A pinhole intraocular lens (Pinhole IOL) is a premium intraocular lens that applies the pinhole (stenopeic) principle to the lens surface. By allowing only thin central light rays through a small aperture and eliminating peripheral scattered light, it reduces the circle of blur on the retina and deepens the depth of focus.
The pinhole effect has long been used in ophthalmology in various forms such as pinhole occluders, glasses, and surgical miosis of the iris, but in recent years this concept has been introduced into intraocular lenses.
Advantages and disadvantages of the pinhole principle:
Multifocal intraocular lenses split incoming light into multiple focal points to provide near and distance vision, but are prone to glare and halos. Pinhole intraocular lenses have no diffractive rings and extend depth of focus through the pinhole effect, resulting in less glare and halos. However, because the aperture limits light, vision may decrease in dim environments.
Symptoms reported by patients who are candidates for pinhole intraocular lens implantation are as follows.
Eyes indicated for IC-8 intraocular lens
Mild astigmatism: Patients with corneal astigmatism less than 1.5 D.
Increased higher-order aberrations: Eyes with aberration >0.5 μm, potentially unsuitable for multifocal intraocular lenses.
Intermediate pupil size: Patients with mesopic pupil diameter ≤6 mm.
Eyes indicated for Xtrafocus intraocular lens
High irregular astigmatism: Moderate to severe irregular astigmatism due to keratoconus, post-trauma, post-penetrating keratoplasty, or post-radial keratotomy.
Photophobia: Intractable photophobia such as in Urets-Zavalia syndrome.
The IC-8 intraocular lens is a monofocal pinhole intraocular lens that uses the same principle as the KAMRA Corneal Inlay.
Structural features:
Insertion method:
Visual outcomes:
Optical advantages:
The Xtrafocus intraocular lens is a small-aperture IOL designed for piggyback implantation in the ciliary sulcus in pseudophakic eyes with an existing lens in the capsular bag. It received CE marking in 2016 and is undergoing FDA trials.
Structural features:
Visual outcomes:
Special notes:
Extended depth of focus intraocular lenses use diffractive or refractive optical designs to extend the depth of focus but may cause glare and halos. The IC-8 intraocular lens mechanically extends depth of focus through the pinhole effect and has no diffractive rings, so optical phenomena (glare, halos) are less common. It may be more suitable than EDOF lenses for eyes with macular disease or large higher-order aberrations.
Indications:
Contraindications/Cautious use:
Primarily intended for patients with moderate to severe irregular astigmatism due to keratoconus, trauma, full-thickness corneal transplantation, or radial keratotomy. Because the small aperture and opaque optic may significantly restrict peripheral vision, patient selection and thorough explanation are important.
The principle of the pinhole optical system is to increase depth of focus by limiting the numerical aperture. While a larger pupil increases the circle of confusion due to aberrations, a small aperture blocks peripheral rays (rays deviating from paraxial rays), thereby deepening the depth of focus.
Effects of small aperture on visual characteristics:
By being placed close to the nodal point of the eye, it has higher robustness against decentration (optical axis misalignment) compared to corneal inlays (e.g., Kamra inlay). This is one of the advantages of intraocular lenses.
The Xtrafocus intraocular lens received CE marking in 2016, but is awaiting an FDA clinical trial by Morcher in the United States. Reports on its use for intractable photosensitivity (Urets-Zavala syndrome) have shown significant improvement, and further case accumulation is expected.
Although at the case report level, it has been shown that retinal surgery can be performed without major obstacles in eyes with a pinhole intraocular lens, and future expansion of indications is being considered.
As a future challenge, the combination of an accommodative intraocular lens that preserves the posterior capsule and a pinhole optical system is being studied. Maintaining the integrity of the posterior capsule is essential for the function of accommodative intraocular lenses, and compatibility with prevention of posterior capsule opacification is being considered.
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Vukich J, Modi S, Fisher BL, Stonecipher K, Lin L, Michna M. Clinical Comparison of a Small-Aperture Intraocular Lens Versus a Monofocal Control. J Refract Surg. 2024;40(11):e824-e835. PMID: 39530983. DOI: 10.3928/1081597X-20240731-02 ↩
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Ho VWM, Elalfy M, Hamada S, Lake D. One-year visual outcome of secondary piggyback pinhole device implantation in pseudophakic eyes with irregular corneal astigmatism and iris trauma. Eye (Lond). 2022;36(4):812-817. PMID: 33888865. DOI: 10.1038/s41433-021-01537-7 ↩
Ang RET, Araneta MMQ, Cruz EM. Review of surgical devices using small aperture optics. Taiwan J Ophthalmol. 2022;12(3):282-294. PMID: 36248074. DOI: 10.4103/tjo.tjo_45_21 ↩
