Pietro Ducoli

Analysis of retinal capillaries in patients with type 1 diabetes and nonproliferative diabetic retinopathy using adaptive optics imaging.

Purpose: To illustrate a noninvasive method to analyze the retinal capillary lumen caliber in patients with Type 1 diabetes. Methods: Adaptive optics imaging of the retinal capillaries were acquired in two parafoveal regions of interest in eyes with nonproliferative diabetic retinopathy and unaffected controls. Measures of the retinal capillary lumen caliber were quantified using an algorithm written in Matlab by an independent observer in a masked manner. Comparison of the adaptive optics images with red-free and color wide fundus retinography images was also assessed. Results: Eight eyes with nonproliferative diabetic retinopathy (eight patients, study group), no macular edema, and preserved visual acuity and eight control eyes (eight healthy volunteers; control group) were analyzed. The repeatability of capillary lumen caliber measurements was 0.22 &mgr;m (3.5%) with the 95% confidence interval between 0.12 and 0.31 &mgr;m in the study group. It was 0.30 &mgr;m (4.1%) with the 95% confidence interval between 0.16 and 0.43 &mgr;m in the control group. The average capillary lumen caliber was significantly narrower in eyes with nonproliferative diabetic retinopathy (6.27 ± 1.63 &mgr;m) than in the control eyes (7.31 ± 1.59 &mgr;m, P = 0.002). Conclusion: The authors demonstrated a noninvasive method to analyze, with micrometric scale of resolution, the lumen of retinal capillaries. The parafoveal capillaries were narrower in patients with Type 1 diabetes and nonproliferative diabetic retinopathy than in healthy subjects, showing the potential capability of adaptive optics imaging to detect pathologic variations of the retinal microvascular structures in vaso-occlusive diseases.

Variations in image optical quality of the eye and the sampling limit of resolution of the cone mosaic with axial length in young adults

PURPOSE: To evaluate the variation in higher‐order ocular wavefront aberrations and the Nyquist limit of resolution of the cone mosaic (Nc) in a population of young healthy subjects and the relation to axial length (AL). SETTING: Fondazione G.B. Bietti IRCCS, Rome, Italy. DESIGN: Case series. METHODS: An adaptive optics retinal camera prototype (rtx1) was used to image the cone mosaic. Cone density and Nc were calculated at fixed eccentricity between 260 μm and 600 μm from the foveal center. Ocular higher‐order wavefront aberrations were measured using the OPD Scan II device. The coefficient of variation (CoV) was used to analyze the variation in optical and retinal parameters. The correlation of optical and retinal parameters with AL was performed using Pearson analysis. RESULTS: Twelve subjects (age 24 to 38 years; AL 22.61 to 26.63 mm) were evaluated. A high interindividual variation in the higher‐order wavefront aberrations was found, ranging from 26% for corneal higher‐order aberrations (HOAs) to 41% for intraocular HOAs. The CoV of cone density and Nc were 16% and 5%, respectively. The decline in cone density and Nc with AL was statistically significant at all retinal eccentricities (R2 > 0.44, P<.001). CONCLUSIONS: Although there appeared to be random variation in the eyes optical wavefront aberration from subject to subject, the cone‐packing density and Nc were highly correlated with AL. Although the eyes overall image optical quality in the emmetropic group and the myopic group was comparable, the spatial sampling of the cone mosaic decreased with increasing AL. Financial Disclosure: No author has a financial or proprietary interest in any material or method mentioned.

Eccentricity dependent changes of density, spacing and packing arrangement of parafoveal cones

To investigate the distribution of cone density and spacing as well as the preferred packing arrangement of the cone mosaic as a function of retinal eccentricity.

Influence of posterior corneal astigmatism on total corneal astigmatism in eyes with moderate to high astigmatism

Purpose To evaluate the influence of posterior corneal astigmatism on total corneal astigmatism in patients with 1.00 diopter (D) or more of corneal astigmatism. Setting Private practice, Bologna, Italy. Design Prospective case series. Methods Corneal astigmatism was measured using a Scheimpflug camera combined with a corneal topographer (Sirius). Keratometric astigmatism, anterior corneal astigmatism, posterior corneal astigmatism, and total corneal astigmatism were evaluated. Vector analysis was performed according to the Næser method. Results One hundred fifty‐seven eyes were enrolled. Keratometric astigmatism was with the rule (WTR), against the rule (ATR), and oblique in 84.0%, 11.5%, and 4.5% of eyes, respectively. Posterior corneal astigmatism exceeded 0.50 D and 1.00 D in 55.4% of eyes and 5.7% of eyes, respectively. The mean posterior corneal astigmatism was 0.54 D, inclined 91 degrees in relation to the steeper anterior corneal meridian. The steepest meridian was vertically aligned in 93.0% of cases. Compared with total corneal astigmatism, keratometric astigmatism overestimated WTR astigmatism by a mean of 0.22 D ± 0.32 (SD), underestimated ATR astigmatism by 0.21 ± 0.26 D, and overestimated oblique astigmatism by 0.13 ± 0.37 D. In the whole sample, a difference in astigmatism magnitude of 0.50 D or more was detected between keratometric astigmatism and total corneal astigmatism in 16.6% of cases and the difference in the location of the steep meridian was greater than 10 degrees in 3.8% of cases. Conclusion In patients who are candidates for surgical correction of astigmatism, measuring only the anterior corneal curvature can lead to inaccurate evaluation of the total corneal astigmatism. Financial Disclosure Mr. Versaci and Mr. Vestri are employees of Costruzione Strumenti Oftalmici Srl. No author has a financial or proprietary interest in any material or method mentioned.

Biomechanical changes in the human cornea after transepithelial corneal crosslinking using iontophoresis

Purpose To evaluate the corneal response to variable intraocular pressure (IOP) in human eye globes after ultraviolet‐A (UVA) transepithelial corneal crosslinking using iontophoresis. Setting Fondazione G.B. Bietti IRCCS, Rome, Italy. Design Experimental study. Methods Four human donor eye globes were treated with transepithelial crosslinking using iontophoresis and rapid UVA corneal irradiation, and 4 globes had standard crosslinking. Inflation experiments were performed on the globes before and after crosslinking. Topographic maps of the anterior and posterior cornea were acquired using Scheimpflug topography. Images were obtained using a mechanical regimen to analyze corneal strain in response to cyclic stress. Corneal shape changes were analyzed as a function of IOP, and corneal stress–strain curves were generated. Results Before crosslinking, instillation of hypotonic riboflavin‐5–phosphate sodium 0.1% solution using iontophoresis increased corneal thickness by 5% and instillation of dextran‐enriched riboflavin 0.1% solution decreased corneal thickness by 13%. Five minutes after treatment, both crosslinking procedures reduced corneal thickness by 2%. Young’s modulus (E) of the anterior cornea increased by a mean of 1.8 times (from 1.6 to 2.9 MPa) and 1.9 times (from 1.3 to 2.5 MPa) after transepithelial crosslinking using iontophoresis and standard crosslinking, respectively. The E value of the posterior cornea also increased after both procedures (mean 1.7 times versus 3.1 times). Conclusions Transepithelial crosslinking using iontophoresis increased the biomechanical strength of human corneal tissue in inflation testing of donor eye globes. The effect on corneal stiffness was almost comparable to that of standard crosslinking. Financial Disclosure No author has a financial or proprietary interest in any material or method mentioned.

Interocular symmetry of parafoveal photoreceptor cone density distribution.

Purpose: To investigate the variation and symmetry of cone density distribution along the nasal and temporal retina of fellow eyes. Methods: An adaptive optics retinal camera (rtx1; Imagine Eyes) was used to obtain images of the parafoveal cone mosaic in 20 healthy subjects. Cone density was estimated at 250, 420, 760, and 1,300 &mgr;m eccentricity from the fovea along the nasal and temporal retina of both eyes in each subject. The coefficient of variation and the intraclass correlation coefficient were used to calculate the variation and absolute agreement of cone density between the same retinal eccentricity locations of fellow eyes, respectively. Results: A considerable variation of cone density between subjects was found at all eccentricities along the nasal and temporal retina (intersubject coefficient of variation ≥ 11%, P < 0.001). The intrasubject variation of cone density was, however, moderate (coefficient of variation ⩽ 13% in 95% of the subjects); a high agreement was, on average, found between the cone density estimates at the same eccentricity along the nasal and temporal retina of fellow eyes (intraclass correlation coefficient ≥ 0.86, P < 0.001). Conclusion: Cone density follows a symmetrical distribution between fellow eyes. A systematic distribution of parafoveal cones between fellow eyes may provide an anatomical basis for the involvement of the photoreceptor layer in the first step of binocular spatial sampling.

Evaluation of Femtosecond Laser Clear Corneal Incision: An Experimental Study

PURPOSE To evaluate the changes of corneal topography following femtosecond laser and manual clear corneal incision (CCI). METHODS Inflation testing was performed in 14 human eye globes to evaluate the topographic response of the cornea to CCIs. In seven samples (femtosecond laser group), a 2.75-mm three-plane CCI was created using the iFS femtosecond laser (Abbott Medical Optics, Inc., Santa Ana, CA); the remaining seven samples (control group) received a 2.75-mm manual CCI using disposable angled knives. Topographic maps of the anterior and posterior cornea were acquired using a Scheimpflug topographer Pentacam HR (Oculus Optikgeräte GmbH, Wetzlar, Germany). Keratometric data were used to analyze the curvature changes of the cornea. The changes of corneal astigmatism were analyzed by vector analysis. RESULTS After CCI, the mean change of the anterior keratometric power was 0.04 ± 0.39 and 0.05 ± 0.51 diopters (D) (analysis of variance, P > .05) in the femtosecond laser and control groups, respectively. The mean change (P > .05) of the posterior corneal keratometric power was 0.16 ± 0.19 and 0.15 ± 0.18 D, respectively. The average change of the anterior and posterior corneal astigmatism vector magnitude was 0.17 D or less in both groups (P > .05). A slight against-the-rule astigmatic change of the anterior and posterior corneal interfaces was found after both CCI techniques. CONCLUSION The 2.75-mm three-plane CCI created with femtosecond laser showed minimal changes of the anterior and posterior corneal topography, comparable with those of single-plane angled manual incision.

Influence of sampling window size and orientation on parafoveal cone packing density.

We assessed the agreement between sampling windows of different size and orientation on packing density estimates in images of the parafoveal cone mosaic acquired using a flood-illumination adaptive optics retinal camera. Horizontal and vertical oriented sampling windows of different size (320x160 µm, 160x80 µm and 80x40 µm) were selected in two retinal locations along the horizontal meridian in one eye of ten subjects. At each location, cone density tended to decline with decreasing sampling area. Although the differences in cone density estimates were not statistically significant, Bland-Altman plots showed that the agreement between cone density estimated within the different sampling window conditions was moderate. The percentage of the preferred packing arrangements of cones by Voronoi tiles was slightly affected by window size and orientation. The results illustrated the high importance of specifying the size and orientation of the sampling window used to derive cone metric estimates to facilitate comparison of different studies.

Influence of intraocular lens haptic design on refractive error

Purpose To assess the influence of intraocular (IOL) haptic design on the refraction prediction error in patients having cataract surgery. Setting Private practice. Design Comparative case series. Methods Corneal power and axial length were measured with the same devices in eyes with a 3‐piece Acrysof IOL and eyes with a 1‐piece Acrysof IOL and were entered into the Haigis, Hoffer Q, Holladay 1, and SRK/T formulas. The median absolute error and mean absolute error in refraction prediction (ie, difference between expected refraction and actual refraction) were assessed 1 month postoperatively. Results The study evaluated 110 eyes with the 3‐piece IOL and 84 eyes with the 1‐piece IOL. With all formulas, the median absolute error was lower with the 3‐piece IOL. It ranged between 0.15 diopter (D) (Haigis and Holladay 1) and 0.19 D (SRK/T) with the 3‐piece IOL and between 0.23 D (Haigis) and 0.30 D (SRK/T) with the 1‐piece IOL. With all formulas, a higher percentage of eyes with the 3‐piece IOL were within ±0.25 D and ±0.50 D of the target refraction. Conclusions Three‐piece IOLs may yield better refractive outcomes than 1‐piece IOLs. A possible reason is that once the early forward IOL shift previously observed with the 3‐piece design occurs because of the haptic‐compression force decay typical of these IOLs, the rigid haptics of 3‐piece IOLs still exert more pressure against the capsular bag than the haptics of 1‐piece IOLs. Therefore, 3‐piece IOLs may better resist subsequent capsule contraction and provide a more predictable effective lens position. Financial Disclosure Dr. Hoffer receives royalties for his book IOL Power, Slack, Inc., and formula royalties from all manufacturers using the Hoffer Q formula. No other author has a financial or proprietary interest in any material or method mentioned.

Optimal parameters to improve the interface quality of the flap bed in femtosecond laser-assisted laser in situ keratomileusis

PURPOSE: To analyze the interface quality of the anterior stroma after femtosecond laser flap creation using atomic force microscopy. SETTING: IRCCS Fondazione G.B. Bietti, Rome, Italy. DESIGN: Experimental study. METHODS: A 110 μm depth flap was created in 20 human corneal tissues using a femtosecond laser platform (Intralase iFS). Tissues were divided into 4 groups of various cutting parameters: pulse energy and spot separation of 0.75 μJ and 6 μm (Group 1), 0.65 μJ and 5 μm (Group 2), 0.55 μJ and 4 μm (Group 3), and 0.45 μJ and 4 μm (Group 4). Four additional tissue sections were cut using a motorized microkeratome (Hansatome). Atomic force microscopy (Autoprobe CP) analysis was performed on the stromal bed of each sample. RESULTS: The corneal tissues treated with higher pulse energies and wider spot separations (Groups 1 and 2) showed a rougher stromal bed interface (root mean square [RMS] rough = 0.23 μm ± 0.008 (SD) and 0.24 ± 0.009 μm, respectively) than tissues in Groups 3 and 4 (RMS rough = 0.18 ± 0.006 μm and 0.18 ± 0.008 μm, respectively; P<.001, 1‐way analysis of variance). The stromal surface quality of tissues treated with pulse energies of 0.55 μJ or lower and 4 μm spot separation compared favorably with that of tissues cut by the microkeratome (RMS rough = 0.17 ± 0.006 μm; P>.05, Tukey). CONCLUSIONS: The femtosecond stromal interface quality was improved with pulse energy lower and spot separations narrower than those currently used in the clinical setting. The flap interface smoothness created by the femtosecond laser was comparable to that created by the microkeratome. Financial Disclosure: No author has a financial or proprietary interest in any material or method mentioned.