Preferred Retinal Locus (PRL) & Eccentric Viewing: Shifting Gaze Past Macular Scars

In an eye with an absolute central scotoma of $10^\circ$ diameter, attempting to look 'straight' at an object places the image directly onto necrotic scar tissue where zero functioning photoreceptors survive.

To read or recognize faces, the patient must identify an intact patch of parafoveal retina possessing sufficient cone density—most commonly in the superior retina (looking downward) or nasal retina. This functional island is designated the Preferred Retinal Locus (PRL).

Identifying and stabilizing a patient's PRL is performed using a Scanning Laser Ophthalmoscope (SLO) Microperimeter (such as the CenterVue MAIA):

$$\text{Eye Tracker Sampling: } 25\ \text{Hz} \quad [\text{Micron-accurate Retinal Stimulus Projection}]$$

The microperimeter maps the exact boundaries of the scotoma onto a live infrared fundus image while calculating Fixation Stability (Bivariate Contour Ellipse Area, BCEA). Through audio biofeedback training, patients learn to lock onto the PRL with rock-solid stability within 4 to 8 rehabilitation sessions.

In clinical practice, low-vision specialists train patients using the Clock-Face Method:

'Imagine a large clock in front of you. Look at the number 12, but pay attention to what you can see down at the center of the clock.' If the 12 o'clock gaze brings words into clear view, the patient has established a superior retinal PRL.

In certain patients, neuro-optometrists incorporate Base-In or Yoked Prisms into spectacle reading lenses, optically bending light away from the dead central fovea directly onto the trained PRL without requiring unnatural, fatigue-inducing neck or head tilting.