Maurizio Zanini

Influence of pupil size and cataract on retinal nerve fiber layer thickness measurements by Stratus OCT.

AimTo investigate whether retinal nerve fiber layer (RNFL) thickness, as measured by optical coherence tomography (OCT), is influenced by pupil size and cataract. MethodsRNFL thickness was measured by means of Stratus OCT (RNFL Thickness 3.4 acquisition protocol) in a group of consecutive patients undergoing phacoemulsification and intraocular lens implantation. Measurements were taken preoperatively without pupil dilation (PR1), preoperatively with pupil dilation (PR2), and 1 month postoperatively without pupil dilation. ResultsTwenty-five eyes of 25 patients were enrolled in the study and underwent statistical analysis. Pupil dilation caused RNFL thickness measurements to increase slightly in PR2 compared with PR1; the difference showed to be statistically significant in the 360-degree average measurement (P=0.0456) and in the nasal quadrant (P=0.032), but not in the remaining quadrants. Postoperative measurements were higher than those of PR1 in all quadrants (temporal P=0.011; superior P=0.0098; nasal P<0.0001; inferior P=0.0081) and in 360 degrees average (P<0.0001), suggesting that the presence of cataract significantly influences RNFL thickness as measured by Stratus OCT. More advanced degrees of lens opacity were correlated to a higher decrease in RNFL thickness values (r=0.4071, P=0.0434). ConclusionsWhile pupil size only marginally affects RNFL measurements performed by Stratus OCT, the presence and degree of cataract seem to have a significant impact. This effect should be taken in consideration when using this technology for the diagnosis of glaucoma and other neuro-ophthalmologic disorders possibly affecting the RNFL.

Correlation Between Attempted Correction and Keratometric Refractive Index of the Cornea After Myopic Excimer Laser Surgery

PURPOSE Given that the standard keratometric refractive index of 1.3375 is no longer valid after excimer laser surgery, we aimed to investigate how this value changes postoperatively and if any correlation to the attempted correction exists. METHODS The pre- and postoperative data of 98 patients who underwent either myopic photorefractive keratectomy (PRK) or LASIK were reviewed. Using postoperative videokeratography, the corneal radius (r) was obtained; the corrected corneal power (Pc) was measured by separately calculating the dioptric power of the anterior and posterior corneal surfaces. The postoperative index of refraction (n(post)) was derived from these values using the formula: n(post) = (rPc) +1. RESULTS As the amount of refractive change increases, n(post) progressively decreases (P < .0001, r = 0.9581). Linear regression provided the subsequent formula to calculate the postoperative index of refraction: n(post) = 1.338 + 0.0009856 x attempted correction. CONCLUSIONS Myopic PRK and LASIK induce a decrease in the keratometric refractive index. This reduction correlates to the amount of attempted correction. When the latter is known, calculating n(post) may enable the measurement of corneal power and thus provide an additional method for calculating intraocular lens power in eyes that have undergone myopic PRK or LASIK.

Corneal power measurements with the Pentacam Scheimpflug camera after myopic excimer laser surgery

PURPOSE: To evaluate corneal power measurements by a rotating Scheimpflug camera (Pentacam, Oculus) in eyes that have had myopic excimer laser surgery. SETTING: Private practice, Bologna, Italy. METHODS: This prospective comparative interventional case series comprised 16 eyes of 16 patients who had myopic excimer laser surgery and for whom all perioperative data were available. Four corneal power measurements obtained with the Pentacam (simulated keratometry, true net power, equivalent K reading, and BESSt formula) were analyzed and compared with values derived using the clinical history method and 2 other formulas for calculating corneal power after refractive surgery (modified keratometric refractive index according to Savini et al. and separate consideration of the anterior and posterior corneal curvatures according to Speicher). RESULTS: Analysis of variance showed a statistically significant difference between all methods (P<.0001). Bonferroni multiple comparison tests showed that the only Pentacam measurements not statistically different from the corneal power values derived using the clinical history method were the equivalent K readings at 1.0 mm, 2.0 mm, and 3.0 mm and those derived with the BESSt formula; however, considerably large 95% limits of agreement (LoA) were calculated between each of these values and those obtained with the clinical history method. CONCLUSIONS: The Pentacam device gave corneal power measurements that did not statistically significantly had differ from those predicted by the clinical history method in eyes that had previous myopic excimer laser surgery. Wide LoA are a potential source of error in intraocular lens power calculation in such patients.

Filtering blebs imaging by optical coherence tomography

Purpose:  To assess the ability of standard optical coherence tomography to visualize filtering blebs after glaucoma surgery.

Ocular surface changes in laser in situ keratomileusis-induced neurotrophic epitheliopathy.

PURPOSE To evaluate the ocular surface changes in patients with laser in situ keratomileusis (LASIK)-induced neurotrophic epitheliopathy. METHODS Seven consecutive patients with LASIK-induced neurotrophic epitheliopathy were studied prospectively and compared to a control group (seven consecutive patients who had LASIK- but without neurotrophic epitheliopathy). Bilateral sequential LASIK was performed at a 1-week interval; the first operated eye of each patient was considered for statistical analysis. Blinking, corneal sensitivity, tear break-up time, tear secretion and clearance were measured preoperatively (T0) and postoperatively at 1 week after surgery on the first eye (T1), and 1 week (T2), 1 month (T3), and 3 months (T4) after surgery was performed on the second eye. RESULTS Laser in situ keratomileusis-induced neurotrophic epitheliopathy occurred bilaterally in all patients. During follow-up, patients with LASIK-induced neurotrophic epitheliopathy showed a significant decrease in blinking (P = .0002), which was not observed in cases without LASIK-induced neurotrophic epitheliopathy [corrected] Compared to eyes without LASIK-induced neurotrophic epitheliopathy, those with LASIK-induced neurotrophic epitheliopathy revealed lower values of sensitivity in the central cornea preoperatively and early postoperatively (T0, P = .004; T1, P = .003; T2, P = .003). A trend towards reduced sensitivity was also detected in the central cornea in late follow-up and in the superior, temporal, and nasal sectors of the flap at all examinations. No significant differences were observed in break-up time, tear secretion, or clearance within or between the two groups. CONCLUSION Decreased blinking seems to be involved in the pathogenesis of LASIK-induced neurotrophic epitheliopathy. The reduction probably depends on the lower levels of corneal sensitivity and induces the epitheliopathy by increasing the ocular surface exposure.

Monomanual Pupil Stretcher

The monomanual pupil stretcher is a new instrument that allows the authors to easily, quickly, and safely stretch the pupil. The specific features of the hooks allow pupil stretching to be performed in a single maneuver and in a more effective manner.

Ocular findings in mitochondrial neurogastrointestinal encephalomyopathy: a case report

PurposeTo describe the ocular features of a patient with mitochondrial neurogastrointestinal encephalomyopathy (MNGIE) due to a homozygous G1443A mutation in the thymidine-phosphorylase gene.MethodsA case report with extensive ophthalmological investigation over a 9-year period, until death at age 38 years. Measures used included standard ophthalmological examination, visual field examination and optical coherence tomography (OCT).ResultsPtosis and external ophthalmoplegia progressively worsened during the follow-up, as did the neurological and general status. Corneal and optic disc alterations were also observed at the last visit. Glaucomatous changes of the optic disc were confirmed by the visual field examination and OCT.ConclusionIn addition to previously described alterations such as ptosis and external ophthalmoplegia, MNGIE may be associated with glaucomatous-like optic neuropathy.

Induced astigmatism after near-clear hinge incision

Purpose: To evaluate astigmatism induced by the near‐clear hinge incision. Setting: Casa di Cura Villa Toniolo, Bologna, and Day Hospital Nuova Ricerca, Rimini, Italy. Methods: The results in 100 eyes having phacoemulsification with a 3.2 or 4.1 mm temporal near‐clear hinge incision were evaluated for a maximum of 6 months. Corneal curvature was measured using computerized videokeratography, and surgically induced astigmatism was computed by vector analysis. Surgically induced corneal topographic changes were also evaluated. Results: Mean induced cylinder in the 3.2 mm incision group was 0.4 diopter (D) ± 0.2 (SD) 6 months after surgery; there was no significant difference in the values at 4 days and 6 months. Mean induced cylinder in the 4.1 mm incision group was similar at 1 and 6 months (0.47 and 0.45 D, respectively). However, it was significantly higher at 4 days (0.56 D). Vector decomposition analysis showed that the with‐the‐rule component was prevalent and remained constant over 6 months. Topographic analysis showed localized wound‐related flattening with minimal central corneal changes. Conclusion: The near‐clear hinge incision was almost astigmatically neutral and resulted in self‐sealing incisions that did not leak.

Determining intraocular lens power following corneal refractive surgery

Corneal power after refractive surgery is difficult to assess, which makes it hard to calculate the appropriate intraocular lens power in the event that the patient needs cataract surgery later on. In the last 5 years, a variety of methods have been described to improve the accuracy of keratometric measurements in patients who have undergone corneal refractive corrections. We review the factors that make keratometric measurements inaccurate before discussing the traditional and novel methods developed to obtain reliable measurements in these patients. As patients who have undergone corneal refractive surgery get older, their chance of developing a visually impairing cataract increases. Unfortunately, the traditional methods used to measure corneal power (i.e., keratometry and videokeratography) are inaccurate after radial keratotomy, photorefractive keratectomy and laser in situ keratomileusis. This inaccuracy can easily lead to refractive surprises after phacoemulsification and intraocular lens implantation. For over 10 years, surgeons were obliged to rely on clinical history and contact lens over-refraction as the only methods to obtain a relatively predictable estimate of postrefractive surgery corneal power to be entered into intraocular lens calculation formulae. As interest in this topical issue continues to grow, more methods to accurately measure postrefractive surgery corneal power have been described. In addition, new technologies, such as the slit-scanning topography system (combined with Placido-disk videokeratography) and the rotating Scheimpflug camera, have been developed with the aim of determining the true corneal power after corneal refractive surgery.