How to ensure the highest level of safety & efficacy for refractive surgery

The field of refractive surgery has evolved remarkably over the past two decades, shifting from an innovative but niche specialty to a mainstream, evidence-driven discipline. 

However, despite substantial technological advancements and a growing body of clinical evidence, scepticism persists. Concerns about the safety and predictability of refractive surgery, especially when compared to contact lens use, are often rooted in outdated perceptions.^1-3  

Today, laser eye surgery demonstrates excellent safety profiles that not only rival but, in many cases, surpass long-term contact lens wear.^{2, 4}  

This article delves into four critical pillars of modern refractive surgery: epithelial mapping for keratoconus detection, Presbyond laser-based presbyopia correction, advanced techniques for implantable collamer lens (ICL) sizing, and cutting-edge methods for addressing complications.  

By detailing these advancements, we aim to foster greater collaboration between optometrists and refractive surgeons for the benefit of patient care. 

1 Epithelial Mapping in the Screening of Keratoconus 

There are now several optical coherence tomography devices available within clinical practice that have the ability to map the corneal epithelium. Epithelial mapping plays a pivotal role in keratoconus screening by leveraging the corneal epithelium’s adaptive properties to identify or rule out stromal irregularities.  

The studies reveal that the corneal epithelium adjusts its thickness to mask underlying stromal abnormalities, making epithelial mapping essential for detecting subtle irregularities that might evade traditional topography.^{5, 6} 

Using very-high frequency (VHF) ultrasound, it has been demonstrated that the thickness of the corneal epithelium is not uniform. Instead, on average the corneal epithelium is thicker inferiorly than superiorly, and thicker nasally than temporally.  

In keratoconus, epithelial thinning directly over the stromal cone, coupled with thickening in adjacent areas, forms a characteristic ‘doughnut’ pattern as seen in figure 1. This unique epithelial profile is highly indicative of keratoconus, even in cases where anterior corneal topography appears normal. The absence of such patterns, particularly over areas of steepening seen in topography, can confidently exclude keratoconus.  

Figure 1: Mean epithelial thickness profile for a population of 110 normal eyes (A) and a population of 54 keratoconic eyes (B)

For instance, in suspect cases where topographic abnormalities raised concerns, the presence of a normal epithelial profile ruled out keratoconus and allowed safe Lasik procedures, as highlighted in the studies reviewed.^7-10 

The specificity and sensitivity of epithelial mapping surpass conventional methods by addressing limitations in detecting subclinical keratoconus. When integrated with posterior elevation metrics from tools like the Pentacam or MS39, epithelial mapping significantly enhances diagnostic accuracy.  

The studies demonstrate that combining epithelial thickness profiles with posterior elevation data can identify early keratoconus masked by epithelial compensation, preventing potential postoperative ectasia.¹¹  

Furthermore, the detection of early keratoconus can facilitate the start of corneal cross-linking (CXL) to prevent further progression of the condition.  

Moreover, clinical outcomes support its efficacy: in cases with suspicious topography but normal epithelial profiles, Lasik stability and safety were comparable to those in eyes without keratoconus suspicion, with no reported cases of ectasia during follow-up.¹⁰ 

These findings validate epithelial mapping as a transformative adjunct, ensuring better patient selection and surgical outcomes in refractive surgery and avoiding potential complications, thus setting a gold standard for screening for keratoconus. 

2 Use of Laser Eye Surgery for Correcting Presbyopia in the Absence of Cataracts 

Presbyopia affects nearly everyone by middle age, manifesting as a decline in near vision due to the loss of lens flexibility. While glasses and contact lenses remain popular corrective options, surgical alternatives like Presbyond Laser Blended Vision and clear lens exchange (CLE) are gaining traction as permanent solutions for presbyopia. 

Presbyond: A non-invasive corneal approach 

Presbyond is a Lasik-based procedure for the correction of presbyopia. The method can correct myopia and hyperopia in presbyopic patients and employs a customised wavefront profile to extend depth of field by modulating spherical aberration while preserving binocular visual function and stereoacuity.  

Unlike traditional monovision, which compromises binocular vision by assigning one eye for near tasks and the other for distance, Presbyond can help maintain seamless vision across all focal points ensuring clear and continuous vision at distance, intermediate and near.^12-15  

Due to the spherical aberration induction and the low level of anisometropia induced (1.50 D), Presbyond Laser Blended Vision Lasik is well tolerated by 95% of patients,^12-15 whereas the reported tolerance for traditional contact lens monovision corrections is between 59% and 67% of patients.¹⁶ The other main aim of Presbyond Laser Blended Vision Lasik is to maintain safety and quality of vision.  

Therefore, the Presbyond ablation profiles were designed to control the induction of spherical aberration using a continuous aspheric profile, as opposed to intending to create corneal multifocality as in multifocal PresbyLasik.  

There are now 18 peer-reviewed publications worldwide on Presbyond consistently demonstrating the efficacy of Presbyond in myopic, hyperopic and emmetropic presbyopes.^{12-15, 17-25}  

In a cohort study of over 500 patients, 95% achieved an uncorrected distance visual acuity (UDVA) of 20/20 or better and a near visual acuity of J2 (N5). Satisfaction rates exceed 98%, with minimal reports of glare, halos or contrast sensitivity loss.^12-14  

In a study of commercial presbyopic pilots, for whom visual precision and quality at all distances is paramount, have successfully undergone Presbyond Lasik, with 100% meeting stringent aeromedical certification requirements.²¹ 

CLE and multifocal IOLs 

CLE for presbyopia is a surgical procedure that involves replacing the eye’s natural crystalline lens with an artificial multifocal intraocular lens (IOL), such as the Zeiss at Lisa trifocal, BVI FineVision, J&J Eyhance or Alcon Vivity.  

While these lenses offer spectacle independence, with studies reporting satisfaction rates between 87% to 100%. It is interesting to note that despite this level of satisfaction, only 54% to 72% of patients in these same studies achieved UDVA of 20/20.^26-29  

Multifocal IOLs are often associated with side effects, including glare, halos and reduced contrast sensitivity, particularly under dim lighting.³² These side effects, while manageable for many, can pose challenges for patients who are particularly sensitive or who engage in activities that require optimal vision in varying lighting conditions.  

While patient satisfaction remains high with multifocal IOLs due to careful preoperative counselling, fewer visual disturbances are seen with Presbyond make it an attractive alternative for younger presbyopic patients without cataracts.^{33, 34}  

In conclusion, while multifocal IOLs serve an important role in presbyopia correction, Presbyond offers a safer and less invasive alternative that preserves natural contrast sensitivity and accommodation.  

Furthermore, Presbyond is reversible and does not preclude future interventions, making it particularly suitable for patients whose visual needs may evolve over time. 

3 Using VHF Digital Ultrasound to Optimise the Safety of ICL Surgery 

During implantable collamer lens (ICL) surgery a lens is placed in the anterior chamber in front of the crystalline lens. ICL surgery is often the preferred solution for patients with high refractive errors or thin corneas that may be unsuitable for laser procedures.  

In the UK, the ICL is available to treat myopia up to -20.00 D, hyperopia up to +10.00 D and astigmatism up to 6.00 D. Several studies have demonstrated high predictability and favourable visual outcomes especially in the correction of high refractive errors.³⁵ ICLs are available in the following sizes 12.1, 12.6, 13.2 and 13.7mm.  

Selecting the correct lens size is crucial to achieving an optimal postoperative vault – the space between the ICL and crystalline lens – is critical for long-term safety. Vaults that are too low and close the crystalline lens increase the risk of cataracts, while excessively high vaults may lead to angle-closure glaucoma or endothelial cell loss.³⁶ 

Limitations of traditional sizing methods 

Many formulas are available to calculate the correct ICL size for implantation to achieve an optimal vault. Traditional ICL sizing formula relies on white-to-white (WTW) and anterior chamber depth (ACD) measurements.  

However, these methods rely on external measurements of the eye which lack precision, achieving vaults within ±100 microns in only 32% and 40% of cases, respectively. Calculations involving sulcus-to-sulcus (STS) measurements improve accuracy, with 50-55% of cases falling within this range.³⁷ 

VHF digital ultrasound ciliary body inner diameter based sizing 

VHF digital ultrasound measurement provide unparalleled precision by imaging the posterior chamber and measuring critical parameters like the ciliary body inner diameter (CBID), and STS lens-rise to calculate the optimal ICL size.  

A recent publication based on these measurements, demonstrate achieved vaults within ±100 microns in 62% of cases and within ±300 microns in 94%, vastly outperforming traditional methods.³⁸ 

This improvement not only reduces the need to perform a second procedure to exchange the ICL for a more appropriate size, but also enhances patient safety and satisfaction.  

By adopting VHF ultrasound to measure the eye and select an optimal lens size, refractive surgeons can ensure precise sizing, minimising the risk of complications and optimising long-term outcomes. 

4 Advanced Techniques for Correcting Surgical Complications 

Despite the remarkable advancements in modern refractive surgery, complications can occasionally arise, presenting challenges for both patients and surgeons. Irregular astigmatism, corneal haze and higher-order aberrations (HOAs) may occur due to factors like healing variability, surgical decentration or pre-existing ocular irregularities. 

 These complications, while uncommon, can significantly impact visual quality and patient satisfaction if not addressed effectively. Advanced therapeutic techniques have been developed, using precise technology and personalised approaches, to improve visual clarity and restore optimal vision. 

Trans-epithelial PTK 

Trans-epithelial phototherapeutic keratectomy (PTK) targets irregular astigmatism by selectively removing epithelial tissue and stromal peaks, smoothing the corneal surface. It is particularly effective for treatment of patients with irregularly irregular astigmatism.³⁹ 

Topography-guided ablation 

Topography-guided ablation reshapes the cornea based on detailed topographical maps, addressing regularly irregular astigmatism caused by decentration or small optical zones arising from refractive surgery.  

This technique often results in remarkable visual improvements, with many patients achieving 20/20 vision following the procedure.⁴⁰ 

Wavefront-guided treatments 

Wavefront-guided ablation corrects HOAs that contribute to glare, halos and loss of contrast sensitivity. By targeting these higher order aberrations, wavefront-guided treatments can enhance overall visual quality.⁴¹ 

By leveraging these cutting-edge techniques, surgeons can effectively address even the most complex cases, ensuring significant improvements in visual clarity and optimising patient outcomes. 

5 Contact Lens Safety vs Laser Eye Surgery 

While contact lenses remain a popular correction for myopia, hyperopia and presbyopia, their long-term safety pales compared to modern laser eye surgery.^1,2,4 Even the safest lenses, such as daily disposables, which minimise the risks associated with handling and maintenance, they do not entirely eliminate the potential for complications.⁴²  

Refractive surgery has evolved considerably over the years with advancements to technology and postoperative care improving both efficacy and long-term safety.⁴³  

Risks of contact lens wear 

Daily wear contact lenses are associated with a spectrum of complications, including microbial keratitis, corneal neovascularisation and giant papillary conjunctivitis.⁴ Microbial keratitis alone affects one to four per 10,000 wearers annually, with some cases resulting in permanent vision loss.⁴  

A comparison of post- Lasik patients and contact lens wearers found that after five years of daily soft contact lens wear there were significantly more cases of microbial keratitis with contact lenses, or approximately three times as many cases with contact lenses when compared with Lasik.  

In comparison, advancements in Lasik technology have led to fewer cases of flap related complications,⁴³ and improved preoperative imaging and nomograms have led to more accurate procedures with a lower risk of ectasia.⁴⁴  

Over a lifetime, the cumulative risk of losing two lines of best-corrected visual acuity (BSCVA) with contact lenses equals or exceeds that of laser surgery.² 

Safety of laser eye surgery 

In contrast, modern laser eye surgery offers an exceptional safety profile and repeatable outcomes. Small incision lenticule extraction (Smile) is the latest innovation in laser eye surgery and involves a keyhole method of correcting refractive error that is minimally invasive leading to a faster recovery. 

 A London Vision Clinic study involving 4,000 myopic Smile cases reported a 0.08% incidence of eyes losing two or more lines of corrected distance visual acuity (CDVA), with all affected patients regaining their vision after treatment.⁴⁵  

A recently published study treating myopia up to -14.00 D with Smile also demonstrated excellent visual outcomes and safety with no eyes losing two or more lines of CDVA.  

This level of safety and predictability positions laser eye surgery as a compelling alternative for patients seeking freedom from glasses or contact lenses, particularly those who have struggled with the demands or risks of long-term lens wear. 

Conclusion 

Modern refractive surgery combines cutting-edge technologies and meticulous surgical planning to deliver safe, effective and long-lasting results. From epithelial mapping to Presbyond, and from VHF ultrasound to advanced therapeutic techniques, the field has set a new standard in patient care. 

For optometrists, embracing these advancements is crucial in providing patients with informed guidance, ensuring optimal outcomes, and improving quality of life. Through collaboration, we can help patients navigate the expanding landscape of vision correction with confidence and clarity.  

• Professor Dan Z Reinstein is the founder and medical director of the London Vision Clinic, and holds Professorships at Columbia University Irving Medical Center, New York; Ulster University, UK; and Sorbonne University, France. He has been specialised in refractive surgery for over 30 years, has published over 215 peer-reviewed scientific papers and is the editor for the textbook The Surgeon’s Guide to Smile. 

• Financial disclosure: Consultant for Carl Zeiss Meditec (Jena, Germany), CSO Italia (Florence, Italy), and BVI Medical (Waltham, USA). Financial interest in ArcScan Inc (Morrison, USA) and holds patents in VHF digital ultrasound, Smile and Presbyond. 

References 

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