Biomedical subjects

Habib Hamam

Publications and source records attributed to Habib Hamam.

6 recordsLinked to original sources

PubMed2004

Lau array illuminator.

Spatial coherence can be created by appropriate spatial arrangements of incoherent point sources. Lau used a source of extended light and two amplitude gratings of identical periods, separated by the quarter Talbot distance, to provide coherent light. Because of the two successive amplitude gratings, most of the power is lost. By modifying the geometry of the second grating, I designed an array illuminator, providing several compression ratios and various topologies of the output plane, with significantly reduced losses. To further improve the power efficiency of the system, I used a longitudinal mirror system to collect the light rays that are lost in the initial Lau setup. Both one- and two-dimensional geometries are considered.

Journal Article↗

PubMed2003

Talbot imaging and unification.

The fractional Talbot effect brings into play a superimposition of shifted and complex weightedreplicas of the original object. This phenomenon can be used to replicate images of nonperiodic objects by means of Talbot array illuminators. These diffractive elements can also be used to concentrate replicas into a single image. These techniques are useful for several applications such as beam shaping.

Journal Article↗

PubMed2003

Optical quality of the eye with the Artisan phakic lens for the correction of high myopia.

PURPOSE: To evaluate the optical quality of the eye before and after the insertion of an Artisan phakic intraocular lens for the treatment of high myopia. METHODS: Consecutive patients implanted with the Artisan lens by a single surgeon between June 2001 and April 2002 were enrolled prospectively. One eye per subject was tested. The wavefront aberration was calculated from images recorded with a Hartmann-Shack sensor. This wavefront aberration was expressed as a Zernike polynomial expansion from the third up to the seventh order. Root mean square wavefront error was used as a parameter of optical quality. Point-spread function and modulation transfer function were also computed from the wavefront aberration. RESULTS: The mean age of the four patients (four eyes) was 46 +/- 11 years. The preoperative mean spherical equivalent was -14.13 +/- 3.19 D (range, -20.50 to -9.75 D), with a best-corrected visual acuity of 20/25 or better in three of the four eyes. No complications were encountered. Postoperatively, the mean spherical equivalent was -0.22 +/- 0.30 D (range, -0.75 to +0.38 D). An uncorrected visual acuity of 20/40 or better was observed in three eyes. Overall, for each combination of order (third, fourth, and fifth to seventh) and pupil size (3, 4, and 5 mm), the mean postoperative root mean square values for the four subjects were lower than the mean preoperative values. However, because of the small size of the study population (four patients), this improvement did not reach a statistically significant level. CONCLUSIONS: Preliminary data using the Hartmann-Shack wavefront sensor have not revealed a tendency toward deterioration of the optical performance after the insertion of an Artisan lens for the treatment of high myopia. The Hartmann-Shack sensor was a useful tool for the objective assessment of the image optical quality of eyes with a phakic intraocular lens.

Adult↗

PubMed2003

A new measure for optical performance.

Because diffraction and aberration affect the performance of the optical system, a new metric is advanced that emphasizes the link between these three aspects. In general, the modulation transfer function is used as a measure for contrast sensitivity reduction, whereas the root mean square error is often used to quantify the optical quality of the system. However, for a given object, wavefront aberrations can alter the output image very differently even though they have the same root mean square error and modulation transfer function profile. A distinction between coherent and incoherent illumination is made, and a new measure, called optical transfer error, is defined to characterize optical performance complementarily to root mean square and modulation transfer function. The optical transfer error measures the optical excellence in terms of the shape of the wavefront as well as the theoretical performance results. Several illustrations are presented to better discuss optical performance.

Contrast Sensitivity↗

PubMed2003

Monochromatic aberrations as a function of age, from childhood to advanced age.

PURPOSE: To describe monochromatic optical aberrations of the eye as a function of age. METHODS: One hundred fourteen subjects with a spherical equivalent within +/-3.50 D from emmetropia, corrected visual acuity of 20/40 or better, and normal findings in an ophthalmic examination were enrolled. The mean age was 43.2 +/- 24.5 years (range, 5.7-82.3). Monochromatic optical aberrations were measured with a Hartmann-Shack wavefront sensor after pharmacological dilation and cycloplegia. RESULTS: For a 5-mm pupil and for third- to seventh-, third-, fourth-, and fifth- to seventh-order aberrations, as well as for coma and spherical aberrations, the root mean square (RMS) error as a function of age was modeled by a second-order polynomial regression. It decreased progressively through childhood, adolescence, and early adulthood; reached a minimum level during the fourth decade of life, then increased progressively with age, to age 82. For a 5-mm pupil, the mean modulation transfer function (MTF) was reduced in both the child-teenage (5-20 years; n = 29) and the elderly (61-82 years; n = 37) groups versus the middle-aged adult group (41-60 years; n = 24; P < 0.05). In young adults (21-40 years; n = 23) and elderly subjects, the MTF curves were very close and almost superimposed at spatial frequencies higher than 38 cyc/deg. CONCLUSIONS: Aberrations of the whole eye were objectively measured from early childhood to an advanced age, and the relationship between monochromatic aberrations and age has been shown to fit a quadratic model. The results suggest that the definition of emmetropization should be broadened to include the reduction of higher order aberrations.

Adolescent↗

PubMed2002

Objective measurement of optical aberrations in myopic eyes.

PURPOSE: To determine whether the degree of myopia affects the optical quality of the retinal image after appropriate correction, monochromatic aberrations of the human eye were measured as a function of the degree of myopia. METHODS: Using a modified Hartmann-Shack method, a population of 27 myopic (up to -9.25 D) and 7 emmetropic optometry students (18-32 years) were objectively evaluated before and after pupil dilation. We then identified for each subject the most influential aberration types, and we calculated the profile of wavefront aberration. To study the behavior of aberration as a function of the degree of myopia, we determined the maximum value of aberration as well as the root mean square (rms) value. RESULTS: It turned out that aberration increases with the refractive error in a quasi-linear relationship for pupil diameters of 5 and 9 mm. This result is valid for both rms and maximum values. CONCLUSIONS: We objectively showed that optical quality decreases as myopia increases and as the pupil gets larger. Coma is more frequent in high myopia, and spherical aberration occurs more frequently for dilated pupils.

Adult↗