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Optical Issues in Measuring Strabismus.

Irsch K - Middle East Afr J Ophthalmol (2015 Jul-Sep)

Bottom Line: Potential errors and complications during examination and treatment of strabismic patients can be reduced by recognition of certain optical issues.This articles reviews basic as well as guiding principles of prism optics and optics of the eye to equip the reader with the necessary know-how to avoid pitfalls that are commonly encountered when using prisms to measure ocular deviations (e.g., during cover testing), and when observing the corneal light reflex to estimate ocular deviations (e.g., during Hirschberg or Krimsky testing in patients who do not allow for cover testing using prisms).

View Article: PubMed Central - PubMed

Affiliation: Laboratory of Ophthalmic Instrument Development, The Wilmer Eye Institute, The Johns Hopkins University School of Medicine, Baltimore, Maryland, USA ; Clinical Investigation Center - CIC 1423 INSERM, Quinze-Vingts National Eye Hospital, Paris, France.

ABSTRACT
Potential errors and complications during examination and treatment of strabismic patients can be reduced by recognition of certain optical issues. This articles reviews basic as well as guiding principles of prism optics and optics of the eye to equip the reader with the necessary know-how to avoid pitfalls that are commonly encountered when using prisms to measure ocular deviations (e.g., during cover testing), and when observing the corneal light reflex to estimate ocular deviations (e.g., during Hirschberg or Krimsky testing in patients who do not allow for cover testing using prisms).

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Interface between two stacked prisms. While the first glass prism is in the Prentice position, with the light ray being perpendicular to the first surface of the prism, the second glass prism is nowhere near the Prentice position, with the light ray going in at an angle far from perpendicular (adapted from reference 4)
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Figure 4: Interface between two stacked prisms. While the first glass prism is in the Prentice position, with the light ray being perpendicular to the first surface of the prism, the second glass prism is nowhere near the Prentice position, with the light ray going in at an angle far from perpendicular (adapted from reference 4)

Mentions: Stacking prisms together in the same direction, especially if one is of high power, when measuring large strabismic deviations may also result in large errors. For example, adding a 5Δ prism to a 40Δ prism, results in 58Δ of effect, and a 10Δ prism added to the 40Δ prism can result in more than 100Δ of effect.4 This can be understood by looking at the interface between two stacked prisms [Figure 4]. Even if the first prism is held in its proper position, the second prism is nowhere near its calibrated position, leading to a stronger prism effect than simply the sum of the two prisms. Therefore, prisms do not add linearly and should never be held in contact with each other in that manner.


Optical Issues in Measuring Strabismus.

Irsch K - Middle East Afr J Ophthalmol (2015 Jul-Sep)

Interface between two stacked prisms. While the first glass prism is in the Prentice position, with the light ray being perpendicular to the first surface of the prism, the second glass prism is nowhere near the Prentice position, with the light ray going in at an angle far from perpendicular (adapted from reference 4)
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4502167&req=5

Figure 4: Interface between two stacked prisms. While the first glass prism is in the Prentice position, with the light ray being perpendicular to the first surface of the prism, the second glass prism is nowhere near the Prentice position, with the light ray going in at an angle far from perpendicular (adapted from reference 4)
Mentions: Stacking prisms together in the same direction, especially if one is of high power, when measuring large strabismic deviations may also result in large errors. For example, adding a 5Δ prism to a 40Δ prism, results in 58Δ of effect, and a 10Δ prism added to the 40Δ prism can result in more than 100Δ of effect.4 This can be understood by looking at the interface between two stacked prisms [Figure 4]. Even if the first prism is held in its proper position, the second prism is nowhere near its calibrated position, leading to a stronger prism effect than simply the sum of the two prisms. Therefore, prisms do not add linearly and should never be held in contact with each other in that manner.

Bottom Line: Potential errors and complications during examination and treatment of strabismic patients can be reduced by recognition of certain optical issues.This articles reviews basic as well as guiding principles of prism optics and optics of the eye to equip the reader with the necessary know-how to avoid pitfalls that are commonly encountered when using prisms to measure ocular deviations (e.g., during cover testing), and when observing the corneal light reflex to estimate ocular deviations (e.g., during Hirschberg or Krimsky testing in patients who do not allow for cover testing using prisms).

View Article: PubMed Central - PubMed

Affiliation: Laboratory of Ophthalmic Instrument Development, The Wilmer Eye Institute, The Johns Hopkins University School of Medicine, Baltimore, Maryland, USA ; Clinical Investigation Center - CIC 1423 INSERM, Quinze-Vingts National Eye Hospital, Paris, France.

ABSTRACT
Potential errors and complications during examination and treatment of strabismic patients can be reduced by recognition of certain optical issues. This articles reviews basic as well as guiding principles of prism optics and optics of the eye to equip the reader with the necessary know-how to avoid pitfalls that are commonly encountered when using prisms to measure ocular deviations (e.g., during cover testing), and when observing the corneal light reflex to estimate ocular deviations (e.g., during Hirschberg or Krimsky testing in patients who do not allow for cover testing using prisms).

Show MeSH
Related in: MedlinePlus