phoropter , hypermetropia and astigmatism

what are the advantages of using a phoropter

lenses do not become dirty or scratched

What are the disadvantages of using a phoropter

• The phoropter hides the patient face so determining patient’s reactions to lens choice is more difficult.

• When completing the reading addition in presbyopic patient the patient is not in a relaxed reading position.

• If the patient’s head is tilted during the refraction the cylindrical axis may be inaccurate.

• It is not portable

when should you use a trial frame

• domiciliary visits

• near vision assessments, allowing patients to adopt their natural reading posture.

• children and patients with binocular vision anomalies, as they allow for more natural interaction and less proximal accommodation.

• patients with visual impairment, hearing difficulties, or high refractive errors, where precise vertex distance and flexibility in head positioning are crucial

• Trial frames also facilitate over-refraction in multifocal contact lens fittings

in hypermetropia the image focuses _____ the retina

behind

The hypermetropic eye is too weak to suit

its axial length

what is manifest hypermetropia

That amount of hypermetropia that is exhibited
through the maximum plus refraction

which type of refraction is required to fully reveal a hypermetropia

cycloplegic refraction

what are symptoms of uncorrected hypermetropia

1. usually asymptomtomatic under 1.00DS

2. blur during reading or prolonged near activities

3. frontal headaches

4. asthenopia - uncomfortable vision , tired eyes

what is the vertical 90 degree meridian refered to as

with the rule astigmatism

what is the horizontal 180 degree meridian referred to as

against the rule

what is an oblique astigmatism

the steepest meridian in regular astigmatism is neither horizontal nor vertical

what are the symptoms of uncorrected astigmatism

• Asthenopia.

• Headaches (frontal and associated with the visual task.

• Low amounts of astigmatism < 0.75DC asthenopia symptoms at far and near.

• High degree astigmatism > 0.75DC near asthenopia, reduce vision for distance and near targets

what are considerations for patients with astigmatism

If the axis is altered , the patient may perceive marked tilting of the floor and the walls.

Large changes in the cyl or axis, may indicate marked changes in the corneal curvature e.g. keratoconus.

Oblique Astigmatism

• The eye has two main focusing directions (principal meridians).

• In oblique astigmatism, these meridians are slanted, not straight up-and-down or side-to-side.

• Example: 45° and 135°.

• Vision may feel tilted or distorted because the blur is on a diagonal.

Bioblique Astigmatism

• The two principal meridians are not at 90° to each other, which is abnormal.

• Example: 20° and 110° (not perfectly perpendicular).

• This usually happens due to irregular corneal shape.

what are the types of simple Astigmatism

Only one meridian has a focusing problem; the other is normal.

a) Simple Myopic Astigmatism

• One meridian focuses in front of the retina.

• The other focuses on the retina.

• Causes blur mainly at distance in one direction.

b) Simple Hypermetropic Astigmatism

• One meridian focuses behind the retina.

• The other focuses on the retina.

• Causes blur especially for near vision.

what are the two types of Compound Astigmatism

Both meridians are faulty.

a) Compound Myopic Astigmatism

• Both meridians focus in front of the retina.

• One is more myopic than the other.

b) Compound Hypermetropic Astigmatism

• Both meridians focus behind the retina.

• One is more hypermetropic than the other.

Mixed Astigmatism

• One meridian focuses in front of the retina (myopic).

• The other focuses behind the retina (hypermetropic).

• The retina lies between the two focal points.