Pinhole Pupilloplasty for Keratoconus

Irregular astigmatism and higher-order aberrations (HOAs) degrade visual quality, and because their presentation varies widely among patients with keratoconus, visual rehabilitation can be challenging. This article briefly describes our experience with pinhole pupilloplasty (PPP) for the rehabilitation of keratoconic eyes.

Pinhole Sizing

We have performed PPPs in eyes with keratoconus and corneal ectasia, including those with intrastromal corneal ring segments (Intacs, Addition Technology; Figure 1); those with a history of deep anterior lamellar keratoplasty; and eyes with corneal scarring, high amounts of irregular astigmatism, or HOAs. Both the size and the location of the pinhole can be customized. Preoperatively, the patient subjectively chooses the pinhole size that provides them with the best visual acuity. A Holladay pinhole (Epsilon) is used for this purpose. It has pinhole sizes ranging from 0.5 to 4 mm in 0.5-mm increments.^1-3 Our patients usually choose a 1- or 1.5-mm pinhole. In on our experience, the higher the HOA wavefront error is, the more likely the patient is to choose the 1-mm size.

The pupil size achieved intraoperatively is measured with a calibrated reticle in the microscope eyepiece or with a Kallonikov gauge (Epsilon), which has 1- and 1.5-mm apertures on a scale that can be introduced into the anterior chamber.

Single-Pass Four-Throw Pupilloplasty

Although any pupilloplasty technique may be used for a PPP, we prefer a single-pass four-throw pupilloplasty because it is relatively simple and requires only one pass through the anterior chamber to achieve closure.

A 9-0 or 10-0 polypropylene suture is passed through the proximal and distal iris tissue, and the suture needle is inserted into a 26-gauge needle introduced through a distal paracentesis. The suture needle is pulled out, a Lester hook is introduced through the same paracentesis, and a suture loop is pulled out through it. The suture end is passed through the loop four times in the same direction, and then both suture ends are pulled, drawing the four throws into the anterior chamber and approximating the proximal and distal iris tissue. The suture ends are cut with end-opening microscissors.

During PPP, a single-pass four-throw pupilloplasty is performed at least three times because the pupil must be closed from all quadrants. The newly formed pupil is centered on the Purkinje I reflex, which acts as the marker for centration. Unequal pulling during the pupilloplasty can obscure the Purkinje I reflex with iris tissue. If this occurs, the tissue obscuring the reflex may be cut away with a vitrectomy probe using a low cut rate and a low vacuum setting.

When a PPP Is Not Centered

The PPP is usually centered on the Purkinje I reflex. Centration on a scar, however, is not a viable option. In eyes with central corneal scarring, the PPP may be centered on the closest available clear cornea, away from the scar.

In our study of off-center PPPs in eyes with scarred corneas, the visual acuity of every patient improved, yet HOA values obtained before surgery did not change.¹ The reason is that the PPP leaves the corneal surface essentially unchanged; instead, it alters visual potential principally by manipulation at the iris plane.

PPP Grading

PPPs are classified into four grades according to their distance from the corneal vertex³:

• Grade 1. A central PPP is centered on the Purkinje I reflex emanating from the corneal surface.
• Grade 2. A paracentral PPP is placed 2 mm from the vertex normal, which is the visual axis.
• Grade 3. A decentered PPP is placed 3 mm from the vertex normal. Although decentered, it still lies over the IOL optic.
• Grade 4. An eccentric PPP is positioned at least 4 mm from the vertex normal, so eccentric that the IOL optic does not cover the newly positioned pupil. A partial-thickness scleral flap and a sclerotomy with a 23-gauge needle are therefore made on the side where the PPP will sit, and the haptic of a three-piece IOL is externalized through the sclerotomy and tucked into a scleral pocket created with a 26-gauge needle, as in a glued IOL procedure.

Wavefront-Guided PPP

In patients with keratoconus, a Zernike analysis of the wavefront map (Pentacam, Oculus Optikgeräte) identifies the sweet spot (ie, the least aberrated part of the cornea; Figure 2). With the Zernike map superimposed on the clinical image, the exact location for PPP centration can be marked on the corneal surface.

Centering the PPP there puts it over the least aberrated area, and the PPP itself offsets peripheral corneal aberrations by channeling the central rays of light.

A Paradigm Shift

Deep anterior lamellar keratoplasty, penetrating keratoplasty (PKP), and intrastromal corneal ring segments can restore vision to patients with keratoconus, but these modalities tend to induce astigmatism. That astigmatism should not be neutralized with arcuate keratotomy or limbal relaxing incisions, because the cornea is highly aberrated and the potential for crisp vision is limited. A PPP can help these patients achieve a higher quality of vision. Rather than treat the scar or opacity, a PPP bypasses it by creating a decentered pinhole pupil.

A PPP allows many patients to avoid undergoing a PKP or deep anterior lamellar keratoplasty, the procedures' associated complications, and the long course of postoperative medication entailed. Not every case, however, can be managed with a PPP. Some require keratoplasty,

An Adjustable and Reversible Procedure

If the pinhole is not optimally positioned, its location can be adjusted. If progressive corneal thinning later necessitates a PKP, the procedure can be performed with the PPP in place, and the pinhole may reduce the visual effects of PKP-induced astigmatism.

Conclusion

PPP can be a technically demanding procedure to perform. A high level of comfort with pupil and iris repair techniques is essential for managing complex cases.

In our series, only approximately 10% of patients reported decreased illumination at twilight or at night. For patients who experience difficulty in dim light, the pinhole aperture can be enlarged with an Nd:YAG laser pulse at the edge of the PPP.