W8 Spectacle Lens Corrrection

What is the structure of the eye?

…

What are the 2 surfaces of the cornea according to Gullstrand?

Anterior corneal surface (radius of curvature 7.7mm) and posterior corneal surface (radius of curvature 6.8mm)

What’s the structure of the crystalline lens according to Gullstrand?

Lens grow throughout life, becoming axial thicker with age as does radius of curvature as accommodation also alters the thickness and radius of curvature

What are the 4 surfaces of the crystalline lens?

2 cortex surfaces and 2 nucleus surfaces (anterior and posterior)

What is the axial length of the eye?

24.385mm

What is the focal length of the eye?

16.67mm

What is the refractive indices of the eye?

1.333

What is the axial length of the eye?

22.22mm

What is the power of the eye?

60D

What is the far point of the eye?

If light comes in from infinity and lands on the fovea, it would shine back out at infinity

What is emmetropia?

When the second focal point coincides with the macula

What are reasons someone is myopic?

Axial myopia: Ideal axial length (22.22mm) is increased

Index myopia: refractive index (1.333) is increased

Refractive myopia: refracting surfaces power (60D) has increased

How do we correct myopia?

Corrected with a negative lens with its second focal point placed at the eyes far point

Why does a person have hyperopia?

The far point in hyperopia lies a finite distance behind the eye

What are reasons someone might have hyperopia?

Axial hyperopia: axial length (22.22mm) is decreased

Refractive hyperopia: refracting surface power (60D) is decreased

Index hyperopia: refractive index (1.333) is decreased

How do we correct hyperopia?

Corrected by a positive lens with its second focal point placed at the eyes far point

What is the relationship between the distance of spectacle lens and a myopic eye?

Further the spectacle lens is placed away from the eye the more powerful the lens must become to correct the eye

What is the relationship between a hyperopia eye and the distance of the spectacle lens?

The further the spectacle lens is placed away from the eye, the less powerful the lens must become to correct the eye