Photometers use correction filters to adjust spectral responsivity of sensors so that the combined spectral responsivity approximates the responsivity of the human eye V(λ). However, the combination of these components is hardware based, and the quality of the photometer depends on this combination. We propose a meter that uses an RGB sensor, a LED and an artificial neural network that transforms the output of the sensor into luminous transmittance, without the need of a filter. The ANN was trained and validated with two different spectra datasets and generated results with error values below 3%. The methodology presents an option for a meter with calibration that depends only on a software. This allows the development of a low cost and compact photometer.
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.
In ophthalmology the research using "in vitro" corneas are an excellent model for studies of new ophthalmologic
procedures, enabling the analysis of effectiveness, performance and even safety parameters of the procedure. In this
work we studied four "in vitro" human corneas preserved in OPTISOL-GS, with initial average pachymetry of 542
microns and a post-mortem average of 6 days. The corneas were preserved in OPTISOL-GS and were washed with
saline solution to remove the excess the preservative medium. The corneas were placed in a device aligned with an
ultraviolet source of 3mw/cm2 and an optical fiber positioned after the device near the endothelium of the cornea.
The UV transmittance spectra in the region of 360-370nm were captured by the emission of UV source for 3
seconds. These spectra were captured every 5 minutes in a total of 60 minutes, resulting in 13 spectra per cornea. The
measured average initial UV transmittance was 73% and after 50 minutes of dehydration there was no significant
difference in the corneal teansmittance properties. However, for the last 10 minutes we have observed a decrease in the
UV transmittance of 4%, probably indicated by corneal dehydration and swelling (wrinkling of the cornea tissue. The
final average pachymetry was 421 microns and the UV transmittance after the 60 minutes was 69%. Therefore we
can suppose that the UV transmittance of corneas "in vitro" is invariant over a period of up to 60 minutes, even with
the thickness decrease, since the material that absorbs in the UV region remains intact and only water loss occurs.
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.
The transmittance of UVA light through the human preserved cornea of over 400μm thickness during the corneal
collagen cross-linking procedure has been measured spectroscopically. The 25 corneas, (average thickness of 570 μm),
preserved in OptisolGS, were washed with saline, desepithelization was performed, and the cornea was laid on the lid of
a Chiron Ophthalmics corneal storage chamber. A UV-VIS optical fiber was positioned at the crystalline position (10mm
after the endothelium) and fixed in a 3mm hole of the chamber and then connected to a spectrophotometer to detect the
amount of delivered UVA light on the endothelium. Current procedure protocol was performed, i.e., one drop of
riboflavin 0.1%, 400 mOsm, was applied on the naked cornea, every 5 minutes (total of 12 drops). The UV irradiation
(365±5 nm, 3mW/cm2, 1.51 mW, 5.405 J/cm2) was performed after 30 min of instillation for an additional 30 min. The
average transmittance of the desepithelized cornea without Riboflavin at the crystalline position is 65.8%'; after the 1st
drop of Riboflavin, transmittance is 51.4%; after 2nd drop, 46.1%; after 3rd drop, 41.9% ; after 4th drop, 38.7%; after 5th
drop, 35.9%; after 6th drop 33.6% ; after 7th drop, 31.0%; after 8th drop; 28.8%; after 9th drop, 27.2%; after 10h drop,
25.4%; after 11th drop, 23.9%; and finally after 12th drop, 22.5%. The average transmittance in terms of energy during
the 30 min irradiation procedure fluctuated from 0.930 to 0.675mW/cm2.
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.
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.
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 it's 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.