An Update on Corneal Biomechanics and Architecture in Diabetes.

In the last decade, we have witnessed substantial progress in our understanding of corneal biomechanics and architecture. It is well known that diabetes is a systemic metabolic disease that causes chronic progressive damage in the main organs of the human body, including the eyeball. Although the main and most widely recognized ocular effect of diabetes is on the retina, the structure of the cornea (the outermost and transparent tissue of the eye) can also be affected by the poor glycemic control characterizing diabetes. The different corneal structures (epithelium, stroma, and endothelium) are affected by specific complications of diabetes. The development of new noninvasive diagnostic technologies has provided a better understanding of corneal tissue modifications. The objective of this review is to describe the advances in the knowledge of the corneal alterations that diabetes can induce.

Computational Simulation of Scleral Buckling Surgery for Rhegmatogenous Retinal Detachment: On the Effect of the Band Size on the Myopization.

A finite element model (FE) of the eye including cornea, sclera, crystalline lens, and ciliary body was created to analyze the influence of the silicone encircling bandwidth and the tightness degree on the myopia induced by scleral buckling (SB) procedure for rhegmatogenous retinal detachment. Intraocular pressure (IOP) was applied to the reference geometry of the FE model and then SB surgery was simulated with encircling bandwidths of 1, 2, and 2.5 mm. Different levels of tightening and three values of IOP were applied. The anterior segment resulted as unaffected by the surgery. The highest value of Cauchy stress appeared in the surroundings of the implant, whereas no increment of stress was observed either in anterior segment or in the optic nerve head. The initial IOP did not appear to play any role in the induced myopia. The wider the band, the greater the induced myopia: 0.44, 0.88, and 1.07 diopters (D) for the 1, 2, and 2.5 mm bandwidth, respectively. Therefore, patients become more myopic with a wider encircling element. The proposed simulations allow determining the effect of the bandwidth or the tightness degree on the axial lengthening, thus predicting the myopic increment caused by the encircling surgery.

Assessment of corneal biomechanical properties and intraocular pressure in myopic spanish healthy population.

Purpose. To examine biomechanical parameters of the cornea in myopic eyes and their relationship with the degree of myopia in a western healthy population. Methods. Corneal hysteresis (CH), corneal resistance factor (CRF), Goldmann correlated intraocular pressure (IOP), and corneal compensated IOP (IOPcc) were measured using the ocular response analyzer (ORA) in 312 eyes of 177 Spanish subjects aged between 20 and 56 years. Refraction was expressed as spherical equivalent (SE), which ranged from 0 to -16.50 diopters (D) (mean: -3.88 ± 2.90 D). Subjects were divided into four groups according to their refractive status: group 1 or control group: emmetropia (-0.50 ≤ SE < 0.50); group 2: low myopia (-0.75 ≤ SE < 3.00 D); group 3: moderate myopia (-3.00 ≤ SE ≤ -6.00 D); and group 3: high myopia (SE greater than -6.00 D). We analyzed the relationship between corneal biomechanics measured with ORA and SE. Results. CH in the emmetropia, low myopia, moderate myopia, and high myopia groups was 11.13 ± 0.98, 11.49 ± 1.25, 10.52 ± 1.54, and 10.35 ± 1.33 mmHg, respectively. CH in the highly myopic group was significantly lower than that in the emmetropic group (P = 0.07) and low myopic group (P = 0.035); however, there were no differences with the moderate myopic group (P = 0.872). There were no statistically significant differences regarding IOP among the four groups (P > 0.05); nevertheless, IOPcc was significantly higher in the moderately myopic (15.47 ± 2.47 mmHg) and highly myopic (16.14 ± 2.59 mmHg) groups than in the emmetropia (15.15 ± 2.06 mmHg) and low myopia groups (14.53 ± 2.37 mmHg). No correlation between age and the measured parameters was found. CH and IOPcc were weakly but significantly correlated with SE (r = 0.171, P = 0.002 and r = -0.131, P = 0.021, resp.). Conclusions. Present study showed only a very weak, but significant, correlation between CH and refractive error, with CH being lower in both moderately and highly myopic eyes than that in the emmetropic and low myopic eyes. These changes in biomechanical properties of the cornea may have an impact on IOP measurement, increasing the risk of glaucoma.

Evaluation of in vitro efficacy of combined riboflavin and ultraviolet a for Acanthamoeba isolates.

PURPOSE: To evaluate in vitro the amoebicidal effects of riboflavin and ultraviolet A (UVA) collagen cross-linking. DESIGN: Experimental study, laboratory investigation. METHODS: Two different strains of Acanthamoeba species were tested identically. Four treatment groups were considered: group 1 consisted of 0.1% riboflavin and 30-minute UVA irradiation; group 2 consisted of 0.1% riboflavin and 60-minute UVA irradiation; group 3 consisted of no riboflavin and no UVA exposure; group 4 consisted of 0.1% riboflavin and no UVA exposure. The application of UVA was performed under the parameters used for in vivo corneal collagen cross-linking. RESULTS: In all cases, cysts and trophozoites were detected 24 hours after treatment at a radial distance from the center of the seeding point more than 5 mm, indicating that the amoebae were viable. All treated and untreated groups of amoebae from the 2 strains exhibited growth (radii of 14 to 15 mm in groups 1, 3, and 4; radius of 12 mm in group 2). The final morphologic features of the 2 strains of trophozoites that received treatment were similar to those of the initial seeding group and the untreated control group. CONCLUSIONS: The results obtained in our study show that a single dose (30 or 60 minutes) of cross-linking cannot achieve eradication in the 2 different Acanthamoeba strains examined. However, in vitro results do not always indicate in vivo efficacy, so future studies should test the validity of this treatment for Acanthamoeba keratitis.

An unusual case of cocaine-induced maculopathy.

PURPOSE: Cocaine is one of the most common substances of abuse. When used intranasally, cocaine is cut with a variety of agents, which may increase local and systemic toxic reactions. METHODS: We examined a 34-year-old man who complained of color disturbance. The patient reported a 10-year history of daily intranasal cocaine use, but denied use during the last year. Color vision testing showed a dysregulation of blue -yellow color vision. Electroretinogram revealed significantly reduced blue cone responses. Dilated fundus examination of both eyes revealed a bilateral maculopathy. Fluorescein angiography disclosed an early hyperfluorescence in both foveal areas which maintained in late phase. Optical coherence tomography was normal in both eyes. The patient was diagnosed with an unusual maculopathy related to a long-term intranasal cocaine use. RESULTS: All 6 eyes exhibited pigmentary changes located along the border of the staphyloma, and also radially to it, giving a particular T-shaped pattern of pigmentary changes. These changes were visible as either a linear strip or a triangular or oval-shaped area. Three eyes had a documented history of subretinal leakage that mimicked central serous chorioretinopathy, a well-known complication of tilted disk syndrome. CONCLUSIONS: Ocular complications from topical cocaine abuse are rare. Impaired color vision, as in our patient, has been reported in cocaine-withdrawn patients. To our knowledge, this is the first described case of a bilateral and symmetric maculopathy associated with long-term intranasal cocaine use. To avoid a delay of treatment, ophthalmologists should be aware that a maculopathy with small defects in color vision may be related to adulterants added to cocaine when it is used intranasally.

Effect of limbal relaxing incisions during phacoemulsification surgery based on nomogram review and numerical simulation.

PURPOSE: To determine the effect of the parameters related to limbal incisions (length, depth, optical zone, and so on) by revision of different nomograms and analyzing the outcomes of numerical simulation of incisions with a biomechanical model of the cornea. METHODS: The Cristóbal nomogram was developed based on our experience on the performance of relaxing incisions to correct astigmatism. A numerical model of the eye was used to analyze the effect induced by variation of each parameter compiled in nomograms. The biomechanical properties remained invariable for all cases. Different incisions were simulated to study the influence of each parameter, being one varied while the others remain constant, under equal biomechanical conditions, ignoring the human factor. RESULTS: Quantitatively, simulation of incisions of 45, 60, and 90 degrees; optical zone of 10 mm; and depth of 90% of the thickness induced astigmatic changes of 1.2, 1.4, and 1.9 diopters (D). Paired incisions at 7.5-mm optical zone and 90-degree length induced astigmatic changes of 0.7, 2.6, and 4.4 D for 40%, 75%, and 90% depth, respectively. Paired incisions of 90-degree length and 90% depth for 10- and 7.5-mm optical zones induced 1.9 and 4.4 D, respectively. Qualitatively, the results confirm the guidelines compiled in nomograms. CONCLUSIONS: The revision of some nomograms for limbal incisions to correct astigmatism, compared with the outcomes of numerical simulation, leads to common guidelines. Numerical simulation supplies theoretical outcomes that the clinician can take into account to decide the values of the parameters for the surgery, in addition to their clinical experience.

Biomechanical properties of the cornea in Fuchs' corneal dystrophy.

PURPOSE: To investigate the effects of Fuchs' corneal dystrophy (FCD) on corneal biomechanical properties and the results of IOP readings in relation to changes in corneal hysteresis (CH) and central corneal thickness (CCT). METHODS: Corneal biomechanical properties, including CH, corneal resistance factor (CRF), and CCT, were measured with the ocular response analyzer (ORA) in 11 eyes of 11 patients with clinically confirmed FCD and 12 eyes of 12 healthy subjects. The ORA was also used to determine the values of intraocular pressure (IOP(g)) and corneal compensated IOP (IOP(cc)). Goldmann applanation tonometry (GAT) was also measured. RESULTS: CH measured 10.3 +/- 1.6 mm Hg (range, 8.7-13.8) in normal eyes and 6.9 +/- 1.8 mm Hg (range, 4.6-11.7) in FCD eyes (P = 0.001). CRF in the normal and FCD eyes was 10.5 +/- 1.5 mm Hg (range, 8.5-13.3) and 8.1 +/- 1.9 (range, 4.5-11.2), respectively (P = 0.005). CCT was higher in FCD eyes (606 +/- 20 microm; range, 578-635) than in normal eyes (538.4 +/- 24.9 microm; range, 495-575; P = 0.0001). IOP(g) was 16.2 +/- 2.2 mm Hg (range, 13.5-18.7) in control eyes compared with 17.6 +/- 2.7 mm Hg (range, 12.8-18.6) in FCD eyes (P = 0.201). However, IOP(cc) in the FCD group (21.8 +/- 4.6 mm Hg; range, 12.8-29.0) was higher than in the control group (16.5 +/- 3.4 mm Hg; range, 11.9-23.9; P = 0.006). GAT in the normal and FCD eyes was 16.7 +/- 2.1 mm Hg (range, 12.8-18.6) and 16.9 +/- 2.3 mm Hg (range, 13.1-19.0), respectively (P = 0.205). CONCLUSIONS: FCD led to a change of corneal biomechanical properties. CH and CRF were significantly lower in FCD eyes than in normal eyes. IOP(cc) was significantly higher in FCD eyes than in control eyes. These values may be useful in addition to CCT when assessing corneal rigidity. Thus, FCD may cause an underestimation error in IOP measurement.