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Pinhole pupilloplasty enhances visual acuity and image quality
The procedure is easy to perform, is cost-effective and does not require any special device.
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Both the front and back parts of the globe are essential for optimal vision. When we focus on the anterior segment of the eye, the cornea, pupillary opening and lens play a significant role in the quality of vision. With technological advances, lens-related issues such as cataract can usually be dealt with optimally. However, when we look at the cornea, especially when dealing with significant irregular corneal astigmatism, this can be a challenge even to the well-experienced corneal and anterior segment surgeon. In such cases with significant irregular corneal astigmatism, the surgeon may consider shifting the focus away from the cornea to the size of the pupillary opening.
With decreasing pupil size, the image quality improves and the aberrations decrease. However, with decreasing pupillary size, it needs to be emphasized that the precise positioning of the smaller pupillary opening becomes more important. Additionally, with a smaller pupillary opening, there is a reduction in retinal illuminance, and this may affect dim light situations. However, this can possibly be overcome with adaptation. Also, with decreasing pupil size, the depth of focus increases while there usually is no significant decrease in stereoacuity, and there is a reduction in the diffusion circle of light, thus increasing the image quality and, hence, improved vision.
In this column, Drs. Narang and Agarwal describe their surgical technique of pinhole pupilloplasty in dealing with select cases of irregular corneal astigmatism. Further studies with larger case series are important to fully evaluate the overall reproducibility, patient satisfaction and visual outcomes.
Thomas “TJ” John, MD
OSN Surgical Maneuvers Editor
Pinhole vision has always served as a benchmark for judgment of maximum level of visual acuity that can be attained in a patient with refractive error in the outpatient department. In patients with higher-order aberrations, pinhole vision cuts off the aberrated peripheral rays and helps to focus the more central rays. Working on a similar principle, pinhole IOLs have been designed and can be placed in the capsular bag as well as in the sulcus. Availability of pinhole IOLs can be a cause of concern, and under such circumstances, performing a pinhole pupilloplasty (PPP) can be helpful and cost-effective, as all it needs is a 10-0 suture and surgical judgment.
Source: Priya Narang, MS, and Amar Agarwal, MS, FRCS, FRCOphth
PPP is a surgical maneuver performed in cases of higher-order aberrations, and it has been documented to enhance the visual potential by inducing a pinhole effect (Figures 1 and 2). The pupillary aperture is targeted to be 1.5 mm. Studies have documented that with the decrease in size of pupillary aperture, the chord mu values also decrease. Ideally, a subject-fixated coaxial light reflex should be employed, but as the PPP procedure is performed under local anesthesia, a coaxially sighted corneal light reflex is employed.
The pinhole effect blocks distorted and unfocused light rays emanating from the peripheral cornea and isolates more focused central and paracentral rays through the central aperture, thereby enhancing visual acuity and image quality. The pinhole effect that can be achieved with surgical pupilloplasty reduces the circle of confusion on the retina and results in a sharper image. Secondly, when the pupil is narrowed down, the entire light spectrum enters the eye through the small central pinhole pupil. According to the Stiles-Crawford effect, light that enters near the center of the pupil produces a greater photoreceptor response as compared with the light that enters through the edges of the peripheral pupillary margin. Therefore, with the pinhole effect, the patient sees the object clearly and well illuminated due to greater photoreceptor sensitivity.
Technique
The PPP procedure is performed with the single-pass four-throw (SFT) technique as multiple attempts are needed to achieve a pinhole, and the SFT technique helps to achieve it with minimal passes through the anterior chamber (Figures 3 and 4).
In brief, SFT pupilloplasty is performed by passing a 10-0 suture attached to a long arm needle from the proximal iris defect threaded into the barrel of a 26-gauge needle introduced from the opposite side. A Sinskey hook is introduced inside the anterior chamber, and a loop is withdrawn. The suture end is passed through the loop four times, and both suture ends are pulled. The knot slides inside the eye and is cut with micro-scissors (Figures 5 to 7).
In PPP, coaxially sighted corneal light reflex is employed, and the Purkinje image P1 reflex emanating from the coaxial tube of the Lumera microscope (Zeiss) is enveloped by the pupillary margin. The procedure of SFT is repeated until adequate size of the PPP is achieved.
Discussion
The principle of achieving a pinhole effect has been employed at the level of the cornea and the level of the lens to enhance depth of focus. The authors attempted to achieve pinhole acuity in cases with irregular corneal astigmatism by modifying the pupil size, which is targeted to be around 1.5 mm in diameter. It has been contemplated that following PPP, there is a decrease in the values of chord mu (Figure 8), which translates into better and crisp vision in the postoperative period.
The major limitation that a surgeon can come across after doing a PPP is the scope of visualizing a fundus. With the procedure of SFT, it has been documented that after mydriasis there is sufficient dilation of the pupil to allow adequate fundus visualization. The advantages of a PPP are that it is easy to perform, is cost-effective and does not require any special device to perform the procedure.
- References:
- Narang P, et al. Eur J Ophthalmol. 2017;doi:10.5301/ejo.5000922.
- Narang P, et al. J Cataract Refract Surg. 2019;doi:10.1016/j.jcrs.2018.12.007.
- Narang P, et al. J Cataract Refract Surg. 2019;doi:10.1016/j.jcrs.2019.02.037.
- For more information:
- Amar Agarwal, MS, FRCS, FRCOphth, can be reached at Dr. Agarwal’s Eye Hospital and Eye Research Centre, 19 Cathedral Road, Chennai 600 086, India; email: aehl19c@gmail.com.
- Priya Narang, MS, can be reached at Narang Eye Care & Laser Centre, Ahmedabad, India; email: narangpriya19@gmail.com.
- Edited by Thomas “TJ” John, MD, a clinical associate professor at Loyola University at Chicago, and in private practice in Oak Brook, Tinley Park and Oak Lawn, Illinois. He can be reached at email: tjcornea@gmail.com.
Disclosures: Agarwal, Narang and John report no relevant financial disclosures.