Automated Objective Refraction

What is automated objective refraction

an estimation of the refractive error of an eye without the need of responses from patient

could also provide corneal curvature

What is AR used for

estimate refractive error as a starting point for subjective refraction

screening

confirm a difficult or unusual refraction

refraction of nonverbal patient

Research

Why is AR used for research

removes examiner bias, provides standardization and comparability measures, more repeatable

What are the common characteristics of AR

Accommodation control, near infrared radiation, dioptric range, linearity, pupil limits, vertex distance, achievement off endpoint

How does AR control accommodation

most use fogging lenses

provide a distance target to prevent proximal accommodation

What is near infrared radiation

800 +- 80nm

not visible to the eye, fundus reflects back approximately 35%

What is the range for sphere

25-30 D

0.12 or 0.25 increments

What is te range of Cylinder

12 D

Cylinder axis

180

When is AR more accurate

closer to emmetropic

What are the pupil limits

samples over the center 2.5-3mm

too small also affects accuracy

What is the vertex distance

the distance between the cornea and spectacle plane

When is endpoint achieved

Nulling or open loop

What is nulling

power needed to neutralize the refractive error

can handle more noise

What is open loop

measures radiation exiting the eye

doesn’t actually correct the refractive error

faster

What is repeatability

minimum variability between test methods

What is reproducibility

maximum variability between test method

AR results are typically

repeatable

Cylinder axis repeatability depends on

the amount of cyl

What are reasons for variability

changes in fixation, pupil diameter, accommodation

corneal and ocular surface

media opacities

amblyopia

instrument or operator variability

What is validity

closeness of agreement between average value of large series of results and accepted reference value

What is the Gold standard

subjective refraction results, repeatability

95% agreement within 0.50 D

Sphere agreement

high %

Cylinder agreement

reasonable

Cylinder axis agreement

lower

What are the reasons for variations in validity

Measurement bias, accommodative abnormalities, intraocular lenses, ant and post seg abnormalities, refractive surgery

There is better agreement between subjective and AR results in patients that are

cyclopleged to prevent accommodation

What are anterior segment abnormalities

opacities, distorted pupils, irregular astigmatisms

What are posterior segment abnormalities

retinopathies, staphyloma, retinal detachment

What data do we use from the print out

bracketed

Advantages to AR

speed, efficiency, tech can perform, less examiner bias, easy to use

Advancements in AR

Keratometry readings, wavefront technology, may include acuity charts

What does wavefront tech do

account for aberrations of the eye, considers topography of entire cornea

What are the acuity charts they may include

glare testing and contrast testing