19. Subjective and objective refraction. Prescription of glasses.

Question 1

what is refractive error

Answer 1

optical defect which causes the light not to be in sharp focuss on the retina , resulting blurredd vision

Question 2

what is objective refraction ?

Answer 2

refactory examination using different instruments without receiving any feedback from patient

Question 3

what instrument if used in objective refraction ?

Answer 3

retinoscopy - projects a streak of light - intercept

intercept passes through the pupil to shine on the retina and a produce retinoscopic reflection

Question 4

how do you know from retinoscopy there is only a spherical error ? (the eye is either too large or too small )

Answer 4

parallel alignment of the intercept and retinoscopic reflex in all meridans

Question 5

how do we know if there is a cylindrical error ( when the optical power of the eye is too powerful or too weak - lens , cornea- irregular in shape asytgmatism , aqueous humour) present in retinoscopy ?

Answer 5

if the intercept is not parallel to the retinoscopic reflex (anterior or posterior pole)- cylindrical error

Question 6

how with retinoscopic reflex would we know if the patient is myopic or hyperopic ?

Answer 6

the intercept sweeps across the patients pupil
retinoscopic reflex in the same direction of the intercept -
plus lenses needed - hyperopic patients

plus lenses to get neutralised to bring the focus back on the retina

opposite direction - minus lenses needed
myopic patients

emmetropic patients - no motion of reflex observed in person

procedure performed until pupillary reflex fills the whole pupillary aperture - no movement detected - point of neutralization

Question 7

what is subjective refraction ?

Answer 7

after the objective retinoscopy for more accurately refining the measured refractive error

relies on the patient’s response to alterations in lens power and orientation, using the objective patient’s current refractive correction as the starting point

and using combination of sphere and cylindrical lenses

Question 8

how is spherical correction checked ?

Answer 8

initially increasing the plus power to overcome accommodative efforts until the clearest image is obtained!

Question 9

what is scissors reflex ?

Answer 9

when two bands reflexes seen- keratoconus- cornea astigmatism

Question 10

when you do retinoscopy normal red reflex must be seen ?

Answer 10

yes otherwise it is an emergency

if red reflex is absent / white reflez - can be due to cataract or leukocaria, retinoblastoma