15 Pinhole Pupilloplasty

Summary

The chapter explains the concept and applicability of performing pinhole pupilloplasty in cases with higher order irregular corneal astigmatism. The pinhole effect channelizes the incident light through the narrow aperture and blocks the peripheral stray light induced from peripheral irregular cornea.

15.1 Introduction

Corneal astigmatism may be of the regular or irregular variant. With regular variant, good visual acuity can be attained either by correction with glasses or surgically by performing astigmatic keratotomy. The irregular variant is difficult to correct with spectacles due to induced aberrations. Therefore, for such cases, other interventions like placing the corneal inlays and pinhole intraocular lenses (IOLs) have been suggested. The concept of pinhole or small aperture optics has established a definite value in the field of ophthalmology. ^{1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 , 9 , 10}

Pupilloplasty ^{11 , 12 , 13 , 14 , 15} is usually performed to achieve adequate pupil shape and size, following any disruption in the pupil architecture. Pinhole pupilloplasty (PPP) is a concept put forward to narrow down the pupillary aperture and achieve a pinhole kind of functionality, thereby benefitting patients suffering from higher order irregular corneal astigmatism. David Chang suggested the terminology of PPP (▶Video 15.1).

15.2 Principle

By creating a pinhole or a small aperture (▶Fig. 15.1), the impact of higher order aberrations caused by irregular corneal astigmatism can be minimized. The pinhole allows passage of rays of light from the central aperture and blocks the rays emanating from the peripheral irregular cornea.

Another possible mechanism could be “the Stiles–Crawford effect” ^{16 , 17} of the first kind (▶Fig. 15.2). In this phenomenon, the light entering the eye near the edge of the pupil produces a lower photoreceptor response compared to the light of equal intensity entering near the center of the pupil. Therefore, it is conceptualized that the photoreceptor response is significantly lower than expected by the reduction in the photoreceptor acceptance angle of light entering near the edge of the pupil. The Stiles–Crawford effect of the first kind is the phenomenon by which light passing through the periphery of the pupil appears to be dimmer than light passing closer to the pupil center.

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