Corneal topographic patterns.pptx
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Corneal topography maps the curve of the cornea to detect conditions like astigmatism. It classifies patterns into round, oval, steepened areas, irregular, symmetric and asymmetric bowties, and other patterns. Rabinowitz studied topography patterns in 1996, identifying 11 main patterns including symmetric/asymmetric bowties that are prolate, oblate, or with/against the rule astigmatism. Regular astigmatism shows a bowtie pattern with an axis angle under 20 degrees, while irregular astigmatism has a bi-oblique bowtie with an axis angle over 20 degrees. Other patterns include mixed, triple, and horseshoe.
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Astigmatism is a condition where the eye's refractive power varies in different meridians, causing blurred vision. It is caused most commonly by corneal irregularities, and results in light rays forming an image called the Sturm's conoid instead of focusing on the retina. Astigmatism can be regular, irregular, or oblique depending on the orientation of the steepest meridians. It is classified and treated based on whether the refractive error causes light to focus in front of, on, or behind the retina. Treatment options include corrective lenses, contact lenses, and refractive surgeries like astigmatic keratotomy.
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This document discusses frame adjustment and quality checking. It describes 7 off-face adjustments including x-ing, temple spread, pantoscopic angle, temple fold angle, pad angles, face form, and 4-point touch. It also discusses 7 on-face adjustments including horizontal alignment, vertex distance, frame height, segment height, temple bend, pad contact, and skin/lash clearance. Key details are provided about properly adjusting specific angles and alignments during the fitting process.
Astigmatism, presbyopia and aphakia
This document discusses astigmatism, presbyopia, and aphakia. It defines these conditions and describes their causes, symptoms, diagnosis, and treatment options. For astigmatism, it covers the different types including regular, irregular, and mixed astigmatism. It discusses optical correction using lenses, refractive surgery options like LASIK, and intraocular lenses. For presbyopia, it defines the condition, describes the age-related decline in accommodation, symptoms, and treatments like multifocal lenses, contact lenses, and refractive surgery options.
Astigmatism
Astigmatism
BY
RAIN HEALTH CARE
WHAT IS ASTIGMATISM
TYPES OF ASTIGMATISM
SYMPTOMS OF ASTIGMATISM
TREATMENT OF ASTIGMATISM
ASTIGMATISM & ITS MANAGEMENT.pptx
This document discusses astigmatism, including:
- Astigmatism occurs when parallel rays of light are not brought to a single focal point on the retina.
- There are different types of astigmatism including regular, irregular, simple, compound, and mixed. Regular astigmatism has two focal meridians at right angles.
- Sturm's conoid is used to visualize how light rays are refracted by an astigmatic optical system, forming two focal lines instead of a single point.
- Astigmatism can be investigated using retinoscopy, autorefraction, subjective refraction, keratometry, and other techniques. The axis is refined using tools
Scheimpflug imaging in ophthalmology
The Scheimpflug principle allows for imaging of the anterior eye segment with maximal depth of focus. Scheimpflug systems like the Pentacam and Orbscan use this principle to provide detailed tomography and topography maps of the cornea and anterior chamber. The Pentacam uses a rotating Scheimpflug camera combined with a static camera to construct a 3D model from 25,000 data points. It analyzes parameters like corneal thickness, curvature, astigmatism, and anterior chamber dimensions. The Orbscan uses slit scanning to create elevation maps of the anterior and posterior corneal surfaces and measure pachymetry. Both devices help evaluate conditions like keratoconus and guide refractive surgery planning.
Aberration.pptx
Aberrations are defects in an optical system that prevent light from being brought to a single focus. There are two main types: chromatic aberration, caused by the wavelength-dependent refractive index of materials, and monochromatic aberration, caused by flaws in the lens design. Five primary monochromatic aberrations were described by Seidel: spherical aberration, coma, astigmatism, field curvature, and distortion. Spherical aberration occurs when peripheral rays converge at a different point than paraxial rays, degrading image focus. Coma and astigmatism affect image sharpness for off-axis points. Field curvature results in a curved image plane rather than a flat one. Distortion al
Perpendicular Offset
Offsets are lateral measurements taken to locate ground features in relation to survey lines. There are two main types of offsets - perpendicular offsets, which are taken at right angles to the survey line, and oblique offsets, which are taken at non-right angles. Various instruments can be used to measure and set offsets precisely, including tapes, cross staffs, optical squares, and prism squares. The 3-4-5 method can also be used to establish perpendicular offsets from a survey line using basic geometry principles.
Orientation jaw relations & face bow
This document provides an overview of orientation relations and facebows. It defines key terms like jaw relation, orientation relation, and facebow. It describes the transverse hinge axis and sagittal plane. It discusses different types of facebows like kinematic, arbitrary, and earpiece facebows. It covers the procedure for taking a facebow record and potential errors. The document also reviews literature on controversies around locating the hinge axis and accuracy of arbitrary vs kinematic facebows. It provides a brief history of the development of facebow instruments over time.
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- 1. Corneal Topographic Patterns By Afaf Johar
- 2. Corneal Topography • Corneal topography is a computerized test that maps the curve of your cornea. It can show problems with your eye's surface, like swelling or scarring, or conditions such as astigmatism. You might have it before you get surgery, a cornea transplant, or a contact lens fitting.
- 3. Uses • Refractive surgery • Keratoconnus • Post surgery astigmatism • Effect of corneal and ocular surface disorders: Disorders such as pterygium • Other uses : Contact lens fitting etc
- 4. History • Classification of corneal topography patterns based on the study by Rabinowitz et al in 1996.. • (1) Round, • (2) Oval, • (3) Superior Steepening, • (4) Inferior steepening, • (5) Irregular, • (6) Symmetric bowtie with skewed radial axis, • (7) Asymmetric bowtie with inferior steepening,
- 5. • (8) Asymmetric bowtie with superior steepening • (9) Asymmetric bowtie with skewed radial axis • (10) Symmetric bowtie. • (11) Horse shoe shape • (12) Triple pattern • (13) Mixed pattern
- 8. Prolate The cornea appears to have increased dioptric power (steeper) centrally than at the periphery. Prolate symmetric bowtie Prolate asymmetric bowtie
- 9. Oblate A cornea of decreased power (flatter) centrally than peripherally. Oblate symmetric bowtie Oblate asymmetric bowtie
- 10. With the Rule astigmatism
- 11. Against the rule Astigmatsim
- 13. Regular Astigmatism • Regular astigmatism is usually presented topographically by a bow tie pattern that can be symmetrical or asymmetrical. Any pattern presenting with an angle α between the axis of the two halves of the bow tie of less than 20° , was defined as regular astigmatic. • Regular symmetrical astigmatism • Regular asymmetrical astigmatism
- 14. Irregular Astigmatism Pattern • If the two steepest semimeridia were at an angle α to each other which was greater than 20°, this astigmatism was defined as irregular. This is represented topographically as a “bi-oblique” bow tie pattern.
- 15. Symetric with skewed radial axis Asymetric with skewed radial axis
- 16. Mixed Pattern Features of both oblate and prolate shape are present at different corneal areas.
- 17. Triple pattern: characteristically, three distinct areas of radial steepening were identifiable Horseshoe” pattern: in this configuration, a C-shaped area of increased corneal power could be identified at the graft host interface