS-CoV-2, the risk of infection via transplants is considered low, a residual risk remains for presymptomatic new infections. However, our investigations provide the first indications that, with organ cultures, the risk of virus transmission is minimized due to the longer minimum culture period.

Electrospun nanofibers - A promising solid in-situ gelling alternative for ocular drug delivery.

A serious problem of the treatment of eye diseases is the very short residence time of the drug. The majority of the drug is cleared within few seconds due to the poor capability of the eye to accommodate additional liquids. We developed a new ocular drug delivery system, which is applied in dry form and forms immediately a gel after administration. The system is based on gellan gum/pullulan electrospun nanofibers. The rheological behavior of the spinning solution was investigated followed by further characterization of the in situ formed gel. Three-dimensional X-ray imaging with nanometric resolution (nano-CT) and electron scanning microscopy were used for a detailed characterization of the diameter and alignment of the fibers. A high porosity (87.5 ± 0.5%) and pore interconnectivity (99%) was found. To ensure a good fit to the eye anatomy, the prepared fibers were shaped into curved geometries. Additionally, a new innovative moistening chamber for the in vitro determination of the ocular residence time in porcine eyes was developed which mimics the tear turnover. A clear prolongation of the fluorescein residence time compared to conventional eye drops was achieved with the application of the curved nanofiber in situ gelling mat. In summary, the developed in situ gelling system with adapted geometry is a promising alternative system for ocular drug delivery.

Toric intraocular lenses--theory, matrix calculations, and clinical practice.

PURPOSE: To describe 1) how to determine toric (posterior chamber) intraocular lenses (IOLs) with standard formulas, 2) a matrix-based calculation scheme for determining toric IOLs using 4x4 matrices, 3) a method to determine residual refraction after implantation of an arbitrary toric lens, and 4) to address clinical aspects. METHODS: Formulas and metrics are reviewed for determining IOL power and residual refraction after toric IOL implantation. RESULTS: From 4x4 refraction and translation matrices characterizing refractive surfaces and interspaces between refractive surfaces, a system matrix is determined characterizing the entire optical system paraxially. Toric posterior chamber IOLs are determined by solving a linear equation system. In a second step, the same methodology is used for estimation of the residual refraction at the spectacle plane after implantation of an arbitrary toric lens. The methodology is applied to working examples, and the calculation procedure is described in a step-by-step approach. CONCLUSIONS: A straight-forward en bloc concept is demonstrated for determination of toric IOLs and estimation of the residual refraction. The applicability is shown in working examples, and clinical aspects such as rotation of the lens implant are addressed.

[Determination of toric intraocular lenses]. / Berechnung torischer Intraokularlinsen.

BACKGROUND: In the last decades, toric posterior chamber lenses (TPCLs) for cataract surgery and phakic toric lenses (PTLs) for refractive surgery have become more and more popular for correcting high or excessive corneal astigmatism. The purpose of this article is to present a vergence-based calculation scheme for TPCLs and PTLs. METHODS: In Gaussian optics (in the paraxial space), spherocylindrical optical surfaces can be described in a mathematically equivalent formulation as vergences. There are dual notations: The standard notation is used for transforming vergences through a homogeneous optical medium, and the component notation is applied to add up the power of a refractive surface to the vergence. Both notations can be used interchangeably. For calculating TPCLs, the vergences in front of and behind the predicted pseudophakic lens position are determined and subtracted. For calculating PTLs, the anterior vergence at the predicted lens position is estimated for the preoperative and postoperative states, and the difference between the two yields the desired lens power. WORKING EXAMPLES: In the 1(st) example, the power of a thin TPCL is determined step by step by applying the presented calculation scheme, which was designed to be transferred directly to a simple computer program (e.g., Microsoft Excel). In the 2(nd) example, the postoperative refraction is estimated for a simulation in which a TPCL similar to that in example 1 is implanted in a slightly misaligned orientation. In a 3(rd) example, the power of a PTL is determined step by step using the above-mentioned calculation scheme. CONCLUSIONS: The presented calculation scheme allows determination of"thin" TPCLs or PTLs to achieve spherocylindrical target refraction with a cylinder axis at random or to predict the postoperative refraction for any toric lens implanted in any axis. The concept can be easily generalized to"thick" toric intraocular lenses if the geometric data and refraction index of the material are known.