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Investigating the correlation between scleral spur angle and intraocular lens tilt
Journal of Cataract & Refractive Surgery 52(6):p 582-587, June 2026. | DOI: 10.1097/j.jcrs.0000000000001877
According to the paper, the Vtx-SSA quantifies the angular displacement of the ocular system along the nasal-temporal axis. The core finding is that this specific measurement, easily obtained during routine optical biometry, is highly predictive of postoperative horizontal intraocular lens (IOL) tilt ($r^2 = 0.97$).Accurately anticipating IOL tilt is a significant hurdle in optimizing refractive outcomes, particularly when assessing a patient's suitability for premium IOLs or calculating toric lens power. Because postoperative tilt can induce astigmatism and degrade image quality, using the Vtx-SSA as a preoperative screening tool provides a practical alternative to measuring crystalline lens tilt—which often requires specialized equipment and can be hindered by small pupils.
More explanation from quickguide.org:
To understand the Vertex-Scleral Spur Angle (Vtx-SSA), it helps to break down the anatomy it references and why it is becoming a highly valuable metric in modern optical biometry.
1. The Anatomical Baseline: The scleral spur is a ring of dense connective tissue located where the cornea transitions into the sclera. It serves as a crucial anchor point for the ciliary body and the iris. If you were to draw a straight line connecting the scleral spur on the nasal side to the scleral spur on the temporal side, you would establish the anatomical baseline of the anterior chamber. Because the ciliary body (which holds the capsular bag) is attached right at this junction, this scleral spur plane dictates the physical orientation of the crystalline lens.
2. The Optical Baseline: The Corneal Vertex. When a patient looks straight ahead into a biometer, the machine uses a fixation target. The corneal vertex is the highest point of the cornea, and the line projecting straight out from this point (the vertex normal) serves as a reliable approximation of the patient's visual axis—the actual path light travels to hit the fovea.
3. The Angle- The human eye is not perfectly symmetrical; the optical anatomy is almost always slightly offset from the actual line of sight. The Vtx-SSA quantifies the tilt of the eye's internal anatomy relative to how the patient actually looks at the world. Technically, the Vtx-SSA is the angle between two perpendicular lines: A line extending 90 degrees perfectly straight up from the scleral spur connection line. A line extending 90 degrees perfectly straight out from the corneal vertex plane.
Why Does This Matter Clinically? Historically, anticipating how an intraocular lens (IOL) would tilt after surgery was difficult because imaging the full equator of the crystalline lens requires specialized, highly penetrating swept-source OCTs. The Vtx-SSA solves this by using easily visible anterior chamber landmarks to calculate that same internal tilt.Because the capsular bag is structurally tethered to the anatomy just behind the scleral spur, its resting orientation is closely aligned with the scleral spur plane. If a patient's entire anterior anatomical segment is tilted relative to their visual axis (indicated by a large Vtx-SSA), the implanted IOL will inherently adopt that same tilt.Implications for Premium IOLs and Diagnostics.
Understanding this angular displacement is critical when analyzing biometric data or building clinical decision support systems for premium IOL suitability.
Aberrations: When an IOL tilts, it does not sit completely flat against the incoming light. This physical tilt induces optical artifacts—primarily regular astigmatism and higher-order aberrations like coma. If diagnostic tools like the iTrace reveal elevated internal coma postoperatively, an anatomically driven IOL tilt is often the root cause.Toric and Multifocal Screening: Precise alignment is paramount for premium lenses. A high preoperative Vtx-SSA acts as a red flag. The resulting postoperative IOL tilt can degrade the visual quality of a multifocal lens or alter the effective power of a toric lens, potentially leading to refractive surprises and patient dissatisfaction.By measuring the Vtx-SSA, clinicians can preoperatively flag eyes with "tilted anatomy" and adjust their surgical planning accordingly.
Summary of the study:
Objective
The study aimed to determine if the preoperative vertex-scleral spur angle (Vtx-SSA)—a metric quantifying how much the eye's anterior anatomy deviates horizontally from the visual axis—can reliably predict postoperative horizontal intraocular lens (IOL) tilt following routine cataract surgery.
Methodology
Participants: 72 eyes from 72 patients who underwent uneventful cataract extraction and IOL implantation.
Measurements: Researchers used the Anterion SS-OCT to measure the preoperative Vtx-SSA. They used the Eyestar 900 SS-OCT to measure preoperative crystalline lens tilt and postoperative IOL tilt.
Analysis: To isolate specific predictive factors, the researchers decomposed the overall lens tilt vectors into independent horizontal and vertical components.
Key Findings
Horizontal Dominance: Tilting of the IOL along the horizontal axis was the primary source of deviation, accounting for nearly 80% of the total tilt magnitude.
High Predictability for Horizontal Tilt: The preoperative Vtx-SSA demonstrated a very strong positive correlation with postoperative horizontal IOL tilt (r2=0.97). Preoperative horizontal crystalline lens tilt showed an equally strong correlation (r2=0.97).
Role of Axial Length: Both the Vtx-SSA and horizontal IOL tilt were negatively correlated with the eye's axial length, indicating that shorter (more hyperopic) eyes tend to exhibit larger angles of horizontal tilt.
The Vertical Limitation: IOL tilt along the vertical meridian was notably harder to predict. It showed a comparatively weaker correlation with preoperative vertical crystalline lens tilt (r2=0.78) and demonstrated absolutely no correlation with axial length (r2=0.00). The Vtx-SSA does not account for vertical tilt at all.
Clinical Conclusions
The Vtx-SSA is an effective, easy-to-obtain preoperative surrogate for estimating the majority of postoperative IOL tilt (the horizontal component).
This is highly useful for cataract surgeons because estimating postoperative tilt usually requires measuring the crystalline lens—a difficult process that requires specialized imaging devices and is often hindered if the patient has small pupils. Measuring the Vtx-SSA bypasses this hurdle, allowing clinicians to screen for eyes at risk of clinically significant IOL tilt (which can degrade image quality and induce astigmatism), provided they remember it does not factor in vertical tilt deviations.
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Influence of Nd:YAG laser capsulotomy on toric intraocular lens rotation and change in cylinder power
Journal of Cataract & Refractive Surgery 50(1):p 43-50, January 2024. | DOI: 10.1097/j.jcrs.0000000000001306
Objective
The study investigated whether performing an Nd:YAG laser capsulotomy to treat posterior capsule opacification (PCO) induces physical rotation, tilt, or decentration in implanted toric monofocal intraocular lenses (TIOLs), and whether this physical shift alters the lens's cylinder power.
Methodology
Participants: A prospective case series involving 41 eyes (from 41 patients).
Measurements: Clinicians evaluated the eyes before the Nd:YAG laser capsulotomy and 1 month after.
Diagnostic Tools: A Scheimpflug camera was used to measure TIOL tilt and decentration. Ray tracing aberrometry was utilized to measure TIOL axial rotation and any induced changes in cylinder power.
Key Findings
Rotational Shift: Following the capsulotomy, absolute TIOL rotation was measured at 2.75 ± 1.94 degrees. Rotational misalignment increased from an average of 4.65 degrees pre-procedure to 6.97 degrees post-procedure.
Cylinder Power Alteration: The absolute change in cylinder power was 0.34 ± 0.22 Diopters (D), increasing from an average of 0.24 D before the procedure to 0.56 D after.
Tilt and Decentration: The procedure caused a significant decrease in both horizontal and vertical IOL tilt, alongside a significant increase in overall decentration.
Risk Factors: The amount of time that had passed since the original cataract surgery (average 33 months) and the horizontal decentration of the IOL were identified as independent factors affecting how much the lens rotated after the laser treatment.
Clinical Conclusions
Nd:YAG laser capsulotomies can physically disrupt the resting position of a toric IOL, leading to minor rotation, tilt, and decentration that ultimately alters its corrective effect on corneal astigmatism. While the observed changes in this study were generally considered clinically insignificant, surgeons should be mindful that early capsulotomies may pose a higher risk of inducing rotational misalignment in patients with toric lenses
