Sidney Júlio de Faria e Sousa

Uso experimental da biomembrana de látex na reconstrução conjuntival

INTRODUCTION: The biomembrane of natural latex is believed to promote neoformation of biological tissues and to be biocompatible. In animal studies, enhancement of wound healing in the esophagus, peritoniostomy, and pericardiostomy has been observed. It was used in chronic phlebopatic cutaneous ulcer and otologic surgeries in human subjects. PURPOSE: To study the effect of biomembrane of natural latex in ocular surface. METHODS: In fifteen New Zealand white rabbits, the superior nasal conjunctiva was removed from both eyes. In the right eyes, the biomembrane of natural latex was sutured to the conjunctiva with continuous 10.0 monofilament thread. In the left eye, the sclera was left bare. The rabbits were sacrified and the eyes were submitted to histological analysis on days five, seven, fourteen, twenty-one and twenty-eight. The eyes of a rabbit with no surgery were enucleated and sent for histological analysis of the normal conjunctiva. RESULTS: Considering the whole period of the experiment, the number of eyes with satisfactory healing was greater in the biomembrane group than in the bare sclera group (p=0.06). The number of perilimbic vessels was significantly higher in the biomembrane group than in the bare sclera group (p=0.0284). The infection rate was similar in both groups. CONCLUSION: Similar to prior studies, the biomembrane of natural latex seemed to benefit conjunctival reconstruction and neoangiogenesis. Depending on the results using human eyes, this material might be a new type of therapeutic resource for conjunctival replacement, especially in cases of desirable tissue revascularization.

System for measuring the transmission spectrum of 'in vitro' corneas

We have developed a spectroscopy system dedicated to eye banks in order to standardize the evaluation of the donated corneas, with respect to their transparency. The system for measuring the corneal transmission spectrum basically consists of a conventional spectroscopy single beam optical apparatus, with particularities in order to attend to the needs of the eye banks, having a linear CCD (2048 sensors) as a detector. The range of evaluation of the system is from 400 to 700 nm, which is the range of interest for these kinds of sample (corneas). Dedicated software has been developed in order to acquire the data from the system and to provide the graphical interface for the user. The software is quite easy to manipulate and provides the diagnostic with respect to the transparency of the cornea, which is based on research done in association with the clinicians of the Eye Bank of Hospital das Clínicas de Ribeirão Preto (Brazil). The system presents a resolution of 9 nm (which is good enough for this kind of measurement, that presents large bandwidths) and it is in agreement with the spectra obtained from commercial spectrophotometers (the correlation factor between our system and a Beckman DU-70 is 0.995 43 for samples of well defined bandwidths, and 0.989 73 for corneas--large bandwidth).

Bilateral Acanthamoeba ulcer in a user of disposable soft contact lenses: a tragic incident or a consequence of the aggressive policy of soft contact lens trading?

This is the report of a case of bilateral Acanthamoeba keratitis in a 19-year-old woman who bought a pair of disposable soft contact lenses in a boutique. She wore this same pair of lenses for 3 months daily without the appropriate care. This led to bilateral corneal transplantation with cataract extraction and also trabeculectomy in the right eye. When last seen, both grafts were crystal clear but the visual acuities were far from satisfactory. She also had bilateral secondary glaucoma, barely controlled by topical medication. Actually, the physical features and the wearing time characteristics of the disposable soft contact lenses created unprecedented difficulties to the medical surveillance of their wearers. Without the right assistance they tend to become careless regarding routine cleaning. They also feel free to buy less expensive lenses, to use saline instead of lens solutions, to violate the limits of wearing time and to extend the use over the sleeping period. Additionally, the aggressive marketing and the wide distribution of these lenses increase the chances that economically or educationally unprepared people will acquire them. The question that remains is: Is the present case an accidental event or an example of what is likely to happen in the future if the indiscriminate selling of disposable soft contact lenses continues to evolve?

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.

Identification and segmentation of cells in images of donated corneas using mathematical morphology

The most effective optical method for evaluating donated corneas is to count the number of living endothelial cells. The evaluation of the whole endothelium is usually done in a slit lamp, and the aspects of the cells are subjectively observed. In order to overcome the limitations of subjective observation and to provide an analysis of several parts of the cornea, we have developed a system, attached to the slit lamp, with a dedicated software package for image treatment and cell counting using mathematical morphology. The results are in good agreement with measurements done with the interactive counting method (the correlation coefficient is 0.95798).

Detection system for ocular refractive error measurement.

An automatic and objective system for measuring ocular refractive errors (myopia, hyperopia and astigmatism) was developed. The system consists of projecting a light target (a ring), using a diode laser (lambda = 850 nm), at the fundus of the patients eye. The light beams scattered from the retina are submitted to an optical system and are analysed with regard to their vergence by a CCD detector (matrix). This system uses the same basic principle for the projection of beams into the tested eye as some commercial refractors, but it is innovative regarding the ring-shaped measuring target for the projection system and the detection system where a matrix detector provides a wider range of measurement and a less complex system for the optical alignment. Also a dedicated electronic circuit was not necessary for treating the electronic signals from the detector (as the usual refractors do); instead a commercial frame grabber was used and software based on the heuristic search technique was developed. All the guiding equations that describe the system as well as the image processing procedure are presented in detail. Measurements in model eyes and in human eyes are in good agreement with retinoscopic measurements and they are also as precise as these kinds of measurements require (0.125D and 5 degrees).

Optical projection mires for measurements of the radii of curvature of the cornea in biomicroscopes

Keratometry is currently achieved by projecting a circular mire onto the patients cornea and analyzing the size and shape of its reflected image. The projection mires are decisive for the precision of the measurement. We have previously developed a keratometric module for slit lamps, and the development of four projection mires are presented. Mire 1 is composed of optical fibers and electrical cables; Mire 2, 48 LEDs; Mire 3, optical fibers and no electrical cables; and Mire 4, mechanical parts--cable free. Mires 2-4 provide accurate keratometry measurements at slit lamps. Mire 4 is the most adequate for the clinical environment.

Automated keratometry at low cost

Describes an automatic optical system that is attached to a slit lamp in order to provide automatic keratometry at low cost. The system consists of projecting a light ring as a target onto the patients cornea as well as analysis of the deformation of the target in order to obtain the radius of curvature and the axis of the associated astigmatism. The reflected image of the target is displayed on a PC monitor, while dedicated software performs the analysis of the image, which provides the corneal keratometry.

Evaluation of a New System for Obtaining Donor Lamellar Grafts

Purpose: To evaluate the performance of a new system for obtaining corneal lamellar grafts of preset sizes. The system consists of the combination of an artificial anterior chamber (MALKS) and an automated microkeratotome (MASYK). Methods: A prospective study was performed. Lamellar tissue was obtained with the microkeratotome from 40 human corneoscleral buttons mounted in the artificial anterior chamber. The instrument was set to cut lamellae with a center thickness of 350 μm and a diameter of 10 mm. A new cutting blade for the microkeratotome was used for every 8 cases. Thickness was measured by ultrasound pachymetry. The lamellar diameter was assessed with a micrometric caliper. Results: The center thickness of the corneal lamellae ranged from 230 to 430 μm (mean, 322 ± 48 μm; 95% confidence interval [CI], 307-337 μm). The diameter of the stromal ranged from 9.26 to 10.74 mm (mean, 10 ± 0.27 mm; 95% CI, 9.9-10 mm). There were no cases of perforation or incomplete/irregular lamellae. The interface between the residual stroma and the lamellae was macroscopically smooth. The repetitive use of the same blade up to 8 times did not significantly change these results. Conclusion: The MALKS and MASYK system showed good accuracy in obtaining lamellae of specific thickness and size taken from human corneoscleral buttons. It is a promising instrument for use in deep lamellar keratoplasty. The technique may be useful in obtaining precut lamellar donor tissue for distribution by eye banks.

MALKS®: especificações e desenvolvimento

PURPOSE: To describe the characteristics of a new artificial anterior chamber (MALKS®, Loktal, Sao Paulo, Brasil). METHODS: Characteristics analysis and description of a new artificial anterior chamber MALKS® (Micro automated lamellar keratoplasty system). RESULTS: MALKS®is composed of eight parts: a) artificial chamber; b) corneas fix ring; c) nut to join the corneas fix ring; d) rail and adjuster of lamellar diameter; e) flatteners, to pre-determine lamellar diameter; f) infusion system, that allows the digital objective peroperative control of the intracameral pressure; g) automated microkeratome, and h) marker. CONCLUSION: MALKS® uses the same automated microkeratome developed for LASIK, can allow corneal lamella obtention with predetermined thickness and diameter, as well as the digital objective peroperative control of the intracameral pressure. This new artificial anterior chamber can be an important tool for superficial and endothelial keratoplasty.