Comparison of Automated Keratometer and Scheimpflug Tomography for Predicting Refractive Astigmatism in Pseudophakic Eyes.

PURPOSE: To analyse the correspondence between refractive astigmatism and corneal astigmatism in pseudophakic eyes with non-toric intraocular lenses. SETTING: Yeouido St. Mary hospital, Seoul, Republic of Korea. DESIGN: Evaluation of a diagnostic test instrument. METHODS: This retrospective study included 95 eyes of 95 patients. Corneal astigmatism was measured with an automated keratometer (RK-5, Canon) and Scheimpflug tomography (Pentacam HR, Oculus). Refractive astigmatism was compared to keratometric astigmatism (based on anterior corneal measurements only), equivalent K-reading, and total corneal astigmatism (both based on anterior and posterior corneal measurements). Vector analysis was carried out by Næser's polar value method. The accuracy was defined as the average magnitude of the vectorial difference in astigmatism (DA). Each corneal measurement was optimized in retrospect by a multiple linear regression equation between refractive and corneal astigmatism. RESULTS: Keratometric astigmatism overestimated with-the-rule (WTR) refractive astigmatism and underestimated against-the-rule (ATR) refractive astigmatism. Several measurements based on both corneal surfaces' values did not show any statistically significant difference with respect to refractive astigmatism. The mean corneal astigmatism by total corneal refractive power (TCRP) at 4.0 mm (zone/pupil) produced the lowest mean arithmetic DA and the highest percentage of eyes with a DA ≤ 0.50 dioptre. After optimization, the accuracies of automated KA and TCRP 4.0 mm (zone/pupil) were similar. CONCLUSIONS: Total corneal astigmatism measured by Scheimpflug tomography at a 4.0 mm zone centered on the pupil accurately reflects the refractive astigmatism in pseudophakic eyes. However, the accuracy of total corneal astigmatism is not different from automated KA after optimization.

A rare case of lacrimal sac angioleiomyoma managed with dacryocystectomy and turbinectomy.

We report a rare case of a lacrimal sac angioleiomyoma. A 56-year-old woman complained of pain in the right medial canthal region over a period of 2 years. There were no complaints of epiphora or ocular infection, and no visible or palpable masses in the medial canthal region. Computed tomography scan revealed a solid tumor of the lacrimal sac expanding to the nasolacrimal duct and protruding under the inferior turbinate. The tumor was removed by external dacryocystectomy combined with endonasal, endoscopic anterior turbinectomy, and nasal mucosal resection. Histological and immunohistological findings were consistent with an angioleiomyoma of the venous type. There was no recurrence of the tumor at the three-year follow-up. Angioleiomyomas should be included in the differential diagnosis of lacrimal sac tumors. The definitive diagnoses rely on histology and immunohistological reactions. The treatment is complete surgical resection.

Precision of the Nidek Tonoref II autokeratometer: how many repeated measurements are required?

PURPOSE: To determine the minimal number of repeated measurements required for precise Nidek Tonoref II autokeratometry. METHODS: This prospective, non-intervention study was performed at the Department of Ophthalmology, Randers, Denmark. We used the Nidek Tonoref II autokeratometer to perform 10 successive measurements on 100 right eyes of cooperative individuals. Each keratometry was converted to the spherical equivalent power (SE), while the net astigmatism was converted to polar values along zero (KP(0)) and 45 degrees (KP(45)). All units were in dioptres (D). The precision was calculated as the mean absolute difference between paired measurements, using one or the average of two, three, four or five autokeratometries. Statistical assessment was performed with Dunn's test for repeated measurements with a Bonferroni correction. RESULTS: The precision of SE, KP(0) and KP(45) increased statistically significantly from one to three measurements, with no significant improvement for autokeratometries based on four or five measurements. There was no significant precision difference between one and two measurements. CONCLUSION: A single keratometry is inadequate, but the vector average of three measurements is sufficient for precise autokeratometry with the Tonoref II device. The consistent use of three keratometries with this device may increase the precision of spherical and toric IOL calculation.

Comparison of 13 formulas for IOL power calculation with measurements from partial coherence interferometry.

BACKGROUND/AIMS: To compare the accuracy of 13 formulas for intraocular lens (IOL) power calculation in cataract surgery. METHODS: In this retrospective interventional case series, optical biometry measurements were entered into these formulas: Barrett Universal II (BUII) with and without anterior chamber depth (ACD) as a predictor, EVO 2.0 with and without ACD as a predictor, Haigis, Hoffer Q, Holladay 1, Holladay 2AL, Kane, Næser 2, Pearl-DGS, RBF 2.0, SRK/T, T2 and VRF. The mean prediction error (PE), median absolute error (MedAE), mean absolute error and percentage of eyes with a PE within ±0.25, ±0.50, ±0.75 and ±1.00 diopters (D) were calculated. RESULTS: Two hundred consecutive eyes were enrolled. With all formulas, the mean PE was zero. The BUII with no ACD had the lowest standard deviation (±0.343 D), followed by the T2 (0.347 D), Kane (0.348 D), EVO 2.0 with no ACD (0.348 D) and BUII with ACD (0.353 D) formulas. The difference among the MedAEs of all formulas was statistically significant (p<0.0001); the lowest values were achieved with the Kane (0.214 D), RBF 2.0 (0.215 D), BUII with and without ACD (0.218 D) and SRK/T (0.223 D). A percentage ranging from 80% to 88.5% of eyes showed a PE within ±0.50 D and all formulas achieved more than 50% of eyes with a PE within ±0.25 D. CONCLUSION: All investigated formulas achieved good results; there was a tendency towards better outcomes with newer formulas. Traditional formulas can still be considered an accurate option.

Surgically induced astigmatism made easy: calculating the surgically induced change in sphere and cylinder for corneal incisional, corneal laser, and intraocular lens-based surgery.

Net cylinder and spherocylinder formats characterize individual keratometries and prescriptions but must be converted to dioptric vectors to allow for calculations and statistical analyses. Næser's polar value system was specifically developed for the analysis of the surgically induced refractive change along the surgical meridian. This study provides a short description together with a practical manual and a computer program for the use of this dioptric vector method. Measurement techniques, vector equations, statistical methods, and terminology are reviewed. The analysis is identical for corneal and refractive measurements and for corneal incisional, corneal laser, and intraocular lens-based surgery. The choice of appropriate surgical reference meridians for standard surgical procedures is demonstrated. The Excel file may be used by the reader for future studies.

Bilateral dacryocystitis complicated by unilateral retrobulbar abscess in a five-week-old infant.

Retrobulbar orbital abscess in children is a rare condition, and diagnosis and management can be challenging. We report the case of a 5-week-old male infant with retrobulbar orbital abscess secondary to acute dacryocystitis developed from a dacryocystocele. The patient presented with respiratory difficulty, sepsis and progressive clinical findings suggestive of post-septal cellulitis. He was successfully treated with endonasal incision of subturbinate dacryocystoceles followed by probing of the lacrimal ducts. Congenital dacryocystocele must be considered a differential diagnosis in infants with respiratory difficulty and may develop into a vision- and life-threatening condition requiring immediate intervention.

Accuracy of thick-lens intraocular lens power calculation based on cutting-card or calculated data for lens architecture.

PURPOSE: To compare the accuracy of a thick-lens intraocular lens (IOL) power formula using the manufacturer's cutting-card information (the Næser 1 formula) and calculated data from open sources (the Næser 2 formula) for IOL architecture; and to compare these results with the achievements of the Barrett Universal II, Haigis, Hoffer Q, Holladay 1, and SRK/T formulas. SETTING: IRCCS GB Bietti Foundation, Rome, Italy. DESIGN: Retrospective case series. METHODS: For each IOL power formula, the prediction error in refraction was retrospectively calculated in eyes after phacoemulsification with implantation of the SN60WF posterior chamber IOL. The predictions made using the different formulas were optimized in retrospect by adjusting the respective constants. The mean arithmetic error (ME), the variance, and the median absolute error (MedAE) were calculated, as well as the dependency of the arithmetic error on the axial length. RESULTS: The study comprised 151 eyes. The Næser 1 and Næser 2 formulas were identical clinically and statistically. The ME (P = .278 with a one-way analysis of variance) and the variances for arithmetic errors (P = .248 with Levene's homogeneity test) were similar for all 7 formulas. A combined metric of ME, variance, MedAE, and arithmetic error on the axial length suggested the Næser 2 formula as the most accurate, followed by the Næser 1, Barrett Universal II, Haigis, SRK/T, Hoffer Q, and Holladay 1 formulas. CONCLUSIONS: The Næser thick-lens IOL power equations based on calculated and manufacturer's IOL data provided similar accuracies and performed approximately as the best thin-lens formulas. Cutting-card information is not necessary in current IOL power calculation.

Customized Toric Intraocular Lens Implantation in Eyes with Cataract and Corneal Astigmatism after Deep Anterior Lamellar Keratoplasty: A Prospective Study.

PURPOSE: To investigate the effectiveness of toric intraocular lenses (IOLs) for treating corneal astigmatism in patients with cataract and previous deep anterior lamellar keratoplasty (DALK). SETTING: San Giovanni-Addolorata Hospital, Rome, Italy. DESIGN: Prospective interventional case series. METHODS: Patients undergoing cataract surgery after DALK for keratoconus were enrolled. Total corneal astigmatism (TCA) was assessed by a rotating Scheimpflug camera combined with Placido-disk corneal topography (Sirius; CSO, Firenze, Italy). A customized toric IOL (FIL 611 T, Soleko, Rome, Italy) was implanted in all eyes. One year postoperatively, refraction was measured, the IOL position was recorded, and vectorial and nonvectorial analyses were performed to evaluate the correction of astigmatism. RESULTS: Ten eyes of 10 patients were analyzed. The mean preoperative TCA magnitude was 4.92 ± 1.99 diopters (D), and the mean cylinder of the IOL was 6.18 ± 2.44. After surgery, the difference between the planned axis of orientation of the IOL and the observed axis was ≤10° in all eyes. The mean surgically induced corneal astigmatism was 0.35 D at 20°. The mean postoperative refractive astigmatism power was 1.13 ± 0.94 D; with respect to preoperative TCA, the reduction was statistically significant (p < 0.0001). The mean change in astigmatism power was 3.80 ± 1.60 D, corresponding to a correction of 77% of preoperative TCA power. Nine eyes out of 10 had a postoperative refractive astigmatism power ≤ 2D. CONCLUSIONS: Toric IOLs can effectively correct corneal astigmatism in eyes with previous DALK. The predictability of cylinder correction is partially lowered by the variability of the surgically induced changes of TCA. This trial is registered with NCT03398109.

Age-related changes in with-the-rule and oblique corneal astigmatism.

PURPOSE: To describe the age-related changes in with-the-rule (WTR) and oblique keratometric astigmatism (KA), posterior corneal astigmatism (PCA) and total corneal astigmatism (TCA). METHODS: We used a Pentacam HR (high-resolution) rotating Scheimpflug camera to determine the KA, PCA and TCA in the right eyes of 710 patients, aged from 20 to 88 years. The age-related changes along the vertical, horizontal and oblique meridians were analyzed with Naeser's polar value method in a cross-sectional study. RESULTS: In the whole group, all meridional astigmatic powers and polar values were stable in the age groups from 20 to 49 years, followed by a 1.0 dioptre (D) against-the-rule (ATR) change in KA and TCA, and a 0.12 D reduction in against-the-rule PCA. A nasal rotation of the steep meridian in KA and TCA was noted in the 70-88 years old. The PCA averaged approximately 0.25 D ATR in all age groups. Females displayed the same early astigmatic stability as in the whole group, while male eyes demonstrated a linear decay from 1.5 D WTR at 20 years to 0.5 D ATR astigmatism for the oldest patients. CONCLUSION: Corneal astigmatism is stable until the age of 50 years; thereafter both keratometric and total corneal astigmatism show a 0.25 D ATR change per 10 years. The average 0.25 D ATR PCA compensates the predominant keratometric WTR astigmatism in the younger patients and increases the TCA in the elderly with keratometric ATR astigmatism. The gender-based differences in age-related astigmatism require further studies.

Optimized keratometry and total corneal astigmatism for toric intraocular lens calculation.

PURPOSE: To compare keratometric astigmatism (KA) and different modalities of measuring total corneal astigmatism (TCA) for toric intraocular lens (IOL) calculation and optimize corneal measurements to eliminate the residual refractive astigmatism. SETTING: G.B. Bietti Foundation IRCCS, Rome, Italy. DESIGN: Prospective case series. METHODS: Patients who had a toric IOL were enrolled. Preoperatively, a Scheimpflug camera (Pentacam HR) was used to measure TCA through ray tracing. Different combinations of measurements at a 3.0 mm diameter, centered on the pupil or the corneal vertex and performed along a ring or within it, were compared. Keratometric astigmatism was measured using the same Scheimpflug camera and a corneal topographer (Keratron). Astigmatism was analyzed with Næser's polar value method. The optimized preoperative corneal astigmatism was back-calculated from the postoperative refractive astigmatism. RESULTS: The study comprised 62 patients (64 eyes). With both devices, KA produced an overcorrection of with-the-rule (WTR) astigmatism by 0.6 diopter (D) and an undercorrection of against-the-rule (ATR) astigmatism by 0.3 D. The lowest meridional error in refractive astigmatism was achieved by the TCA pupil/zone measurement in WTR eyes (0.27 D overcorrection) and the TCA apex/zone measurement in ATR eyes (0.07 D undercorrection). In the whole sample, no measurement allowed more than 43.75% of eyes to yield an absolute error in astigmatism magnitude lower than 0.5 D. Optimized astigmatism values increased the percentage of eyes with this error up to 57.81%, with no difference compared with the Barrett calculator and the Abulafia-Koch calculator. CONCLUSION: Compared with KA, TCA improved calculations for toric IOLs; however, optimization of corneal astigmatism measurements led to more accurate results.

Estimating Total Corneal Astigmatism From Anterior Corneal Data.

PURPOSE: To determine keratometric astigmatism (KA), posterior corneal astigmatism (PCA), and total corneal astigmatism (TCA) in 951 normal eyes, to establish a model for estimating TCA from anterior corneal data, and to test this method in a new group of eyes with toric intraocular lenses (TIOLs). METHODS: We used a Pentacam HR (high-resolution) Scheimpflug camera to determine KA, PCA, and TCA in 951 normal eyes. A model to estimate TCA from anterior corneal data was evaluated by the difference (=error) between the measured TCA and the estimated value. The model was tested in 40 eyes with TIOLs. RESULTS: KA, TCA, and PCA averaged 1.06 (±0.85) D, 1.05 (±0.83) D, and 0.33 (±0.17) D. The error of the model to estimate TCA averaged zero with an SD of ±0.21 D. Application of this model and of direct Pentacam TCA measurements in TIOL calculation gave similar results, namely a slight reduction of overcorrection in with-the-rule astigmatism, but an eradication of undercorrection in against-the-rule astigmatism. CONCLUSIONS: It was possible to estimate TCA accurately from anterior corneal data with a new formula. However, application of both this model on keratometric data and of direct Pentacam measurements in a group of 40 eyes with TIOLs did not completely eradicate the refractive error in TIOL calculation. More studies comparing Pentacam TCA and refractive astigmatism are required.

Total Corneal Astigmatism Measurements: Agreement Between 2 Rotating Scheimpflug Cameras.

PURPOSE: To investigate agreement between rotating Scheimpflug camera (Pentacam HR, Oculus) and rotating Scheimpflug camera combined with Placido disc corneal topography (Sirius, CSO) in measuring total corneal astigmatism (TCA). METHODS: In this observational study, all patients undergoing cataract surgery with preoperative measurement of TCA by both devices and a validated corneal topographer (Keratron, Optikon 2000) were retrospectively evaluated. Astigmatism analysis was performed with and without vector analysis separately in eyes with with-the-rule, against-the-rule, and oblique astigmatism. Vector analysis was performed using the Næser polar system. RESULTS: In 130 eyes of 130 subjects, nonvectorial analysis revealed that the mean TCA values obtained with the Sirius were higher than the corresponding values given by the Pentacam HR in all subgroups, although the difference was statistically significant only in eyes with against-the-rule astigmatism (P = 0.0009). This finding was confirmed by vector analysis. A TCA magnitude difference greater than 0.5 diopters was observed in 20.8% of cases, and a TCA axis difference greater than 10 degrees was observed in 45.4% of cases. Axis differences dropped to 18.5% when only eyes with astigmatism >0.75 diopters were analyzed and 3 measurements were averaged. The mean difference in the meridional and torsional power of TCA was close to zero in all subgroups, but with relatively large standard deviations (approximately 0.5 D). CONCLUSIONS: Agreement between both devices in measuring TCA is only moderate with respect to both magnitude and axis orientation.

Influence of Posterior Corneal Astigmatism on Total Corneal Astigmatism in Eyes With Keratoconus.

PURPOSE: To measure posterior corneal astigmatism (PCA) and investigate its influence on total corneal astigmatism (TCA) in eyes with keratoconus. METHODS: Keratometric astigmatism (KA), PCA, and TCA were investigated by means of a dual Scheimpflug analyzer in patients with keratoconus. Vector analysis was carried out with the Næser polar value method. RESULTS: We enrolled 119 eyes. PCA magnitude averaged 0.77 ± 0.43 diopters (D) and exceeded 0.50, 1.00, and 2.00 D in 73.9%, 21.8%, and 16.8% of eyes, respectively. PCA averaged 0.95 ± 0.48, 0.55 ± 0.28, and 0.70 ± 0.35 D in eyes with with-the-rule (WTR), against-the-rule (ATR), and oblique astigmatism. The steepest posterior meridian was oriented vertically (between 61 and 119 degrees) in 55.5% of eyes, thus generating ATR astigmatism. The difference between the location of the steepest meridian of KA and that of TCA was >10 degrees in 8.4% of eyes. On average, KA overestimated TCA in eyes with WTR astigmatism by 0.16 D and underestimated TCA in eyes with ATR astigmatism by 0.22 D. The PCA power oriented along the steeper anterior corneal meridian averaged -0.83 ± 0.40, -0.40 ± 0.37, and -0.53 ± 0.43 D for WTR, ATR, and obliquely astigmatic eyes, respectively. Linear regression disclosed a statistically significant correlation (P < 0.0001, r = 0.16) between the meridional powers of TCA and PCA. CONCLUSIONS: In eyes with keratoconus, PCA displays large, variable values and is correlated to TCA. The influence of PCA on TCA cannot be disregarded when planning astigmatism correction by toric intraocular lenses.

Corneal powers measured with a rotating Scheimpflug camera.

BACKGROUND/AIM: Keratometry measures the anterior corneal curvature only. Corneal power is calculated by multiplication with the keratometric refractive index, which takes into account the average negative posterior corneal power. The aim of this study was to calculate and compare various expressions for total corneal power assessed with Scheimpflug camera techniques, which also measure the posterior corneal curvature. METHODS: We used the Pentacam rotating Scheimpflug camera to measure the equivalent power, total corneal refractive power (based on Snell's law ray tracing), and simulated keratometry (keratometric refractive index=1.3375) over the central 3.0 mm zone in 951 eyes. The keratometric refractive index of the equivalent power and the total corneal refractive power was calculated as the ratio between these values and the anterior corneal curvature. RESULTS: The equivalent power, total corneal refractive power, and simulated keratometry all differed statistically significantly (analysis of variance, p<0.001) and averaged 42.26 (±1.46) dioptres (D), 42.78 (±1.51) D and 43.42 (±1.49) D. The calculated keratometric refractive indices for equivalent and total corneal refractive power averaged 1.3284 (±0.0009) and 1.3324 (±0.0015). The error of using these calculated keratometric refractive indices rather than the measured values for equivalent and total corneal refractive power averaged 0 (±0.11 D) and -0.01 D (±0.19). CONCLUSIONS: Pentacam rotating camera assessment of total corneal power over the central 3.0 mm zone differed significantly for simulated keratometry, equivalent power and Snell's law ray tracing.