Victor A. C. Lincoln

Ultraviolet analysis of donated corneas: a portable prototype

As technology improves human vision, some procedures currently performed may be causing a decrease of the natural UV protection of the cornea. A portable dual beam system prototype was assembled for physicians for clinical studies of these effects on the corneas endowing two types of 300-400 nm evaluations: 1, regularly donated corneas and 2, simulating refractive keratectomy by corneal lamellae removal. The system performs 500 measurements/s, providing ±0.25% precision for the transmittance. The measurements performed on the prototype are 95% in agreement with Cary 17 and HR4000CG-UV-NIR Ocean Optics spectrophotometers. Preliminary studies on cadaveric corneas demonstrate that, as the stromal layer is reduced (∼150 μm depth), there is significant loss--an average of 7.1%.--of the corneas natural UV protection. The prototype is being tested in an eye bank for routine evaluation of donor corneas.

Self-service kiosk for testing sunglasses

BackgroundSunglasses users may only be assured on their ultraviolet protection by purchasing certified products, however they are not able to check if sunglasses are still ultraviolet (UV) protected as they age, unless they resort themselves to a professional who is qualified for using a spectrophotometer and is acknowledged on the standards for providing a report for the user. Current literature establishes safe limits on the exposure of the eyes relatively to the ultraviolet radiation exposure for the UVA and UVB ranges (280 nm – 400 nm). The UV protection is category dependent. Sunglasses are categorized from 0 to 4 and the categories are determined by the lenses transmission’s percentage on the visible range (380 nm – 780 nm).MethodsIn order to overcome inaccessibility of such measurements on sunglasses, a prototype for testing ultraviolet protection on sunglasses, according to Brazilian Standards, has been developed for amateur use. The system consists of assembling UVA and UVB light sources and two UV responsive photodiode sensors, with Erythema action response for measuring UV protection; for categories measurements, combination of white light and LEDs were used for the visible range, as well as a light sensor having spectral response similar to the human eye. Electronics has been developed for controlling the measurements and software has been implemented for providing the report as well as for the user’s interface.ResultsAll the system was embedded as a self-service touch screen kiosk and provides transmittance measurements that are within the deviation limit required by NBR15111, i.e., 0.25%. Measurements were performed in over 45 sunglasses and compared to CARY 5000 – VARIAN spectrophotometer and present a good correlation for the measurements of transmittance in the visible spectral range (r2 = 0.9999) and in the ultraviolet range (r2 = 0.9997).ConclusionsThe prototype identifies the UV protection, for non-corrective sunglasses, according to category of the lens and is available for the public. In addition to educating the population about the importance of wearing protected sunglasses, the prototype has also allowed the public to have access to information about the quality of protection of their own sunglasses in an easy and free testing method.

Critical evaluation of the ultrasonic pachymetry for "in-vitro" corneas

The measurement of central corneal thickness (CCT) is vastly useful for diagnostic and therapeutic evaluation. The ultrasound pachymetry is currently the most common CCT technique. This study was undertaken to determine the precision and correlation of measurements obtained by mechanical and ultrasound pachymetry. The ultrasound pachymetry was determined using an A-scan ultrasonic pachymeter. The probe tip was held perpendicular on the central cornea by a support that goes down smooth to avoid excessive pressure and instability. The mechanical pachymetry was determined using a micrometer with a tip of 2mm of diameter. The tip of the micrometer was held perpendicular on the central cornea by a support that keeps stabilized. A 10x optics increase and a digital video camera shows real time image of approach and full contact of the tip with the cornea. Eight human corneas were obtained from cadaveric eyes. Measurements in both systens were taken for three different users, each one performed five readings. The results for both systems has an average SD of 33 microns refers to the systematic error between users (for positioning, center, pinching). But the difference between systems was 120 microns, possibly refers to the imprecision of ultrasound pachymetry in measuring in vitro corneas.

UV transmittance during the crosslinking procedure: tunable treatment

The transmittance of UVA light through the in vitro human cornea over the thickness of 400um during the corneal collagen cross-linking procedure has been measured using an optical fiber (600 μm core diameter) fixed just before the cornea and attached to Spectrophotometer. The 10 corneas, (average of 6 days post-mortem) were washed with saline and cross-linked with the currently used protocol. To enhance absorption of UV radiation, Riboflavin solution (0.1% and 400 mOsm) was applied prior to and during exposure. The UVA beam - 365nm ± 5nm at 3mW/cm2 ± 0.003mW/cm2 - was focused directly onto the corneal stroma. The measured average transmittance of the cornea without Riboflavin was 64.1%. Preceding the irradiation but after 6 applications of Riboflavin at 5min intervals (total of 30min) transmittance decreased to 21.1%. The 30min of irradiation were then accompanied by an additional 6 applications of Riboflavin at 5min intervals (for a total of treatment time of 1h), resulting in a further decrease in transmittance to 12.2%, which is in agreement with current literature. The average transmittance in terms of energy during the 30 minutes irradiation procedure fluctuated from 0.63 to 0.37 mW/cm2. These results indicate different levels of UV transmittance during treatment, leading to consider a new personalized treatment with tunable UV power irradiation.

A prototype for measurements in visible light transmittance of sunglasses

The measurements of the transmittance of ultraviolet and infrared radiation through sunglasses are standard requirements for certification of these lenses. According to Brazilian Standard NBR15111(2004), the electromagnetic spectrum relative to UVA, UVB and UVC (100 - 400nm) and infrared (700-1400nm) must be protected, by filters, according to the lens category. The categories are in a scale of 0 to 4, according to the amount of visible light transmitted through the sunglasses. An opto-electronic set up was assembled in this work, using light sources (set of LEDs), which cover the electromagnetic spectrum in the range of 380nm - 780nm; one visible light sensor for measuring the visible light transmission through the lens of the sunglasses; and an electronic circuit to control the intensity of the LEDs light. The device performs the calibration of the light source to match the requirements by the standard. The prototype has an accuracy of 0.1% for transmission; resolution of 0.1% and correlation factor of r2 = 0.991 for the tested lenses compared to CARY 5000 - Varian spectrophotometer.

Portable prototype for ultraviolet analysis of donated corneas

A prototype was built to provide means for clinical studies of alterations on the cornea UV natural protection from current procedures, such as the refractive surgery and corneal crosslinking. The prototype consists of an optical dual beam UVA/UVB system, for measuring the transmittance of the cornea at the 300nm - 400nm range. The system performs 500 measurements/s (±0.25% precision for the transmittance). It has been correlated to spectrophotometer (0.985) for donated human corneas. Preliminary studies on human corneas demonstrate that as the stromal layer is reduced, there is significant loss of the cornea natural UV protection.

Ultraviolet analysis on in vitro corneas following tissue removal

Exposure to ultraviolet (UV) radiation, even in small quantity, can cause several damages to the human eye. Continuous exposure the ultraviolet rays may cause corneal swelling, lens opacity (cataract), harms to the retina and pterygium. The purpose of this work is the study of the alteration of the corneal tissue and its UV natural protection in different scenarios, using a device previously developed, which provides measurements of corneal transmittance in the UV range. The device consists of ultraviolet source and detector, digital processing and visualization of results in real time. The dual beam system provides tissue UV transmission with accuracy of 0.25%. A protocol has been established for testing the UV protection on the cornea, as well as performing the removal of the corneal tissue, simulating refractive keratotomy. We have observed that its evident that each corneal layer has influence in the UV absorbance, the results show the influence of the epithelial layer (~50μm depth), the little endothelium influence (~10μm depth), and the stroma layer is responsible for the strongest influence (~350μm depth). Preliminary studies on 42 human corneas lead to demonstrate that as the stromal layer is reduced, there is significant loss of the natural UV protection of the cornea, sometimes presenting a very restricted protection.

MEASURING UV SYSTEM FOR ”IN VITRO” CORNEAS

This paper presents the development of a system for measuring the transmittance of the human cornea of ultraviolet light (UVA and UVB). The equipment consists of photodiodes and a lamp in the ultraviolet range - 280nm - 410nm, a transimpedance amplifier circuit, a digital potentiometer, a LCD display, and a microprocessor of the MSP430 family, which is responsible for the overall control of the system. The system provides the threshold of the UV transmittance of the cornea in different scenarios, such as the influence of substances and ophthalmic procedures (photorefractive keratectomies and crosslinking).

System for Evaluating UV Radiation in Ophthalmic Lenses

The aim of this work is the development of a prototype for measuring the ocular protection of the UVA and UVB radiations offered by ophthalmic lenses. The prototype is an optoelectronic device, composed by ultraviolet radiation sources and detectors, having electronic components for the digital processing and results visualization. The UV source is a Sankyo Denki BLB 6W light. A PIN type silicon photodiode was selected to detect the transmitted radiation through the lenses. In order to display the percentage of transmitted radiation by the lenses in a graphic display, the analog/digital electronic circuit has been projected in accordance with the sensor electrical signal features. The prototype projects the ultraviolet beams within the range of 280nm-410nm through the tested lenses and the transmitted light is observed in a amplified photodiode sensor. Tests on several lenses and polarizers were performed and the results have been compared to measurements on commercial spectrophotometer.