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Dr.
O’Donnell and his Focus on Glaucoma
Dr. John O’Donnell is a Board Certified Optometrist at our Harrisburg Premier Eye Care Group office.
He is a Diplomate in the Glaucoma Section of the American Academy of Optometry – one of just five in the world! This impressive accomplishment is achieved by dedicated optometrists who strive to attain a level of excellence beyond the regular American Academy of Optometry Fellowship program. It took Dr. O’Donnell about five years to complete this elite program and he is dedicated to being a lifelong learner in the field of optometry, specializing in glaucoma.
Practicing since 1983, Dr. O’Donnell is a well-educated and dedicated optometrist. He graduated from St. Joseph’s University and then went on to complete his optometric education at the Pennsylvania College of Optometry. O’Donnell completed externships with honors at the Walson Army Hospital, at Lynch Pediatric Unit of the Eye Institute, and in contact lens with Dr. Joseph Gurwood. Upon graduation, he was recognized with clinical excellence awards for his internship at the Eye Institute and Externship at the Lynch Pediatric unit.
Upon completing these externships, Dr. O’Donnell decided to practice in an MD/OD group setting and continues that role today at Premier Eye Care Group in Harrisburg, PA. An MD/OD group setting simply refers to an eye care practice that features both Ophthalmologists (who have their Doctor of Medicine degree – referred to as an “MD”) and Optometrists (who have their Doctor of Optometry degree – referred to as an “OD”).
Board certification became available for Dr. O’Donnell in 2011. He pursued this credential for a number of reasons: personal and professional development, commitment to his patients for lifelong learning and equality among his ophthalmologist colleagues. You’ll notice that part of Dr. O’Donnell’s title is “FAAO” – which stands for Fellows of the American Academy of Optometry. The FAAO designation means they are recognized by their colleagues as knowledgeable and experienced professionals who have met the highest standards of professional competence in a broad range of eye care issues.
Dr. O’Donnell’s strong work ethic and commitment to his patients and practice have set him apart from many other optometrists. Below you will find just some of his great accomplishments in the world of optometry:
Diplomate in the Glaucoma Section of the American Academy of Optometry
Elected to the Optometric Glaucoma Society in 2017
Member of the American Optometric Association
Member of the Pennsylvania Optometric Association
Member of the World Glaucoma Association
Recognized by Who’s Who in US Medicine and Health Care
Past president of both the Pennsylvania Optometric Association and Central Pennsylvania Optometric Society
Since the late 1990s, glaucoma patients make up most of Dr. O’Donnell’s patient base at Premier Eye Care Group. The American Academy of Ophthalmology defines glaucoma as a disease that damages your eye’s optic nerve. Sadly, it is the leading cause of irreversible blindness in the world. There are two main types of glaucoma: open angle and closed angle. The “angle” refers to the opening where fluid drains from the eye. In closed (or narrow) angle, the passage is blocked and the fluid cannot exit the eye. With open angle glaucoma, the channel is not obstructed. It is important to get glaucoma treated early on to prevent blindness. The use of topical medication (eyedrops), laser therapy, surgery or a combination of treatments can help to lower eye pressure, which will cause less vision loss.
Glaucoma can be diagnosed at any age – but it is more common after the age of 40. It is important to attend routine eye examinations as an adult to try and prevent eye diseases, such as glaucoma. Dr. O’Donnell refers to glaucoma as the “silent thief of sight” because there are no symptoms until late in the disease, when vision loss is inevitable. It is estimated that there are nearly one million people in the United States with glaucoma that are currently undiagnosed because of lack of symptoms and failure to attend routine eye exams. Don’t be part of that statistic – be proactive and schedule an eye examination with a trustworthy optometrist at Premier Eye Care Group today.
Over the years, Dr. O’Donnell has been interviewed and has even written magazine articles about glaucoma.
If you are over the age of 40, have a family history of glaucoma or any other eye risk factors – be sure to have your eyes examined regularly. Visit Dr. O’Donnell and the other optometrists at Premier Eye Care Group in the Harrisburg, PA region and SEE THE POSSIBILITIES! With their vast knowledge, years of experience, and the latest diagnostic technology, you’re in good hands.
Contact us today at (717) 232-0843 or via our website to help restore your eyesight.
O'Donnell C.
F. inertial navigation. Analysis and design
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M.: Publishing House "Nauka" 1969 - 592 pages. Ch. ed. Phys.-Math. Literature Ed. N.P. Bukanova. Per. from English. V.L.Leonidov and I.Ya.Lekhtman The book was written by a team of American experts who participated in the practical development of inertial and astroinertial systems. Both the principles of inertial navigation and the use of various structural elements, including the most new. After an introductory chapter of a general nature, follow: description basic inertial elements (gyroscopes, accelerometers, optical heads), inertial platforms and auxiliary systems (computational and optical), presentation of instrumentation methods implementation of basic equations, algorithms and error analysis, questions corrections and methods for constructing guidance systems for ballistic shells. The experience of designing an inertial system is described, used on an American submarine that passed through North Pole. An extensive bibliography is provided.
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M.: FIZMATLIT, 2006. - 424 p. The means, methods and algorithms for obtaining and processing navigation information in the complexes of orientation and navigation (ON) of moving objects are considered. The information core in most complexes is a strapdown inertial navigation system, corrected from a satellite navigation system. A generalized idea of the structure and functional composition of KOH is given and examples of technical solutions are given. ..
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Transport, 1980 - 85 p. The book discusses the state and prospects for the development of control systems for aircraft power plants, structural diagrams and features of domestic and foreign systems. The issues of detection of failures of elements of the power plant and the control systems themselves are outlined. An analysis of the possibilities, shortcomings and ways to improve the control systems of modern power plants of aircraft is given. Attention is paid to the trans...
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Stavropol: Publishing House of the Stavropol All-Union Aviation Administration of Air Defense named after. Sudtsa V.A., 1995, 54 p. The principle of operation of an inertial system of the IS-1 type, the basics of building systems of power gyroscopic stabilization and horizontal correction are outlined. descriptions of the units included in the inertial system, their purpose and a brief description of the device are given. Attention is paid to the operation of the inertial system and its built-in control. Content. Heading vertical KV-1P. Amplifier block...
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M.: FIZMATLIT, 2003 - 280 p. The main approaches, methods and algorithms for forming the appearance of integrated navigation and control systems for unmanned maneuverable aerial vehicles of various classes are outlined. The concept of "look" includes: the composition, structure and algorithms of the corresponding integrated system. The structure of the formed integrated systems includes a strapdown inertial system and a multi-channel GPS/GLONASS receiver. Discussing questions...
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Coursework on APIC for the 4th course (Calculation of static characteristics. Calculation of a sensitive element. Calculation of a transfer-multiplier mechanism. Calculation of electrical circuit parameters. Calculation of a ratiometer with a moving magnet. Calculation of a dynamic characteristic. Calculation and analysis of errors). Plus a drawing of a pressure gauge made in a compass.
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Calculation of aircraft DC generator is given. 39 pages. Exercise. Initial data. The choice of basic dimensions with the calculation of options. Generator electromagnetic power, choice of number of pole pairs and pole arc ratio. Choice of anchor sizes. Calculation of the dimensions of the generator housing. Selecting the type and calculation of the armature winding. Choice of armature winding type. Armature winding calculation. Calculation of additional anchor dimensions. Collector and brushes. Calculation of magnetic...
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St. Petersburg: GUAP, 2002. - 70 p. The manual outlines the theoretical foundations and physical principles of radio navigation measurements, methods for estimating radio navigation parameters, analysis of the accuracy of determining the location of aircraft in the navigation space. The textbook is intended for students of full-time, evening and correspondence courses in the specialties 2007 "Radio Engineering" and 2013 "Technical operation of transport radio equipment".
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Reference book. M.: Mashinostroenie, 1982, 165 p. The book outlines the basic principles for the construction of hydraulic stabilizers for various purposes and gyroscopic orientation systems and analyzes their dynamic errors. The physical essence of the phenomena occurring in this case is considered. The book is intended for specialists involved in the development of gyroscopic instruments and orientation and stabilization systems, and may also be useful for a teacher...
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Design of devices, systems and measuring and computing P 55 complexes: lecture notes for students of the specialty 20010365 / comp. V. N. Shivrinsky. - Ulyanovsk: UlGTU, 2009. - 116 p. The abstract of lectures was compiled in accordance with the work programs of the courses "Fundamentals of Designing Devices and Systems" and "Designing Measuring and Computing Complexes"; introduces students to the device of various measuring information systems, principal ...
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Definition of information. Phases of information circulation. Eliminate redundant information. Types of information. measures of information: structural, statistical, semantic. Geometric structural measure of information. combinatorial measure. Additive Hartley measure. Probability and information. Entropy. The amount of information on Shannon. Signals and their characteristics. Signal analysis. Deterministic fluctuations and their classification. Analytical description of periodic,...
Optical aberrations of the eye in keratoconus | Averich V.V., Egorova G.B.
Introduction
With the help of visual perception, a person receives 80% of incoming information [1]. Visual perception includes a number of anatomical and optical elements of the eyeball, the state and balanced work of which ultimately determine the quality of the image formed in the fovea of the retina and processed by the central visual analyzer. The human eye, being a complex optical self-regulating system, is far from perfect from the point of view of geometric optics and has a certain number of optical errors [2]. As a result of the discrepancy between the optical system of the eye and the ideal physical model, deviations of light rays occur, passing through the refractive media of the eyeball, which leads to the formation of so-called optical aberrations (from the Latin aberrare - “to evade, err”), which, reaching certain values, can significantly reduce visual functions.
Optical aberrations
“Aberration is any angular deviation of a narrow parallel beam of light from the point of ideal intersection with the foveola as it passes through the entire optical system of the eye” [3]. The quality of the optical system is determined by the characteristics of the wavefront of a light wave: an “ideal” eye with emmetropia, which does not have aberrations, forms a spherical wavefront and provides a full projection of the perceived image of a point source on the macula, limited only by light diffraction, the so-called Airy disk, the size of which is directly proportional to the pupil diameter [3–6].
In 1960, the Dutch physicist and Nobel Prize winner Fritz Zernike proposed an approximation of wavefront aberrations into a mathematical system of polynomials or polynomials, which is successfully used to this day [7–9]. This approach makes it possible to represent a wave front of any complexity as a series of polynomials that fully describe all the optical aberrations included in it. Each Zernike polynomial is associated with a certain type of aberration and is expressed as a mode: Z m n , where m is a positive or negative number describing the meridional frequency of the polynomial mode and n is an integer representing the sinusoidal frequency of the polynomial mode.
Polynomials are usually represented graphically in the form of a pyramid, each level of which corresponds to a certain degree of the radial component. In turn, each radial mode consists of aberrational modes with a certain meridional frequency (Fig. 1).
Optical aberrations are divided into lower (1st and 2nd, or low order aberrations, LOA) and higher (3rd and 4th, or high order aberrations, HOA) order aberrations. Aberrations of the 1st order, or Tilt, characterize the action of the prism, i.e., the tilt relative to the vertical (Z -1 1 ) or horizontal (Z 1 1 ) axis. Like the zero polynomial (Z 0 0 ), Tilt is usually not taken into account when measuring an aberrational wavefront. 2nd order aberrations include defocus or ametropia (Z 0 2 ) and astigmatism (Z -2 2 , Z 2 2 ). The most significant 3rd and 4th order aberrations are coma (Z -1 3 , Z 1 3 ), spherical aberration (Z 0 4 ) and -Z 053 3 3 , Z 3 3 ) [3, 4].
Coma is a spherical aberration of oblique beams of light incident at an angle to the optical axis of the eye. This type of aberration is based on the asymmetry of the optical center of the two main refractive media of the eye with the macula - the cornea and the lens [3, 10, 11]. Spherical aberration is characterized by a difference in the degree of refraction of parallel rays passing at the periphery and paracentrally of the optical axis, relative to rays refracted in the center. Trefoil is an optical aberration that occurs when the surface of the optical elements of the eye is irregular on their periphery and forms a different linear optical magnification in different parts of the image [3, 11].
In addition to the main ones listed above, there are a number of other aberrations - secondary spherical, secondary coma, secondary trifoil, quadrafoil, pentafoil, etc. Aberrations up to the 7th order are included in the standards of the American Optical Society. However, in the course of clinical studies, it was proved that with a visual acuity of 100%, the effect of optical aberrations above the 4th order on visual functions is minimized [12]. In parallel with this, it was proved that in a conditionally normal eye with emmetropic refraction, there is a predominance of aberrations only up to the 2nd order, and all polynomials above tend to zero on average. Other studies also confirm this fact: more than 90% of all wavefront aberrations are low-order aberrations, 80% of them are related to defocus or ametropia [13]. This is achieved due to the symmetry of the location of the optical centers and the transparency of the structures of the refractive media of the eye.
Optical aberrations in keratoconus
It is known that among all the refractive structures of the eye, the cornea plays the most important role. The occurrence of irregularity of its surface, optical inhomogeneity, and violation of the transparency of the layers of the cornea lead to a sharp change in the aberration pattern of the wavefront of the eye towards higher orders [14–17]. In particular, these changes in the cornea are characteristic of a disease such as keratoconus (KK) [14–25].
This disease is the most common form of primary ectatic corneal disease. The characteristic clinical manifestations of CC are topographic changes in the shape and thickness of the cornea (a decrease in the radius of curvature and thinning in the ectasia zone), in the initial stages of the process leading to a shift in clinical refraction towards myopia and the formation of irregular astigmatism, and in the terminal stages to a decrease in the transparency of the cornea.
The study of CC based on the data of videokeratotopography of the anterior surface of the cornea and the decomposition of keratometric parameters into a set of orthogonal Zernike polynomials were first proposed in 1992 [26]. Later, the accumulation of clinical data and the development of wavefront probing methods made it possible to obtain more accurate measurements of wave aberration during QC [27].
Numerous studies on the assessment of eye wavefront aberrations in CC have proven a statistically significant increase in higher order aberrations, among which the coma index is subject to the greatest changes [16–25, 28, 29].
A cohort observational study of 73 eyes with CC showed a statistically significant increase in higher-order total ocular aberrations: coma, trifoil, and spherical aberration. The total standard deviation of the Zernike coefficients of the 3rd order with a pupil diameter of 6 mm was 0.28±0.15 µm in 870 eyes in the control group and 3.10±2.28 µm in the CC group. In addition, the study noted that vertical coma was an aberrational predictor of CC, showing a specificity of 71.9% and sensitivity 89.3%. If a subclinical form of CC is suspected, the vertical coma index should be below 0. 12 microns. The clinical form is characterized by an indicator of 0.3 µm and below [29]. This discovery was taken into account in the future in the protocols of the study of patients with CC.
In the literature, there are publications in which, on the contrary, an increase in higher-order aberrations due to horizontal coma is noted [14]. Different meridional frequency of coma-like aberrations may be associated with topographic features of the location of ectasia and the stage of the disease.
With the advent of the possibility of separating the picture of the wavefront of the eye into general and corneal aberrations in the studies of eyes with CC, a significant correlation was revealed between the values of the aberrations of the anterior surface of the cornea and general ocular aberrations, which made it possible to formulate a hypothesis about the predominance of the corneal component in the general wavefront of the eye [16, 20 ]. In more recent studies, these data have been applied to the diagnosis of subclinical CC. The combination of videokeratotopography based on the Placido disc with Hartmann-Shack aberrometry revealed a combination of an increase in the values of vertical coma and keratotopographic indices (in particular, the Rabinovich index, I-S) as characteristic patterns for subclinical and initial CC [22].
Let us return to the definition of coma-like aberrations: "this type of aberration is based on the asymmetry of the optical center of the two main refractive media of the eye with the foveola - the cornea and the lens" [3]. Thus, the predominance of this type of high-order aberrations in QC becomes quite understandable. The incoming light wave, passing through the irregular surface of the cornea, will be distorted at each point of such a cornea in different ways. Figure 2 shows a general aberration map of the wavefront of the eye with CC (A) and with a conditionally normal cornea (B) with a pupil diameter of 6 mm. The picture of corneal aberrations of the eye in CC undergoes significant changes (C) in comparison with the norm (D). With the help of color mapping, various values of high-order aberration errors are depicted: areas with aberrations that have positive values are marked in red and orange, areas with negative values are indicated in blue and green. Yellow and light green colors indicate areas where aberrations have values close to zero. In the given example of an eye with QC, the contribution of vertical coma-like aberrations was -1.87 μm for the total aberration pattern (A) and -2.91 µm for corneal (C) respectively. For an eye with a conditionally normal cornea, the contribution of coma-like aberrations to the total corneal aberrations averages -0.17 μm [16].
The improvement of diagnostic equipment gave impetus to the differentiation of higher-order corneal aberrations into aberrations of the anterior and posterior surfaces. However, in clinical practice of CC screening, the values of aberrations of the posterior surface of the cornea were inferior in significance to the data of aberrations from its anterior surface [30, 31]. Despite this, the question of the influence of the posterior surface of the cornea on the indicators of general astigmatism and the wavefront of the eye is of increasing scientific and clinical interest among ophthalmologists [32]. It is generally accepted that the main contribution to corneal astigmatism and indicators of the aberration pattern is made by the anterior surface of the cornea, while the data of the posterior surface are practically not taken into account due to the significant difference between the refractive indices "air - anterior surface of the cornea" and "posterior surface of the cornea - aqueous humor” [4, 32].
In the first case, this indicator is 0.376 (1.376-1), and in the second - only -0.04 (1.336-1.376). According to the analysis of the optical properties of the cornea, it was found that only 10% of its total optical power falls on the posterior surface [33]. In addition to the difference in refractive indices, this insignificant contribution is due to the sphericity and regularity of both the anterior and posterior surfaces of the cornea, as well as to some extent their "parallelism", which is not observed in keratectasia. In a retrospective study based on scanning keratotopography according to the Scheimpflug principle, the ratio of the cylindrical components of the anterior and posterior surface of the cornea was studied in 1273 patients with CC and in 1035 healthy volunteers. The mean values of anterior and posterior surface astigmatism in the CC group were 4.49±2.16 diopters and 0.90±0.43 diopters, respectively, which is 4.8 and 3.5 times higher than the same values in comparison with the group of persons with conditionally normal corneas [33]. A similar trend is revealed in another study [34].
In parallel with an increase in the cartometric values of the posterior surface of the cornea, its contribution to the general aberration background also increases. In a number of studies, it was found that the main part of the internal aberrations of the eye in CC are aberrations of the posterior surface of the cornea [35, 32]. The mean standard error of higher order aberrations for the posterior surface of the cornea was 1. 04±0.31, 0.54±0.21, and 0.24±0.05 µm for stages III, II, and I, respectively. For conditionally normal eyes, this indicator corresponded to 0.19±0.05 µm. The mean root mean square value of coma as the most dominant aberration of the posterior surface of the cornea in the eyes with CC was 0.93±0.35, 0.46±0.23, and 0.12±0.06 μm. In the control group, this parameter corresponded to 0.09 ± 0.06 μm, i.e., the mean square value of the coma of the posterior surface of the cornea in CC was 10.5 and almost 1.5 times higher than the coma parameters of conditionally normal corneas [35].
The authors also describe the potential effect of self-compensation of astigmatism and, as a consequence, aberrations of the cornea by its surfaces, similar to the mechanism of compensation for lens and corneal aberrations. From 17% to 20% of corneal astigmatism and up to 24% of aberrations such as coma of the anterior surface of the cornea was compensated by its posterior surface [35, 36]. However, against the background of a general increase in these indicators during QC, this effect of self-compensation by surfaces is insignificant.
Another potential reason for the increase in the level of aberrations in CC is the accompanying signs of dry eye syndrome (DES) [37]. The tear film is not only the first refractive surface that a light beam encounters when passing through all the structures of the eye, its normal state is one of the important criteria for the functioning of the cornea as the main refractive medium of the eye [38]. A stable tear film provides a smooth optical surface, thereby minimizing light scattering from the anterior surface of the cornea. Studies show that with any change in the stability of the tear film, there is a sharp increase in the values of high-order aberrations [39]. An additional factor influencing the increase in aberrations can be keratopathy that occurs against the background of a deterioration in the state of the tear film [38, 39].
Keratoconus Aberration Compensation
The appointment of a combination of tear replacement and reparative drugs allows you to almost completely level the phenomena of keratoconjunctival xerosis. If a patient with CC has initial signs of DES, it is advisable to use non-preserved low-viscosity tear substitutes based on hyaluronic acid of various concentrations. If the patient uses contact correction for the prevention of hypoxic complications, the appointment of methyl-ethylpyridinol, eye drops 10 mg / ml (Emoxipin ® ) [40, 41], which has antiplatelet and antihypoxic effects. Interacting with lipid peroxide and hydroxyl radicals, methylethylpyridinol inhibits free radical oxidation of the latter, increasing the activity of antioxidant enzymes, which leads to stabilization of cell membranes and a decrease in cell apoptosis. In a study, administration of Emoxipin ® instillations to 1% of patients with hypoxic complications while wearing soft contact lenses made it possible to level hypoxic changes in the cornea and improve the state of the tear film [41]. In addition, the effectiveness of this drug has been proven in a number of clinical studies in the complex treatment of glaucoma, as well as various retinal diseases [42, 43]. In the presence of keratopathy, it is recommended to add a gel root protector containing 5% dexpanthenol in its composition to accelerate epithelialization processes, restore tear film stability and, as a result, reduce DES-induced optical aberrations.
An increase in the level of optical aberrations in QC leads to a significant decrease in spatial contrast sensitivity [2], deterioration of visual functions and, as a result, to visual disability [2, 11, 44].
If we talk about methods for compensating optical aberrations in CC, then today contact correction with rigid gas-permeable lenses (RHCL) remains the most effective and predictable method of visual rehabilitation in terms of functional results and safety [45, 46–48].
The possibility of a significant reduction in the level of higher-order aberrations was proved (at stage I of the disease - by 38.2%, at stage II - by 55.5%, at stage III - by 54.9% and by 55.2% at stage IV) with the use of GLCL, which is accompanied by an increase in spatial contrast sensitivity and visual performance [48]. In addition, wearing the FCL contributes to a change in the direction of the vertical coma from -0.185 to 0.134 µm, and the total aberrations of higher orders decrease from 0.54 to 0.36 µm [49]. However, it is impossible to completely level the effect of aberrations with the help of the GGCL. The level of residual aberrations in the LCL in some cases remains higher, and visual performance remains lower than in healthy eyes [32]. The reasons may be rotation and unstable fit of the LCL, wear of the lens material, as well as incompletely compensated higher-order aberrations of the posterior surface of the cornea [35, 36, 47]. The residual average value of aberrations above the 3rd order in LGCL is 0.8, 0.5, and 0.34 μm for stages III, II, and I of QC, respectively [35].
To minimize the influence of wavefront aberrations of the eye and increase visual functions, the structures and materials of the LCL are constantly being improved. To date, the use of scleral rigid gas permeable lenses (RHGCL) is promising in the correction of aberrations in CC [50]. Due to the large diameter, the supporting part of the lens is located on the bulbar conjunctiva, which ensures its stable fit on the eye and subjective comfort on the part of the patient, even with severe corneal deformity. The presence of the so-called lacrimal clearance between the posterior surface of the FGCL and the anterior surface of the cornea makes it possible to neutralize irregular corneal astigmatism and higher-order aberrations induced by it, thereby creating a single structure with lower optical errors.
Conclusion
Thus, the irregularity and high values of astigmatism of the anterior and posterior corneal surfaces, which occur in such a corneal pathology as CC, make a significant contribution of higher-order aberrations to the general aberration background of the eye, significantly reducing visual functions. The put forward theory of the origin of residual aberrations in FCL from the posterior surface of the cornea in CC requires further clarification both from a scientific point of view and from a practical point of view (their significant impact on visual acuity). In addition, the search for optimization of optical rehabilitation in CC, which contributes to the maximum neutralization of higher-order corneal aberrations, remains relevant.
CREDITS :
Averich Veronika Valerievna - Candidate of Medical Sciences, Junior Researcher of the Department of Refractive Disorders of the Federal State Budget Scientific Institution "NIIGB"; 119021, Russia, Moscow, st. Rossolimo, d. 11A, B; ORCID iD 0000-0001-5778-4123.
Egorova Galina Borisovna - Doctor of Medical Sciences, Chief Researcher of the Department of Refractive Disorders of the Federal State Budget Scientific Institution "NIIGB"; 119021, Russia, Moscow, st. Rossolimo, d. 11A, B; ORCID ID 0000-0001-8557-0288.
O’Donnell and his Focus on Glaucoma
Joseph Gurwood. Upon graduation, he was recognized with clinical excellence awards for his internship at the Eye Institute and Externship at the Lynch Pediatric unit.
There are two main types of glaucoma: open angle and closed angle. The “angle” refers to the opening where fluid drains from the eye. In closed (or narrow) angle, the passage is blocked and the fluid cannot exit the eye. With open angle glaucoma, the channel is not obstructed. It is important to get glaucoma treated early on to prevent blindness. The use of topical medication (eyedrops), laser therapy, surgery or a combination of treatments can help to lower eye pressure, which will cause less vision loss. 
Don’t be part of that statistic – be proactive and schedule an eye examination with a trustworthy optometrist at Premier Eye Care Group today. 
F. inertial navigation. Analysis and design 
45 MB 
The experience of designing an inertial system is described, used on an American submarine that passed through North Pole. An extensive bibliography is provided. 
.. 
Sudtsa V.A., 1995, 54 p. The principle of operation of an inertial system of the IS-1 type, the basics of building systems of power gyroscopic stabilization and horizontal correction are outlined. descriptions of the units included in the inertial system, their purpose and a brief description of the device are given. Attention is paid to the operation of the inertial system and its built-in control. Content. Heading vertical KV-1P. Amplifier block... 
The structure of the formed integrated systems includes a strapdown inertial system and a multi-channel GPS/GLONASS receiver. Discussing questions... 
95 MB 
The textbook is intended for students of full-time, evening and correspondence courses in the specialties 2007 "Radio Engineering" and 2013 "Technical operation of transport radio equipment". 
V. N. Shivrinsky. - Ulyanovsk: UlGTU, 2009. - 116 p. The abstract of lectures was compiled in accordance with the work programs of the courses "Fundamentals of Designing Devices and Systems" and "Designing Measuring and Computing Complexes"; introduces students to the device of various measuring information systems, principal ... 
Signals and their characteristics. Signal analysis. Deterministic fluctuations and their classification. Analytical description of periodic,... 
Each Zernike polynomial is associated with a certain type of aberration and is expressed as a mode: Z m n , where m is a positive or negative number describing the meridional frequency of the polynomial mode and n is an integer representing the sinusoidal frequency of the polynomial mode. 
2nd order aberrations include defocus or ametropia (Z 0 2 ) and astigmatism (Z -2 2 , Z 2 2 ). The most significant 3rd and 4th order aberrations are coma (Z -1 3 , Z 1 3 ), spherical aberration (Z 0 4 ) and -Z 053 3 3 , Z 3 3 ) [3, 4]. 
The occurrence of irregularity of its surface, optical inhomogeneity, and violation of the transparency of the layers of the cornea lead to a sharp change in the aberration pattern of the wavefront of the eye towards higher orders [14–17]. In particular, these changes in the cornea are characteristic of a disease such as keratoconus (KK) [14–25]. 
Later, the accumulation of clinical data and the development of wavefront probing methods made it possible to obtain more accurate measurements of wave aberration during QC [27]. 
12 microns. The clinical form is characterized by an indicator of 0.3 µm and below [29]. This discovery was taken into account in the future in the protocols of the study of patients with CC. 
The combination of videokeratotopography based on the Placido disc with Hartmann-Shack aberrometry revealed a combination of an increase in the values of vertical coma and keratotopographic indices (in particular, the Rabinovich index, I-S) as characteristic patterns for subclinical and initial CC [22]. 
With the help of color mapping, various values of high-order aberration errors are depicted: areas with aberrations that have positive values are marked in red and orange, areas with negative values are indicated in blue and green. Yellow and light green colors indicate areas where aberrations have values close to zero. In the given example of an eye with QC, the contribution of vertical coma-like aberrations was -1.87 μm for the total aberration pattern (A) and -2.91 µm for corneal (C) respectively. For an eye with a conditionally normal cornea, the contribution of coma-like aberrations to the total corneal aberrations averages -0.17 μm [16]. 
Despite this, the question of the influence of the posterior surface of the cornea on the indicators of general astigmatism and the wavefront of the eye is of increasing scientific and clinical interest among ophthalmologists [32]. It is generally accepted that the main contribution to corneal astigmatism and indicators of the aberration pattern is made by the anterior surface of the cornea, while the data of the posterior surface are practically not taken into account due to the significant difference between the refractive indices "air - anterior surface of the cornea" and "posterior surface of the cornea - aqueous humor” [4, 32]. 
In a retrospective study based on scanning keratotopography according to the Scheimpflug principle, the ratio of the cylindrical components of the anterior and posterior surface of the cornea was studied in 1273 patients with CC and in 1035 healthy volunteers. The mean values of anterior and posterior surface astigmatism in the CC group were 4.49±2.16 diopters and 0.90±0.43 diopters, respectively, which is 4.8 and 3.5 times higher than the same values in comparison with the group of persons with conditionally normal corneas [33]. A similar trend is revealed in another study [34]. 
04±0.31, 0.54±0.21, and 0.24±0.05 µm for stages III, II, and I, respectively. For conditionally normal eyes, this indicator corresponded to 0.19±0.05 µm. The mean root mean square value of coma as the most dominant aberration of the posterior surface of the cornea in the eyes with CC was 0.93±0.35, 0.46±0.23, and 0.12±0.06 μm. In the control group, this parameter corresponded to 0.09 ± 0.06 μm, i.e., the mean square value of the coma of the posterior surface of the cornea in CC was 10.5 and almost 1.5 times higher than the coma parameters of conditionally normal corneas [35]. 
If a patient with CC has initial signs of DES, it is advisable to use non-preserved low-viscosity tear substitutes based on hyaluronic acid of various concentrations. If the patient uses contact correction for the prevention of hypoxic complications, the appointment of methyl-ethylpyridinol, eye drops 10 mg / ml (Emoxipin ® ) [40, 41], which has antiplatelet and antihypoxic effects. Interacting with lipid peroxide and hydroxyl radicals, methylethylpyridinol inhibits free radical oxidation of the latter, increasing the activity of antioxidant enzymes, which leads to stabilization of cell membranes and a decrease in cell apoptosis. In a study, administration of Emoxipin ® instillations to 1% of patients with hypoxic complications while wearing soft contact lenses made it possible to level hypoxic changes in the cornea and improve the state of the tear film [41]. In addition, the effectiveness of this drug has been proven in a number of clinical studies in the complex treatment of glaucoma, as well as various retinal diseases [42, 43].
In the presence of keratopathy, it is recommended to add a gel root protector containing 5% dexpanthenol in its composition to accelerate epithelialization processes, restore tear film stability and, as a result, reduce DES-induced optical aberrations. 
In addition, wearing the FCL contributes to a change in the direction of the vertical coma from -0.185 to 0.134 µm, and the total aberrations of higher orders decrease from 0.54 to 0.36 µm [49]. However, it is impossible to completely level the effect of aberrations with the help of the GGCL. The level of residual aberrations in the LCL in some cases remains higher, and visual performance remains lower than in healthy eyes [32]. The reasons may be rotation and unstable fit of the LCL, wear of the lens material, as well as incompletely compensated higher-order aberrations of the posterior surface of the cornea [35, 36, 47]. The residual average value of aberrations above the 3rd order in LGCL is 0.8, 0.5, and 0.34 μm for stages III, II, and I of QC, respectively [35]. 
Due to the large diameter, the supporting part of the lens is located on the bulbar conjunctiva, which ensures its stable fit on the eye and subjective comfort on the part of the patient, even with severe corneal deformity. The presence of the so-called lacrimal clearance between the posterior surface of the FGCL and the anterior surface of the cornea makes it possible to neutralize irregular corneal astigmatism and higher-order aberrations induced by it, thereby creating a single structure with lower optical errors. 
In addition, the search for optimization of optical rehabilitation in CC, which contributes to the maximum neutralization of higher-order corneal aberrations, remains relevant. 
