Search PubMed⌕ Search

Biomedical subjects

Dimitri T Azar

Publications and source records attributed to Dimitri T Azar.

At least 37 records · Page 2Linked to original sources
PubMed2004

Astigmatism outcomes of horizontal temporal versus nasal clear corneal incision cataract surgery.

PURPOSE: To compare the short- and long-term astigmatism outcomes after cataract surgery using temporal clear horizontal corneal incisions and nasal horizontal clear corneal incisions. SETTING: Wilmer Eye Institute, Johns Hopkins Hospital, Baltimore, Maryland, USA. METHODS: This retrospective study included a consecutive series of eyes having phacoemulsification with implantation of a 6.0 mm foldable acrylic intraocular lens through a 3.5 mm horizontal clear corneal incision at 180 degrees (temporal incision in right eyes, nasal incision in left eyes). Astigmatism was measured by keratometry readings before surgery and 6 weeks and 12 months postoperatively. RESULTS: The mean preoperative astigmatism in the 178 eyes (94 right, 84 left) of 161 patients was 0.78 diopter (D); 54.5% of eyes had against-the-rule (ATR) astigmatism, 22.5% had with-the-rule (WTR) astigmatism, and 14.0% were astigmatically neutral. A significant shift toward WTR astigmatism occurred postoperatively. At 6 weeks, 48.3% of eyes had WTR astigmatism and 23.0% had ATR astigmatism. At 12 months, 43.8% had WTR astigmatism and 25.8% had ATR astigmatism. Vector analysis revealed a mean surgically induced astigmatism (SIA) of 1.17 D at 6 weeks and 1.04 D at 12 months. The side of the incision significantly affected SIA. At 6 weeks, temporal incisions yielded a mean SIA of 0.74 D and the nasal incisions, of 1.65 D. This trend in SIA persisted at 12 months: 0.71 D for temporal incisions and 1.41 D for nasal incisions. CONCLUSIONS: Cataract surgery using a horizontal clear corneal incision induced WTR astigmatism 6 weeks and 12 months postoperatively. Temporal incisions induced significantly less astigmatism than nasal incisions.

Aged↗
PubMed2004

Corneal asphericity change after excimer laser hyperopic surgery: theoretical effects on corneal profiles and corresponding Zernike expansions.

PURPOSE: To determine the theoretical relationships between the changes in corneal paraxial power, asphericity, and the corresponding Zernike polynomial expansion after conventional and customized excimer laser correction of hyperopia. METHODS: The initial corneal profile was modeled as a conic section of apical radius of curvature R1 and asphericity Q1. The theoretical value of the postoperative apical radius of curvature R2 was computed by using a paraxial formula from the value of R1 and hyperopic defocus D. The postoperative asphericity Q2 of the corneal surface was computed within the optical zone of diameter S after the delivery of a Munnerlyn-based profile of ablation for hyperopia using conic section-fitting and minimization of the squared residuals. These calculations were repeated for different values of defocus, initial apical radius of curvature, and asphericity. Taylor series expansions were also used to provide an approximation aimed at predicting change in asphericity. The coefficients of a Zernike polynomial expansion of the rotationally symmetrical corneal profile (defocus C2(0), spherical aberration C4(0), secondary spherical aberration C6(0)) were also computed, by using scalar products applied to the considered corneal profile modeled as a conic section and were expressed as a function of both its apical radius and asphericity. This allowed approximation of the variations of the Zernike polynomial expansion of the corneal profiles by subtracting the postoperative coefficient weighting a particular aberration from that of the preoperative one in different theoretical situations, after both conventional and customized hyperopia treatments aimed at controlling the postoperative corneal asphericity and delivered over a normalized pupil diameter. RESULTS: Conical least-squares fitting was unambiguous, allowing approximation of the postoperative corneal profile as a conic section of apical radius R2. After a Munnerlyn-based hyperopia treatment, the sign of the asphericity of this profile remains theoretically unchanged, but its value decreased for initially oblate and increased for initially prolate corneas, respectively. A similar trend was noted with the approximation obtained by the Taylor series expansion. The alteration of the apical radius and/or of the asphericity of the corneal surface resulted in variations of both the corneal profile Zernike coefficients C2(0) and C4(0). The former was essentially dependent on the variation of the apical radius and the latter essentially on the variation of both apical radius and asphericity. CONCLUSIONS: Conventional and customized profiles of ablation for hyperopia alter the postoperative corneal asphericity and the Zernike coefficients of the corneal profile. The results of this study may be useful in the interpretation of the postoperative variations of the corneal profile and their impact on corneal wavefront expansion variations after both conventional and customized profiles of ablation.

Cornea↗
PubMed2004

Photochemical keratodesmos for bonding corneal incisions.

PURPOSE: To evaluate the immediate and long-term effectiveness of a dye-plus-laser irradiation treatment (photochemical keratodesmos [PKD]) for sealing corneal incisions. METHODS: Incisions (3.5 mm) in rabbit corneas were treated on the incision walls with rose bengal dye followed by exposure to 514-nm laser radiation. PKD was evaluated in three groups (n = 3-6) using laser fluences of 115, 153, or 192 J/cm(2) (180-, 240-, and 300- second exposures, respectively) compared with an untreated group (n = 8). The intraocular pressure at which leakage occurred (IOP(L)) during infusion of saline into the anterior chamber was determined. In a long-term study, treated and control corneas were observed weekly for 10 weeks for the appearance of neovascularization, anterior chamber inflammation, iridocorneal adhesion, corneal melting, and scarring. RESULTS: Immediately after treatment, the IOP(L) increased with increasing laser fluence, producing IOPs of 230 +/- 90, 370 +/- 120, and more than 500 mm Hg at 115, 153, and 192 J/cm(2), respectively, compared with 40 +/- 20 mm Hg in control eyes (P < 0.005). No reduction in the IOP(L) was observed up to 14 days after surgery. Corneal melting in PKD-treated or control eyes was not observed in the 10-week healing study. Neovascularization, which peaked at 4 weeks but resolved by 8 weeks, was detected around the incision in both PKD-treated and control eyes. CONCLUSIONS: Immediate and lasting sealing of corneal incisions was obtained in eyes treated with PKD, using short irradiation times. These results suggest that PKD has potential for improved corneal tissue bonding.

Animals↗
PubMed2003

Epithelial ingrowth in the flap-graft interface after microkeratome-assisted posterior penetrating keratoplasty.

A 79-year-old woman with pseudophakic bullous keratopathy had microkeratome-assisted posterior keratoplasty for the treatment of clinically significant corneal edema. An island of epithelial ingrowth was noted in the flap-graft interface that was not communicating with the flap periphery. Partial lifting of the anterior corneal flap and removal and irrigation of the epithelial cells were successfully performed. A review of reports of microkeratome-assisted posterior penetrating keratoplasty shows epithelial ingrowth is common after this procedure. The presence of posterior sutures, a central location of the epithelial cells, communication with the periphery, and evidence of stromal melting should prompt immediate surgical intervention.

Aged↗
PubMed2003

Laser in situ keratomileusis and intrastromal corneal ring segments for high myopia. Three-step procedure.

We describe a surgical procedure to correct relatively high myopia in patients with thin corneas. The technique combines laser in situ keratomileusis (LASIK) and intrastromal corneal ring segment (ICRS) implantation. The 3-step procedure comprises ICRS channel formation, LASIK, and segment insertion. The technique was used in 2 eyes of 2 patients with low pachymetry values and high myopia. One patient achieved an uncorrected visual acuity (UCVA) of 20/30 and a best spectacle-corrected visual acuity (BSCVA) of 20/25 with +0.50 -1.75 x 101. The other patient achieved a UCVA of 20/30 and a BSCVA of 20/20 with +0.75 -1.50 x 80.

Adult↗
PubMed2003

Characteristic clinical findings and visual outcomes.

PURPOSE: To describe a potentially serious complication of laser in situ keratomileusis (LASIK) that can masquerade as a persistent epithelial defect. SETTING: Refractive surgery centers in academic institutions. METHODS: Charts of 4 eyes in which epithelial-defect-masquerade syndrome was diagnosed were reviewed to determine the time to diagnosis and the presence of associated features that may have contributed to the delay in diagnosis. Clinical findings and outcomes of medical and surgical intervention were recorded. RESULTS: All eyes developed an epithelial defect involving the edge of the flap during surgery. The diagnosis of epithelial ingrowth was delayed because of the presence of stromal edema (n = 4), diffuse lamellar keratitis (n = 3), and contraction of the flap leading to gutter widening (n = 4). Epithelial ingrowth was diagnosed 5, 7, 15, and 60 days after LASIK. All eyes satisfied the following criteria: convexity of the peripheral epithelium at the edge of the flap associated with light reflections at the end of the flap, fluorescein pooling in the gutter, stromal edema, reduced best spectacle-corrected visual acuity (<20/60 in 3 eyes), and partial healing of the epithelial defect limited to the flap hinge. One eye developed stromal scarring and ulceration that required fortified antibiotics. Surgical repair included epithelial scraping after the flap was lifted and ironing followed by placement of a contact lens after surgery. The epithelial defect healed 5, 7, 21, and 24 days after surgery. The final uncorrected visual acuity ranged from 20/15 to 20/100. CONCLUSIONS: Epithelial ingrowth following LASIK-associated epithelial defects may masquerade as stromal edema associated with a persistent epithelial defect. A high index of suspicion for epithelial ingrowth is essential to avoid a delayed diagnosis, which can result in irreversible visual loss due to stromal melting and infectious keratitis.

Adult↗
PubMed2003

Infectious keratitis after laser in situ keratomileusis: results of an ASCRS survey.

To investigate the incidence, culture results, treatment, and visual outcomes of infectious keratitis after laser in situ keratomileusis (LASIK) worldwide, the Cornea Clinical Committee of the American Society of Cataract and Refractive Surgery (ASCRS) contacted 8600 United States and international ASCRS members by e-mail and asked them to respond to a questionnaire about post-LASIK infectious keratitis. One hundred sixteen infections were reported by 56 LASIK surgeons who had performed an estimated 338 550 procedures. Seventy-six cases presented in the first week after surgery, 7 during the second week, 17 between the second and fourth weeks, and 16 after 1 month. Forty-seven cases were not diagnosed on initial presentation. The most common organisms cultured were atypical mycobacteria and staphylococci. Empiric therapy is not recommended as most of the organisms are opportunistic and not responsive to conventional therapy. Flap elevation and culturing should be performed when post-LASIK infectious keratitis is suspected.

Bacteria↗
PubMed2003

LASEK results.

Laser subepithelial keratomileusis (LASEK) has become a viable alternative to photorefractive keratectomy (PRK) and laser in situ keratomileusis (LASIK) in selected patients. LASEK may decrease the complications associated with PRK, including postoperative pain and slow visual rehabilitation. In this article, the authors present the visual outcomes and complication rates of LASEK based on the retrospective case review of 101 consecutive patients (163 eyes) treated with LASEK surgery over the past 6 years. Seventy-eight percent of these eyes showed complete epithelial healing by day 3, and there were no incidents of recurrent erosions. As with LASIK, the achieved correction for LASEK was greater than the treatment dose (requiring undercorrection nomogram adjustments). Mean logMAR UCVA was 0.03 (20/20) at 1 year. LASEK seems to be a safe and effective option for patients who request refractive surgery.

Adult↗
PubMed2003

Corneal neovascularization after excimer keratectomy wounds in matrilysin-deficient mice.

PURPOSE: Matrilysin, matrix metalloproteinase (MMP)-7, is upregulated in the corneal epithelium during wound healing after excimer keratectomy wounds. The purpose of this study was to determine the role of matrilysin in maintaining corneal avascularity during wound healing. METHODS: Matrilysin-deficient mice (n = 17) and their age-matched wild-type littermates (n = 18) were treated with 193 nm argon-fluoride excimer keratectomy (experiment I). The percentage of corneal surface occupied by neovascularization was measured with a computer image-analysis program adjusted for parallax. In another experiment (experiment II), epithelial closure was monitored with slit lamp biomicroscopy and fluorescein staining, and corneal neovascularization was confirmed by india ink perfusion, electron microscopy, and immunolocalization of CD31 and type IV collagen. Corneal micropocket assays were performed to compare the area of corneal neovascularization in matrilysin-deficient mice and wild-type littermates (experiment III). To determine whether the differences in corneal neovascularization were related to differences in angiogenic factors, the levels of basic fibroblast growth factor (bFGF) were compared with those of vascular endothelial growth factor (VEGF) in matrilysin-deficient and wild-type mouse corneas (experiment IV). RESULTS: The percentages of the corneal surface occupied by neovascularization after excimer laser keratectomy in the matrilysin-deficient mice measured 21.3% +/- 5.2% and 18.7% +/- 5.8% at days 3 and 7, respectively, compared with 5.3% +/- 2.4% and 5.5% +/- 3.4% in the wild-type littermates at days 3 (P < 0.01) and 7, respectively (P < 0.05; experiment I). No significant differences in the rates of epithelial closure of corneal wounds were observed between matrilysin-deficient and wild-type mice after wounding. Corneal neovascularization in the matrilysin-deficient mice was confirmed by india ink present in the corneal stromal blood vessels (extending from the limbus to the wound), immunohistochemical staining, and electron microscopy. Gram, Giemsa, calcofluor white, and acridine orange stains and electron microscopy showed no evidence of corneal infection (experiment II). The area of corneal neovascularization in matrilysin-deficient mice was not significantly different from that of wild-type littermates after implantation of bFGF pellets (0.91 +/- 0.55 mm(2) and 0.77 +/- 0.34 mm(2), respectively; experiment III). The levels of bFGF and VEGF (VEGF, VEGF-B, and VEGF-C) in corneal epithelial cells were not elevated in matrilysin-deficient mice compared with the wild-type mice (experiment IV). CONCLUSIONS: Matrilysin may play an important role in maintaining corneal avascularity during wound healing. The differences in corneal neovascularization between matrilysin-deficient mice and wild-type littermates seem unrelated to the bFGF and VEGF levels in the corneal epithelium.

Animals↗
PubMed2003

Expression of type XVIII collagen during healing of corneal incisions and keratectomy wounds.

PURPOSE: To determine the distribution of type XVIII collagen in mouse ocular tissues and to investigate the expression of type XVIII collagen during healing of corneal incisions and keratectomy wounds. METHODS: Immunohistochemical analysis of type XVIII collagen was performed in mouse ocular tissue, with polyclonal antibodies to the hinge domain. For wound-healing experiments, excimer laser keratectomy and single linear incisions were performed on mouse corneas. The corneas were harvested at various time points after wounding and processed for immunohistochemistry, in situ hybridization, competitive reverse transcription-polymerase chain reaction (RT-PCR), and Western blot analysis. RESULTS: In the unwounded mouse cornea, type XVIII collagen was expressed by the corneal epithelial cells. Type XVIII collagen was immunolocalized to the mouse corneal epithelium, epithelial basement membrane, Descemet's membrane, ciliary epithelium, lens capsule, retinal inner limiting membrane, and Bruch's membrane. In the early stages of wound healing after excimer laser keratectomy (days 3 and 7), type XVIII collagen staining of the epithelial basement membrane was absent, whereas its localization to Descemet's membrane was unchanged. After linear corneal incisions, however, type XVIII collagen was clearly seen in the stroma and in the epithelial basement membrane. Type XVIII collagen immunolocalization to the subepithelial stromal wound region peaked at 1 week after wounding, and its mRNA showed a corresponding temporal increase in expression within the same region after linear corneal incisions. CONCLUSIONS: The results suggest that type XVIII collagen is broadly expressed in ocular tissues and that it may have a role in wound healing, especially after incisional corneal wounds.

Animals↗
PubMed2002

Confocal and electron microscopic studies of laser subepithelial keratomileusis (LASEK) in the white leghorn chick eye.

OBJECTIVES: To evaluate the effect of 20% alcohol on the white leghorn chick cornea and to determine the confocal and electron microscopic findings of laser subepithelial keratomileusis surgery in the white leghorn chick corneal model. METHOD: Laser subepithelial keratomileusis surgery was performed on chick corneas and the morphologic changes were examined by transmission electron microscopy. Chick corneas were exposed to 20% alcohol for 30 and 45 seconds or 1 and 2 minutes (5 chicks per group) to evaluate the effect on the corneal epithelium. Photorefractive keratectomy using either mechanical or 20% alcohol-assisted debridement (5 chicks per group) was also performed. Keratocyte and epithelial cell deaths were analyzed 4 hours after surgery using terminal deoxynucleotidyl transfer-mediated biotin-dexoyuridine 5-triphosphate nick-end labeling (TUNEL) staining and transmission electron microscopy. RESULTS: Exposure of the corneal epithelium to 20% alcohol for 30 seconds or longer allowed reproducible separation of epithelial flaps in white leghorn chick eyes. Transmission electron microscopy immediately after alcohol treatment showed that exposure to 20% alcohol for 30 seconds or less had minimal adverse effects on the corneal epithelium. The TUNEL staining of corneas obtained 4 hours after surgery revealed TUNEL-positive cells in the central superficial stroma and more abundantly in the peripheral superficial stroma around the epithelial flap margin and in the epithelial flap itself, particularly in the basal epithelial layer. Transmission electron microscopy showed similar evidence of apoptosis in the epithelium and anterior stroma. CONCLUSIONS: The white leghorn chick eye seems to be a reasonable model for laser subepithelial keratomileusis surgery. Treatment with 20% alcohol for 30 seconds results in reproducible epithelial flap creation in the chick cornea and in relatively low levels of stromal and epithelial cell death after surgery.

Animals↗
PubMed2002

Corneal flap displacement and drift in LASIK: comparison of Hansatome and Automated Corneal Shaper microkeratomes.

PURPOSE: To describe and compare the displacement of corneal flaps created during laser in situ keratomileusis (LASIK) procedures performed with two different microkeratomes and analyze parameters (for example, pupil-to-hinge distance, drift during suction) that might affect the flap displacement or be influenced by flap displacement. DESIGN: This work was based on a cross-sectional study design. METHODS: Images copied from video recordings of 206 consecutive LASIK surgeries were analyzed to determine the distance from pupil center to corneal flap hinge (pupil-to-hinge distance), the hinge size, the distance from the center of the pupil to the margins of the flap, and the positions of the suction ring before and after vacuum in corneal flaps created by the Hansatome and the Automated Corneal Shaper (ACS) microkeratomes. Accurate measurements of all these variables could be obtained in 121 eyes (Hansatome: n = 66, right eye (OD) = 27 eyes, left eye (OS) = 39 eyes; ACS: n = 55, OD = 25 eyes, OS = 30 eyes), which were included in the analysis. Formulas were derived to calculate from the measurements the magnitude and direction of the drift of the suction ring during vacuum and the final displacement of the corneal flap. RESULTS: The mean +/- standard deviation (SD) drift of eyes during suction with the Hansatome was 0.27 +/- 0.02 mm and with the ACS was 0.12 +/- 0.02 mm (P <.001). The Hansatome induced, on average, more biased (temporal vs random) drift than did the ACS. The mean final displacement of the center of the flap from the center of the pupil was of equal magnitude for the two instruments (0.37 +/- 0.02 mm and 0.36 +/- 0.02 mm with the Hansatome and ACS, respectively). CONCLUSION: The drift induced by the Hansatome contributes to the horizontal component of the final decentration of the corneal flaps. This tendency for drift and the resultant decrease in pupil-to-hinge distance should be considered to minimize flap displacements during LASIK.

Corneal Stroma↗
PubMed2002

Vector summation of anterior and posterior corneal topographical astigmatism.

PURPOSE: To determine whether vector addition of posterior corneal astigmatism improves the correlation between topographical and refractive astigmatism. SETTING: Massachusetts Eye and Ear Infirmary and Harvard Medical School, Boston, Massachusetts, USA. METHODS: Orbscan topographical maps of 40 eyes (31 patients) showing 1.0 to 6.0 diopters (D) of astigmatism were analyzed. Topographical anterior and posterior corneal surface astigmatism was determined. Refractive astigmatism was compared to topographical astigmatism using 3 methods: anterior topographical astigmatism, overall topographical astigmatism obtained by vector summation of anterior and posterior topographical astigmatism, and simulated keratometry (SimK). RESULTS: Refractive astigmatism ranged from 0.25 to 5.00 D. The mean error in magnitude between topographical and refractive astigmatism was significantly smaller with the overall topographical method (1.06 D +/- 0.92 [SD]) than the anterior topographical method (1.37 +/- 1.04 D) (P <.0001). The mean error in axis between topographical and refractive astigmatism was smaller with the overall topographical method (10.4 +/- 13 degrees) than with the anterior topographical method (15.5 +/- 30.6 degrees) and with SimK (13.3 +/- 15.1 degrees), but these differences were not statistically significant. CONCLUSION: Consideration of the Orbscan measurement of posterior corneal surface toricity may improve the prediction of the magnitude of refractive astigmatism.

Astigmatism↗