George Stamatelatos

Customized photoastigmatic refractive keratectomy using combined topographic and refractive data for myopia and astigmatism in eyes with forme fruste and mild keratoconus

PURPOSE: To examine the outcomes of photoastigmatic refractive keratectomy using corneal and refractive parameters for myopia and astigmatism in eyes with forme fruste and mild keratoconus. SETTING: Private practice, Melbourne, Australia. METHODS: Photoastigmatic refractive keratectomy was performed with a Star 1 or Star 2 laser (Visx) in 45 eyes with forme fruste or mild keratoconus using the Alpins vector planning technique. Inclusion requirements were best corrected visual acuity (BCVA) 20/40 or better, no slitlamp signs of keratoconus, mean keratometry less than 50.00 diopters (D), and corneal and refractive stability for at least 2 years. RESULTS: Thirty‐two eyes had follow‐up of 5 years and 9 eyes, of 10 years. Preoperatively, the mean refractive astigmatism was −1.39 DC ± 1.08 (SD) (range 0.45 to −5.04 DC) and the mean corneal astigmatism was 1.52 ± 1.18 D (range 0.35 to 4.75 D) by manual keratometry and 1.70 ± 1.42 D (range 0.32 to 5.32 D) by topography. Twelve months postoperatively, the mean refractive astigmatism was −0.43 ± 0.40 D and the mean corneal astigmatism was 1.05 ± 0.85 D by keratometry and 1.02 ± 0.83 D by topography. At 12 months, the uncorrected visual acuity was 20/20 or better in 56% of eyes and 20/40 or better in all eyes. The BCVA was 20/20 or better in 89% of eyes and 20/30 or better in all eyes. Seven eyes had a loss of BCVA, and 16 eyes had a gain. There were no cases of keratoconus progression. CONCLUSIONS: Photoastigmatic refractive keratectomy in eyes with forme fruste and mild keratoconus was safe and effective for myopia and astigmatism in carefully selected patients with refractive and corneal stability. The incorporation of the corneal astigmatism data into the applied treatment parameters may improve visual and total astigmatism results.

Clinical outcomes of laser in situ keratomileusis using combined topography and refractive wavefront treatments for myopic astigmatism

PURPOSE: To evaluate outcomes of laser in situ keratomileusis (LASIK) guided by wavefront alone versus wavefront plus topographic data. SETTING: NewVision Clinics, Cheltenham, Australia. METHODS: Twenty‐one eyes (14 patients) were distributed into 2 groups in a prospective double‐masked study. One group was treated by wavefront parameters alone (WF, n = 11), and the other, by wavefront combined with topography values (WF&VP, n = 10) using vector planning. All treatments were performed using Visx Star S4 CustomVue software. In the WF&VP group, the treatment profile was calculated using simulated keratometry readings from the Humphrey Atlas topography and 2nd‐order Zernike coefficients defocus 4 and astigmatism 3 and 5 from the WaveScan wavefront display of the entire eye. RESULTS: Mean corneal astigmatism preoperatively was 1.07 diopters (D) ± 0.54 (SD) in the WF group and 1.50 ± 0.87 D in the WF&VP group. At 6 months, it was 0.67 ± 0.57 D (39% reduction) and 0.83 ± 0.55 D (44% reduction), respectively. The WF&VP group had a greater reduction in horizontal coma. The mean gain in low‐contrast visual acuity under mesopic conditions was 0.06 in the WF group and 0.11 in the WF&VP group and the mean gain in high‐contrast visual acuity, 0.02 and 0.05, respectively. Two patients reported a change in the preferred eye postoperatively to the eye treated using vector planning. No result demonstrated statistical significance. CONCLUSION: The WF&VP group had greater reduction in corneal astigmatism and better visual outcomes under mesopic conditions than the WF group and equivalent higher‐order aberrations.

New method of quantifying corneal topographic astigmatism that corresponds with manifest refractive cylinder.

PURPOSE: To derive a method of quantifying corneal topographic astigmatism (CorT) that accurately represents manifest refractive cylinder. SETTING: Private practice, Melbourne, Australia. DESIGN: Retrospective study. METHOD: Axial power measurements obtained using topography in right eyes and left eyes were analyzed. For each Placido ring, an astigmatism value was calculated. The ring astigmatism values were combined via vector summation to create a new measure termed CorT. This parameter was assessed against other commonly used measures of corneal astigmatism using the ocular residual astigmatism (ORA) and its standard deviation (SD) on how closely each measure matched manifest refractive cylinder. The flat meridian of the CorT can also be used to conceptually divide the cornea into 2 hemidivisions and a CorT value subsequently calculated for each hemidivision of the cornea. RESULTS: The CorT was assessed against other commonly used measures of corneal astigmatism using the ORA (0.62 diopters [D] ± 0.33 [SD]) and had better correlation with manifest refractive cylinder than manual keratometry (K) (ORA 0.68 ± 0.38 D), simulated K (ORA 0.70 ± 0.35 D), corneal wavefront (ORA 0.74 ± 0.36 D), and paraxial curvature matching (ORA 0.85 ± 0.48 D). The SD of the ORA for CorT was significantly less than the other measures of astigmatism (P<.001). CONCLUSIONS: An alternative measure of corneal astigmatism, known as CorT, corresponded better to manifest refractive cylinder than other commonly used measures. A hemidivisional CorT can also represent the nonorthogonal asymmetrical astigmatism in irregular corneas. Financial Disclosure: Dr. Alpins and Mr. Stamatelatos have a financial interest in the ASSORT software program used to support the planning and analysis of astigmatic correction. Dr. Ong is an employee of ASSORT.

Refractive surprise after toric intraocular lens implantation: Graph analysis

Purpose To determine the refractive cylinder effect of rotating a toric intraocular lens (IOL) and identify the sources of refractive astigmatic surprise after toric IOL implantation. Setting Private practice, Melbourne, Australia. Design Experimental study. Methods Vergence formulas using a standard reduced eye model were used to bring all lens powers to the corneal plane. Double‐angle vector diagrams were then used to (1) determine the refractive cylinder effect of rotating a toric IOL and (2) show how the prevailing astigmatism and the various planning and surgical steps involved in implanting a toric IOL contribute to the postoperative manifest refractive cylinder. Results An example calculation is given to illustrate the method. Conclusions Refractive cylinder surprises can occur after toric IOL implantation. Understanding the causes enables surgeons to address contributory factors and choose an appropriate surgical method for managing individual cases of refractive cylinder surprise. Financial Disclosure Dr. Alpins and Mr. Stamatelatos have a financial interest in the Assort software program used to support the planning and analysis of astigmatic correction. Dr. Ong is an employee of Assort.

Corneal topographic astigmatism (CorT) to quantify total corneal astigmatism.

PURPOSE To evaluate the performance of corneal topographic astigmatism (CorT) based on total corneal power measurements. METHODS Anterior, posterior, and total corneal power measurements of 526 virgin eyes obtained using the CSO Sirius tomographer (Costuzione Strumenti Oftalmici, Scandicci, Florence, Italy) were analyzed. Individual CorTs were created from each set of data. These CorTs were assessed using ocular residual astigmatism (ORA), which quantifies corneo-refractive differences. A low standard deviation of the ocular residual astigmatism (ORAsd) indicates a low variability between corneal astigmatism and refractive cylinder. A low mean of the ORA magnitude indicates a close correlation of refractive cylinder and corneal astigmatism. RESULTS The CorT based on total corneal power measurements had an ORAsd of 0.30 diopters (D) and a mean ORA magnitude of 0.53 D. The CorT candidates based on anterior corneal power measurements all had an ORAsd of at least 0.32 D, and the mean ORA magnitudes were all 0.64 D or greater. Both the ORAsd and mean ORA magnitude of the CorT based on total corneal power measurements were significantly less than those of the CorT based on anterior corneal power measurements (both P < .001, as estimated via bootstrapping). CONCLUSIONS The CorT based on total corneal power measurements corresponds better, both in variability and closeness, with manifest refractive cylinder than the CorT based on anterior corneal power measurements. This total CorT would be fundamental when planning toric intraocular lenses or limbal relaxing incisions or other corneal astigmatic surgery.

Vector analysis applications to photorefractive surgery

One of the key factors in any successful refractive surgery practice is maximum patient satisfaction, an outcome reflected in the achievement of the full potential of uncorrected visual acuity. The majority of patients undergoing excimer laser photorefractive surgery have some amount of correctable astigmatism, whether it is associated with spherical correction or less commonly cylinder alone. The technique of vector planning is fundamental in planning for and treating and analyzing these patients. It is an invaluable tool that integrates the dual modalities of optical correction and corneal shape into the laser paradigm, allowing a customized treatment plan to be employed. The examination of astigmatism outcomes by vector analysis has been described by a number of authors in various ways. The methodology in this chapter addresses planning of photoastigmatic refractive surgery as well as the analysis requirements of corneal and refractive astigmatism. The refractive surgeon needs not only to address and quantify the astigmatism that is to be treated but to calculate targets to quantify errors and adjustments. Periodic and frequent analysis of results for ongoing nomogram refinement enables incremental improvement of future treatments and outcomes to be refined.

Corneal coupling of astigmatism applied to incisional and ablative surgery

Purpose To redefine measures of corneal coupling for use with incisional and ablation procedures for astigmatism. Setting Private clinics, Melbourne, Victoria, Australia. Design Retrospective nonrandomized study. Methods The measures known as the coupling ratio (CR) and coupling constant (CC) were redefined to ensure validity in most cases of incisional procedures and laser vision correction procedures. In addition, a new measure—the coupling adjustment (CAdj)—was developed to quantify the amount of spherical adjustment that must be applied to compensate for coupling that occurs as a result of astigmatism treatment. These quantitative measures of coupling were applied to retrospective data to show their applicability. Results Pure myopic, compound myopic, and compound hyperopic astigmatism excimer laser treatments showed a CR close to zero, a CC close to 0.5, and a CAdj close to zero. Incision LRIs showed a CR close to 1.0 and a CC close to zero. In all cases, the coupling measures were consistent for treatments with a larger astigmatic component (>1.0 diopter) but variable when the astigmatic component of the treatment was smaller. Conclusions The revised definitions of CR and CC can be used with incisional and ablative surgery. Incorporating the CAdj into the planning of spherocylindrical treatments allows one to factor in the effect of the astigmatic treatment on the spherical component and thus to more accurately target the desired spherical equivalent. Financial Disclosure Dr. Alpins and Mr. Stamatelatos have a financial interest in the Assort software program. Dr. Ong is an employee of Assort.

Asymmetric Corneal Flattening Effect After Small Incision Cataract Surgery

PURPOSE To determine whether the flattening effect of corneal incisions differs between the right and left eye. METHODS A retrospective study of preoperative and postoperative corneal astigmatism was performed for patients who had bilateral cataract surgery by a right-handed surgeon. The change in corneal astigmatism was attributed to the 2.2-mm phacoemulsification incision, and the incisional flattening effect was calculated. The incisions were grouped by position on the eye and whether they were performed on the preoperative steep corneal meridian. RESULTS A total of 1,298 eyes of 649 patients were evaluated. The flattening effect of temporal 2.2-mm incisions performed on the preoperative corneal steep meridian was different for right eyes (0.53 diopters [D]) and left eyes (0.34 D) (P = .017). The flattening effect of superior 2.2-mm incisions performed on the preoperative corneal steep meridian was equivalent in the two eyes. CONCLUSIONS The flattening effect of a corneal incision may depend on whether it has been performed on the right or the left eye. [J Refract Surg. 2016;32(9):598-603.].

Astigmatism Surprise After Refractive Surgery

Misalignment of the surgical treatment is the major source of refractive surprise in relation to astigmatism. Sources of misalignment include cyclotorsion from the seated to supine position, a physical turning of the patients head or intentionally placing a cataract incision on a meridian other than the steepest corneal meridian due to ergonomic factors or to more accurately neutralise the corneal astigmatism using a toric IOL. Corneal incisions, no matter how small, should be analysed vectorially to determine what effect, if any, they have had on the preoperative corneal astigmatism. Refractive cataract surgeons employing a technique to correct astigmatism at the time of surgery (toric IOLs, LRIs, etc.) need to consider the effect of the phaco incision on the remaining astigmatism; otherwise, the IOL or LRI will be misaligned and/or undercorrected. The forces acting to change the corneal structure in a misaligned treatment are flattening (or steepening) and torque. These result in a reduction (or increase) of astigmatism at the intended meridian and also a change (rotation) in the meridian of the astigmatism. Furthermore, placing the toric IOL at an axis that is not the steepest corneal meridian or the toric IOL rotating over time. Vector analysis is a useful tool to calculate the effects of a misaligned treatment on the remaining astigmatism.

Refractive, corneal, and ocular residual astigmatism: distribution in a German population and age-dependency: the Gutenberg health study

Dear Editor, There is much interest in the paper that appeared online in Graefe ’s Archive for Clinical and Exper imental Ophthalmology by Karl-Georg Schuster A, Pfeiffer N, Schulz A et al. examining the Ocular residual astigmatism (ORA) of 13,558 healthy astigmatic eyes [1]. The ORA is a parameter introduced in 1997 [2] quantifying the vectorial difference between corneal and refractive (corneal plane) astigmatism measures. In normal eyes the ORA typically ranges from 0.73 to 0.81 dioptres [2, 3]. The ORA can be higher in more irregular corneas such as in those with keratoconus (1.34D) [4]. The ORA, like all vectors, can only be positive, a convention confirmed by Jaffe and Clayman in their description of surgically induced astigmatism (SIA) in 1975 [5]. A calculated negative vector requires reversal of polarity to render it positive and meaningful. In practical terms, a pilot would not radio his position as −200 km south of an airport when in fact he was situated 200 km north. It appears that this paper and its examination of ORA did not adhere to this convention, creating confusion for the reader and a potential misinterpretation of the findings, which is unfortunate since the study is a valuable one for comparisons with other studies that comply with sign convention, using the ORA and other vectors in the manner they were developed [6–9]. As a result of calculating a negative ORA, the summated vector mean axis of the ORA was found to be 90 degrees in this study [1] when in other series including our own it is usually 180 degrees [2–4, 6–9]. It would be helpful for this paper to be modified at this late stage by expressing the ORA in positive terms to be consistent with other papers the authors wish it to be compared with. Future publications would benefit from the same guiding principles so that a common sign convention can be maintained.