Refraction

Question 1

1.What is Emmetropia?

2. What is Ametropia?

Answer 1

1.Refractive state of an eye when parallel rays of light are focused on the sensitive layer of retina when accommodation is at rest.

2.Refractive state of an eye when parallel rays of light are not focused on the sensitive layer of retina when accommodation is at rest.
3 types
Hypermetropia,Myopia and Astigmatism.

Question 2

Hypermetropia Rays of light focused behind retina.
Diagnosed on retinoscopy,A scan
1.What are its Causes?

2.Can physiological hypermetropia occurs? How much diopters?

3.what are the complications of hypermetropia?

4.Treatment options?

Answer 2

1. Axial length of eyeball shortens.
   curvature of cornea or lens becomes flat.
   R.Index of lens decreases,in cortical cataract.
   Lens displaced posteriorly
   Aphakia

2.Yes at birth all eyes are hypermetropic to the extent of +2.5 to +3 diopters.

3. Amblyopia

4.Convex lens
Photo refractive keratectomy…ant surface of peripheral cornea is ablated therefore centre becomes steeper.
LASIK…laser in situ keratomileusis.

Question 3

Myopia
Rays of light focused in front of retina.
Dx on retinoscopy,A scan and corneal topography.

1.What are the causes?

2. Difference bw simple and pathological myopia.

3.What are the signs in pathological myopia?

4.Treatment options?

Answer 3

1.increase in curvature of cornea or lens.
Increase in axial length.
R.Index of lens increases as in nuclear cataract.
Ant displacement of lens.

2.simple myopia seldom exceeds 6 diopters and it has no degenerative changes in fundus.
Pathological myopia reaches 15 to 20 diopters and is progressive.

3.peripapillary atrophy,lacquer cracks(breaks in Bruchs memb), choroidal neo vascularization,foster fuchs spots(dark hemorrhagic pigmentation in retina), posterior staphyloma,holes in retina.

4….concave lenses
…….Radial keratectomy…radius of corneal curvature is reduced…corrects upto 4 D.
…..photo refractive keratotomy…central corneal surface
is ablated,cornea flattens.
….LASEK
….LASIK…Most effective due to less post-op pain and rapid visual rehabilitation.
….Lens extraction and phakic posterior chamber implant.

Question 4

Astigmatism
1. The interval bw two focal points is called?

2.What are the types of Astigmatism?

3.what are the types of regular astigmatism?

Answer 4

Type of refractive error when parallel rays of light are not focused on a single point but form a focal line.

It occurs because refractive power of cornea and lens is not same in all meridians.

1. Sturm’s conoid

2.Regular astigmatism…
1.simple
2.compound
3.Mixed
Irregular astigmatism

Question 5

Explain the following:
1.Simple myopic astigmatism

2.simple hypermetropic astigmatism

3.compound myopic astigmatism

4.Compound hypermetropic astigmatism

5.Mixed

Answer 5

1.rays of one meridian focused on retina and one is focused in front of retina.

2. Rays of one meridian focused on retina and the other is focused behind the retina.

3.Rays of both meridians focused in front of retina.

4.Rays of both meridian focused behind the retina.

5.Rays of one meridian focused in front and one behind the retina.

Question 6

Explain the following
1.With the rule astigmatism

2. Against the rule astigmatism

3.oblique astigmatism

Answer 6

1.vertical meridian is more curved/steep….
Require convex cylindrical lens at 90 degrees or concave cylindrical at 180 degrees.

2.Horizontal meridian is more steep …
Requires concave cylindrical lens at 90 degrees and convex cylindrical lens at 180 degrees.

3.These two meridians are not horizontal or vertical but are at right angles to one another e.g 45 and 135 degrees.

Question 7

Define
1.Accommodation

2.Presbyopia and its ttt

3.isometropia

4.Anisometropia

5. Anisekonia

Answer 7

1.it is a mechanism In Which eyes change the refractive power to focus the near objects clearly.

2.It is physiological insufficiency of accommodation due to advanced age resulting in recession of puncta proxima.
Due to physiological decrease in elasticity of lens.
Treated by convex lens

3.state of eye where both eyes have equal refraction.

4.a condition when two eyes have unequal refraction. It can be
Simple….one eye normal,one is myopic or hypermetropic.
Compound…both eyes are myopic or hypermetropic,but one is having higher refractive error than other.
Mixed…one eye is myopic one is hypermetropic.

5.Aniseikonia is when images of the two eyes are unequal in size and shape.

Question 8

What is the effect of anisometropia when
1.refractive error is less than 3 diopters?

2.when refractive error is high in one eye and age is below 9 years?

Answer 8

1. BSV is maintained.

2.amblyopia occurs.