Biomedical subjects

Siamak Ansari-Shahrezaei

Publications and source records attributed to Siamak Ansari-Shahrezaei.

7 recordsLinked to original sources

PubMed2006

Magnification-corrected photodynamic therapy.

BACKGROUND: To present a method for performing photodynamic therapy (PDT) with a constant predictable light fluence based on actual laser spot magnification. METHODS: A calibrated Gullstrand-type model eye with a scale of half circles in the centre of the artificial fundus was used for this study. The axial length of the model eye was set to different values ranging from 20 to 31 mm, and the actual laser spot magnification of four indirect condensing laser lenses were determined using a PDT laser unit. RESULTS: Equations for determining the actual laser spot magnification were calculated for each laser lens. The total change in laser spot magnification from hyperopia (axial length 20 mm) to myopia (axial length 31 mm) was -20% to +24.8% for Mainster Standard lens (Ocular Instruments Inc, Bellevue, Washington, USA), -15.7% to +27.7% for Mainster Wide Field lens (Ocular Instruments Inc), -16.3% to +33.1% for Volk Transequator lens (Volk Optical Inc, Mentor, Ohio, USA), and -19.2% to +24.4% for Volk PDT Laser lens (Volk Optical Inc). CONCLUSIONS: Axial length of the eye has a considerable effect on PDT laser spot magnification when an indirect laser lens is used. By calculating the actual laser spot magnification in conjunction with knowledge of the true greatest linear dimension of the neovascular lesion, the clinician may be able to deliver a constant predictable amount of light fluence to the fundus independent of the axial length of the PDT treating eye.

Choroidal Neovascularization↗

PubMed2006

The effect of axial length on photodynamic therapy.

PURPOSE: To determine the effect of the axial length of the eye on photodynamic therapy (PDT) light fluence. DESIGN: Laboratory investigation. METHODS: A calibrated Gullstrand-type model eye was used for this study. The axial length of the model eye was set to different values ranging from 20 to 31 mm, and the light fluence rate for treating a spot of 4 mm was recorded and compared with a fluence rate of 600 mW/cm2 with four indirect condensing laser lenses. RESULTS: The axial length of the eye is inversely related to light fluence. From myopia to hyperopia, the total deviation from 600 mW/cm2 was -37.7% to +53.8% (Mainster Standard; Ocular Instruments Inc, Bellevue, Washington, USA), and -48.3% to +20.5% (Mainster Wide Field; Ocular Instruments Inc), -52.3% to +16.7% (Volk Transequator; Volk Optical Inc, Mentor, Ohio, USA), and -52.3% to +15.3% (Volk PDT Laser; Volk Optical Inc). CONCLUSIONS: Axial length of the eye has a considerable effect on PDT light fluence rate in this model. These findings may be important for optimizing PDT, particularly in eyes with high refractive errors.

Body Weights and Measures↗

PubMed2006

Photodynamic therapy with verteporfin and intravitreal triamcinolone acetonide in the treatment of neovascular age-related macular degeneration.

PURPOSE: To examine the efficacy of photodynamic therapy (PDT) with verteporfin and intravitreal triamcinolone acetonide in the treatment of neovascular age-related macular degeneration (AMD). DESIGN: Retrospective, interventional case series. METHODS: Sixty eyes of 56 patients with neovascular AMD were treated with PDT with verteporfin followed by an intravitreal injection of 4 mg triamcinolone acetonide. The main outcome measures were visual acuity (VA), retreatment frequency with PDT (and triamcinolone), and frequency of side effects. RESULTS: Mean follow-up was 15.9 months (range 12 to 30 months, median 15 months). Twenty-three (38.3%) of 60 eyes had a stable result at 12 months' follow-up (that is, loss/gain <three lines) and 34 (56.7%) of 60 had a loss of 3 lines or more. Three patients (5%) had an improvement of 3 lines or more. Lesion type, patient age, and lesion size had no influence on the outcome, but baseline VA had a statistically significant effect (P = .006). The median number of PDT-intravitreal triamcinolone acetonide treatments was one. One-third (20 of 60) of all eyes had an increase in intraocular pressure (IOP) that required therapy. There were no cases of endophthalmitis, but 13 patients (21.6%) developed severe cataract that required surgery. CONCLUSIONS: The combination of PDT and intravitreal triamcinolone acetonide requires careful consideration as a treatment option for neovascular AMD. In our case series, this treatment combination did not prevent a considerable decrease in VA. The main benefit of this combination treatment was a low number of verteporfin treatments. Baseline VA was the main predictor of the final outcome.

Aged↗

PubMed2005

Digital area measurement of fundus landmarks.

PURPOSE: To present and validate an image analysis technique for the calculation of the true projection area of fundus landmarks from a digital fundus image. The authors present the description, technical details and results of the study. METHODS: Experimental study using a calibrated Gullstrand-type model eye with a scale of half circles in the centre of the artificial fundus. The axial length of the model eye was set to different values ranging from 21 mm to 29 mm, and the area of a half circle was calculated from digital fundus images with a magnification-calibrated image analysis program (UTHSCSA Image Tool). The calibration was based on Littmann's formula for correcting the magnification of fundus images. RESULTS: The maximum deviation of the calculated area size from the true fundus object area was -3.7% under myopic and +3.4% under hyperopic conditions. The 95% confidence interval for repeated area measurements was from +1.83 to -1.46%. CONCLUSIONS: The magnification-calibrated image analysis technique based on Littmann's formula is a non-invasive, accurate and reproducible tool for true area measurement of fundus landmarks.

Calibration↗

PubMed2005

The effect of digital measurement software on photodynamic therapy.

BACKGROUND: To investigate the effect of refraction-corrected digital measurement software on photodynamic therapy (PDT) treatment spot size. METHODS: Experimental study using a calibrated Gullstrand-type model eye. The axial length of the model eye was set to different values, ranging from 20 to 31 mm, and the PDT treatment spot sizes obtained from refraction-corrected digital measurement software and manual measurement with a fixed-magnification factor, as well as four different indirect contact laser lenses, were calculated and compared for a treatment spot with a diameter of 4 mm. RESULTS: The maximum deviation from the treating laser spot was +39.6% under myopic and +17.4% under hyperopic conditions when the refraction-corrected digital measurement software was used. The maximum deviation was +14.2% under myopic and +13.3% under hyperopic conditions when the manual measurement with the fixed-magnification factor was used. CONCLUSIONS: The use of refraction-corrected digital measurement software produces a larger deviation from treating laser spot than the use of manual measurement with a fixed-magnification factor. Therefore, refraction-corrected digital measurement software might not be suitable for calculating the recommended PDT treatment spot size in eyes with high refractive errors.

Choroidal Neovascularization↗

PubMed2004

Magnification-corrected indirect biomicroscopy of the optic nerve head.

BACKGROUND: Proper use of the new Super VitreoFundus and SuperPupil XL non-contact slit-lamp lenses for clinical disc biometry requires knowledge of their comparative magnification. METHODS: The optical performance of each fundus lens is described in terms of axial magnification, lens position, and the correction factor p (in degrees per millimeter) using a calibrated Gullstrand-type model eye adjusted for axial ametropia between -12.5 D and +12.6 D. RESULTS: The total change in axial magnification from myopia to hyperopia was -13.3% to +15.6% (Super VitreoFundus lens), and -13.9% to +14.1% (SuperPupil XL lens). When the fundus lens position was altered with respect to the model eye by +/-2 mm under myopic conditions the change in axial magnification was -5.1% to +7.7% (Super VitreoFundus lens), and -6.5% to +9.7% (SuperPupil XL lens). In the hyperopic condition the change was -3.8% to +5.8%, and -4.9% to +7.3%. Both fundus lenses exhibited a linear relationship between p and degree of ametropia of the model eye, while only the Super VitreoFundus lens displayed a constant relationship between p and ametropia of -5 D to +5 D. CONCLUSIONS: Using the fundus lens correction factor (p), the clinician may be able to estimate the dimensions of optic nerve head features with sufficient accuracy to allow clinical decisions to be made in the evaluation of patients with diagnosed or suspected glaucoma.

Fundus Oculi↗

PubMed2002

Magnification characteristic of a +90-diopter double-aspheric fundus examination lens.

PURPOSE: To investigate the magnification characteristic of the +90-D double-aspheric fundus examination lens for biomicroscopic measurement of the optic disc. METHODS: A calibrated Gullstrand-type model eye adjusted for axial ametropia between -12.5 and +12.6 D was used to measure the change in magnification of the system with refractive error and variation in fundus lens position. A correction factor p (in degrees per millimeter) at different axial ametropias was also calculated. RESULTS: The total change in magnification of the system from myopia to hyperopia was -15.1% to +13.7%. When the fundus lens position was altered with respect to the model eye by +/-2 mm under myopic conditions, the change in magnification of the system was -4.8% to +8.1%. In the hyperopic condition the change was -4.8% to +6.0%. The fundus lens exhibited a linear relationship between p and the degree of ametropia of the model eye and a constant relationship between p and ametropia of -5 to +5 D. CONCLUSIONS: Axial ametropia has a significant effect on biomicroscopic measurement of the optic disc with the +90-D lens. Therefore, a correction factor (p) was calculated that can be used in calculations for determining true optic disc size. These findings may be important for improving clinical disc biometry.

Fundus Oculi↗