Winter 2017

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Page 23 of 35

An overflowing scleral lens prior to insertion. described as having touch (bearing), alignment, or clearance (pooling). The peripheral curves of the GP or edge lift are often quantified as minimal (<1mm), moderate (~1mm), or exces- sive (>1mm). The hallmark signs of a steep fitting GP are central pooling, midperipheral bearing, and minimal edge lift. In contrast, a flat fitting GP bears centrally, and has pooling in the midperiphery and periphery. To aid in fluorescein pattern as- sessment, consider ordering GP lenses plasma treated. Plasma treatment is actually a "deep cleaning" of the GP lens after it is manufactured to elimi- nate any residual resin or areas of poor wetting. This is accomplished using polarized gas molecules to improve the attraction between the GP lens materi- al and the tear film. Although there is a slight additional cost, the GP lenses tend to wet very well and may improve the initial patient experience. A simi- lar effect can be achieved if the lenses are cleaned well with an alcohol based solution, rubbed thoroughly, and soaked for at least 24-48 hours prior to dispense. When fitting challenges are en- CLSA EyeWitness Winter 2017 22 countered, consider the suggested changes in the table above. If a GP lens appears too flat or steep and a base curve adjustment needs to be made, it is important to remember that the contact lens pow- er also needs to be changed. When the base curve changes, this causes a change in the lacrimal lens shape, which will affect the overall correcting power. Therefore, remembering the acronym SAM-FAP is useful. SAM- FAP stands for: Steeper Add Minus, Flatter Add Plus. Any dioptric value change in base curve will be equivalent in contact lens power. For example, if a lens will be flattened by 0.50D, then add 0.50D of plus to the contact lens power to compensate for the lacrimal lens power change. Lens Designs GP contacts are available in single vi- sion, toric, multifocals, as well as large diameter sclerals, reverse geometry, and other specialty contact lens de- signs. The most common designs are single vision, toric, and multifocal. Sin- gle vision GP contacts can be spheri- cal or toric. Spherical GP lenses have one base curve whereas toric lenses often have two base curves. A toric GP is usually considered when a patient has between 2.50D to 3.00D of cor- neal astigmatism. Astigmatism can be corrected by making the front, back, or both surfaces of the GP toric. Let your GP consultant recommend which design is best based on each patient's spectacle refraction and keratometry values. For some patients with limbus to limbus astigmatism, both the base curve and the peripheral curves need to be toric to achieve an aligned fit. To- pography is a great way to tell how to- ric each curvature should be. Multifocal GP lenses are either a concentric, simultaneous design, or they are translating, similar to a lined bifocal. Again, eyelid positioning is crucial to the success of either design. Concentric designs must center on the cornea in order for the optics to work optimally. If the lower eyelid rests right at the inferior limbus or slightly above, a translating design may work well. If the eyelids are too lax and the GP slides under the lid margin in down gaze, then adequate near vision may not be achieved. If the lens is sliding under the lower eyelid, flattening the base curve, increasing the prism ballast, or truncating the lens will help improve upward translation over the superior limbus when the patient is looking in downgaze. It is also important to assess how quickly the GP drops to rest on the lower lid otherwise the patient may be looking through the reading por- tion each time they blink. Increasing the lens diameter or center thickness of a lid attached multifocal may help the lens drop faster so the patient can quickly focus through the distance por- tion after each blink. Tricks of the Trade • Depending on the size of the GP and pupils, occasionally patients will com- plain of glare and flare especially at night. When pupil size increases, often the transition between the optic zone and the peripheral curve can cause light to scatter. Increasing the optic zone often eliminates this problem. PROBLEM Not lid attaching Poor centration Excessive movement Insufficient movement Lateral decentration Inferior lens drop SOLUTION 1. Flatten the base curve 2. Increase the OAD 3. Flatten the peripheral curve system 1. Steepen the base curve 2. Increase the OAD or increase the OZD 3. Steepen the peripheral curve system 1. Steepen the base curve 2. Increase the OAD or increase the OZD 1. Flatten the base curve 2. Decrease the OAD or decrease the OZD 1. Steepen the base curve 2. Increase the OAD or increase the OZD 3. Steepen the peripheral curves 1. Steepen the base curve if fitting flat 2. Flatten the base curve if fitting steep

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