W2 Magnification/Field of View

What’s magnification?

How much bigger the object appears through the ophthalmoscope than if observed with the naked eye

How do you calculate magnification?

Angular size of object through ophthalmoscope/ angular size of object at least distance of distinct vision (image in focus)(25cm generally)

Beta/ alpha

What’s the magnification in a standard emmetropic eye?

X15

What’s the magnification for an ammetropic eye?

Myope- larger than x15

Hyperope- smaller than x15

What is the equation for magnification?

(Fe (60) / 4 ) x 1/ (1- working distance x ocular refraction) )

How do you calculate size of blur circle?

Pupil size x (ocular refraction - recpircal of wd) / 60

What does the blur circle equation show?

• If working distance is larger, field of illumination is smaller

• If pupil size is smaller, field of illumination is smaller

• If Rx is +ve, field of illumination is larger

• If Rx is -ve, field of illumination is smaller

WD IS ALWAYS -VE

What are factors that affect field of view and magnification?

• Pupil size

• Sight hole size

• Working distance

• Subject ammetropia (myope/hyperope/astigmatism)