Presbyopia is a challenging condition that some surgeons are now choosing to correct with corneal inlays.
Presbyopia remains a challenging condition for refractive surgeons, however it has gained significant interest as it is part of the way the human lens ages and, therefore, eventually effects everyone. Dr. Damien Gatinel, Rothschild Ophthalmology Foundation, Paris states that the average median age in France is 40. This is reflective of developed countries and, therefore, indicates that almost half the population is experiencing some level of presbyopia.1
Accommodation, or the ability to change focus from distance to near, decreases as we age. This is because the human lens continues to produce lens fibres throughout life, laying them down peripherally, causing the central part of the lens to become compressed. In general, a person is considered presbyopic when they experience a loss in amplitude of accommodation accompanied by symptoms of blur and ocular discomfort at near distances. Solutions for presbyopia have been the use of reading, bifocal or multifocal glasses, or contact lenses that create monovision or are multifocal. Refractive solutions include monovision with LASIK/PRK/SMILE/Implantable Contact lenses (ICLs) or Intraocular Lenses (IOLs), multifocal IOLs and corneal inlays.
A number of surgeons have also investigated multifocal corneal ablations. Many consider clear lens surgery or early cataract surgery too invasive, thus the interest in corneal inlays, which are additive and do not remove tissue.
almost half the population is experiencing some
level of presbyopia
The ideal patient for an inlay is a presbyope between 45 to 60 years of age. With LASIK, the inlays can be combined with emmetropia, myopia, hypermetropia and astigmatism. Ametropia can range from -5.00D to +3.00D and astigmatism up to 3.00D. Patients should be free of ocular surface disease, dry eye and blepharitis, keratoconus and cataracts. They should be trialled first with monovision to determine their ability to cope with losing some binocular vision. The inlay is placed in the non-dominant eye, which will reduce some vision in the distance for this eye. Only the eye with the inlay will read if the patient is truly presbyopic, unlike reading glasses, which enable both eyes to read. Reading glasses also have some magnification unlike corneal inlays. Monovision can change depth perception, however inlays have little or no effect on stereopsis.
Other considerations for exclusion include corneal scarring, corneal infections including herpes simplex virus, severe glaucoma, retinal diseases, nystagmus, amblyopia, uncontrolled diabetes and autoimmune diseases. It can be considered in post refractive cases and pseudophakia.
The procedure is performed under topical anaesthesia combined with oral Valium. The inlays can be inserted into a stromal pocket or under a corneal flap and can be combined with LASIK. This is all performed with a femtosecond laser and an excimer laser. The stromal pocket is shaped like a keyhole and is situated under the LASIK flap deep within the cornea. Both the inlay and the LASIK can be performed together or separated by several weeks. Post-op, the patient is given antibiotic drops and steroid drops intensively for seven to 10 days, then steroid drops, in decreasing amounts, for up to 12 months after the surgery.
Proper centration, within 300 microns of the visual axis, is very important for good results. The inlay is best placed over the first Purkinji image or visual axis. These are most accurately determined with the acutarget system, which identifies the centre of the pupil and the visual axis. At the same time, this system can record the quality of the tear film and quantify the amount of cataract (optical scatter index). Corneal topography will not help with centration.
At the moment only three inlays are available in Australia:
A small aperture inlay or KAMRA developed by AcuFocus (Irvine, California) was approved by the US Food and Drug Administration (FDA) in April 2015 and CE marked for sale within the European Economic Area in 2005.
The first corneal inlays were implanted in a rabbit model by Barraquer in 1949 with a synthetic material within a freehand dissected corneal pocket.2 The first small aperture inlay was made from medical grade Dacron fabric and was implanted in Mexico by Dr. Arturo Chayet in 2002. These early implants proved the concept that monocular implantation of an artificial small aperture in a cornea could expand the depth of focus for patients with presbyopia. However inlay materials and design were issues. Early models had a light transmission of 10 per cent to 15 per cent through the inlay material, causing visual symptoms. They were degraded by UV light, causing a loss of colour in the inlay and limited long term viability.
The inlay today is a very small donut shape with an outer diameter of 3.8mm and a central hole of 1.6mm. It is made of polyvinylidene fluoride, with nanoparticles of carbon to block light, and is UV resistant. The inlay is six microns thick with 8,400 tiny holes to allow oxygen and nutrients to flow across the cornea. The holes range from 5.5 microns to 11.5 microns with no holes at the five micron edge in the inner and outer rim, which provides mechanical strength in the inlay. The inlay has a radius of 7.5mm to mimic the curvature of the cornea and the opaque inlay body allows 100 per cent light transmission through the centre aperture and 5 per cent light transmission through the micro perforations. It is placed in the non-dominant eye over the visual axis to create a pinhole effect, cutting the peripheral out-of-focus rays. With or without LASIK, the inlay is placed deep in the cornea (>200 microns) preferentially in a pocket which can be created with a femtosecond laser. With Intralase, a masking technique is used to create the pocket and with the Ziemer femtosecond laser, the pocket is part of the software.
In 2010 Dr. Minori Tomita developed a procedure known as combined LASIK KAMRA. This procedure involved creating a 200 micron flap with a femtosecond laser, performing the refractive procedure with an excimer laser and then implanting the inlay under the flap.3
In 2011, Dr. Tomita developed a procedure called post-LASIK KAMRA, which involved inserting the inlay into a femtosecond laser lamellar pocket 100 microns below the previous LASIK flap, and inserting the inlay at a minimum of 200 microns below the corneal surface. Outcomes with this dual interface approach have the same level of acuity as the combined LASIK KAMRA and provide significant improvement in refractive stability and dry eye symptoms.4 This modification has allowed the surgeon to perform a standard LASIK procedure without a thick flap and then implant the inlay into a secondary pocket interface one month after the LASIK procedure. This delay allows time for the eye to heal from LASIK and for the patient to realise they would need a further procedure to restore reading. The surgeon can also address any unwanted residual refractive error prior to inlay implantation.
The target refraction in the inlay eye is -0.75 and the dominant eye is corrected for distance. This small amount of myopia simultaneously achieves an improved near vision without disadvantaging distance vision. The residual stromal bed of 250 microns is recommended if combined with LASIK and 100 microns is recommended between the LASIK flap and the pocket. This means the central corneal thickness should be above 500 microns depending on the excimer LASIK treatment. Patients with previous LASIK treatment, require a central corneal thickness of 450 microns and the flap should be <160 microns.
As a result of the movement to pocket-based procedures, results with KAMRA have become more predictable and stable. The largest reported series of presbyopia correction inlay to date, of 180 eyes implanted with the current version of KAMRA inlay that also underwent simultaneous LASIK, was published by Tomito M et al.3 At six months, with data available for one third of the eyes, mean uncorrected near visual acuity (UNCVA) in the treated eyes improved by seven lines in hyperopic eyes, six lines in emmetropic eyes and two lines in myopic eyes; mean uncorrected distance visual acuity (UCDVA) improved by three lines, one line and 10 lines, respectively. All patients had binocular UCDVA of 20/20 or better. Intermediate visual acuity with this small inlay is quite good, with 91 per cent seeing at 20/23 at intermediate and significant improvements in the ability to perform intermediate tasks without correction.
The FDA trials involved 24 multi-centre sites with 508 operated eyes. The preclinical studies on a mathematical model of the human eye with KAMRA indicated approximately 2D increased depth of focus with J2 near visual acuity. The human studies showed a 0.6 per cent loss of best corrected distance visual acuity of two lines or more with no subject with best corrected best corrected distance visual acuity (BCDVA) worse than 6/12. Inlay removal was 8.7 per cent. Dryness was the most common problem. The studies conclude that KAMRA extends the depth of focus in presbyopic patients and supports its safety. The level of uncorrected near visual acuity was sufficient to read most texts in magazines and newspapers.
In 2012 at the ASCRS in Chicago I presented our KAMRA results on 17 patients, average age 52 years. I reported a reduction in the UCDVA of almost two lines in the KAMRA eye, an improvement of one line binocularly, intermediate vision improved three lines in the KAMRA eye and binocularly and near vision improved five lines in the KAMRA eye and four lines binocularly.
Refracting these patients post-operatively is challenging as they tolerate a wide range of refractive errors, reflecting the increased depth of focus. Autorefraction is unreliable for refraction in these patients, biasing hyperopia.
Corneal topography may reveal a mild steepening over the inlay. If topography indicates a central flattening and changes in refraction, this suggests an aggressive wound healing response and may require further dry eye treatment or steroid drop therapy.
Surface ablation is possible if refractive enhancement is required, however creating a LASIK flap over an inlay is not recommended. At this stage there is no record of KAMRA implant after PRK. Cataract surgery and YAG capsulotomy are possible with the inlay in place. For retinal laser procedures and glaucoma laser procedures the inlay is best removed, however vitrectomy, pneumatic retinoplexy and scleral buckle are possible with the inlay in place.5
Postoperatively achieving the recommended refraction of -0.75 in the KAMRA eye is important for achieving reading vision. If hyperopic they will lose reading, if myopic they will lose distance acuity. Fluctuations in vision are usually due to dry eye. Shadowing and double vision may indicate poor KAMRA centration.
Neuroadaptation is also important for patient satisfaction and may take longer in some patients. A prospective study showed no significant change in stereopsis six months after implantation.6
Raindrop near vision inlay is a corneal inlay developed by ReVision optics (Lake Forest, California, USA). It is a 2mm diameter hydrogel with a hyperprolate shape and water content and refractive index very similar to the cornea. The Raindrop is placed under a LASIK flap of 130 to 150 microns. The edge of the inlay is 10 microns thick and the central thickness is about 30 microns. The flap can be created with a femtosecond laser or a microkeratome. The Raindrop has no refractive power, however it elevates a small bump in the central cornea to create an area of increased curvature (prolate) and therefore higher refractive power for reading and intermediate vision with minimal impact on distance vision. Slight hyperopia should be aimed for because this will compensate for the myopic effect of the inlay.
Results indicate five-line improvement in UCNVA by one-month post-op with 78 per cent of the implanted eyes achieving 20/25 or better. Uncorrected intermediate vision improved by four lines and mean UCDVA was 20/25.7 In another series involving 25 hyperopic presbyopes, 80 per cent had J1 or better at one-month for UCNVA and uncorrected intermediate visual acuity (UCIVA) improved by five lines. UCDVA improved by an average two lines with one patient losing one line.8
Presbia Flexivue Microlens
Presbia Flexivue Microlens (Los Angeles, California, USA) is a transparent hydrogel with a diameter of 3mm. It has a central plano zone surrounded by multiple rings of progressively increasing powers. Thus different powers can be used in each patient for different reading requirements. The powers vary from +1.50 to +3.0D with the lens thickness varing between 15 to 20 microns, depending on power add.
Emmetropia is the best condition to be treated with the Presbia Flexivue Microlens.
The lens is ideally placed in a pocket deep within the corneal stroma (300 microns). The use of glaucoma and retinal lasers is safe, however YAG laser has not been tried. It has a 0.15mm opening in the centre to facilitate fluid and nutrient flow.
A prospective study of 47 emmetropes implanted in the non-dominant eye with a corneal pocket found that UCNVA was 20/32 or better in 78 per cent of eyes at 12 months. Mean UCDVA decreased three lines from 20/20 to 20/50 although binocular UCDVA was not affected. Thirty-seven per cent of patients lost one line of BCDVA in the operated eye but no patient lost two lines. There is a statistically significant decrease in mesonic and photopic contrast sensitivity and increase in higher order aberrations. Overall patient satisfaction and spectacle independence was high but 12.5 per cent of patients experienced glare and halos at 12 months.9
Eighty-one eyes were reviewed in 2015 by Alex Malandrini and showed an improvement in UCNVA and UCDVA. However, 62 per cent of eyes lost one line of UCDVA and 5 per cent lost two lines. Eight per cent lost more than one line of CDVA at 36 months. There was a reduction in mesopic and photopic contrast sensitivity and six eyes needed explantation because of halos, glare
and reduced UCDVA.10
Some disadvantages of inlays include a loss of best corrected distance visual acuity, the use of reading glasses or contact lenses after surgery as the inlay is not enough, experience of halos, glare and ghosting particularly at night, loss of contrast sensitivity and difficulty reading in dim light. Corneal haze has been noted as well as lens decentration. Potentially, the lens can cause infection and scarring in the cornea, leading to corneal thinning and endothelial cell loss. Rigid contact lenses may have to be considered and even corneal graft. One main problem is dry eye which can cause blurred vision, a scratchy or burning sensation and discomfort in the eye. Dry eye should be assessed pre-op and punctual plugs may be needed. Dry eye should be managed actively post-operatively.
There is a chance the inlay may have to be removed if symptoms persist. The removal rate of KAMRA in a pocket is about 2 per cent. When removed early, faster recovery in acuity and stabilisation of vision has occurred. In analysis of 63 patients who required removal, 61 recovered their pre-op BCDVA by six months; the remaining two patients had a one-line loss in pre-op BCDVA.11
In conclusion, corneal inlays provide a form of monovision, improving reading vision while at the same time maintaining adequate distance vision. Cornea inlays are important for patients with early presbyopia, however once the patient develops cataract their reading effect is decreased. Complete independence from glasses should never be guaranteed as none of the available devices completely replicate accommodation.
Dr. Kerrie Meades MBBS(Hons), FRANZCO is a refractive and cataract surgeon, an approved Kamra inlay surgeon and the founder of Personal Eyes. Dr. Meades is passionate about refractive surgery including surface treatments, LASIK, phakic IOLs, customised cataract surgery, intracorneal rings, cross linking and presbyopia. She has special interests in cataract and refractive surgery, medical retina including fluorescein angiography and laser. A pioneer of laser cataract surgery; she was the first ophthalmologist to perform Intracor in Australasia, and was also involved with the introduction of Supracor and Kamra.
Dr. Meades has published many papers in cataract, refractive surgery and general ophthalmology and has presented at events in Australia and overseas. She is a member of RANZCO, ASO, ASCRS, AAO, founding member of AUSCRS, on the advisory board of ALCON and co-chairperson of women in ophthalmology.
1. Damien Gatinel MD, Rothschid Ophthalmology Foundation, Paris. Cataract and refractive surgery today Europe March 2014
2. Barraquer J. Queratoplastia refrativa estudios e informaciones oftalmologia 1949;2:10
3. Tomito M. Simultaneous corneal inlay implantation and LASIK for presbyopia in patients with hyperopia, myopia or emmetropia;6 months results JCRS 2012;38:495-506
4. Tomito M el al. Small aperture corneal inlay implantation to treat presbyopia after LASIK JCRS;2013 june;39(6):898-905
5. Seyeddain O, Hohensinn M,Riha W et al. Small aperture corneal inlay for the correction of presbyopia;3year follow up J Cat Ref Surg 2012;38:35-45.
6. Linn S, Hoopes PC. Stereopsis in patients implanted with a small aperture corneal inlay. Ophthalmol Vis Sci 2012;53:abstract 1392.
7. Porter T, Lang A, Holliday K etal. Clinical performance of a hydrogel corneal inlay in hyperopic presbyopes Invest Vis Ophth Sci 2012 53; abstract 4056
8. Lang AJ, Porter T, Holliday K et al. Concurrent use of the ReVision Optics intracorneal inlay with LASIK to improve visual acuity at all distances in myopic presbyopes Invest Ophthal Vis Sci 2011;52 abstract 5765
9. Limiopoulou AN, Bouzoukis DI, Kymionis GD et al. Visual outcomes and safety of a refractive corneal inlay for presbyopia using femtosecond laser J Refract Surg 2013;29:12-18.
10. Malandrini A, Gianluca M et al. Bifocal refractive corneal inlay implantation to improve near vision in emmetropic presbyopic patients. J Cat Refract Surgery Vol 41 Sept 2015:1962-1972.
11. Vilupuru S and Tomito M. Visual recovery following removal of small aperture intracorneal inlay ARVO 2014 poster