Knowing Iris Repair: Pinhole Pupilloplasty Instead of Keratoplasty

There are many conditions where the presence of a corneal scar necessitates a penetrating keratoplasty (PK). When the scar traverses through the centre of the visual axis, the indication for a PK is generally considered absolute for visual rehabilitation. Other conditions where a PK is not a must but still often opted for include a scar close to the visual axis and a central scar almost but not fully covering the pupil. In all these cases, the higher-order aberrations are quite significant; and even if the visual axis is spared, a PK is often still performed to attain a more uniform surface and, thereby, better visual quality.

However, PK has its own disadvantages, including the risk of permanent vision-threatening complications such as expulsive haemorrhage, endophthalmitis, and traumatic wound dehiscence. In addition, other intraoperative complications such as difficult surgery, risk of vitreous loss and lens, or IOL expulsion, as well as postoperative complications (such as irregular astigmatism, rejection, glaucoma, surface- and suture-related complications, and Urrets-Zavalia syndrome), can result in limitation of vision or progressive loss of vision, pain, and cosmetic disfigurement.

Primary or secondary comorbidities such as corneal neovascularisation and peripheral anterior synechiae are often seen in such patients, and performing corneal transplantation in such conditions can greatly increase the chances of rejection of the graft. Thus, PK in patients with corneal scars on or near the visual axis is not always an uncomplicated way forward. The pinhole pupilloplasty (PPP) technique is an option to overcome the disadvantages of PK in such situations, and it can give visual results as good or even better than a PK would have despite the persistence of the corneal scar.

Preoperative marking and assessment

Patients with corneal scar very close to the visual axis causing irregular astigmatism may undergo PPP instead. The desired location of the pinhole pupil is marked preoperatively by slit lamp examination over the coaxially sighted corneal light reflex (CSCLR). While marking, the patient fixates with the eye on the slit lamp light kept perpendicularly and with the other eye occluded. If the CSCLR overlies a large scar covering the pupil, the pinhole pupil is shifted slightly.

The size of the pinhole pupil is determined preoperatively by using the Holladay pinhole device, which essentially consists of an opaque disc with a series of different-sized apertures created on a metal template. The patient will view the visual acuity chart through the template and try different apertures. The desired pinhole pupil size is the one the patient sees most clearly through. The Holladay device is autoclavable and can also be used intraoperatively to assess the created pupil size. However, as the corneal magnification factor comes into play intraoperatively, the apparent size of the pupil created is larger than the real size by about 8 to 10%. Therefore, the real pupil size may be created very slightly smaller than that estimated by the Holladay device.

Surgical technique

It is important to preoperatively mark the CSCLR while still avoiding the scar. During surgery, this mark acts as a guide to position the eye under the reflection of the operating microscope lights.

Since the pupil will be fixed into a pinhole size and multiple needle passes go through the iris close to the pupil, the patient undergoes phacoemulsification with IOL implantation in the same sitting just before iris surgery. The anterior chamber (AC) is then filled with viscoelastic in an eye with an intact posterior capsule. In a vitrectomised eye, a trocar anterior chamber maintainer is used. The patient’s head and eye position are first adjusted to avoid parallax error by bringing the first and fourth Purkinje images to overlap. This is easily possible if the scar does not cut across the first Purkinje image.

Pupilloplasty is then performed using any preferred technique, such as the single-pass, four-throw pupilloplasty (SFT) or the modified Siepser knot technique. For SFT, essentially a 10-0 or 9-0 polypropylene suture on a straight needle is drawn through the proximal and distal iris segments, following which a loop of the suture from ahead of the proximal pass moves through the distal paracentesis. The distal end of the suture is then cut and passed through this loop four times, and the two suture ends on either side of the limbus are drawn apart to pull the loop into the AC and tighten the knot. A few knots are taken consecutively next to each other on either side of the pupil to decrease the pupil size to the desired diameter. The pupil location is also shifted to the desired spot. It is important to ensure a careful needle pass to avoid tearing the iris stroma. Knots are cut close without long ends.

With the Zeiss Lumera™ microscope, if the pupil touches the Purkinje image (P1) all around, the size is around 1.0 mm, and if the pupil is just slightly larger than the P1, the size of the pupil is approximately 1.5 mm. In case the pupil becomes too small, it can be enlarged to the desired side using either a retinal endodiathermy probe (iridodiathermy) applied to the iris stroma on the side needing pupil enlargement or a vitrector for trimming iris tissue gently and carefully using a low cut rate and vacuum. A not-so-round pupil can similarly be made more circular using either the vitrector or endodiathermy probe.

Pinhole optics

A pinhole narrows the beam of light entering the eye, thereby decreasing image blurring on the retina. It decreases peripheral aberrations and increases visual acuity and depth of focus. The decreased pupillary size also lowers the chord mu value. Pinhole optics may be used non-surgically via pinhole glasses or contact lenses. They may also be implanted into the eye either within the cornea—e.g., the Kamra™ inlay (Acufocus)—or as an intraocular lens, such as the IC-8 Apthera (Bausch + Lomb) and the XtraFocus (Morcher). For these implants, the aperture comes in fixed sizes. Additionally, the location of the aperture in pinhole IOLs is generally controlled by IOL centration within the bag. Intracorneal synthetic devices such as the Kamra may be associated with haze and other complications.

The advantage PPP holds is the individual customisation of the location and size of the pupil. It can be performed by anyone without large additional costs, such as those associated with flap creation or IOLs, and the pinhole size is easily reversible postoperatively if required, as a YAG laser can be used to enlarge the pupil. A disadvantage is the greater learning curve needed for surgery.

A disadvantage of all pinhole optics also includes possible decreased retinal illumination, diffraction rings, and mild visual field narrowing. Therefore, excessively small pupil size to less than 1.0 mm should be avoided to retain a balance between vision, illumination, and field.

Dr Soosan Jacob is Director and Chief of Dr Agarwal’s Refractive and Cornea Foundation at Dr Agarwal’s Eye Hospital, Chennai, India, and can be reached at dr_soosanj@hotmail.com.