It is important that for the first fitting, you leave the contact lens to sit on the eye for a few minutes to allow it to settle down, before assessing the fit. For the aftercare appointment, remember to tell your patients that they need to wear their contact lens for at least an hour before the examination! 

An acronym to remember when assessing the fit of soft contact lens is 2CMAPRS
  • Coverage
    • Is there at least 0.5-1.0 mm of coverage extending past the limbus in all gazes? 
  • Centration
    • Is the lens decentred? If yes, which direction; nasal, temporal, inferior or superior?
    • It is important that the limbus does not rub against the edge of the lens to prevent corneal and gimbal trauma
  • Movement
    • Assess when px blinks normally, and when they move their eyes left to right (lag) and up and down (sag)
    • Ideal amount of movement is 0.3-0.7mm; too much movement can cause poor acuity and decreased comfort. However movement of the lens is important as it promotes post-lens tear film exchange. 
  • Acuity
    • Is the px happy with the vision when using the contact lens? i.e. does the vision with the contact lens meet the patient's visual demands and needs?
    • If not, refine VA using over-refraction. Consider toric lens if patient's astigmatism is >0.75D.
  • Push-up
    • When pushing the lens upwards using the patient's inferior lids, is the lens easily moved? Does it rapidly and reliably return back to the central location? 
  • Rotation (if toric contact lens)
    • Using the reference mark on the lens, is the lens rotated? If yes, estimate the direction and degree of rotation.
      • <10 degrees of rotation is acceptable
      • ≥10 degrees of rotation, use LARS (left add, right subtract to the prescribed axis)
  • Stability (if toric contact lens)
    • Again, using the reference marks on the lens, assess whether the lens the stable with each blink. i.e. is the degree of rotation constant between normal blinks. 
    • If lens is not stable, reassess lens and consider a different type.
      • Causes of unstable lens include; BOZR is too flat, lens diameter is too small or the lid-lens interaction is causing the stabilisation methods to fail.

Remember, it is important that the lens completely covers the cornea and does not rub against the limbus and a bit of movement in the lens is essential, but too much and the patient won't like it. If the toric lens is unstable, consider a different lens type!

Don't forget to assess the quality of the lens itself on slit lamp! Look for any lens deposits and even tears and scratches! 

Keep these in mind when assessing the fit of the contact lens on your patient. As you see more patients, these will come naturally to you, and just by looking at the lens, you will already have an idea if the lens is suitable for your patient.



References
  • https://www.ncbi.nlm.nih.gov/pubmed/8728492
  • https://www.ncbi.nlm.nih.gov/pubmed/11352451
  • https://www.ncbi.nlm.nih.gov/pubmed/19167261