Patients who have presbyopia and who are emmetropic or have low amounts of hyperopia present unique challenges. Up to the point of developing presbyopia, they have been relatively free of vision correction and now need near-vision correction. For those who have hyperopia, there is an additional need for distance vision correction.
Some patients who fit this description may be motivated to wear contact lenses. And, while there are numerous soft and GP lens options for daily wear that would satisfy their visual needs, there is an additional novel option that would provide visual correction and additionally allow patients to be free of contact lenses during waking hours—hyperopic orthokeratology. Though currently there are no U.S. Food and Drug Administration-approved hyperopic ortho-k lens designs, these designs do exist and can be designed with the aid of computer software or of consultants from GP laboratories.
Corneal shape changes that take place beneath the reverse geometry lens designs used in ortho-k involve fluid forces of the tear film, lid pressure in the closed-eye environment, and surface tension of the tears at the lens edge (Mountford et al, 2004). The forces act by both compression and tension at the different sites across the corneal surface.
A hyperopic ortho-k lens has three key elements: 1) a zone of apical clearance, which allows for central corneal steepening (Figure 1); 2) a contact zone of 2mm to 3mm from the geometric center of the lens that aids in lens centering and midperipheral flattening; and 3) a relief zone in the midperiphery (Figure 2).
Presbyopic emmetropes are fitted with the lens in their nondominant eye only. The resultant steepening in their central cornea provides them with a monovision style “add.” The amount of corneal steepening depends on near vision requirements and their current level of accommodative ability.
The amount of corneal steepening achievable maxes out at around 3.00D. The central base curve (a.k.a. mold curve) should be steeper compared to the patients’ flat K by the amount of corneal steepening desired. For example, if a patient is best served with an add of 1.50D in the nondominant eye, the base curve would be chosen 1.50D steeper than the flat K; in this case, for a flat K of 43.00D, the central base curve would be 44.50D.
Individuals who have hyperopia and presbyopia would have their full hyperopia correction in their dominant eye; in the nondominant eye, it would additionally correct over the necessary hyperopic error by the amount of required add yielding the needed monovision correction.
Though not a traditional form of vision correction, using hyperopic ortho-k lenses for patients who have hyperopia and presbyopia presents a unique visual solution while allowing them to be free from contact lenses during waking hours. CLS
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