VF Flashcards
Making the field larger
Expansion
Helping the patient use what they have better
Enhancement
Mechanisms for VF enhancement
Scanning Reversed telescopes Fresnel prisms Mirrors Concave lenses
Candidates for VF enhancements
- > 20 degrees generally do not rewuire special assistive devices, but could potentially use orientation and mobility evaluation
- 10 degrees-define mobility evaluation
- 5-10 degrees may use up 10x magnification if they have good scanning skills
- <5 degrees will rewuire special training, especially mobility skills
Reversed telescope
- apparent increase in FOV approximately equal to the pier of the telescope
- image is minified by approximately the same amount
- spectacle mounted vs hand held
Patients BCVA is 20/100. VF is 5 degrees in widest diameter. What size field would you anticipate with a 2.5x galilean hang held telescope used for field enhancement? what VA would you expect when used for visual field enhancement?
5x2. 5=12.5 degrees
100x2. 5=20/250
O cute how image minifier
- crisp, undistorted, flat field
- wide ocular lens permits scanning through device
- 50% field enhancement effect (0.5x)
- spectacle mounted, or handheld with neck strap
- adjustable focus allows optimum focus for each patient
- huge depth of field
Minus lenses for VF enhancement
- essentially creates a reverse Galilean telescope
- pateitnt must accommodative or use add to use it
- order lens blanks form the optical lab and have edges polished
Epidemiology of VF defects
VF defections affect 20 to 57% of stroke survivors
-spontaneous improvement may occur for 3 months or sometimes more
Hemianopsia
- lesion in visual pathway leading to VF deficit
- patients often do not undersdetand that they have lost vision in both eyes, they associate the loss with the eyes on the side of the field loss
- right hemispheric strokes often associated with visuo-spatial neglect
Common complains if hemianopsia
- bumping into things on affected side
- difficult with depth preception
- difficulty reading
- desire to drive
Recovery of VF defects
Can occur for up to a year, but the majority of recovery occurs in the 1st 1-2 months
-recovery of visuo-spatial neglect may take longer (up to 12 weeks)
Fresnel prisms
- goal: move image of an object from patient’s non seeing area closer to the functional viewing area
- prism usually of 15-25 PD range
- temporary-patient May remove later
Fresnel disadvantage
- image jump
- image degradation
- chromatic aberration
- more noticeable for higher power PD
Fresnel prism for homonymous heminopia field loss
- apply 15-25 PD to the eye on the side of the field loss, i.e. left loss-prism on left eye
- base of prism foes in the direction of the field loss, left loss-prism base left
- split the pupil with the edge of the prism to start
- as the patient develops their scanning abilities, the nasal edge of the prism will be moved more temporally
- ultimately, the patient will no longer need the prism
Permanent systems for heminoptic defects
Button prism
Sector prism
Peli prism
Fit them on the upper and lower edge of the iris.
Better for driving
Oblique Pelli prism
Gives more expanded central vision than the other types o prism. Can’t see out quite as far but still better to have central vision
Results of peli prism sturdy
- a signification higher proportion said yes to real than sham prisms
- at the end of the crossover, 61% continued prism wear in oblique group and 60% in the horizontal group
- those who continued wear after 6 months reporters grater improvement in mobility with real than sham prisms at crossover end
- participant who discontinued wear reported no difference
- at the long term interview, 36% and 47% were still wearing the prism glasses in each group, respectively
- overall continuation rate at 6m months was 41%
Peli prism demonstration
They make devises to mount to the glasses for demonstration purposes
Scanning
- requires coordinated efforts of head and eyes to develop a systematic search for objects in tje envrinmooent
- typically taught by OT or O and M
Dynavsion scanning training
- trains systematic strategy
- also works on dual attention skills
- similar to a lot of sports vision reactions training
Reading for VF enhancement
- Use line guide
- draw colored line at end of the text on affects side
- turn Paige sideways and read vertically
- read upside down
Hemineglect
- occurs mostly with right parietal lobe CVA
- may or may not have concurrent hemianopsia
- often also have attention deficits
