It can be frustrating for both eyecare professionals and their patients when a patient who has a seemingly slam-dunk, –3.25D OD/OS spectacle prescription struggles in three different pairs of off-the-shelf soft contact lenses that all exhibit poor fitting relationships during an initial soft contact lens fit (Figure 1).
Perhaps the first trial lens is moving too much and is characterized as “too flat.” So, practitioners go to their contact lens diagnostic room to find a lens that has a steeper base curve. Unfortunately, and in line with trends of the soft contact lens industry, the lens manufacturer/type that was just trialed is available in only one base curve/diameter combination.
Next, they jump to another manufacturer. Again, a decentered, poorly fitting lens. Third time is the charm, right? Onto trial number three, manufacturer number three. Strike out. Practitioners must then tell their patients that they will order some additional trials and call them back when the lenses arrive. The practitioners feel deflated. Their patients leave disappointed. At this point, we must ask ourselves the following questions.
1) Did you get a thorough history of previous contact lens use?
Patients who indicate that they have struggled with soft contact lens use in the past are a red flag. If they had a period of successful lens wear and then gradually developed an intolerance, this could be indicative of tear film instability issues.
Patients who report that they have never been comfortable with soft lens wear may have ocular features that are outside of population norms and were never addressed in previous fits.
2) Did you have a clear idea of the corneal geometry?
While autokeratometry readings are great for screening the status of a patient’s corneas, they are limited in the information that they can provide. Practitioners will get an idea of how steep or how flat the cornea is and the amount of corneal astigmatism, but that’s about it. Topography can provide information on the distribution of astigmatism across the corneal surface as well as the rate of flattening of the cornea from the center out to the periphery.
3) Was the size of the eye outside of expected norms?
Reports show that corneal diameter highly influences the sagittal height of the eye and, ultimately, overall soft contact lens fit (Young, 1992). Horizontal visible iris diameter (HVID), which is the best in vivo estimate of true corneal width, follows a bell-shaped, normal distribution pattern, with average values between 11.4mm to 11.8mm. Eyes that fall outside of this range—because they are either too small or too large—often exhibit decentration issues when a standard soft contact lens is fit on eye.
Eyes Are Not Created Equal
If a patient’s anterior ocular health is found to be unremarkable, but a poor soft contact lens fit is observed, consider the above corneal anatomical features that may warrant a customized contact lens fit. We can’t expect all eyes to fall within normal limits. CLS
For references, please visit www.clspectrum.com/references and click on document #277.