Presbyopia / SPO - 3.1.3. Efficacy and Complications of Surgery at the Corneal Plane

3.1.3. Efficacy and Complications of Surgery at the Corneal Plane

Manuela Cidade

ALM-Oftalmolaser, Lisboa, Portugal

INTRODUCTION

Corneal surgery has been considered for several years as one of the most promising approaches for the correction of presbyopia. Calling on several methods, it is the least invasive and potentially the safest approach.

Most current procedures seek to increase depth of field, but it is possible to resort to several therapeutic strategies, from the use of Monovision, with intervention to be performed in one eye, with the purposeful induction of ametropia (LASIK, PRK, IC), or bilaterally, correcting any ametropia for distance that may exist in the eye, to bilateral presbyopic correction strategies performed with Laser Excimer (central and peripheral PresbyLASIK with induction of multifocal profiles) or using various types of IC. There are also techniques that intend to modify the corneal profile by altering the structure of the stroma (conductive keratoplasty, thermal laser keratoplasty, intrastromal procedures performed with femtosecond laser – Intracor and, more recently, Cross Linking).

The multiplicity of procedures in use in clinical practice and the improvements successively introduced therein show that the ideal solution is not yet found. In fact, all techniques require a good adaptation of the patient to the new refractive state and require some degree of neuroadaptation, and a compromise between distance and close vision of the patient is usually used (Table 1).

If in all refractive surgery situations it is important to evaluate the patient in advance, namely the psychological profile, the needs and the expectations, these aspects of the analysis are particularly important in the preliminary examination of candidates for presbyopia surgery.

MONOVISION

The use of Monovision as compensation for presbyopia has been used for many years with partially satisfactory results. It is based on the capacity of interocular suppression of the monocular blur, when in binocular vision¹. This goal is more difficult to achieve in patients who already have high anisometropia or poor stereopsis². The correction is made so that one eye is focused for far and the other for close, being that the dominant eye is usually used for distance vision and the non-dominant for near vision.

This type of correction was particularly welcomed among contact lens wearers, with several works that attribute success rates ranging from 50 to 76%^3,4. These analyses also demonstrated a reduction in binocular visual acuity and stereopsis.

With the advent of refractive surgery, especially after the introduction of Excimer laser treatments, this solution gained more expansion, reaching even higher levels of satisfaction (72% to 96%)^5,6.

The observed reduction in distance binocular visual acuity is more evident when the dominant eye (used for distance vision) has an oblique residual astigmatism⁷, hence the importance of the previous existence or the attainment of an emmetropia in the dominant eye⁸. This imperative led to a greater number of reinterventions in the dominant eye (21%) than in the non-dominant (7%) according to the results of this group. In another study, carried out by M. Garcia-Gonzalez, this difference was not so evident⁹. Interocular suppression of the blurred image is less effective in poorly lit environments¹⁰, so in these conditions the reduction in visual acuity for far is more pronounced.

Contrast sensitivity is also reduced in patients with Monovision corrected with contact lenses¹¹, and there seems to be a direct relationship with the degree of monocular blurring, since over 2.5 D of anisometropia the effect of binocularity is lost due to the suppression of the image of the blurred eye. Wright¹² evaluated the contrast sensitivity of patients in whom Monovision was induced by PRK and confirmed that the change produced was similar to that induced in patients whose refractive target was emmetropia. The same happens when the procedure used is LASIK, since when the induced myopia is equal to or less than 1.5 D the values of contrast sensitivity in binocular vision are similar to those of the general population⁹. The adaptation phase generally lasts 6 to 8 weeks but the adaptation period may be much longer.

The most limiting effect associated with Monovision is the decrease in stereopsis that occurs in all patients treated with contact lenses^3,5,13, also present, although apparently less evident, in patients treated with both PRK and LASIK, and this is proportional to the induced anisometropia¹⁴. On the other hand, Fawcett et al found that in these patients prolonged Monovision led to worse performance in the Worth-4-point test at 3 m, and the worst results were seen in patients with higher induced anisometropia¹⁵.

The most positive aspect of Monovision is that it allows a relative independence of optical correction, both for far and near, being easily reversible with glasses, whenever considered necessary by the patient (especially if the induced anisometropia is less than 1.5 D). However, the partial and progressive loss of the effect is to be noted, as the accommodative function still existing at the time of the surgical act is lost.

CONDUCTIVE KERATOPLASTY

This technique used radiofrequency to modify the corneal profile and was based on the same principles of Laser Thermokeratoplasty. Although it was not invasive and reasonably safe, it presented very high regression rates¹⁵, which required multiple retreatments, and as other presbyopia-correcting techniques were introduced, it was progressively abandoned.

INTRACORNEAL INCISIONS – INTRACOR

Fig. 1 After Intracor treatment. Photo: Technolas Perfect Vision

The development of corneal treatment options using the femtosecond laser, with the possibility to perform deep intrastromal incisions and patterns, allowed its application in the surgical treatment of presbyopia, aiming at corneal modulation without the inconveniences usually attributed to the Excimer laser. That is, preserving the epithelium, membrane of Bowman and anterior stromal fractures, and minimizing postoperative pain, inflammation, infection, turbidity or corneal biomechanical instability, while simultaneously avoiding endothelial repercussions has been proven16.

In 2009 Ruiz17, using this technology and the Technolas femtosecond laser with the Intracor platform, presented the results of its first 63 treated eyes (follow-up time of 6 months). The intervention consisted of making a series of cuts in concentric intrastromal circular lines, creating a structure that induces a localized biomechanical alteration, with 1-2 diopter central curving, modifying not only the spherical aberration such as corneal asfericity, but also giving rise to to a central multifocal cornea, with the consequent improvement from near vision. In nearsighted patients intrastromal radial incisions to optimize vision away. This type of correction has the effect of entirely modulating the various aberrations, giving rise to a negative deviation in primary spherical aberration associated with a positive deviation in secondary spherical aberration. Studies however, showed that there was a risk of initial myopic leakage and loss of best visual acuity greater than 2 lines in about 8% of eyes at 3 months18. There seemed to be however a progressive improvement in far away vision, at least up to 12 months. The reduction in best corrected distance visual acuity was probably due to a slight central irregularity and is not likely to be corrected with glasses and is a contraindication for any other laser procedure. It was also verified that all patients had at least initially complaints related to decreased sensitivity to contrast, halos and glare, especially at night19. Although some authors have presented a rate of 90% satisfaction after 5 years of follow-up20, they also found that in about 10% of patients the procedure had no effect and there was no other possibility of compensation. On the other hand, treatment was usually applied only to the non-dominant eye, and, despite its profile, presented some of the drawbacks of Monovision, without any possibility of total or partial reversion of the effect.

Intracor did not get the big clinical spread expected, and the company stopped innovating in this area and this technique has since been suspended. However other algorithms are being developed for use with other equipment, with apparently satisfactory results, and long-term studies are needed to establish improvements that may have been introduced.

MULTIFOCAL CORNEAL ABLATIONS

Excimer lasers have great flexibility with regard to possible ablation patterns. Several algorithms have been developed that perform multifocal corneal ablations that allow the modification of spherical aberration and increase the depth of focus, and in some cases the amount of tissue removed is now much smaller than with previous platforms, which gives greater safety to the procedures. Also, in the 1980s, ablations were performed which, in hyperopic patients, modified the cornea giving it a vertical multifocal profile. Despite results that showed an improvement in near vision, this procedure was not widely accepted, mainly because it induced significant vertical coma21. The introduction of the corneal analysis data obtained with wavefront systems and the realization that corneal aberrations could be used to increase depth of field22 allowed the creation of customized and optimized treatments, often associated with some degree of micro-Monovision, leading to a substantial improvement of the results and an easier fusion of the two images, giving satisfactory functional visual acuities both for far and near. The corneal approach performed by the various platforms is variable:

Presbyond Laser Blended Vision (Carl Zeiss Meditec)

This technique is based on an optimized bilateral laser treatment, which aims to reduce the difficulties of adaptation to Monovision. The dominant eye is used for far vision and treated so as to become emmetrope. The non-dominant eye, specialized for near vision, is treated so as to become slightly short-sighted (usually -1.5 D). The treatments are performed using an optimized ablation profile, with data obtained by wavefront analysis, which creates a continuous variation of the refractive corneal power throughout the optical zone, increasing the depth of field and facilitating the fusion of the images. According to the characteristics of the patient, a small myopia can also be induced in the dominant eye in order to minimize the refractive difference between the two eyes, thus being halfway between a Monovision and a micro-Monovision. As there is an area where the sharpness is similar in the two eyes (blend zone), it is easier to integrate the two images, allowing them to be merged.

Reinstein et al23 found a high degree of patient satisfaction, noting that 96% of emmetropic patients and those with myopic astigmatism achieved uncorrected visual acuity for near of J2. In the hyperopic presbytes 81% read J3 on the Jaeger scale.

Fig. 2 Blend Zone. Promoter Scheme – Carl Zeiss.

PresbyLasik

Fig.3 Multifocal ablation profiles. a) Peripheral Presbilasik; b) Central presbilasik

Ablation techniques have been also developed that use a corneal modulation, preferably of bilateral use, whose objective is to produce a multifocal profile, allowing each eye to have a good vision both for near and far, with a transition zone that is used for the intermediate vision. These techniques are collectively commonly referred to as PresbyLasik and there are two basic techniques used:

In peripheral Presbilasik the central cornea is intended for distance vision, while the peripheral cornea is used in near vision. A negative peripheral asphericity is created in order to increase the depth of field (Nidek Advanced Vision Excimer Laser).

Pinelli developed this technique using the Technolas 217 Z and inducing a multifocal corneal profile with a diameter of 6.5 mm. The central 6 mm was intended for far vision. This results in a prolate corneal profile with a negative spherical aberration to extend the depth of focus. When presenting their results, it was emphasized that there was a decrease in contrast sensitivity²⁴. Epstein et al²⁵ analyzed the results of treatments using a combination of this technique in the non-dominant eye with a monofocal correction for far in the dominant eye. They included 103 patients, and the follow-up ranged from 1 to 4 years; 91.3% of the patients were independent of wearing glasses, uncorrected distance visual acuity was 20/20 in 67.9% of the hyperopes and in 70.7% of the myopes. At close range, at a distance of 40 cm, 71% of the hyperopes and 65.3% of the myopes had a visual acuity of 20/20; 14.3% of the hyperopes lost 1 line of best-corrected distance visual acuity. Stereopsis showed no significant changes. Note that if there is a pupillary constriction the central positive spherical aberration increases impairing near visual acuity.

Uy et al²⁶ presented their results in 2009 using Nidek's PAC software (Pseudo-accommodative Cornea) in 195 eyes with myopia and presbyopia and 119 emmetropes or emmetropic presbyopic eyes. 83% of the myopic and 87% of the hyperopic, presented at the 3^rd month visual acuity for distant vision (DVA) ≥ 20/30 and visual acuity for near vision (NVA) ≥ J3. In the results presented by El Danasoury²⁷ for patients with one year of follow-up, 54% of the hyperopic and 48% of the myopes were satisfied and independent of glasses, both for far and near. This author found that 2% of patients had a loss of best corrected visual acuity for distance.

Other researchers used the same Laser platforms but with different approaches, particularly with respect to optical and transition zone diameters, with satisfactory results. As this technique requires the removal of a large amount of tissue to induce the necessary modification of the peripheral corneal profile, it is mostly used in hyperopic or low myopic presbyopia patients.

In Central PresbiLasik the central cornea is used for near vision, whereby the treatment induces an increase in curvature in that area, and the surrounding, flattened cornea is used for far vision. There is an increase in the central negative spherical aberration with an increase in the depth of focus. This type of profile suits the pupil's natural movements. When in near vision this one contracts the central opening – myopic – continues to be available with the more peripheral rays being suppressed. It has also been stated that neuroadaptation is faster with this type of profile. The corneal ablation necessary for its creation is minimal, so it can be used both in hyperopic and myopic, and it is easy to associate in the same surgical plane the correction treatment of previously existing ametropias. The first published results were presented by Alio et al²⁸ in 2006. The analysis involved 25 hyperopic eyes with a follow-up time of 6 months. Overall 64% of patients had uncorrected visual acuity for distance of 20/20 and 72% had near uncorrected visual acuity >20/40. However, 28% presented loss of 2 lines in the best corrected visual acuity for far. There was also a decrease in contrast sensitivity and increase in coma aberrations, although spherical aberrations decreased. Yung et al did not find significant changes in contrast sensitivity or high order aberrations.

This technique is one of the most frequently used nowadays, being applied by several platforms (Supracor – Bausch & Lomb Technolas; PresbyMax – Schiwnd eye-tech-solutions; CustomVue – VISX, among others).

Supracor uses a progressive ablation profile with aberration optimization, inducing a smooth transition between far and near vision, increasing depth of field, which allows satisfactory intermediate visual acuity. Presbymax induces a bi-aspherical profile.

Most surgeons use a mini or micro-Monovision. In some cases, it is used in hyperopic or emmetropic patients, and the multifocal profile is induced in the non-dominant eye. All analyses show that presbyLasik improves functional near vision, while maintaining or even improving vision for distance, and no significant changes in contrast sensitivity have been found. Of the platforms with bilateral application algorithms, Supracor would be the most promising (O'Keefe)²⁰, although there is still a need for some retreatments and there is a risk of loss of the best corrected visual acuity (which can reach 2 lines).

Several improvements have been introduced, both in the performance of the lasers and in the different algorithms created with this principle of action, with numerous publications presenting the results obtained by the various authors. Satisfaction levels range from 76% to 100%.

CORNEAL IMPLANTS

Intrastromal corneal implants have also been used to correct presbyopia. The complications originated by the first models have been corrected and their evolution, in particular with respect to the thickness and biomaterials used, has been continuous since their introduction in clinical practice. Currently they are preferentially placed in a pocket created by a femtosecond laser (advantages: maintenance of corneal sensitivity, non-removal of tissue, preservation of the cornea for other corrections, if necessary, reversibility, among others). They can be used in pseudophakic patients and conjugated with other refractive correction techniques. There are several types of corneal implants that are based on different acting methods. The most used are:

● Flexivue Microlens – Manufactured in hydrogel, it is transparent and alters the refractive index of the cornea – bifocal optics with addition of central positive power.

● Raindrop Near Vision – Also in hydrogel, it changes the corneal curvature due to the difference in thickness between the center (+ curved) and the periphery.

● Acufocus Kamra – Pinhole effect, increasing the depth of field.

Most authors report an improvement in near and intermediate visions with little interference in far vision^28,29. Complications include hyperopic leakage, halos, decreased contrast sensitivity, and even thinning and corneal fusion (primarily in the models and materials used initially). In all cases a perfect centering is fundamental, and a slight deviation can totally compromise the functional result.

There are multiple surgical techniques for the correction of presbyopia in the corneal plane. Some have fallen into disuse, but most continue to evolve, given the improvements introduced in laser equipment, algorithms used and biomaterials. It is often the combination of different principles in an attempt to optimize the results. At present, correction through Laser procedures is the most used. It has evolved significantly in the last few years, after the introduction in the algorithms of the data obtained through the wavefront study of the ocular diopter. They induce increased depth of field and reduction of focal optical aberrations, and it is possible in some of the platforms to program customized ablations. They are, on the whole, safe procedures and produce high levels of patient satisfaction, given the improved quality of life they provide. However, it is essential to evaluate these patients beforehand, namely their psychological profile, expectations and capacity for neuroadaptation, since all of them require a postoperative adaptation. Patients should be advised of the possibility of a slight loss of the best corrected distance visual acuity (which may be 1 or 2 lines in the immediate postoperative period), generally transient, and accept that in more extreme situations (low ambient light, visually-demanding tasks) they may need to resort to a small correction for near. This correction may increase slightly as the remaining accommodative capacity is lost. In addition, it is important to consider that many of these patients will develop cataracts, and the best approach/formula for IOL to be implanted is not yet well established, especially in patients treated with multifocal profile induction. A correct centering of the treatments is fundamental for the success of the surgery.

It is considered that the surgical treatment of presbyopia remains a challenge, and the option adopted should be as personalized as possible, taking into account, in particular, age, refraction, crystalline transparency, professional and leisure activity, adaptability and expectations.

REFERENCES

Schor C, Landsman L, Erickson P. Ocular dominance and the interocular suppression of blur in monovision. Am J Optom Physiol Opt. 1987; 64: 723-73.
Handa T, Shimizu K, Makuno K, Kawamorita T, Uozato H. Effect of ocular dominance on binocular summation after monocular reading adds. Cataract Refract Surg. 2005; 31 (8): 1588-92.
Erickson P, and McGill EC. Role of visual acuity, stereoacuity, and ocular dominance in monovision patient success. Optom Vis Sci. 1992; 69 (10): 761-4.
Evans BJ. Monovision: a review. Ophthalmic Physiol Opt 2007; 27 (5): 417-43.
Goldberg DB. Laser in situ keratomileusis monovision. J Cataract Refract Surg. 2001; 27 (9): 1449-55.
Braun EH, Lee ED, Steinert, RF. Monovision in LASIK. Ophthalmology 2008; 115 (7): 1196-202.
Collins M, Goode A, and Brown B. Distance visual acuity and monovision. Optom Vis Sci 1993; 70 (9): 723-8.
Reilly CD, Lee WB, Alvarenga L, Caspar J, Garcia-Ferrer F, Mannis MJ. Surgical monovision and monovision reversal in LASIK. Cornea. 2006; 25 (2): 136-8.
Garcia-Gonzalez M, Teus MA, Hernandez-Verdejo JL. Visual outcomes of LASIK -induced Monovision in Myopic Patients with Presbyopia. Am J Ophtalmol 2010; 150 (3): 381-6.
Johannsdottir KR, Stelmach LB. Monovision: a review of the scientific literature. Optom Vis Sci. 2001; 78 (9): 646-1.
Sippel KC, Jain S, Azar, DT. Monovision achieved with excimer laser refractive surgery. Int Ophthalmol Clin 2001; 41 (2): 91-101.
Wright KW, Guemes A, Kapadia MS. Binocular function and patient satisfaction after monovision induced by myopic photorefractive keratectomy. J Cataract Refract Surg 1999; 25 (2): 177-82.
Mcgill EC, Erickson P. Sighting dominance and monovision distance binocular fusional ranges. J Am Optom Assoc. 1991; 62 (10): 738-42.
Durrie DS. The effect of different monovision contact lens powers on the visual function of emmetropic presbyopic patients (an American Ophthalmological Society thesis). Trans Am Ophthalmol Soc 2006; 104: 366-401.
Fawcett, SL, Herman, WK, Alfieri CD, Castleberry KA, Parks MM, Birch EE. Stereoacuity and foveal fusion in adults with long-standing surgical monovision. J AAPOS 2001; 5 (6): 342-47.
Moshirfar M, Anderson E, Hsu M, Armenia JM, Mifflin MD. Comparing the rate of regression after conductive keratoplasty with or without prior laser assisted in situ keratomileusis or photorefractive keratectomy. Middle East Afr J Ophthalmology 2012; 19 (4): 377-81.
Thomas BC, Fitting A, Khoramnia R, Rabsilber TM, Auffart GU, Holzer MP. Long term outcomes of intrastomal laser presbyopia correction: 3 years of follow-up. Br J Ophthalmol 2016; 100 (11): 1536-41.
Ruiz LA, Cepeda L, Fuentes VC. Intrastromal correction of presbyopia with a femtolaser laser system. J Refract Surg. 2009; 25 (10): 847-54.
Holzer MP, Knorz MC, Tomalla M, Neuhann TM, Auffarth GU. Intrastromal femtosecond laser presbyopia correction: 1-year results of a multicenter study. J Refract Surg 2012; 28 (3): 182-8.
Fitting A, Menassa N, Auffarth GU, Holzer MP. Effect of intrastromal correction of presbyopia with femtosecond laser (INTRACOR) on mesopic contrast sensitivity. Ophthalmologe 2012; 109 (10): 1001-7.
O'Keefe M, O'Keeffe N. Corneal Surgical Approach in the Treatment of Presbyopia. J Clin Exp Ophthalmol 2016; 7: 512.
Allo JL, Amparo F, Ortiz D, Moreno L. Corneal multifocality with excimer laser for presbyopia correction. Curr Opin Ophthalmol. 2009; 20 (4): 264-71.
Charman WN. Ablation design in relation to spatial frequency, depth-of-focus, and age. J Refract Surg 2004, 20 (5): S542-S549.
Reinstein DZ, Carp GI, Archer TJ, Gobbe M. LASIK for Presbyopia Correction in Emmetropic Patients Using Aspheric Ablation Profile and a Micro-monovision Protocol with the Carl Zeiss Meditec MEL 80 and VisuMax. J Refract Surg 2012; 28 (8): 531-41.
Pinelli R, Ortiz D, Simonetto A, Bacchi C, Room E, Alió JL. Correction of Presbyopia in Hyperopia with a center-distance, paracentral-near technique using the Technolas 217z Platform. J Refract Surg 2008; 24 (5): 494-500.
Epstein RL, Gurgos MA. Presbyopia treatment by monocular peripheral presbyLASIK. J Refract Surg. 2009; 25 (6): 516-23.
Uy E, Go R. Pseudoaccommodative cornea treatment using the NIDEK EC-5000 CXIII excimer laser in myopic and hyperopic presbyopes. J Refract Surg 2009 Jan; 25 (1 Suppl): S148-55.
The Danasoury AM, Gamaly TO, Hantera Multizone LASIK with peripheral zone for correction of presbyopia in myopic and hyperopic eyes: 1-year results. J Refract Surg 2009 Mar; 25 (3): 296-305. Allo
JL, Chaubard JJ, Calaliz A, Room E, Patel S. Correction of presbyopia by multifocal central technician LASIK (presbyLASIK). J Refract Surg. 2006 May; 22 (5): 453-60.
Waring GO 4th, Klyce SD. Corneal inlays for the treatment of presbyopia. Int Ophthalmol Clin.2011; 51 (2): 51-62.
Seyeddain O, Hohensinn M, Riha W, Nix G, Rückl T, Grabner G, Dexl AK. Small-aperture corneal inlay for the correction of presbyopia: 3-year follow-up. J Cataract Refract Surg. 2012; 38 (1): 35-45.

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