Method for determining uncertainty and error in the process of ophthalmic lens calibration

In the present investigation, a scientific procedure was developed, and a mathematical model was proposed, with the objective of determining, under standard conditions, the uncertainty, and the measurement of dioptric power in ophthalmic lenses. The methodology of the scientific procedure is based on the fundamentals of geometric optics, this process guarantees and establishes a standardized uncertainty measure in repeatable and reproducible processes. The methodology is complemented with a proposed mathematical model based on the guide for the expression of uncertainty in measurement - GUM. This model can be applied to lenses used for calibrating eye care equipment (such as lensometers, which are used to diagnose myopia and farsightedness) by evaluating the lenses without having direct contact with patients. When the proposed mathematical model was applied, its experimental result was a maximum expanded uncertainty of ± 0.0079 diopters in a 0.5-diopter lens. This is optimal compared to the result of other authors this article, who reported a maximum expanded uncertainty of ± 0.0086 diopters. In conclusion, the application of this scientific procedure provides manufacturers and users of this type of lenses with a reliable measurement thanks to a calibration process based on geometrical optics and centered on patient safety.

Anthropometric measures and their relationship to corneal refractive power in the United States population

Purpose: To determine the relationship between anthropometric measures and corneal refractive power (CRP). Methods: Participants from the 1999-2008 United States National Health and Nutrition Examination Survey (NHANES) visual exam with demographic, ocular, and anthropometric data (20,165 subjects) were included. Cases with steep cornea were defined by corneal power ≥ 48.0 diopters (n = 171) while controls had dioptric power < 48.0 D (n = 19,994). Multivariable analyses were performed for pooled and sex-stratified populations. Separate models assessed body mass index, height, and weight in relation to steep cornea. Results: A relationship between BMI and steep cornea in the pooled population was not detected (P for trend = 0.78). There was a strong inverse relationship between height and steep cornea in the pooled population (P for trend <0.0001) and women (P for trend <0.0001). For every 1-inch increase in height, there was a 16% reduced odds of steep cornea in the pooled population (OR, 0.84; 95% CI: 0.78-0.91). There was also a significant inverse relationship between weight and steep cornea in the pooled population (P for trend = 0.01) and in men (P for trend = 0.02). For each 10-pound increase in weight there was a 7% reduced odds of steep cornea (OR, 0.927; 95% CI: 0.882-0.975) in the pooled analysis. Conclusions: Greater height and greater weight were associated with a lower risk of steep cornea. These findings can contribute to an improved understanding of the pathogenesis of corneal ectasias.

Combining primary and sulcus piggyback IOLs for the correction of a spherical-cylindrical defect in an eye with abnormal cornea

Introduction: Piggyback IntraOcular Lenses (IOLs), or supplementary secondary implant lenses, have been developed to provide a sufficient dioptric power in eyes with high refractive defects, which are not fully correctable after cataract surgery with single IOL in the range of powers available. These lenses can also be used for the correction of refractive errors that occurred for a wrong choice of the IOL power after cataract surgery. Case description: We report the case of a complete refractive success obtained in a patient with an abnormal cornea, with a central stable ectasia, with thinning, high myopic astigmatism and cataract, obtained with the implant of a primary posterior chamber IOL at the time of cataract surgery and a subsequent implant of a secondary piggyback, sulcus-based customized toric IOL (Camellens FIL 622-2 Toric Monofocal IOL, Soleko, Rome, Italy). Conclusions: This brief report demonstrates the utility of combining primary and piggyback IOLs implant for the correction of a complex spherical-cylindrical refractive defect in a case of abnormal cornea and cataract.

Artificial accommodating intraocular lens powered by an ion polymer-metal composite actuator

The current method of controlling the focus of an accommodating intraocular lens is based on ciliary muscle contraction and cannot be used in older patients with presbyopia. We aimed to develop a dynamically accommodating intraocular lens powered by a membrane-shaped ion polymer metal composite actuator that is thin enough to be inserted in the eye. This study addresses two key problems identified in our previous accommodating intraocular lens prototype: the lack of repeatability due to the use of swine lenses instead of artificial lenses and the occurrence of a sixth order aberration. Thus, we present a new accommodating intraocular lens design and a method to transfer energy to actuators. To accommodate lens deformation and depth of focus, we used a membrane-shaped ion polymer metal composite actuator, thin enough to be inserted in the eye, and used an artificial silicone lens. To prevent the sixth order aberration, we included a ring between the ion polymer metal composite actuator and the lens. Different voltage patterns were applied to the IPMC actuator and changes in focus were observed. We were able to obtain repeatability and prevent the sixth order aberration. The dioptric power changed to ±0.23 D when ±1.5 V was used; however, at >1.5 V, a large accommodating range occurred, in addition to astigmatic vision. Thus, we have developed a novel prototype that is completely artificial, allowing reproducible and repeatable results. Visual accommodative demands were successfully met; however, although astigmatic vision was lessened, it was not completely eradicated.

Weight of Different Intraocular Lenses: Evaluation of Toricity, Focality, Design, and Material

Purpose. To evaluate the weight of intraocular lenses (IOLs) depending on their material, dioptric power, toricity, focality, and haptic design. Methods. Twenty-eight different IOL models from nine different medical companies (a total of 38 IOLs) and 1 capsular tension ring (CTR) were evaluated. IOLs were weighed using a precision scale, in hydrated conditions, as an approximation to their intraocular status. Results. Hydrophilic IOLs were heavier than hydrophobic lenses ( p < 0.001 ). Regarding toricity, no statistical differences were found comparing toric to non-toric models ( p = 0.1 ). Likewise, no differences were found between multifocal IOLs and monofocal IOLs ( p = 0.19 ). Dioptric power did not affect IOL weight: IOLs of <15DP had similar weights to those of ≥15D and IOLs of ≥24D had similar weights to those of <24 D ( p = 0.86 and p = 0.59 , respectively). Plate-design IOLs were significantly heavier than 1-piece C-loop ( p < 0.001 ), 3-piece C-loop ( p < 0.001 ), and 4-haptic lenses ( p = 0.001 ). Conclusions. Of the characteristics analyzed that might influence IOL weight, lenses with hydrophilic material and plate-haptic design were found to be heavier. Toricity, focality, and dioptric power had no influence on IOL weight.