2 Flashcards
The center of curvature of the eye
27mm behind the spec plane
Far point for myopia, emmetrope, hyperope
Myopia- Between the eye and infinity
Emmetrope- infinity
Hyperope- Located behind the retina and considered virtual
What causes night myopia?
Increased sphere aberration and light levels that are too low to fully relax accommodation- Eye doesn’t know where to focus. Trouble fully relaxing accommodation.
Myopia trends
When born, 5-22% of babies are myopic. This decreases by 1 year due to emmetropization, then myopia increases as pt gets older.
20% are myopic and 20 years
30% are myopic at 30 years
Hyperopia trends
The prevalence of hyperopia is 6% in children from 6-15 years old. This prevalence, unlike myopia, does not change with this age range.
One can predict hyperopia based on Rx at 5 years old.
Greater than +1.50 –> pt will be hyperopic at age 15.
Less than +0.50–> Pt will be myopic at age 15.
Types of acuity
Resolution- TAC. Average cut off is 40-60cpd.
Recognition acuity- Snellen. Ability to resolve high frequencies.
Minimal detectable acuity- Thinnest possible wire that is visible. 1 arcsec
Hyperacuity- Directional relationships. When 2 lines are parallel..
MAR: Minimal angle of resolution. Arc mins (1/60 of a degree)
20/20 = 1 MAR = 0 logger
Each letter on the Snellen chart subtends 5 minutes of arc when viewed at 20 feet. Each distinct bar on the E subtends 1 arcmin.
How to document the allen vision test
The examiner determines the longest distance at which the child can resolve the image.
The acuity is expressed as ___/30
__ is in feet
So if a child can see the shape at 12 feet OD, the acuity is 12/30OD
3 examples of matching recognition acuity tests
LEA, STYCAR, HOTV
Difference between static and dynamic retinoscopy
Static- Patient fixates at a distant target. Don’t forget to subtract working distance!!!!
Dynamic- Patient is focused at near, using accommodation. Can measure the patients lag and lead of accommodation. MEM, NOTT, Mohindra
Describe the three types of dynamic ret
MEM: Change lenses to determine pt’s lag/lead
NOTT: Change distance to determine pt’s lag/lead
MOhinDRA: Monocular, performed in the dark at 50 cm, subtract 1.25D from final results. Near ret used to determine distance refraction in children and infants. Not as effective as cyclo refraction.
How to use astigmatic dial
Fog the eye
Ask the patient which lines are darkest
If 9-3 line is darkest, multiply 3 x 30= 90 is the axis
You can’t use Dueochrome red/green test unless acuity is
20/30 or better
Can do on color blind patients since chromatic aberration underlies the test.
ROY G BIV
BIV bends better, meaning shorter wavelength light will focus first.
When to cyclo a patient
Child with convergent strabismus. Must determine if accommodation is contributing.
Child with significant esophoria at near.
If you suspect latent hyperopia
A person uses only __% of his/her accommodation ability comfortably
50%
Near point
Point conjugate to the retina when the eye is achieving max accommodation. Similar to the far point, but now the eye is fully accommodating.
