From this year's offering of lens-related presentations at the annual ARVO meeting, it is evident that corneal refractive therapy remains an area of interest, with a focus on identifying who will do well with such treatment. The ARVO meeting also provides several papers that challenge some standing concepts in lens wear—use of high-water content lenses, risks to diabetic patients and factors contributing to corneal ulcers. Here are some highlights.

Orthokeratology
A number of this year's papers address the issue of predictability of success with corneal refractive therapy. In St. Louis, researchers compared the effectiveness of overnight orthokeratology in RGP wearers and non-RGP wearers. They studied a total of 30 eyes with myopia ranging from
-0.50 to -4.50 D. The average baseline myopia was -2.33 D in the non-RGP group and -2.71 D in the RGP group. Each subject was fit with BE OK lenses (Precision Optics) using Mount-ford's sag fitting approach. Patients were advised to wear their lenses every night for eight to 10 hours.

At one month, the average decrease in myopia was -2.64 D in the non-RGP group and -2.34 D in the RGP group. Using regression analysis, the re-search team determined that eccentricity of the cornea is a better predictor for the RGP group, whereas in the non-RGP group, greater predictability was more related to the patient's baseline myopia; that is, the higher refractive errors had a more predictable change than the lower refractive errors. 3713

Investigators involved in the Lenses and Overnight Orthokeratology (LOOK) study also looked at predictive value, focusing on baseline corn-eal eccentricity. Researchers evaluated data for 39 right eyes and 38 left eyes, examining subjects at the time of lens removal (a.m. visits) and six hours afterward (p.m. visits).

Mean SEQ refractive error was -2.00 D±0.92 OD, -2.07 D±0.82 OS. The average baseline eccentricity value was -0.41 D±0.14 OD and 0.43 D±0.12 OS. Mean SEQ change in refraction was +2.08 D±1.10 OD and +2.16 D±1.16 OS. Their findings did not support that the baseline eccentricity had a predictive value of the success of ortho-k. The research team acknowledges that other contributing factors must be considered, such as what algorithm or which kind of topography is used. 3289

With the field of corneal refractive therapy being relatively new, the op-posing outcomes of the preceding two studies may simply be an indication that all practitioners are not using the same algorithms for corneal change measurement or the same topographers. The interesting point for clinicians is that most doctors fitting these lenses are going to be aware of the patient's pre-fit refractive state, but they're not going to be measuring corneal eccentricity. These papers indicate that baseline corneal eccentricity is something good to note, but whet-her it's really predictive or not, the jury is still out.

A Japanese study found that the asymmetry of irregular astigmatism increased with corneal refractive therapy. This was related to the magnitude of myopic correction: The more myo-pia, the more astigmatism they found, even in patients with good uncorrected acuity.

Researchers examined 59 eyes of 36 patients undergoing overnight ortho-k for myopia. They were followed for a minimum of three months. With ortho-k, regular astigmatism significantly increased for both 3-mm and 6-mm pupils. Similarly, the asymmetry component increased significantly after treatment for 3-mm and 6-mm pupils. No significant changes were observed in higher-order irregularity. The amount of myopic correction was significantly correlated with asymmetry for 3-mm and 6-mm pupils, but not with regular astigmatism.

Clinicians providing ortho-k therapy may want to look for asymmetrical irregular astigmatism when faced with a patient who's had a decrease in myo-pia, but is still not seeing as well as he should be, given other factors. 3685
Practitioners interested in applying corneal refractive therapy to children will be interested in the Children's Overnight Orthokeratology Investigation (COOKI) pilot study, conducted by researchers in Columbus, Ohio, and Boston, and partially supported by Paragon Vision Sciences. The COOKI study proposes that overnight ortho-k is safe and effective in children 8-11 years of age.

Investigators enrolled 29 children in the study and have examined 11 as of the date of publication. Prior to contact lens wear, the mean uncorrected logMAR visual acuity was +0.68 D ±0.22 (Snellen 20/96), and the mean spherical equivalent refraction was -2.50 D±1.37. At six months, the UCVA in the afternoon was +0.15 D ±0.22 (Snellen 20/28), and the spherical equivalent refraction was -0.26 D ±0.81.

Children are a patient group where practitioners are a little concerned about introducing a new therapy, but there are many indications that they may be greatly helped by the temporary myopia reduction provided by ortho-k. 3288

Bifocals/Multifocals
A Canadian research team developed a test to measure halos and used it to examine the effects of spherical defocus on halo size and determine the diameter of halos perceived during multifocal soft contact lens wear.

Researchers enrolled 10 spectacle wearers and 24 presbyopic contact lens wearers in the study. All subjects were well fit with a soft multifocal contact lens and then defocused in .25-D steps up to +1 D over two weeks of lens wear. The study showed an association between the amount of optical defocus and the increase in the halo size. Researchers note that there may be other factors contributing to halos, since the halos perceived did not appear to be solely accounted for by the optical defocus.

Because most multifocal lenses are fit with some degree of defocus for the non-dominant eye for near vision, possibly creating halos, this study may explain why certain patients do not do well with these lenses. 3700

A Japanese look at RGP bifocals shows that wavefront aberrations in-crease as the power of the lens in-creases. Ten eyes with a mean spherical equivalent refractive error of -4.28 D and a mean astigmatic value of -0.98 D were fit with an RGP bifocal contact lens (Menifocal Z, Meni-con Co. Ltd., Japan). Total ocular higher-order aberrations with bifocal contact lenses was higher with higher additional power (+1.5 D, +2.0 D) compared with lower additional pow-er (+1.0 D). Researchers noted that decentration of the lens had an effect on aberrations as well. More important, this study showed that some of the unpredictable aspects of fitting multifocal contact lenses (RGP or soft) have to do not only with visual acuity obtained but with wavefront ab-errations. (Halos are also responsible for some of this unpredictability as noted in the preceding paper.) 3697

Challenging Conventional Wisdom
For many years, conventional thinking has held that as the oxygen permeability of a contact lens increased, the cornea would "restore" itself, consequently increasing corneal sensitivity. An Australian study begs to differ.

Twenty-seven long-term (mean wearing time 13.5±4.7 years) wearers of low oxygen transmissibility soft contact lenses were asked to cease lens wear for one week prior to being refitted with high-Dk silicone hydrogel lenses. Investigators obtained corneal and conjunctival sensitivity threshold measurements during low-Dk wear, following one week of no lens wear and after one, three and six months of high-Dk lens wear. The researchers found that the sensitivity continued to decrease, instead of getting better.

The scientists note that this finding may indicate that factors other than oxygen availability alone are involved in determining the sensitivity of the ocular surface. 3705

Researchers in the United Kingdom examined 19 subjects (16 myopes, 3 hyperopes) to determine if aspheric soft contact lenses (front surface as-pheres) would reduce spherical aberration. Following measurement of the subject's spherical aberration, one contact lens was designed to neutralize the spherical aberration of the subject when wearing the soft contact lens (the custom-made lens), and another to minimize the spherical aberration of the soft lens alone (the aberration-free lens).

This study showed that, at least in myopes, standard lenses are better than aspheric soft contact lenses for decreasing spherical aberrations. The research team concluded that the vis-ual benefits of trying to correct spherical aberration in myopes with these special soft contact lenses are small and hard to predict. 3286

High Water Content Lenses
Two notable papers this year examined the performance of high water content contact lenses vis à vis corneal irregularity and tear film. A Spanish study randomized 30 healthy, non-contact lens wearing subjects into two groups. Group 1 wore non-ionic low water content hydrogel contact lenses (polymacon G); Group 2 wore non-ionic high water content hydrogel contact lenses (alphafilcon A). They found water content of a contact lens to be relevant to the maintenance of corneal regularity. 3701

Japanese investigators found that, in soft contact lens wear, tear volume was considered to be independent of air temperature and relative humidity. Both of these studies came to the same general conclusion: The use of higher water content soft contact lenses results in better visual or comfort outcomes—less corneal irregularity and better tear-film volume. 3695

A study from Memphis also supports the use of higher water content lenses. This paper presented the re-sults of a comparison in the rates of dehydration between ionic group-IV lenses (methafilcon) vs. nonionic group-II lenses (hilafilcon and alphafilcon materials). Twenty lenses from each group were used and controlled for power, lens thickness and water content. 

Investigators found that group-IV lenses dehydrated significantly less than either of the group-II lenses. The mean and standard deviation for the change in lens mass over time for each lens material was 34.10±0.017 mg (hilafilcon), 29.15±0.014 mg (alphafilcon), and 23.42±0.008 mg (methafilcon), supporting the use of group IV-lenses in patients with marginal dry eye or when determining the best lens for use in solution/drug delivery to the ocular surface. 3715

Patient Predictability
Knowing that some literature has demonstrated that diabetic patients suffer increased complications from extended-wear contact lenses, researchers in Galveston, Texas, supported by CibaVision, sought to determine if there are more complications for diabetic patients in daily wear lenses. They conducted a retrospective study of 254 diabetic eyes and 254 non-diabetic control eyes from six clinical practices. The incidence of complications was 21.7 percent among diabetic eyes and 16.9 percent among controls, which wasn't clinically significant. 3284

Ulcers
A research team drawn from Aus-tralia and India continues to try to identify the factors associated with contact lens-induced peripheral ulcers (CLPU). They followed 1,354 eyes of 677 subjects in extended wear soft contact lenses involving either six-night weekly replacement low-Dk soft lenses or 30-night monthly replacement high-Dk soft lenses in three one-year clinical trials.
Their results suggest significant factors of CLPU are: use of ionic (group IV) lenses; contamination of the lens with bacteria (in an overnight lens, or from improper hygiene or finger contamination); tight fit; and presence of a higher level of mucin balls behind the lens. 3287

Artificial Tears
A single application of a thicker preparation of artificial tears, such as Celluvisc (Allergan) and Liquigel (Al-lergan), does not adversely interact with the contact lens material to in-crease the loss in contrast sensitivity, says research supported by Allergan.

Twenty normal subjects participated; 10 were soft contact lens wearers and 10 were RGP wearers. Each subject was examined under four experimental conditions: (1) contact lens + Celluvisc, (2) contact lens + Liquigel, (3) spectacles + Celluvisc, and (4) spectacles + Liquigel.

For all experimental conditions, after the artificial tear was placed on the eye, there was a significant de-crease in contrast sensitivity. The magnitude of this decrease wasn't significantly different between the contact lens and spectacle-wearing conditions for either artificial tear. There was no difference in the length of time this decrease in sensitivity lasted.

This study shows that even the thicker artificial tear preparations can be used safely without affecting vision in the aging contact lens population and as environmental conditions change or worsen. 3675

A New Direction in Research
Researchers in Jacksonville, Fla., offer the latest study using soft contact lenses to deliver ocular medications. They showed it could be done safely if the drugs were diluted, eliminating the acute toxicity previously observed in this delivery method.

Researchers passively transferred diluted drugs (timolol maleate and brimonidine tartrate) to contact lenses under aseptic conditions. They evaluated the uptake and release of drugs by liquid chromatography. Analytical data showed that the two molecules were well-separated upon assay and that their chemical structure did not change upon release from the lens material.
Using soft contact lenses as a delivery device for ocular medications may find some clinical usefulness in patients who find it impossible to use eyedrops or gels or are non-compliant in dosing. 3686