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E.M.A.N. (Eye Movement and Accommodation Analyzer) device for vergence accommodation synkinesis recording and analysis
Published in Jan-Tjeerd de Faber, 28th European Strabismological Association Meeting, 2020
The NIR LED array located at the semilunar shield in aperture of the front-end optics of the videometric unit (Fig. 4) primarilly serves as a source of measuring light for excentric photorefraction. The array simultaneously serves as a source of light generating 1st Purkinje image. Point source offers optimal accuracy for the Hirschberg principle application, whereas array of point sources with different excentricity are beneficial for the excentric, slope-based, photorefraction measurement (Roorda et al. 1997). The array of four LEDs aligned to the row parallel to the pixel columns at which we perform an averaging of light intensity to create the horizontal intensity profile is an effective compromise.
Laser interferometry and axial length measurement in silicone-filled eyes
Published in A Peyman MD Gholam, A Meffert MD Stephen, D Conway MD FACS Mandi, Chiasson Trisha, Vitreoretinal Surgical Techniques, 2019
Houshang Faghiihi, Mohammad Riazi Esfahani, Hassan Hashemi, Gholam A Peyman
The patient’s position is quite similar to that when sitting at the slit lamp; many of the problems with conventional methods can be averted by using this ‘no-touch’ technique.26 The IOLMaster is more patient-friendly than acoustic measurement, there is no risk of spreading infections from patient to patient, and no need for local anesthetics. Working with the IOLMaster is easy; it detects right and left eyes automatically, and the results are less dependent on the technician. It is highly accurate and useful in eyes that are difficult to measure by acoustic biometry (e.g., eyes with intravitreal silicone oil, high myopia, aphakia, or pseudophakia), except for the 10% of cases in which it is not possible to perform an accurate biometry because of poor fixation by the patient, corneal opacity, involuntary eye movements, vitreous opacities, or dense cataract.26 Corneal curvature is measured by detecting six reflections from the cornea (Purkinje images) in a hexagonal pattern, capturing them with a camera, and analyzing them. The measurement can be expressed in diopters or millimeters of corneal radii. Anterior chamber depth measurement is accomplished by evaluation of slit-lamp images using complex image-analysis software.
Laser refractive surgery
Published in Pablo Artal, Handbook of Visual Optics, 2017
Jorge L. Alió, Mohamed El Bahrawy
Measurement of the anterior corneal surface by Scheiner in 1619 set the foundation of refractive surgery depending on the changes in the anterior corneal contour still recognized by ophthalmologists today. Later in 1823, the Purkinje principles and the four Purkinje images provided better understanding of keratometry and theories of visual accommodation, by helping create the keratometer, which was later used by surgeons to measure post cataract surgery astigmatism. The concepts of refractive surgery began as early as the year 1746 and led by a group of Dutch scientists, starting by the idea of removing the natural lens as a way of correcting high myopia when discussed by Herman Boerhaave, followed by the proposition of using incisions across the steep meridian of the cornea to flatten it and neutralize astigmatism by Hermann Snellen in 1869, an idea that was executed nearly two decades later by Faber, when he performed full thickness corneal incisions to decrease the naturally occurring astigmatism enabling a patient to pass his vision test in the royal military academy. It was stated by Leendert Jan Lans that by varying the number, direction, and shape of incisions, it is possible to manipulate the outcomes of visual correction and keratotomy principles that became the standards of refractive surgery. The following years were a phase of trial and error, till the Japanese surgeon Tsutomu Sato applied in 1939 anterior and posterior radial keratotomy based on the principles set by Lans to hundreds of pilots developing astigmatism after trauma and was able to treat up to 6 diopters (D) of astigmatism, but he was unaware of the effect of posterior keratotomy on injuring the endothelium, which led to subsequent development of corneal swelling in these patients; this was followed by several other trials that were focused only on astigmatism without regard to myopia or hyperopia.8
Evaluation of a Hirschberg Test-Based Application for Measuring Ocular Alignment and Detecting Strabismus
Published in Current Eye Research, 2021
Stephanie Suzanne S. Garcia, Alvina Pauline D. Santiago, Princess Mae C. Directo
While deemed to be less accurate than prism cover tests in measuring strabismus, tests employing the corneal light reflex are still frequently used in practice in patients for whom the APCT cannot be performed. These tests rely on the relative location of the first Purkinje image of a fixation light to assess the ocular alignment. Of these, the Hirschberg test is the primary clinical method performed. This is performed by measuring the amount of displacement of the first Purkinje image, also known simply as the corneal light reflex, from the center of the pupil. The degree of ocular misalignment in prism diopters is calculated by multiplying this measurement in millimeters (mm) to the Hirschberg ratio (HR). This value represents the amount of rotation of the eye in prism diopters per millimeter of displacement of the corneal reflex.7 The direction of deviation is determined by the direction of displacement of the corneal reflex relative to the pupil center. Temporal deviation of the corneal reflex indicates esotropia, nasal deviation indicates exotropia, downward deviation indicates hypertropia, and upward deviation indicates hypotropia.
Changes of Melanopsin Expression in the Retina of Guinea Pig during Experimental Myopia and Recovery Period
Published in Current Eye Research, 2023
Hongping Xu, Yan Dong, Fen He, Bo Qin
The diopter of the guinea pigs was measured using the Eccentric infrared photorefraction (EIR), designed by Schaeffel,15 as described previously.16 The measurement was performed in a darkroom without anesthesia or ciliary paralysis. Briefly, after 45–60-s adaptation in the darkroom, the guinea pigs were placed on the measurement platform. Then, gently hold the guinea pigs, adjusted the center of the tested eyes of the guinea pigs to the center of the camera, and measured the refractive force of the guinea pig eyes in the vertical direction. When the Purkinje image was located in the center of the pupil, the diopter value was recorded. The average value of 3 consecutive measurements was taken as the experimental result.
Proparacaine-Induced Mydriasis During Strabismus Surgery
Published in Seminars in Ophthalmology, 2018
Brijesh Takkar, Pradeep Sharma, Nripen Gaur, Ashutosh Kumar Singh, Rashmi Ramachandran
Assessment of Purkinje images for pupil alignment form the backbone of ocular examination for the strabismologist.1 Surgical success is commonly gauged during squint surgery on the basis of degree of pupil alignment; when performing dynamic tests (e.g., Cover test) it is not possible due to general anesthesia (GA). A pupillary distortion, therefore, can seriously hamper the judgment of an unaware surgeon.