Hassan Tahi

Use of human fibrin glue and amniotic membrane transplant in corneal perforation.

Purpose. To repair corneal perforation using human fibrin glue (HFG) and amniotic membrane transplant (AMT). Methods. Three patients in whom central corneal perforations, approximately 2 mm in diameter, occurred after ocular or systemic disease were successfully cured using HFG and AMT. The technique consists first of using a high-viscosity sodium hyaluronate viscoelastic material to restore anterior chamber depth followed by a debridement of the ulcer. The perforation site is filled with the HFG to corneal surface level. The so-formed plug is then secured with an AMT to avoid its extrusion. An extended-wear bandage contact lens and topical antibiotics were used in these patients for 3 weeks. Results. Total reepithelialization was observed after an average of 15 postoperative days. The AMT dissolved within 8 weeks to uncover a whitish scar formed within the perforation sites. No complications were observed in any patients. After a follow-up period of 195–325 days, all corneas remained stable; there was no infection or ulcer recurrence, but some corneal scar thinning was observed in all three cases. Conclusion. The described surgical approach using HFG and AMT allowed a successful repair of corneal perforations with a diameter of 2 mm associated with significant loss of stroma. This method may be a good alternative to delay penetrating keratoplasty for treating corneal perforations, especially in acute cases in which graft rejection risk is high.

Corneal group refractive index measurement using low-coherence interferometry

Purpose: The goal of the study is to measure the group refractive index of the human cornea in vitro to improve the accuracy of corneal thickness measurements. Methods: Corneal buttons were trephined from 23 human cadaver eyes and the group refractive index of the cornea was measured at lambda equals 840 nm using a low-coherence Michelson interferometer and the technique proposed by Sorin and Gray (Phot. Tech. Lett. 4:105 - 107, 1992). The effect of dehydration on the measurement was studied by measuring the corneal optical thickness as a function of time. Results: Preliminary measurements of the group refractive index at 840 nm gave ng equals 1.450 plus or minus 0.024 for the human cornea, which is much higher than a calculated group refractive index of ng equals 1.387. Because of dehydration, the optical thickness of the cornea decreased at a rate of 5.5 micrometer/minute which led to an artificially high value for the group refractive index. Conclusion: The calculated group refractive index of ng equals 1.387 appears to be an accurate value for the purpose of corneal thickness measurements using low-coherence interferometry, and corneal group refractive index measurements can be performed in vitro if the measurements are performed rapidly to avoid the effect of dehydration.

Intraocular implants for the surgical correction of presbyopia

The surgical techniques proposed to restore accommodation past the onset of presbyopia can be categorized in two classes, those based of scleral expansion and those based on intraocular lens implantation and lens capsule refilling. This paper describes and discusses the different techniques and summarizes the results of clinical and experimental animal trials. Restoration of accommodation has been demonstrated by at least two different teams in non-human senile primates using modifications of the lens capsule refilling technique originally described by Julius Kessler in the late fifties. The advent of recent advances in microsurgery, devices, and injectable polymers are very promising and human clinical trials may soon be envisaged.

Small peripheral anterior continuous curvilinear capsulohexis

Cataract surgery is routinely performed using an anterior continuous curvilinear capsulorhexis (CCC). A manual surgical technique is described for performing a small (less than 1.5 mm diameter) anterior CCC. This techniques applications extend from Phaco-Ersatz, a cataract surgical technique designed to restore accommodation to pediatric cataract surgery. An experimental rabbit study was conducted to determine the feasibility of the technique. Up to 9 small peripheral anterior CCCs were made in the same lens capsule without the capsule tearing. The mean diameter of the CCCs was 1.1 mm +/- 0.3 (SD). A 30 gauge needle and Utrata capsulorhexis forceps were used to construct the CCC. This technique shows promise for the successful performance of small CCCs in Phaco-Ersatz procedures and pediatric cataract surgery.

Ex-vivo testing of crystalline lens substitutes: a pilot study

The paper reviews two techniques being developed for ex-vivo testing of crystalline lens substitutes. The techniques may be used to test polymers developed for the Restore Accommodation (RA) project. Harvested rabbit and human lenses were used in preliminary tests to determine the feasibility of topographical analysis of the crystalline lens and ex-vivo cell culturing of the lens capsule. Lens capsules were cultured to test formation of posterior capsule opacification (PCO) in the presence of RA polymers. Feasibility of analyzing lens shape with the PARTM Sys Corneal Topography System was determined using whole lenses. Preliminary results indicate that topography and cell culturing of lens capsules may be used to evaluate RA polymers.

Restoring Accommodation: Surgical Technique and Preliminary Evaluation in Rabbits

Purpose. To evaluate an innovative surgical technique for phaco-ersatz, a cataract surgery designed to restore accommodation. Techniques for very small capsulorhexis as well as the refilling procedure were developed. This study evaluates the feasibility and reproducibility of the surgical technique. Methods. The right eye of 8 NZW rabbits (≈ 2 Kg) were operated following the ARVO Statements for the Use of Animals in Ophthalmic and Vision Research. The surgery is begun by making a small peripheral capsulorhexis of about 1 mm using. The lens content is then removed. The lens is then refilled with a novel in situ polymerizable gel and the corneal incision is closed using one 10/0 Nylon interrupted stitch. Results. The capsulorhexis technique was succesfully performed and reproducible in all animals. The average size of the capsulorhexis opening was 1. 2 mm (±0.14). Lens material removal and refilling of the capsular bag with an in situ polymerizable material was also performed in each trial study. Conclusion. This surgical technique seemed feasible and reproducible.

Measurement of the topography of human cadaver lenses using the PAR corneal topography system

To measure the radius of curvature and asphericity of the anterior and posterior surfaces of crystalline lenses of human Eye-Bank eyes using the PAR Corneal Topography System. The measured values will be used in an optical model of the eye for lens refilling procedures.

Regulation of Cell Proliferation: Role of A Chromosome-Matrix Protein

INTRODUCTION. LFM-1 is a recently described chromosomal-matrix component cell-cycle dependent 1 . Preliminary experiments have suggested a regulatory role of LFM-1 in normal cell proliferation in human epithelia 2 . Lens Posterior Capsule Opacification (PCO) is a common and disabling health condition due to proliferation of Lens Epithelial Cells (LECs) to the posterior capsule of the lens 3 after cataract surgery. PCO is a widely studied condition with no effective medical treatment up to date. The purpose of this work is to develop an assay to control the proliferation of Lens Epithelial Cells by blocking LFM-1 protein synthesis and its potential function(s) in this mechanism. METHODS. LECs were harvested from rabbit’s lens capsules, dissociated and cultured under standard tissue culture conditions to be used as biological model for experiments. Phosphorothioate ODNs 4 (S-oligos, 23-mer) were designed, synthesized in the specific antisense (AS-ODNs) and random directions of the LFM-1 mRNA, and employed for treatment of cells during 4 days with replacement of fresh media/oligos every other day. Indirect immunofluorescence and western blot were performed to study the LFM-1 molecular specie(s), its rate of synthesis and sub-cellular distribution. Cell proliferation was simultaneously asserted by quantization of number of cells, and DNA cellular content measured by spectrofluorometry and video analysis as a function of the LFM-1 knocked translation. RESULTS AND DISCUSSION. Cell proliferation was analyzed as a function of the expression of LFM-1 protein at the translational level. Indirect immunofluorescence images of cells treated with specific LFM-1 antisense oligonucleotides showed inhibition of LFM-1 endogenous synthesis and DNA replication with a 2n DNA content, and concomitant arrest of cell proliferation after 48hs of treatment. Approximately 70% of the cultures consisted of sparse cells, and no groups exceeding 4 cells per islet were observed with a viability rating between 90-96%. In contrast, LFM-1 protein displayed sub-cellular nuclear distribution (sparse fluorescent dots) in untreated and random controls during G1 and S phases of the cell cycle suggesting a co-localization in areas of DNA replication and an involvement in the DNA synthesis machinery. No LFM-1 electrophoresis bands (87kDa precursor, 65-intermedia and 58kDa chromosome polypeptides) were detected in parallel samples treated with LFM-1 AS ODNs confirming the immunofluorescence results and supporting our previous reports in other human epithelia.

Assessment of changes in corneal shape as a function of intraocular pressure: a pilot study

Purpose: To evaluate the effect of increased intraocular pressure (IOP) on the corneal shape of human cadaver eyes. Methods: Eight cadaver eyes, unsuitable for transplantation donated by the Florida Lions Eye Bank, were assessed for overall integrity. The epithelium was debrided, the eye placed into an artificial orbit, and a 30-gauge needle (connected to the IOP monitor) was inserted into the vitreous cavity. The IOP was altered as necessary by adjusting the height of the lactated ringers IV bottle. The surface contour was assessed at pressure levels: hypotony (2-4 mmHG), normal physiologic IOP (12-20 mmHg), hypertony (135-142 mmHg) and again at normal and low IOP. At each pressure level, two corneal topographic measurements (PAR CTSTM Vision Systems Corp.) were captured and averaged. Keratometric analysis was completed to examine the dioptric effects of varying IOP. An elevation analysis was performed to determine the corneal locations which conformed to the pressure adjustments. Results: The keratometric and elevation (both 0 and 90 degree meridians) data revealed decreasing radii with increasing IOP however, variability precluded statistical significance. Both keratometric and elevation data displayed probable plastic deformation, as the radii deviated from the original measurement upon the return to 2-4 mmHg. The elevation analysis did suggest an astigmatic conformation to pressure fluctuations, as 90 degree meridian radii were greater than 0 degree meridian radii. Corneal deformation is minimal in the 2 to 140 mmHg range and the PAR system not sensitive enough to accurately determine changes in curvature. Conclusion: The cornea does not uniformly conform to IOP variation. Further investigations with IOP levels of up to 500 mmHg will provide more information with respect to changes in curvature as a function of IOP.

Discrepancies in Goldmann tonometer readings

Purpose: To evaluate discrepancies in Goldmann tonometer readings in eyes with varying degrees of corneal hydration and stromal amount. Methods. 6 Eye Bank eyes, donated by Florida Lions Eye Bank, were evaluated. Each eye was affixed to a customized artificial orbit system with intraocular pressure (IOP) measured directly by a pressure transducer inserted into the vitreous and with a Goldmann tonometric readings. The eyes were dehydrated for 5-minute intervals in a 30% Dextran-BSS solution, with readings taken between each submersion. Once corneal thickness stabilized, a corneal trephination of 6mm was made. The corneal buttons were frozen and dehydrated by lyophilization and weighed. Results. Preliminary results show a possible overestimation in thicker corneas and an underestimation in thinner corneas, as previously published. Corresponding data on the weight of corneal material is provided. Further studies need to be conducted to determine statistical significance of the data. Conclusion. This study uses Eye Bank eyes with a protocol that produces results similar to previously published results. Further studies in correlating the amount of corneal stroma and discrepancies in Goldmann tonometer readings of intraocular pressure are important especially with the increasing acceptance of corneal refractive surgeries.