Limitations and Sources of Error: Patient Fixation Errors
For most of the instruments, the patient must look at a fixation light. The instrument is aligned based on this fixation. If the patient is not accurately fixating or if the patientΓÇÖs line of sight is quite different from the optical axis of the cornea significant errors can occur. For example, a symmetrical toricity (bowtie pattern) may appear as an asymmetrical toricity if the fixation is not centered.
