Axial Length Flashcards
What is the normal axial length
22-24mm
In combination with the corneal curvature, it determined the refractive state of the eye
Axial length
What is axial length important for
Calculating the power for the IOL along with keratometry
With an axial length of 20mm, we may suspect
HYPEROPE
With an axial length of 26mm, we may suspect
Myopia
Long eye
Myopic
Short eye
Hyperopic
What is the axial length in myopes
Longer than 24mm
What is the axial length in hyperopes
Shorter than 24mm
What does each mm of axial mismatch correspond to
2.3D to 3.4D of a refractive deviation
Separation between the posteiror corners and the anterior lens
Anteiror chamber depth
Normal AC depth
3.0-3.4 mm
What happens to the AC depth with age
Decreases to 2.0mm
What happens to axial length with age
Nothing
AC depth and cataract
Cataracts decrease AC depth
How soon should you treat a closed angle
ASAP, within 2 days
Anterior chamber volume
220 and 171 +- 36 microliters
About 0.007 fluid ounces
Anterior angle chamber (iridocorneal angle) normal range
30 degrees
Anterior chamber angle less than 30
Narrow
Anterior chamber angle more than 30
Wide open
The angle formed by the posteiror cornea at the root of the iris
Anteiror chamber angle
What is associated with small anteiror chamber depth
Cataracts and glaucoma
The measurement of pupil diameter
Pupilometry
Clinical importance for pupilometry
Selection of optical zone in laser refractive surgery
Clinical importance of centroid shift
IOL andLaser ablation centration
Best way to measure pupils
Infrared
What size pupil should you look at when picking optical zone size
Scotopic
Centroid shift
When the pupil dilates, it doesn’t necessarily stay in the center
Cyclotorsion
When pt lay done, there eyes rotate about 10 degrees. You don’t want to be off by more than 3 degrees
Measuring the thickness of the cornea
Corneal pachymetry
Why is it not easy measuring the corneal thickness
It is not the same thickness throughout
What is the most reliable pachymetry
Cornea pachymetry map
The thickness of the cornea at the pupil center
CCT
Where is the cornea thickest
Superonasal
Is corneal thickness symmetric
No
What are the two numbers we report for corneal pachymetry
CCT and MinCT
Corneal enantiomorphic symmetry
Inferotemporal cornea should be the thinnest
Corneal thickness in the morning
Thicker
Measuring corneal pachymetry between two different eyes
Will not give you the same numbers
Where is the corneal thinnest
Apex (minCT), slightly inferotemporal
What is CCT defined at
The pupil center
Average CCT
520-580
CCT and age
No change
When is CCT thicker
Upon waking
Between two different devices, what kind of difference will you see in measuring CCT
20 microns difference
Why is corneal thickness important
It can mask an accurate reading of eye pressure
When is IOP underestimated
Thinner CCT
When is IOP overestimated
Thicker CCT
What kind of cornea will you see in corneal dystrophy
Thick
Ocular health indicators of thick cornea
- endothelial cell damage, Fuchs dystrophy
- corneal edema, bullus keratopathy, posteiror polymorphous dystrophy
- herpes keratitis, DM, hyperglycemia
Principle of operation of scheimpflug image pachymetry
High resolution, high depth of field imaging
What did scheimpflug do
Tilt the lens