Week 2.01 Phoropter & Near Add Flashcards
Why use a phoropter instead of trail frame
- A quicker refraction: It is much quicker to change lens powers for both retinoscopy and subjective refraction in a phoropter compared to a trial frame.
-Less back strain: particularly with digital phoropters. This can be a problem for eye care clinicians
- Greater comfort: A trial frame containing several lenses can become uncomfortably heavy, particularly for older patients with thin skin.
- Jackson cross-cylinder (JCC) accuracy: The JCC is automatically aligned with the cylinder axis in a phoropter.
- No lens smear: Trial case lenses can become covered with fingerprints (particularly in University clinics) and require regular cleaning.
- High-tech appearance: Some patients may have more confidence in the results using phoropters, particular the digital versions, over the ancient-looking trial frame.
- Digital phoropters: These include data links to automated focimeter and/or autorefractor and can provide easy comparison of the patient’s current glasses power with the latest subjective refraction result. The refraction results can automatically be included in the patient’s electronic record.
- Risley prisms: Make measurements of fusional reserves and binocular prism-dissociated balance faster and easier.
When should trial frames be used?
- children and px with BV problems - child can more easily see their parent and feel more at ease. Trial frames can stimulate less proximal accomodation than a phoropter
- px with visual impairments or poor subjective responses - large dioptre changes in sphere and a high JCC power
- When over-refracting patients being fitted with multifocal contact lenses: helps to keep the visual environment, binocularity and pupil size as close to normal as possible.
- px with hearing problems
How much of you amplitude of accomodation do you use to read at working distance
You can only use ~1/2 to read comfortable for a reasonable amount of time. So if u read at 40cm (2.50D) would need amplitude of 5D or more
If you read closer at 33cm (3.00D) u need 6.00D or more
How to calculate tentative add
Many tentative add assessments that provide a starting point to be refined such as amplitude of accomodation e.g. working distance -1/2 amplitude = add
Binocular cross cyl and negative and positive relative accomodation (NRA/PRA)
What is the age and average reading add
45: +1.00
50: +1.50
55: +2.00
Above 60 based on WD alone
60: ~+2.25
65+: ~+2.50
How do u test near add
- Px distance correction in place
- Get px to hold reading car at the distance they usually read or would like to have been reading if they are now having to hold it closer or move it further back to adapt to their loss of focus
- Determine tentative add from age and from working distance
- Add -0.25DS ask if letter become clearer more blurred or same
- If acuity improves or is unchanged with the additional minus, then continue adding -0.25 until near VA is worse
- Add +0.25. If VA is unchanged or decreased do not add. If improves add further plus lenses as long as near VA improve
- Determine range of clear vision with binocular reading add. Range decreases with higher add powers. Imp if used for tasks at diff WD
To determine near endpoint px move card slowly in until frost notice blur and measure this dist
To determine far endpoint of addition range px move the card slowly away from them until best acuity paragraph just blurs - Record final add, acuity, range of clearest vision
Example:
Add +1.50DS@40cm, VA N5 R and L, range 25-67cm
Do we want to keep the addition weak or strong as possible and why?
Keep add as weak as possible to keep the range of clear vision as large as possible
Equation to calculate near add
Near add = WD (D) - 1/2 amplitude of accomodation
Formula to calculate far point of clear vision
Inverse of working distance (D) - 1/2 amplitude
Formula to calculate near point of clear vision
Inverse of WD + 1/2 amplitude
