#51. Astigmatgism. Anisometropy. Eyeglasses - definition of spectacle lenses, magnifying glasses, telescopic spectacles. Contact lenses.

Question 1

What is ASTIGMATISM?

Answer 1

It is the LACK of FOCAL POINT

• It’s characterised by CURVATURE ANOMALY of the REFRACTIVE MEDIA that PARALLEL INCIDENT light DO NOT converge at the point

Question 2

What are the 2 TYPES of ASTIGMATISM?

Answer 2

1) EXTERNAL
- ASTIGMATISM of the ANTERIOR Surface of the CORNEA

2) INTERNAL
- SUM of the ASTIGMATIC Components of OTHER media
——————

A) WITH-the-Rule
- GREATER Refractive Power is VERTICAL = 70 - 110 Degrees

B) AGAINST-the-Rule
- GREATER Refractive Power is HORIZONTAL = 160 - 20 Degrees

B) OBLIQUE
- Refractive Power is OBLIQUE
- BTW 20 - 70 Degrees
- BTW 110 - 160 Degrees

Question 3

What are the CAUSES of ASTIGMATISM?

Answer 3

• Corneal ULCERATIONS, leading to Corneal SCARRING
• PENETRATING Corneal Trauma
• ADVANCED Keratoconus
• Cataract
• Lenticonus

Question 4

What are the SYMPTOMS of ASTIGMATISM?

Answer 4

• DISTORTED Vision
• ASTHENOPIC SYMPTOMS
  a. Burning Sensation in Eyes
  b. Headache1

Question 5

What are the SYMPTOMS of ASTIGMATISM?

Answer 5

• DISTORTED Vision
• ASTHENOPIC SYMPTOMS
  a. Burning Sensation in Eyes
  b. Headache

Question 6

What is the DIAGNOSIS for ASTIGMATISM?

Answer 6

• KERATOSCOPE = Allows GROSS estimation of Astigmatism
  a. REGULAR = Rings are OVAL
  b. IRREGULAR = Irregularly DISTORTED
• VIDEOKERATOSCOPY = Obtain image of DISTRIBUTION of Refractive Values OVER ENTIRE Cornea
• HEMHOLTZ = Measures CENTRAL CORNEAL CURVATURE, determining REFRACTIVE POWER of the Cornea

Question 7

What is the TREATMENT for ASTIGMATISM?

Answer 7

• EARLY Correction
• Rigid Contact Lenses = EXTERNAL Astigmatism
• Keratoplasty / Surgical Correction = For Refractive Error

Question 8

What is ANISOMETROPIA?

Answer 8

When there’s a DIFFERENCE in REFRACTIVE POWER, BETWEEN BOTH eyes

Question 9

What is the CAUSE of ANISOMETROPIA?

Answer 9

• Unknown Cause
• INHERITANCE!

Question 10

What are the SYMPTOMS of ANISOMETROPIA?

Answer 10

• Asymptomatic
• Tendency towards STRABISMUS

Question 11

What is the DIAGNOSIS for ANISOMETROPIA?

Answer 11

Refraction Testing

Question 12

What is the TREATMENT for ANISOMETROPIA?

Answer 12

• Eyeglasses
• Contact Lenses
• IMPLANTATION of Intraocular Lens = Px with Unilateral Aphakia

Question 13

What are the 2 TYPES of EYEGLASSES?

Answer 13

1) SPHERICAL Lenses = Refract light EQUALLY ALONG every axis

2) TORIC Lenses = Refract light ONLY ALONG 1 axis

Question 14

How is the REFRACTIVE POWER of the LENSES Measured?

Answer 14

• Manually
• Automatically = OPTICAL INTERFEROMETER

Question 15

What are the DIFFERENCES between CONTACT LENS

And EYEGLASSES?

Answer 15

CONTACT LENS

• CORRECT the REFRACTIVE ERROR CLOSER to the Location of its Origin
• Hence; QUALITY of OPTICAL IMAGE is HIGHER&raquo_space; than Eyeglasses
• Have LESS INFLUENCE on SIZE of Retinal Image

Question 16

What are the CHARACTERISTICS of CONTACT LENSES?

Answer 16

• DIAMETER of Contact Lens
• RADIUS of CURVATURE of the POSTERIOR SURFACE
• GEOMETRY of the POSTERIOR SURFACE
• Refractive Power
• Material
• OXYGEN PERMEABILITY of the Material