Need to Know: Who Should Receive PPP for Aberropia?

The last article in this series discussed pinhole pupilloplasty (PPP) as a technique of using pinhole optics to correct higher-order aberrations (HOAs) by acting as a wavefront filter. It also discussed the advantages of PPP as compared to other devices, such as pinhole IOLs or pinhole corneal inlays. This article will discuss how to evaluate a patient for PPP and the technique to perform it.

Preoperative evaluation

Preoperatively, the first step is a good refraction and slit-lamp examination. Next, study the corneal tomography and total, lenticular, and corneal ocular aberrations. Then conduct a rigid gas permeable contact lens trial and test pinhole visual acuity with over-refraction.

Patients older than 40 years of age—when accommodative loss has already begun—may be considered for PPP, since the technique also necessitates lens extraction and IOL implantation. Once a PPP is decided, the Holladay pinhole device is used to check for the ideal pupil size that provides the best possible vision. The Holladay pinhole device is a metal occluder plate with multiple precut apertures ranging from 0.5 to 4.0 mm. The patient looks at the visual acuity chart 4.0 m away (or further) through different apertures to determine which gives best clarity of vision. Generally, for patients with a preoperative root mean square HOA less than 5 microns for a 6.0 mm pupil, a 1.5 mm pupil size is suitable. When the HOA is more than 5 microns, a 1.0 mm pupil size is preferred. The smallest size set for the pupil in PPP is 1.0 mm, as sizes below this will create diffraction effects. With the subject fixated, the coaxially sighted corneal light reflex is marked preoperatively with the patient sitting at the slit lamp.

The pinhole pupilloplasty technique

A pinhole pupilloplasty is then performed by making multiple single-pass, four-throw pupilloplasties, preferably under viscoelastic. Vertical bites are usually preferred over horizontal, as hand movement is easier. A 10-0 prolene suture on a long, thin, curved needle is passed from the inferior limbus to take a bite of the iris about 1.0 mm from the margin. A 30-gauge needle is then passed through a paracentesis (ensuring the needle does not get caught in the incisional stroma by moving it gently side to side) and passed through the pupil on the other side, 1.0 mm from the limbus. The first needle is docked into the 30-gauge needle and railroaded out through the incision, followed by a suture loop brought out through the incision using a Kuglen hook. The cut end of the suture is then passed through the loop four times and the sutures on either side pulled outwards to internalise and tighten the knot. The sutures are cut close to the knot using a microscissor.

While passing the needles, care should be taken to be gentle and to avoid tearing the iris. Thin needles should be used, and excessive tug on the prolene suture avoided. A microforceps, passed through a side-port incision to hold the iris firmly, helps facilitate an atraumatic process. Additional passes are made on either side of the pupil as required (typically three on either side). Once the pupil is small, the final positioning and sizing of the PPP is done carefully with a vitrector using a low cut rate. Centration should ideally align with the preoperative mark made on the cornea. It is important to position the patient’s head without any tilt to avoid parallax error. An endodiathermy may also help in adjusting centration and sizing.

Corneal magnification of the pupil size should be considered. For the average corneal radius of curvature and the average pupil distance from the corneal apex, the pupil image is bigger than that of the real pupil by about 8.6%. 

AS-OCT studies have shown that with the Zeiss Lumera microscope, if the pupil touches P1 all around, the size of the pupil is roughly 1.0 mm, and if the size is just larger than P1, pupil size is approximately 1.5 mm. However, the steepness of the cornea will affect the size of P1, making these only rough estimates. The Holladay device is autoclavable and can also be used in the OR to estimate pupil size.

For deep-set eyes, the surgeon can sit (temporally) and perform sequential horizontal SFTs to make access easy. In case of monocameral, vitrectomised eyes, a trocar anterior chamber maintainer may be used instead of viscoelastic to form the anterior chamber. This keeps the AC well-formed and allows better centration and sizing. Despite HOA persistence, visual quality improves postoperatively due to the achieved wavefront filtration.

A simple experiment can demonstrate the effect of a pinhole: A high cylinder is placed in front of the eye, and then vision is checked. Next, the Holladay pinhole device is used to determine the ideal pinhole size. The test can be repeated with higher cylinders, and improved clarity observed with the appropriately sized pinhole. The same test can also be done with spheres of increasing amounts, yielding similar outcomes. Varying combinations of sphere and cylinder are tested, and at even higher combinations, a smaller pinhole aperture improves vision.

Disadvantages of pinhole pupilloplasty

A PPP can limit the examination of the retina, leading to a recommendation of avoiding it in eyes with a history of retinal disease or if the patient is predisposed to retinal disease. Macular pathology will result in the PPP not working as expected and therefore should be avoided in such patients. This also applies to patients with multiple peripheral retinal degenerations or those who might need argon laser photocoagulation.

In all other patients, a thorough retinal examination is conducted preoperatively. Postoperatively, newer wide-angle fundus photography systems allow fundus examination to be done even through the PPP. Since the dilator muscles of the iris are still intact, mild retinal dilatation is still possible between the pupilloplasty knots on the two sides.

For cases requiring future retinal surgery, it is a simple procedure to open the PPP surgically to the desired diameter. If the retinal surgery requires silicone oil, retaining some of the SFT knots also helps decrease the incidence of silicone oil-associated glaucoma in these eyes.

A smaller pupil size may decrease retinal illuminance, affecting vision in dim light situations. However, this may be overcome by neuroadaptation. In addition, these patients are highly aberrated with very low vision that worsens further with pupillary dilatation, resulting in unmasking of more HOA in dim light. The PPP generally thus serves to improve their vision even in dim light situations. If any patient still complains of dim retinal illuminance, the pupil can be enlarged slightly with the YAG laser.

Dr Agarwal’s Eye Hospital has performed visual field testing and found it to be satisfactory in patients with PPP. They are able to function normally, and the hospital team hasn’t seen patients complaining of difficulty navigating or seeing objects in the peripheral field.

For all the above situations, if the patient is still experiencing difficulty, the size of the pupil can be enlarged either using an argon laser or a YAG laser. PPP does have a learning curve, which is possible to overcome with practice.

Despite the learning curve, PPP is a surgical procedure that can be useful in certain scenarios to provide good quality vision to patients with aberrated corneas. This is a surgery that the anterior segment surgeon is well advised to keep in their surgical armamentarium.

This is the sixth in a multipart tutorial on higher-order aberrations. Previous articles in the series can be found at escrs.org/eurotimes.

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.