How Abnormal Is the Noncorneal Biometry of Keratoconic Eyes?

PURPOSE: To determine whether the noncorneal biometry in keratoconic eyes deviates from that in healthy eyes. METHODS: The right eyes of 200 healthy subjects and 76 patients with keratoconus were measured with an autorefractometer, a Scheimpflug tomographer, and an optical biometer. The analysis consisted of a general linear model (GLM), correcting for age and gender effects, comparing keratoconic eyes with healthy eyes, and emmetropic eyes. Next, 20 patients with mild keratoconus in one eye and moderate keratoconus in the fellow eye were analyzed to assess the effect of disease stage. RESULTS: As expected the keratoconic group differed significantly from both the healthy and the emmetropic groups for most refractive, corneal, and anterior chamber parameters (GLM, P < 0.001). For the vitreous depth V and the axial length L, the keratoconic group showed significantly larger values than the emmetropic group (V: +0.68 ± 0.19 mm, P = 0.001; L: +0.63 ± 0.14 mm, P < 0.001), but not larger than the healthy group (V: +0.18 ± 0.20 mm, P = 0.364; L: +0.09 ± 0.14 mm, P = 0.519). Besides the corneal parameters, the stage of the disease led to a significantly deeper aqueous depth (+0.07 ± 0.02 mm; Wilcoxon signed rank, P = 0.002), but no significant difference in axial length (P = 0.940). CONCLUSIONS: Current analysis does not confirm the previously suggested association between keratoconus and higher amounts of axial myopia, which may have been the result of selection bias by using emmetropic eyes as a healthy control group.

Distribution of the Crystalline Lens Power In Vivo as a Function of Age.

PURPOSE: To observe the age-related changes in crystalline lens power in vivo in a noncataractous European population. METHODS: Data were obtained though Project Gullstrand, a multicenter population study with data from healthy phakic subjects between 20 and 85 years old. One randomly selected eye per subject was used. Lens power was calculated using the modified Bennett-Rabbetts method, using biometry data from an autorefractometer, Oculus Pentacam, and Haag-Streit Lenstar. RESULTS: The study included 1069 Caucasian subjects (490 men, 579 women) with a mean age of 44.2 ± 14.2 years and mean lens power of 24.96 ± 2.18 diopters (D). The average lens power showed a statistically significant decrease as a function of age, with a steeper rate of decrease after the age of 55. The highest crystalline lens power was found in emmetropic eyes and eyes with a short axial length. The correlation of lens power with different refractive components was statistically significant for axial length (r = -0.523, P < 0.01) and anterior chamber depth (r = -0.161, P < 0.01), but not for spherical equivalent and corneal power (P > 0.05). CONCLUSIONS: This in vivo study showed a monotonous decrease in crystalline lens power with age, with a steeper decline after 55 years. While this finding fundamentally concurs with previous in vivo studies, it is at odds with studies performed on donor eyes that reported lens power increases after the age of 55.

Feasibility of multifocal intra-ocular lens exchange and conversion to the bag-in-the-lens implantation.

PURPOSE: Our purpose was to evaluate the surgical outcome after intra-ocular lens exchange in patients who presented impairing visual complaints after primary multifocal intra-ocular lens (MIOL) implantation. In particular, the study was undertaken to look at the number of eyes that could be equipped with the bag-in-the-lens (BIL) IOL after MIOL exchange. METHODS: This series consisted of 30 eyes of 21 consecutive patients scheduled for MIOL exchange. In 15 out of the 30 eyes, IOL misalignment was measured on slit lamp anterior segment photo's after defining the mathematical centres of the IOL optic, pupil and limbus. RESULTS: Diffractive MIOL was more frequently explanted (25; 83%) when compared with refractive MIOL (4; 13%) and progressive optic IOL (1; 4%). In 21 out of the 30 eyes (70%) a bag-in-the-lens could be implanted. In 7 out of the 30 eyes (23%), the capsule was not considered sufficiently stable to accommodate an IOL. An iris-fixated IOL or a sulcus-fixated IOL was then implanted. In 2 out of the 30 eyes (6%) the remaining capsular bag could accommodate a traditional lens-in-the-bag only. Eyes that underwent Nd:YAG laser capsulotomy prior to the MIOL exchange needed anterior vitrectomy peroperatively (11 eyes; 37%). Visual acuity improved postoperatively in 13 out of the 30 eyes and remained stable in 17 out of the 30 eyes. CONCLUSIONS: Since the BIL technique requires a very well-preserved capsular bag for the purpose of the IOL implantation, the success rate of BIL implantation after MIOL is a good indicator to evaluate the degree of difficulty to exchange MIOL.

Normative values for corneal densitometry analysis by Scheimpflug optical assessment.

PURPOSE: To describe the normative data for corneal Scheimpflug densitometry based on a cohort of normal participants. METHODS: A total of 445 healthy participants were recruited for assessment (794 eyes). Left and right eyes were considered separately. All participants were assessed using the corneal densitometry analysis add-on to the standard software of the Oculus Pentacam. Densitometry measurements were obtained and expressed in standardized grayscale units (GSU). RESULTS: All participants were Caucasian; 42% were male and 58% were female. The mean age was 48.0 ± 15.3 years (range, 20.2-84.2 years). Mean corneal densitometry over the 12-mm-diameter area was 19.74 ± 3.89 GSU. When divided by radial zone, densitometry values were lowest in the central zone (16.76 ± 1.87 GSU) and highest in the periphery (27.36 ± 7.47 GSU). There was no difference between central zone and the surrounding 2- to 6-mm annulus (P > 0.05), though the 6- to 10-mm and the 10- to 12-mm zones displayed higher densitometry values (P < 0.001). When divided by depth, the anterior layer displayed the highest densitometry reading of 25.81 ± 5.14 GSU, which was significantly higher than that of both the central (P < 0.001) and the posterior layers (P < 0.001). Changes in corneal densitometry were correlated with age, though not within the central 6-mm-diameter ring. No sex difference was seen within the cohort. CONCLUSIONS: This add-on to the standard imaging software allows rapid and objective assessment of the corneal densitometry. We provide normative data that may be used as a reference facilitating research and complementing clinical examination.

Influence of macular pigment on retinal straylight in healthy eyes.

PURPOSE: To study the influence of macular pigment on retinal straylight in healthy eyes. METHODS: This prospective study included 150 eyes of 75 healthy subjects between 12 and 81 years of age (mean, 46.1 years) without a history of ocular surgery or ocular disease known to influence straylight (e.g., cataract). Retinal straylight was measured with the compensation comparison technique, and the known influence of age and axial length was compensated by calculating the base, age, and axial length-corrected (BALC) straylight. Macular pigment optical density (MPOD) was measured using light-emitting diode (LED) heterochromatic flicker photometry. Axial length was determined with a partial coherence biometer and iris color by visual inspection. Data analysis consisted of studying the predictive values between these parameters, after correction for the symmetry between left and right eyes, using linear mixed models. RESULTS: Mean retinal straylight was 1.05 ± 0.18 log units, and the mean MPOD was 0.37 ± 0.19. Age and axial length were found to be important predictors of retinal straylight (P < 0.001 and P = 0.010, respectively) but not of MPOD (P > 0.05). The mean BALC straylight was -0.07 ± 0.13 log units. No significant relationship was found between retinal straylight and MPOD (P > 0.05), even after correction for age and axial length. Also, no significant correlation was found between iris color and BALC straylight or MPOD. CONCLUSIONS: In healthy human eyes, retinal straylight values measured with the compensation comparison technique are not significantly correlated with macular pigment optical density.