Eyedocs instruments Flashcards
The principle of diffraction is used in what?
multi-focal intraocular lenses - interference of waves of light to creat multi-focality
What is the primary focal point?
It is the object location associated with a parallel ray LEAVING the lens
What is the secondary focal point?
It is the image location associated with a parallel ray ENTERING the lens
What is the conjugate point?
Two points that are an object and image of each other
What is the far point?
The point in visual space conjugate with the retina when the eye is not accommodating
What is the aim of spectacle / CL correction?
Place a lens in front of the eye so that the secondary focal point of the lens coincides with the far point of the eye
What is the vertex distance?
the distance between the eye and its corrective lens is the vertex distance (from corneal surface to back of lens)
What is the near point?
The point in space conjugate to the retina when the eye is fully accomodated
What is the distance between far point and near point called?
the accomodative range
What does a spherocylindrical lens consist of?
two cylindrical lenses of differing dioptic powers orientated 90 degrees apart
What is the circle of least confusion?
section of the conoid in which incoming light is the most focused (most-point like)
The smaller the COLC, the better the vision
What are the two techniques used to correct the astigmatic patient?
- Retinoscopy
- Jackson-Cross
What are the refractive types of astigmatism? (5)
- Compound myopic (both focal lines in vitreous)
- Compound hyperopic (both focal lines behind eye)
- Simple Myopic (one line in vitreous, one on retina)
- Simple Hyperopic (one line behind eye, one on retina)
- Mixed (one in vitreous, one behind eye)
What does a -2 sphere do in astigmatism in retinoscopy?
Pushes entire focal lines back - aim is to keep anterior focal line on the retina
What does a +1 cylindrical lens do in astigmatism in retinoscopy?
pulls the posterior focal line forward
What is a Jackson Cross lens?
It is a spherocylindrical lens containing plus and minus cylinders of equal and opposite powers orientated 90 degrees apart with no net spherical equivalent power
What is the main property of the jackson cross lens?
It does not move the circle of least confusion when placed before an astigmatic eye as it has no sphere power
What should you aim for for a Jackson Cross Lens?
Aim for mixed astigmatism with circle of least confusion on the retina before cylinder is introduced
What is with the rule astigmatism?
vertical meridian (180) is steeper than horizontal meridian (90) (squeezing a ball in the vertical axis)
How do you correct with the rule astigmatism?
- minus cylinder at 180 degrees (vertical mer)
- plus cylinder at 90 degrees (horizontal mer)
How do you correct against the rule astigmatism?
- minus cylinder at 90 degrees (horizontal)
- plus cylinder at 180 degrees (vertical)
How do you change prescription from positive cylinder to negative cylinder?
- Add sphere to cylinder
- change cylinder sign
- axis Change by 90 degrees
Large convex lenses (aphakia) produce what effects? (4)
- pin-cushion effect
- ring scotoma
- jack in the box phenomenon
- spherical aberration
Large concave lenses produce what effects (1)
- Barrel disrotion effect of images
What are the contraindications of LASIK surgery (3)
- Long term topical/oral corticosteroids
- Immunocompromised
- Chronic ocular conditions (incl keratoconus with risk of ectasia)
What are base-in prisms used for?
- measurement of horizontal fusional amplitude
What are base-out prisms used for?
- Management of esophoria
- Management of VI nerve palsy
- Improve convergence in patients with convergence insufficiency
- 4 prism base-out prism is used for suppresion scotoma of microtropia
WHich children’s test uses crowded letters?
Which children’s test uses letters singly?
- Sonksen-Silver
- Sheridan-Gardiner
What is the difference bewteen Kay, Keeler and Cardiff Cards?
Kay - matching pictures
Keeler - preferential grating
Cardiff cards - simplistic pictures in white
What is the purpose of a maddox rod?
Identifies presence of
- horizontal deviations
- vertical deviations
- torsional deviations
- latent and manifest strabismus
What is a maddox rod?
series of parallel cylinders lying 3mm apart that converts a POINT source of light to a LINE image.
What are the contraindications to ICG? (5)
- Pregnancy
- Seafood Allergy (not in FFA)
- Iodide Allergy (not in FFA)
- Kidney Failure
- Liver Disease (not in FFA)
What are the contraindications to FFA? (4)
- Previous allergy to fluorescein
- Breastfeeding (not in ICG)
- Kidney failure
- Pregnancy
