ASTIGMATISM Flashcards
Shape of normal cornea?
SOME PEOPLE HAVE A CORNEA THAT HAS A SPHERICAL SHAPE
What does it mean when someone has a Spherical shape
THIS MEANS THAT IT HAS THE SAME CURVATURE OVER IT’S ENTIRE SURFACE
What shape is spherical?
YOU WILL OFTEN HEAR A SPHERICAL CORNEA COMPARED TO THE ROUND SHAPE OF A BASKETBALL (IMAGINE THE BASKETBALL CUT IN HALF).
Spherical Cornea
A SPHERICAL CORNEA IS SLIGHTLY STEEPER IN THE CENTER AND GETS FLATTER TOWARDS THE OUTER EDGES.
Astigmatism Cornea Shape?
AN ASTIGMATIC CORNEA MEANS THAT THE CURVATURE IS NOT SPHERICAL, IT IS NOT THE SAME IN ALL MERIDIANS.
Meridian from a astigmatism eye
THERE WILL BE ONE MERIDIAN THAT HAS A STEEPER CURVE, AND ANOTHER MERIDIAN THAT HAS A FLATTER CURVE.
Shape like what?
YOU WILL OFTEN HEAR ASTIMATISM COMPARED THE SHAPE OF A FOOTBALL. It has 2 different curvatures IN 2 DIFFERENT MERIDIANS!
Lenticular
IT IS ALSO POSSIBLE, THOUGH LESS COMMON, FOR ASTIGMATISM TO BE LENTICULAR (OCCURING WITHIN THE LENS IN THE EYE).
Focal point for sperical eye and for Astigmatism
THE DIFFERENT CURVATURES (WHETHER FROM THE CORNEA OR THE LENS) INHIBIT LIGHT RAYS FROM COMING TO A SINGLE FOCAL POINT. INSTEAD, THERE ARE MULTIPLE FOCAL POINTS
Astigmatism in few people
ASTIGMATISM IS VERY COMMON AND SOME PEOPLE WITH ONLY A SMALL AMOUNT OF ASTIGMATISM MAY STILL BE ABLE TO SEE QUITE WELL
Ways to correct Astigmatism
HOWEVER, IT CAN CAUSE VISION TO BE OUT OF FOCUS AND MAY NEED TO BE CORRECTED FOR IN ORDER TO SEE CLEARLY.
Astigmatism Symtoms
EYE STRAIN HEADACHES DISTORTION GHOSTING
Astigmatism causes
HEREDITARY INJURY/ TRAUMA EYE SURGERY CORNEAL DYSTROPHY
Astigmatism can occur by itself?
ASTIGMATISM CAN OCCUR BY ITSELF OR WITH MYOPIA OR HYPEROPIA
Many types of Astigmatism
7
Many types of Astigmatism
REGULAR SIMPLE MYOPIC SIMPLE HYPEROPIC COMPOUND MYOPIC COMPOUND HYPEROPIC MIXED IRREGULAR
Emmetropic Eye
BEFORE WE GET INTO THE TYPES OF ASTIGMATISM, LET’S RECALL HOW AN EMMETROPIC EYE FOCUSES LIGHT ONTO THE RETINA.
REGULAR ASTIGMATISM how many curvatures? how many degrees? focal point?
the cornea has 2 different curvatures, one flatter and one steeper. They are located 90 degrees away from each other. Instead of light rays being focused onto the retina in one place (one focal point), there will be two different focal points. One is from the steep curve and one from the flatter curve.
Axis
WHEN WE TALK ABOUT ASTIGMATISM, WE NEED TO SPECIFY THE AXIS WHERE THE ASTIMATISM IS OCCURING
Axis degrees?
THE AXIS OF ASTIGMATISM IS ALWAYS BETWEEN 001 AND 180 DEGREES. ASTIMATISM CAN OCCUR AT ANY AXIS WITHIN THIS RANGE
How to determine the 2nd meridian?
SINCE THE 2 MERDIAINS ARE 90 DEGREES APART, YOU ADD OR SUBTRACT 90 DEGREES TO DETERMINE THE 2ND MERIDIAN.
IF THE STEEPER MERIDIAN IS AT 90 DEGREES Whats the flatter?
THE FLATTER MERIDIAN IS AT 180 DEGREES.
IF THE STEEPER MERIDIAN IS AT 45 DEGREES Whats the flatter meridian?
THE FLATTER MERIDIAN IS AT 135 DEGREES.
How types of Regular Astimatism are they
5
What are the Regular Astigmatism
SIMPLE HYPEROPIC SIMPLE MYOPIC COMPOUND HYPEROPIC COMPOUND MYOPIC MIXED
SIMPLE HYPEROPIC ASTIGMATISM
ONE FOCAL POINT IS FOCUSED ON THE RETINA (FROM THE STEEPER MERIDIAN). ONE FOCAL POINT IS FOCUSED BEHIND THE RETINA (FROM THE FLATTER MERIDIAN). THINK OF A HYPEROPIC EYE. 2 IMAGES ARE PRODUCED, ONE CLEAR AND ONE BLURRY (FROM THE FOCAL POINT BEHIND THE RETINA).
SIMPLE MYOPIC ASTIGMATISM Focal point? steeper and meridian?
ONE FOCAL POINT IS FOCUSED ON THE RETINA (FROM THE FLATTER MERIDIAN). ONE FOCAL POINT IS FOCUSED IN FRONT OF THE RETINA (FROM THE STEEPER MERIDIAN). THINK OF A MYOPIC EYE. 2 IMAGES ARE PRODUCED, ONE CLEAR AND ONE BLURRY (FROM THE FOCAL POINT IN FRONT OF THE RETINA).
COMPOUND HYPEROPIC ASTIGMATISM
BOTH FOCAL POINTS ARE FOCUSED BEHIND THE RETINA 2 IMAGES ARE PRODUCED AND BOTH WILL APPEAR BLURRY, AS NEITHER ONE IS FOCUSED ON THE RETINA.
COMPOUND MYOPIC ASTIGMATISM
BOTH FOCAL POINTS ARE FOCUSED IN FRONT OF THE RETINA. 2 IMAGES ARE PRODUCED AND BOTH WILL APPEAR BLURRY, AS NEITHER ONE IS FOCUSED ON THE RETINA.
MIXED ASTIGMATISM
ONE FOCAL POINT IS IN FRONT OF THE RETINA AND THE OTHER FOCAL POINT IS BEHIND THE RETINA. 2 IMAGES ARE PRODUCED AND BOTH WILL APPEAR BLURRY, AS NEITHER ONE IS FOCUSED ON THE RETINA.
WAYS TO MEASURE ASTIGMATISM
KERATOMETRY CORNEAL TOPOGRAPHY RETINOSCOPY OPTICAL BIOMETRY
KERATOMETRY
PERFORMED USING A KERATOMETER (OPHTHALMOMETER). IT HELPS TO OBTAIN THE EXACT RADIUS OF CURVATURE OF THE CORNEA. IT IS VALUABLE IN EYE EXAMINATIONS, PARTICULARLY FOR DETECTING AND MEASURING CORNEAL ASTIGMATISM. IT IS USED A LOT FOR CONTACT LENS FITTINGS.
K
THE RESULT OF KERATOMETRY IS 2 “K” READINGS. ONE CORRESPONDS TO THE STEEP MERIDIAN OF THE CORNEA AND ONE CORRESPONDS TO THE FLAT MERIDIAN. K1: 42.75 @ 070 K2: 44.00 @ 160
CORNEAL TOPOGRAPHY
IMAGING USED TO CHARACTERIZE THE SHAPE OF THE CORNEA AND PATTERNS OF ASTIGMATISM. IT IS USED AS A DIAGNOSTIC TOOL, FOR MONITORING OF CERTAIN CONDITIONS AND IN SCREENINGS FOR REFRACTIVE SURGERIES AND OTHER PROCEDURES.
Placido Disk
the Placido disK WAS THE FIRST TECHNOLOGY USED IN ASSESSING THE SURFACE OF THE CORNEA. IT RELIES ON the reflection of a set of concentric rings off OF the corneal surface. As the image from the Placido disK is projected on the cornea, some of the light is reflected off the tear film-air interface like a mirror. The pattern of light reflection reveals the shape of the anterior surface of the cornea.
1800
THIS TECHNIQUE DATES BACK TO THE LATE 1800s BUT A LOT OF MODERN DAY TECHNOLOGY(COMPUTERIZED CORNEAL TOPOGRAPHERS) USES THIS SAME CONCEPT.
Atlas
post pic
Orbscan
USES A SLIT SCANNING TECHNOLOGY BUT ALSO INCORPORATES A PLACIDO DISK
pet cam
USES A ROTATING CAMERA TO PHOTOGRAPH CROSS SECTIONS OF THE CORNEA AT DIFFERENT ANGLES.
RETINOSCOPY
THE RETINOSCOPE IS A VAUABLE INSTRUMENT IN DETERMINING THE REFRACTIVE ERROR OF THE EYE. IT IS A PURELY OBJECTIVE ASSESSMENT AND IS THEREFORE A GREAT TOOL FOR DETERMINING THE PRESCRIPTION FOR INFANTS & CHILDREN AND OTHER PATIENTS WHO MAY BE UNABLE TO COMMUNICATE WHAT THEY ARE ABLE TO SEE
Retinoscopy exam
RETINOSCOPY ALLOWS YOU TO SEE IF SOMEONE IS MYOPIC, HYPEROPIC, AND/OR HAS ASTIGMATISM
OPTICAL BIOMETRY
AN INSTRUMENT USED TO DETERMINE THE POWER OF AN INTRAOCULAR LENS (IOL) IMPLANT FOR CATARACT SURGERY. IT PROVIDES MEASURMENTS OF THE EYE INCLUDING THE AXIAL LENGTH AND SURFACE CURVATURE. THIS (POSSIBLY ALONG WITH A COMPUTERIZED CORNEAL TOPOGRAPHER) IS USED TO DETERMINE IF A PATIENT IS A CANDIDATE FOR A TORIC IMPLANT (ONE THAT CORRECTS FOR ASTIGMATISM).
IoL master
Post pic
Regular Astigmatism Rule
REGULAR ASTIGMATISM CAN FURTHER BE CLASSIFIED AS “WITH THE RULE”, “AGAINST THE RULE”, OR OBLIQUE.
WITH THE RULE
THE STEEPER AXIS IS LOCATED AT OR NEAR 90 DEGREES IMAGINE A FOOTBALL LAYING ON ITS SIDE MORE COMMON IN CHILDREN
With Rule pic
post pic WITH THE RULE - TOPOGRAPHICAL IMAGING OF REGULAR ASTIGMATISM DEMONSTRATES A BOWTIE PATTERN IN A SINGLE MERIDIAN
AGAINST THE RULE post pic
THE STEEPER AXIS IS LOCATED AT OR NEAR 180 DEGREES IMAGINE A FOOTBALL STANDING UP ON ITS END MORE COMMON IN ADULTS
OBLIQUE
THE STEEPEST CURVE OF THE CORNEA ISN’T VERTICAL OR HORIZONTAL OCCURS BETWEEN 30-60 DEGREES AND 120-150 DEGREES THE AXIS OF THE ASTIGMATISM IN ONE EYE TENDS TO BE (NOT ALWAYS) A COMPLEMENT OF THE AXIS IN THE OTHER EYE (THEY ADD UP TO 180) - 45 DEGREES AND 135 DEGREES - 30 DEGREES AND 150 DEGREES
IRREGULAR ASTIGMATISM
THERE ARE SEVERAL DIFFERENT MERIDIANS WITH DIFFERENT CURVATURES THEY ARE NOT 90 DEGREES APART
KERATOCONUS
A PROGRESSIVE THINNING OF THE CORNEA THAT RESULTS IN A BULGING, CONE SHAPED CORNEA. IT MAY BE RELATED TO GENETICS, ENVIRONMENTAL FACTORS, OR POSSIBLY HORMONES. IT CAN RESULT IN VERY HIGH AMOUNTS OF ASTIGMATISM (IN ADDITION TO MYOPIA).
KERATOCONUS
KERATOCONUS – CORNEAL TOPOGRAPHY SHOWS A “HOT SPOT”
THERE ARE DIFFERENT WAYS TO CORRECT ASTIGMATISM
GLASSES/ CONTACTS ORTHOKERATOLOGY REFRACTIVE SURGERY OTHER SURGERY (CATARACT – TORIC LENS IMPLANTS)
THERE ARE DIFFERENT WAYS TO CORRECT ASTIGMATISM
LENSES SUCH AS GLASSES OR CONTACTS CAN BE USED TO CORRECT ASTIGMATISM.
THE AMOUNT OF ASTIGMATISM IS MEASURED IN
THE AMOUNT OF ASTIGMATISM IS MEASURED IN DIOPTERS (JUST LIKE PLUS AND MINUS LENSES FOR HYPEROPIA AND MYOPIA).
Location Axis
THE LOCATION /AXIS OF THE ASTIGMASTISM MUST ALWAYS BE SPECIFIED. REMEMBER THE AXIS IS BETWEEN 001 AND 180 (000 IS THE SAME AS 180 AND IS NOT USUALLY USED).
THIS INFORMATION (THE DIOPTRIC POWER AND THE AXIS)
THIS INFORMATION (THE DIOPTRIC POWER AND THE AXIS) CAN BE ADDED TO A GLASSES OR CONTACT LENS PRESCRIPTION TO PROPERLY COMPENSATE FOR ANY VISUAL DISTORTIONS THAT MIGHT BE CAUSED BY ASTIGMATISM
CYLINDRICAL
A CYLINDRICAL LENS is used to correct astigmatisM. Imagine a cylinder cut IN HALF. IT HAS POWER IN ONE MERIDIAN AND NO POWER IN THE MERIDIAN 90 DEGREES AWAY FROM THAT.
PATIENT CAN HAVE DIFFERENT AMOUNTS,
A PATIENT CAN HAVE DIFFERENT AMOUNTS, DIFFERENT AXES, AND DIFFERENT TYPES OF ASTIGMATISM IN EACH EYE.
CYLINDER CORRECTION
CYLINDER CORRECTION STARTS AT 0.25 D AND CAN GO UP TO > 6.00 D. SOMEONE WITH ADVANCED KERATOCONUS COULD POTENTIALLY HAVE 10.00D OF CYLINDER!
WE WILL DISCUSS MORE IN THE NEXT LECTURE BUT CYLINDER CORRECTION CAN BE COMBINED WITH PLUS OR MINUS LENSES IF NEEDED, OR THEY CAN BE USED ALONE IF SOMEONE HAS ASTIGMATISM ONLY.
WE WILL DISCUSS MORE IN THE NEXT LECTURE BUT CYLINDER CORRECTION CAN BE COMBINED WITH PLUS OR MINUS LENSES IF NEEDED, OR THEY CAN BE USED ALONE IF SOMEONE HAS ASTIGMATISM ONLY.
ORTHOKERATOLOGY
THE CORNEA CAN BE GRADUALLY RESHAPED USING RIGID CONTACT LENSES. SIMILAR PROCESS TO BRACES.
REFRACTIVE SURGERIES
REFRACTIVE SURGERIES SUCH AS PRK, LASIK, AND LASEK CAN BE USED TO RESHAPE THE CORNEA AND ELIMINATE OR MINIMIZE ASTIGMATISM.
DURING CATARACT SURGERY
DURING CATARACT SURGERY, THE SURGEON CAN USE A TORIC LENS IMPLANT THAT COMPENSATES FOR THE ASTIGMATISM CAUSED BY THE CORNEA. THIS IS EXPENSIVE AND THE PATIENT MUST PAY OUT OF POCKET FOR THIS.
