Prognosis and rehabilitationPathology Visual Prognosis Visual Field Defects Visual Aids (LogMAR)Leber’s amaurosis LP – 1.0 Complete loss Vision substitutionOptic atrophy Variable. HM – 0.3 Paracentral scotomas Good with LVAOptic disc hypoplasia Variable. Good or poor Variable Good with LVACerebral blindness Variable, poor Difficult to test Poor with LVA. Enviromental modificationsDelayed visual development Often normal Normal Good with LVA and/ or trainingAlbinism 1.0 – 0.5 Usually normal Good with LVA (distance)Stargardt’s disease 50% > 0.1 / 50% < 0.1 Central scotoma Good with LVACone dystrophy 1.0 – 0.6 Central scotoma Good with filters (red tint)Best’s disease 1.0 Normal – Central scotoma Variable with LVARetinitis pigmentosa 1.3 - NLP Peripheral constriction and/ Good with LVA and CCTV or central defectX-linked retinoschisis 1.3 – 0.8 Peripheral and central Good with LVA scotomas A.J. Jackson, J.S. Wolffsohn (2007)
Low Vision AidsKids tend to reduce distance in order to gain magnification. But as they growolder and accommodation lags they need to compensate with low vision aids.Aphacic children need to be introduced to magnification as soon as possible.Usually, they require higher amounts of magnification.Children accept low vision aids and other visual modifications easier thanadults. They don’t experience emotions of loss and we meet less denial.What looks a technological challenge for you, for kids is just a game.
Low Vision AidsEye – hand coordination is a very important factor that has to be developedearly with low to moderate magnification (table magnifiers, stand magnifiers,magnifying rulers, etc).Later, when head and ocular motor control is fine tuned magnifying glassescan be used (monocular, prismatic binocular, special bifocals, etc).
Low Vision AidsThe use of hand held magnifiers can usually be incorporated for daily activitieswhen school starts. Combination with eyeglasses can provide patient withhigher magnificactions (with or without illumination, etc).Telescopic systems can be used in a classroom environment too, althoughhardly accepted due to aesthetic reasons (monocular, binocular, fixed,removable, etc).
Low Vision AidsCCTV and other electronic magnifiers can be used when good eye – handcoordination has been established, although they are more necessary inschool years (colored, contrast enhancement, portable, etc).New devices and software allow easy modification of size and spacing ofletters or even text to speech functions (e – readers, tablets, etc).
Definition of Vision Clinicians experience the visual process (apart from their own vision) through testing and therapy, thus each one creates his/ her own model of vision.“Vision is the ability of the organism to derive meaning and direct action, as triggered by light.”
Optics of our visual system A good cell phone camera can provide resolution up to 5 Mpixel.How many Mpixels is thehuman eye?Only 1 Mpixel…!!!
Multi-tasking, simultaneous, exchanging, parallel processing systems.Enriched by multi-sensory perception
Efferent pathwayrepresents about 8% of the optic nerve. This affects almost 90% of the flowback to the brain. Cortical feedback to LGN may have a role in orientation tuning, increasing responses and enhancing contrast gain. Enriched by efferent neural information
References• A.J. Jackson, J.S. Wolffsohn. Low vision manual. Butterworth – Heinemann, 2007.• Worgotter F, Nelle E, Li B, Funke J. The influence of corticofugal feedback on the temporal structure of visual response of cat thalamic relay cell. J. Physiol. 1998;509:797-815.• R.C. Peterson, J.S. Wolffsohn, M. Rubinstein, J. Lowe. Benefits of electronic vision enhancement systems (EVES) for the visually impaired. Br. J. Ophthalmol. 2003;136:1129-1135.• B.P. Rosenthal, R.G. Cole. Functional assessment of low vision. Mosby, 1996.• Przybyszewski AW, Gaska JP, Foote W, Pollen DA. Striate cortex increases contrast gain of macaque LGN neurons. Vis. Neurosci. 2000;17:485-494• S.L. Macknik, S. Martinez-Conde. Sleights of mind. Henry Holt & Company, 2010.• A. Robinson. Cunningham’s textbook of anatomy. Oxford University Press, 1931.• D.N. Spinelli, K.H. Pribram, M. Weingarten. Centrifugal optic nerve responses evoked by auditory and somatic stimulation. Exp. Neurol. 1965;12:303-319.• C. Dickinson. Low vision. Principles and practice. Butterworth – Heinemann, 1998.• W.V. Padula. Neuro-optometric rehabilitation. Optometric Extension Program Foundation, 1996.• B. Silverstone, M.A. Lang, B. Rosenthal, E.E. Faye. The lighthouse handbook on vision impairment and vision rahabilitation. Oxford University Press, 2000.• E.B. Forrest. Visual imagery: An optometric approach. Optometric Extension Program Foundation, 1981.