17. Bag Vs. Sulcus Power -1.50 +28.50 to + 30.00 -1.00 +17.50 to + 28.00 -0.50 + 9.50 to + 17.00 Correction for sulcus placement IOL Power for in bag insertion 0.00 + 5.00 to + 9.00
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23. Advances in IOL technology makes accurate biometry more important than ever before. In order to make the leap into refractive cataract surgery and lens exchange optimization, adoption of third-generation formulas is necessary, and use of fourth-generation formulas is preferable. The time spent optimizing your formula of choice and i mproved results with immersion biometry more than repays your effort to learn it.
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Notes de l'éditeur
The ultrasound probe placed directly on the corneal surface. Quick & easy Variable corneal compression Operator dependant Common reason for IOL power error Anterior lens capsule, retina spikes high and steeply rising The scleral echo should easily be identified Orbital fat echoes should descend quickly and at a steep angle. If there are no scleral or orbital fat echoes visible, the ultrasound beam is most likely aligned with the optic nerve rather than the macula
When the ultrasound beam is properly aligned with the center of the macula, all five spikes (cornea, anterior and posterior lens capsule, retina and sclera) will be steeply rising and of maximum height. a: Probe tip. Echo from tip of probe, now moved away from the cornea and has become visible. b: Cornea. Double-peaked echo will show both the anterior and posterior surfaces. c: Anterior lens capsule d: Posterior lens capsule. e: Retina. This echo needs to have sharp 90 degree take-off from the baseline. f: Sclera g: Orbital fat.
The immersion technique prevents corneal compression and the two-dimensional B-scan display helps guide the superimposed vector A-scan for measurements directly to the fovea. Horizontal axial B-scan taken. Center the cornea and lens echoes in the echogram while simultaneously displaying the optic nerve void near the center. The A-scan vector is then adjusted so as to pass through the middle of the cornea as well as the anterior and posterior lens echoes. Such alignment assures that the vector will intersect the retina in the region of the fovea. This technique is particularly important when the macula lies on the sloping wall of the staphyloma. Most posterior staphylomata are located in the peripapillary region, adjacent to, but not centered at, the macula. When the fovea is situated on the sloping wall of the staphyloma, it may only be possible to display a high quality retinal spike when the sound beam is directed eccentric to the fovea, toward the rounded bottom of the staphyloma. This will result in an erroneously long axial length reading. Paradoxically, if the sound beam is correctly aligned with the refractive axis, measuring to the fovea may result in a poor quality retinal spike and inconsistent axial length measurements.
Immersion biometry is preferred because the two corneal spikes will aid in beam alignment
the patient is seated upright and there is no corneal contact Not only will it do axial length measurements with great precision, but it will also measure the central corneal power by automated keratometry Because the IOLMaster is an optical device, measurements may not be possible in the presence of significant axial opacities, such as a central corneal scar, mature cataract, vitreous hemorrhage, or dense PSC plaque.
Use both axial length and K value to predict ELP Effective lens position ELP: Effective Lens position ACD: Anterior chamber depth AL: Axial Length
This information effectively works as a pattern-recognition system to estimate the Effective Lens Position ( ELP )
If the silicone oil is to remain in the eye for an extended period of time after cataract surgery, an adjustment to IOL power must be made. Holladay and others have recommended that these patients receive a PMMA convex-plano lens, with the plano side oriented so it is facing towards the vitreous cavity, preferably over an intact posterior capsule. This approach prevents the silicone oil from altering the refractive power of the posterior surface of the IOL.
Double K method. Both pre lasik and post lasik k is used
The corneal diameter is less than 11.00 mm.
A second person should repeat the axial length measurements, keratometry readings, and re-run the IOL power calculations for both eyes if:
The gain setting controls the width of the sound beam and the overall sensitivity in detecting peaks.
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