contact lens care
Solving Initial Gas Permeable Lens Nonwetting
BY SUSAN J. GROMACKI, OD, MS, FAAO
A common occurrence with brand new gas permeable (GP) contact lenses is nonwetting. When initial nonwetting occurs, patients usually note lens awareness, decreased comfort, a dry sensation and/or fluctuating vision following lens application and settling. In new lens wearers, the symptoms may mimic those of initial GP lens adaptation -- but for experienced GP wearers, the diagnosis is obvious. A quick biomicroscopic evaluation will confirm your suspicions.
Figure 1. Slit lamp evaluation reveals pitch on the surface of a GP
What Causes Nonwetting?
Most often, the poor initial wettability results from residual pitch on the front surface of the contact lens. Pitch is a waxy substance that attaches the lens button to the brass arbor during the cutting of the anterior and posterior lens curvatures. Labs also use pitch to polish residual lathe marks. Manufacturers attempt to remove pitch with a solvent, but they don't always succeed in removing it completely.
Other less common causes of initial GP lens nonwetting include excess heat during the manufacturing process, poor polishing techniques, an old diamond tool used for cutting and improper solvent exposure.
When pitch remains on the front surface of the contact lens it results in uneven flow or breakup of the tears and fluorescein anterior to the lens. A shiny patch of light (reflections from the slit lamp beam) is the classic appearance (Figure 1). The nonwetting is often so great that it obscures the view of the fluorescein pattern behind the lens.
You can resolve initial GP contact lens non-wetting that results from pitch in two simple ways: 1. Lightly polish the front surface of the lens using your modification equipment; 2. For those who do not have (and even for those who have) in-office modification tools, briefly rub the lens with an alcohol-based solvent cleaner.
Boston Laboratory Lens Cleaner (Polymer Technology) is available for purchase only by eyecare practitioners. Because of its strength, the manufacturer does not recommend it for daily use or for sale to patients. This cleaner contains a mixture of water-soluble surfactants with 10% 2-propanol.
To remove pitch from the surface of a GP contact lens, I place the lens in the palm of my hand and apply three to four drops of the laboratory lens cleaner. I rub the lens deeply for 10 seconds, then rinse it with tap water until the cleaner is removed. The solution is strong, and sensitive patients may react to even a small concentration of cleaner remaining on the lens, so I make sure to rinse the lens completely.
Next, I re-clean the lens with a daily cleaner and rinse. Finally, I rub conditioning solution into the lens in the same manner as I would a daily cleaner. If any non-wetting remains upon slit lamp examination, I repeat the process (or polish the lens with my modification equipment).
Once I remove the pitch, patients usually report optimal comfort and satisfaction. Only in rare cases do I need to return the contact lens to the manufacturer and order a new one.
Dr. Gromacki has a specialty contact lens practice as part of a multi-subspecialty ophthalmology group in Fishkill, NY, and has served as a faculty member at the University of Michigan Department of Ophthalmology and Visual Sciences.