Alignment Fit for Central Zone #

Alignment fit is described as the base curvature that most closely parallels the cornea. There is an evenly thin tear film under the lens, with clearance/edge lift along the periphery. Visually you will see an even, uniform, light green appearance of fluorescein over the entire lens, with thin edge lift indicated by lighter green ring. ¹

During evaluation, your aim is the above mentioned alignment fit- a uniformly thin tear layer over the central part of the cornea/lens. To assess the central fit, simply compare the amount of visible green in the central zone.

Steep Central Fit #

If there is more green in the central zone than the mid-peripheral one, the lens is too steep. This lens will also most likely suction onto the cornea.

Objective findings like Lens Riding too Low, Central Pooling with Ring Touch, Unusual Refraction Change, Bubble Under Lens also supports the steep Fluorescein findings.

Subjective feedback like Pain After Lens Removal or a Burning Discomfort also supports the steep Fluorescein findings. Fluctuating refraction due to the access fluid scattering the light rays will also be present.

Flat Central Fit #

If there is less green (or even black) in the central zone than the mid-peripheral zone, the lens is too flat. The lens is literally pivoting on the cornea apex and long term there will develop scarring on the center of the cornea.

Objective findings like Lens Riding to the Side, Lens Riding too Low, Lens Stays Under the Upper Lid, Lens Displaced by Lid, Lens Falls Out, Central Touch, Fine Stipple Stain, or Unusual Refraction Change also supports the flat Fluorescein findings.

Subjective feedback like discomfort due to the excess edge lift, Difficulty Looking Up, also supports the flat Fluorescein findings.

1. Hom MM and Bruce AS. Manual of contact lens prescribing and fitting, Third Edition. 2006:167-201