The first day featured three prominent international keynote speakers in the field of refractive surgery: Jorge Alio, an ophthalmologist from Alicante, known for both his extensive experience in a wide range of refractive surgery techniques and his prolific publication record, Michael Mrochen, an engineer currently based in Zurich whose research has greatly influenced the development of laser ablation profiles, and Captain Steve Schallhorn from the US Navy Medical Centre in San Diego, an ophthalmologist and previously a Top Gun instructor, who pioneered the use of refractive surgery in the US military

Michael Mrochen, Sunil Shah (BSRS president), Catharine Chisholm (BSRS vice-president), Jorge Alio and Steve Schalhorn at Stratford-on-Avon prior to the congress

Professor Alio described surgical techniques for managing patients who suffer from irregular astigmatism following previous unsuccessful laser procedures. The degree of irregularity can be quantified based on aberrometry and the level of disability reported by the patient (poor night vision, glare and perhaps even monocular diplopia). It also correlates with low contrast acuity although not always high contrast acuity. He pointed out topography does not always reveal the full extent of any irregularity since the cause may be located at flap level or deeper within the stroma. Professor Alio suggested waiting at least one year before attempting retreatment of patient with significant irregularity, using rigid contact lenses to alleviate symptoms during the waiting period. He described two techniques for treating the irregularity, one of which employs sodium hyaluronate mixed with fluorescein to provide a masking substance with the same refractive index as the corneal stroma. The fluorescein allows the elevated areas to be located. He presented successful results for a number of cases but emphasised that it can take up to six months before the final outcome can be seen.

Professor Alio also spoke about refractive surgery as a possible risk factor for retinal problems. He reviewed more than 3000 eyes that he had treated with LASIK for moderate myopia and found only eleven cases of retinal holes or tears (0.36%). The mean age of those who suffered a detachment was 35 years and the mean interval between surgery and detachment was 24.6 months (range 2-61 months). Some case reports have expressed concern that the transient but nevertheless high intraocular pressure required to create the LASIK flap, may cause retinal detachment. He thought that LASIK may provoke a posterior vitreous detachment in some patients but pointed out that the incidence of detachment in myopic patients is 0.71-3.2% (depending on the degree of myopia) and therefore 0.36% does not indicate an increased risk associated with LASIK. In the same group, he reported only ten cases of choroidal neovascular membrane (CNVM - 0.33% - therefore not an increase in incidence). Long-term follow-up has now established the safety of posterior chamber phakic intraocular lenses (PIOL) although some have raised a possible association with retinal complications. Of 294 cases with an average follow-up of 50 months, he reported nine cases of retinal detachment (2.7%) with an interval of 17 months. Two cases had undergone previous prophylactic laser treatments. Again this figure suggests that PIOLs do not increase the incidence compared to untreated myopic individuals. Nevertheless, he stated that it was mandatory to examine the retina preoperatively to exclude the possibility of CNVM since the PIOL procedure appears to accelerate the development of pre-existing membranes.

Michael Mrochen discussed the range of different laser ablation profiles including corneal-based designs such as that based on the Munnerlyn formula, q-value adjusted designs that try to maintain the prolate shape of cornea, and ablations based on topography data. More recently, we have seen the introduction of wavefront optimised profiles (classical ablation profiles adjusted to compensate for the average 0.1m m of spherical aberration induced per dioptre of myopic correction) and of course true wavefront-based customised profiles. He stated advantages and disadvantages for each design but concluded that Munnerlyn, q-value or wavefront optimised ablations were sufficient for primary treatments, with topography or customised profiles reserved for retreatments. The future he thought was the use of raytracing-based ablations using whole eye information.

His second presentation considered a possible technique for increasing the biomechanical strength of cornea, using UV light to create cross links between collagen fibrils. This occurs naturally to a degree in the ageing cornea and in diabetics. An initial study of 22 keratoconus patients followed for 1-3 years demonstrated clear corneas and a halt in progression in all treated eyes. Further follow-up will reveal whether the effect is permanent.

Steve Schallhorn presented data from a large study of wavefront versus conventional LASIK using the VISX laser. The wavefront group showed a two letter improvement over conventional LASIK on the 5% contrast letter chart. This small difference was statistically significant due to the size of the study although not clinically significant since the repeatability of such charts is greater than one line of letters (>5 letters). The wavefront treatment was found to induce fewer aberrations than the conventional treatment and there were fewer complaints of night halos.

The US Navy is particularly interested in PRK as large trials have consistently shown slightly better visual quality for PRK compared to LASIK. PRK but not LASIK is therefore used for aviators. Wavefront-guided LASIK may overcome this disadvantage but wavefront-guided PRK may be even better. Initial results at one and three months following wavefront-guided versus conventional PRK suggest that modifications to the wavefront nomogram are still required since the spherical element is continuously undercorrected. With the small number of subjects assessed so far, no difference in visual performance has been seen.

Captain Schallhorn also gave a fascinating presentation on the role of pupil size in visual outcome and night vision symptoms. Contrary to popular belief, a large pupil does not increase the risk of problems based on the study of a very large number of patients.

Free papers presented at the meeting included a case report by Mr Paul Cherry on steroid induced glaucoma associated with the treatment of diffuse lamellar keratitis. Because fluid collected in the LASIK interface, the intraocular pressure was never elevated which meant that the condition could be missed. Other cases in the literature have reported a massive drop in vision associated with severe visual field defects in some cases. This is certainly a condition to look out for in those placed on steroids following refractive surgery.

©Dr Catharine Chisholm  ( Research Fellow at the Henry Wellcome Laboratories for Visual Sciences, City University. She is also Vice President of the British Society for Refractive Surgery.)

This is a more detailed report as published in Refractive News:

This years BSRS conference, held at the Hilton NEC, Birmingham in May, featured three prominent international keynote speakers: Jorge Alio, an ophthalmologist from Alicante, known for both his extensive experience of a wide range of refractive surgery techniques and his prolific publication record, Michael Mrochen, an engineer currently based in Zurich whose research has greatly influenced the development of laser ablation profiles, and Captain Steve Schallhorn from the US Navy Medical Centre in San Diego, an ophthalmologist and previously a Top Gun instructor, who pioneered the use of refractive surgery in the US military. Presentations ranged from the treatment of surgically-induced irregular astigmatism, developments in the field of UV cross-linking to strengthen the cornea in patients with ectasia, through to investigation of the benefits of wavefront treatments over conventional treatments with particular reference to low contrast vision and night vision. This article will concentrate on the issue of long-term complications after refractive surgery, a theme that formed the basis of one of the symposia during the two day conference.

Some opponents of corneal refractive surgery claim that excimer laser procedures, in particular LASIK, have not been around long enough for us to fully understand the long-term consequences. Potential issues include retinal damage , inaccuracy of future cataract surgery and delayed diagnosis of glaucoma due to modifications in the corneal profile/thickness, and corneal ectasia.

Professor Jorge Alio from Alicante, Spain, provided a thorough review of retinal problems following refractive surgery. Most surgeons and optometrists working in the field of refractive surgery have encountered at least one post-operative patient that has developed a retinal problem. This has led many to suspect that such problems are a complication of refractive surgery, but is this actually the case? We are after all treating a large proportion of individuals who are at a higher risk of developing conditions such as retinal detachment, choroidal neovascular membrane or a macular hole, simply because they are myopic.

In an attempt to answer this question, Professor Alio, who has extensive experience of both excimer laser procedures and intraocular techniques, presented a detailed review of retinal problems among patients treated at his clinic. He began by looking at more than 9000 eyes that had undergone PRK between 1992 and 1998 . Only five cases of retinal detachment occurred (0.08%) at a mean interval of 21 months +/-15.8 months (range 9-48 months). Of these five, one had previously been treated for lattice degeneration. Since the incidence of retinal detachment among myopic patients is 0.71-3.2% (depending on the degree of myopia), an incidence of 0.08% does not support the theory that retinal detachment is a complication of PRK. The time interval between surgery and detachment also challenges the suggestion y some that intraocular shockwaves generated by the laser are the cause of retinal problems.

He then proceeded to present his analysis of 3009 cases of LASIK for moderate myopia (average Mean Spherical Error -13.5D), followed for an average of 48 months . Eleven cases (0.36%) with an average onset of 24.6 months (range 2-61 months) presented with a retinal problem. These were classified as seven tears, three holes and one giant tear. Two had previously between treated for a tear and/or lattice degeneration at a different location on the retina. Surgery to repair the damage was successful in all cases. Creation of the LASIK flap requires the intraocular pressure to be raised significantly to 65mmHg or more for a brief period of time. Although such pressure may provoke a posterior vitreous detachment, the mean time interval and low incidence in his review strongly suggest that LASIK is not a cause of retinal tears or detachment.

Of the 3009 LASIK cases, ten (0.33%) developed a choroidal neovascular membrane (CNVM) with a mean onset of 35.5 months post-surgery, (range 4-84 months). Treatment ranged from direct photocoagulation or membrane extraction, to photodynamic therapy or macular translocation depending on the location of the membrane, with variable visual results. Three eyes had experienced previous macular problems. Again the incidence and onset period make a link between LASIK and the development of CNVM very unlikely, although Professor Alio does believe that LASIK can cause lacquer cracks, which may encourage growth of current CNVM.

Numerous studies have now established phakic intraocular lens (IOL) insertion as a safe procedure, particularly since complications have been reduced by the development of foldable lenses requiring a much smaller incision for insertion. However, some surgeons still have concerns about an increased risk of retinal detachment, neovascular membranes or rupture of the retinal pigment epithelium following surgery. Professor Alio presented initial follow-up results on 294 eyes, in which nine (2.7%) cases of retinal detachment occurred with an onset between 1-44 months (mean 17 months) . Two eyes had undergone previous laser treatment for retinal holes and yet this did not prevent detachment. Although the incidence is greater than that following corneal procedures (note however that the study group was significantly smaller), the incidence is very similar to that of the untreated myopic population, and therefore these detachments are unlikely to be related to the surgery. His research team are currently following up a control group to confirm this. He does however believe that implantation of phakic IOL’s could exacerbate neovascular membranes if already present and therefore it is mandatory to thoroughly examine retina preoperatively, particularly for CNVM.

A very informative presentation from a non-surgical perspective was given by Rebecca Petris founder of the website www.lasermyeye.org. She sent up this consumer advocate organisation for patients who have had or who are interested in laser correction, after undergoing unsuccessful refractive surgery herself. The aim of the organisation is to empower patients who want surgery to ensure that they make the safest possible choice of procedure and surgeon, and to help surgeons better understand patients’ needs.

Common long-term complications that have been reported to her website included visual quality problems, debilitating floaters following LASIK and significant, long-standing dry eye problems. Some visual quality symptoms were associated with monovision treatments but most related to poor contrast vision in the presence of reasonable high contrast acuity, a problem that many complainants felt was not taken seriously by the practitioners involved in their aftercare. The debilitating effects of glare, halos and starbursts was almost impossible for patients to appreciate in advance of surgery and Ms Petris recommended that surgeons used pictures to demonstrate the effect of such visual complications to ensure that patients understood their implications prior to consenting to surgery.

The most frequent complaint reported to the website is long-standing dry eye post-LASIK. This is in contradiction to the literature that suggests that dry eye problems tend to resolve within three to six months of surgery . She pointed out that a large proportion of patients with symptoms had undergone surgery in the first place because they were contact lens intolerant due to poor tear quality. Perhaps we should look again at whether such individuals are actually suitable for LASIK. She also felt that the management of dry eye was generally poor and that patients often had to find their own way of coping. This is one area in which optometrists could get more involved, particularly practitioners who undertake the impending qualifications in therapeutics and supplementary prescribing. Specialised optometrists should also be utilized to cope with patients with severe optical problems who would benefit from rigid gas permeable contact lenses.

Mr Ian Cunliffe, Consultant Ophthalmologist at Birmingham Heartlands and Solihull NHS Trust and the Midland Eye Centre, chaired the special symposium on long-term complications and started the session by discussing the effect of corneal refractive surgery on intraocular pressure measurements. Although open angle glaucoma (OAG) is not thought to be a direct complication of corneal refractive surgery, the underestimation of intraocular pressure as a result of corneal thinning may delay the diagnosis of glaucoma. When compared to manometry, applanation tonometers are most accurate when the corneal thickness is around 550m m. Thinner corneas result in an underestimate but the relationship between thickness and intraocular pressure varies between studies, suggesting that other factors may play a role, such as ethnicity and corneal curvature. He referenced a paper describing an excellent mathematical model for estimating pressure changes in relation to corneal thickness. This paper reports a 0.2mmHg change for each 10m m change in corneal thickness but emphasises that the relationship is non linear.

It is now known that eyes suffering from normal tension glaucoma tend to have thinner corneas, although there is much overlap with the normal distribution of corneal thickness. Those with thinner corneas and an intraocular pressure greater than 25mmHg (ocular hypertensives) have a much higher chance of developing OAG. In addition, those with thinner corneas tend to suffer from more serious glaucoma, perhaps because the disease is diagnosed later.

Another aspect of this debate relates to a small number of case studies in the literature reporting LASIK-induced optic neuropathy. There have been accounts of field defects developing immediately after LASIK, associated with disc changes . Possible mechanisms include barotrauma, ischaemic damage or perhaps some of these individuals were suffering from undiagnosed primary open angle glaucoma prior to surgery. There is evidence to suggest that a short period of suction does not cause any ocular damage but there may be a minority of individuals who are prone to barotraumas. The use of steroids has also been implicated in some cases . Mr Cunliffe concluded by suggesting that we should avoid treating patients who are at risk of glaucoma later in life and he emphasised the importance of creating new baseline post-operative IOP data by taking a series of measurements once any steroid treatment has ceased. This is in line with the recently published ‘Standards for laser refractive surgery’ (Royal College of Ophthalmologists 2004).

Mr Anant Sharma, Consultant Ophthalmologist at Bedford Hospital, discussed the problems of intraocular lens power equations following previous corneal refractive surgery. The majority of equations derive required lens power from a combination of keratometry readings and axial length measurements. Inaccuracies relate to the keratometry readings since the assumptions made by the keratometer about corneal shape and therefore power, no longer hold true following corneal refractive procedures. A traditional keratometer bases the curvature measurement on data collected from only two small regions of the cornea, about 3.0mm from the visual axis. Additional errors stem from the fact that different instruments use different refractive index values for converting between curvature and power. The division of refractive power between the anterior and posterior surfaces of the cornea is also changed by excimer laser surgery. Without knowing the pre-refractive surgery corneal curvature, there is a high risk of refractive surprise and patient dissatisfaction following cataract surgery. The ‘Standards for laser refractive surgery’ (Royal College of Ophthalmologists 2004) state that all patients should be given relevant details relating to their refractive surgery procedure including their preoperative keratometry readings.

Mr Patrick Condon, a Consultant Ophthalmologist and refractive surgeon in Waterford, Eire, spoke about corneal ectasia following LASIK. He defined ectasia as the presence of a topographic step accompanied by a decreased in best-corrected visual acuity and thinning of cornea. Some experts have expressed a concern that we will see a wave of ectasia cases emerging over the next few decades, since LASIK removes the strongest portion of the corneal stroma . The anterior stromal layers are more tightly woven and therefore better able to resist swelling than deeper layers of the stroma.

Mr Condon quoted a review of 62 cases in the literature , many of which could be attributed to undiagnosed forme fruste keratoconus. Another relatively common association was an unintentionally thick flap that was not recognised at the time of surgery, resulting in a stromal bed of less than 250m m following ablation. Mr Condon conveyed his own experience of a single case of ectasia (0.5%) out of 147 highly myopic eyes followed for nine years post-LASIK. He found the insertion of intrastromal ring segments was beneficial initially in this case, although vision has since deteriorated significantly.

He concluded that since the vast majority of ectasia cases can be attributed to a thick flap or undiagnosed keratoconus, we should not expect a surge in cases of ectasia. His guidelines for avoiding iatrogenic ectasia are:

Future management options for keratoconics and post-LASIK ectasia patients may be provided by UV cross-linking technology, a topic introduced to the delegates by Michael Mrochen. Current trials use UV light (365nm) combined with riboflavin to modify the biomechanical properties of cornea by creating additional interfibrillary molecular bonds. This technique is already well established in the areas of larynx and cardiac surgery and occurs to some extent naturally in the cornea with advancing age. Although the death of some keratocytes does occur following treatment, the cells in the stroma recover in much the same way as is seen following exposure to an excimer laser. Results from an initial trial suggest that the elastic module of the human cornea can be increased five-fold. All keratoconic eyes showed a halt in progression at the 24 month follow-up point. It is possible this effect may only last four to five years but nevertheless, this is an exciting development.

www.lasermyeye.com Patient website on refractive surgery

www.rcophth.ac.uk/about/about-college-docs/RefractivesurgerystandardsMay2004.pdf

Royal College of Ophthalmologists ‘Standards for laser refractive surgery’