AAO research highlights LASIK, lens materials, instrumentation

The American Academy of Optometry meeting, held in Dallas in December, featured hundreds of paper and poster presentations addressing topics ranging from refractive surgery to contact lens materials to ocular disease to new myopia treatments to diagnostic instrumentation.

Hioxofilcon A, omafilcon A, dry eye

A study by Colleen Riley, OD, and Neil Pence, OD, of Indiana University, examined the performance of hioxofilcon A and omafilcon A soft contact lens materials in a dry eye population. The goal of the study was to determine whether the use of hioxofilcon A decreased signs or symptoms associated with dry eye among contact lens wearers who had symptoms of dryness.

Forty subjects, with a mean age of 32.7 ± 10.6 years and mean spherical prescription of –3.03 ± 2.17 D, were enrolled in this prospective, single-center, randomized, contralateral cross-over study. Primary control was the baseline state of the treated eye and secondary control was omafilcon A lenses.

Subjects were randomly given a hioxofilcon A contact lens for one eye and an omafilcon A lens for the other eye. The lenses were worn this way for 6 weeks with 2-week lens replacement, then switched for a second 6-week period.

The study found that, compared to symptoms with habitual lenses, there was a significantly lower incidence of dryness, discomfort and blurry vision with both hioxofilcon A and omafilcon A lenses.

Compared to signs with habitual lenses, overall fluorescein staining for both lenses noticeably improved (p<0.05), according to the study abstract. Lissamine green staining showed a significant improvement with omafilcon A (p<0.05). No significant differences were seen in tear break-up time and bulbar redness for either lens material.

The researchers concluded that dry eye symptoms can be alleviated to a great degree by use of hioxofilcon A or omafilcon A lenses and that there are no clinically significant differences between the lenses.

This study was supported by the Hydrogel Vision Corp.

Measuring glaucomatous damage

Asifa Shafi, BA; William Swanson, PhD, FAAO; and Mitchell W. Dul Jr., OD, MS, FAAO, of the State University of New York, studied the structural and functional correlations in patients’ glaucoma using macular perimetry and confocal scanning laser ophthalmoscopy.

Seventeen patients with stable primary open-angle glaucoma were recruited. Visual function was measured with the Humphrey Field Analyzer (Carl Zeiss Meditec, Dublin, Calif.), using the 10-2 SITA Standard algorithm. The clinicians converted perimetric sensitivities from decibel units to linear units. The area of the neuroretinal rim was measured with the Heidelberg Retina Tomograph 2 (HRT 2) confocal scanning laser ophthalmoscope (Heidelberg Engineering, Vista, Calif.). For comparison with macular function, only the area of the temporal rim sector was used.

According to the abstract, the study showed that patients had 10-2 fields with a mean deviation ranging from 0.0 dB to –27.8 dB. The temporal area of the neuroretinal rim ranged from 0.08 to 0.33 mm². The two measures were significantly correlated (r=0.76, p<0.005). Neuroretinal rim area accounted for 57% of the variance in perimetric sensitivity, which is as high as or higher than for studies using the central visual field.

The researchers concluded that macular perimetry is suitable for structural/functional studies of glaucomatous damage and can be an analyzed using the techniques developed for the central visual field.

This study was supported in part by Novartis Ophthalmics.

Flap thickness with IntraLase

Marc R. Bloomenstein, OD, FAAO; Steve Fisher, OD; Kevin Huff, BS; Neeka Najmi, BS; and David Farley, BS, of Barnet Dulaney Perkins Eye Center, studied the accuracy of flap thickness creation with the IntraLase (Irvine, Calif.) femtosecond laser compared to three different microkeratomes: the Hansatome (Bausch & Lomb Surgical, San Dimas, Calif.) the Automated Corneal Shaper (Bausch & Lomb Surgical) and SKBM (Alcon Surgical, Ft. Worth, Texas).

A retrospective analysis of LASIK flap thickness was performed on 101 LASIK patients (202 eyes). The surgeries were performed by three different surgeons between April 2002 and July 2002. The attempted flap thickness for the IntraLase was recorded as the value entered into the laser, and the microkeratome-attempted thickness was based on the plate used.

Preoperative pachymetry was measured and recorded prior to flap creation at the time of surgery. Pachymetry was then measured and recorded on the stromal bed.

According to the abstract, the study showed that the IntraLase flap thickness efficiency (n=101) ranged from –32 microns to +21 microns, with an average flap deviation of ±8.97 microns from the attempted thickness. The SKBM (n=17) ranged from +36 microns to –53 microns with an average flap deviation of ±29.1 microns, and the ACS (n=60) ranged from +35 microns to –150 microns with an average flap deviation of ±57.7 microns. The Hansatome (n=24) ranged from +118 microns to –75 microns with an average flap deviation of ±32.4 microns. The total deviation was ±45.7 microns.

The researchers concluded that the use of the IntraLase femtosecond laser produced flaps that were, on average, within 10 microns of the attempted flap thickness. Because preserving the corneal bed is an important consideration in LASIK, the IntraLase demonstrated an effective way to create a flap of predictable thickness when compared to the flaps created with three mechanical microkeratomes.

Soft contact vs. post-LASIK wavefront

A pilot study conducted by Sri Thota, OD; Shoshanna Nock, OD; and Norman Leach, OD, MS, FAAO, of the University of Houston compared wavefront aberrations found in soft contact lens-corrected myopes before and after LASIK surgery.

Four myopic soft contact lens wearers who expressed an interest in having LASIK surgery were the study participants. Researchers used the following diagnostic tests to determine the patients’ eligibility for LASIK: corneal topography, autorefraction, autokeratometry and wavefront aberration measurements with the Nidek OPD Scan. Wavefront aberration measurements were obtained under three conditions: unaided, with soft contact lenses and post-LASIK surgery. The root mean square (RMS) of the total aberrations under each condition measured was then compared.

The study found that the difference in total aberrations (RMS) between a soft contact lens-corrected eye vs. an unaided eye ranged from 3.25 to 7.78 microns, with a 3.93% average decrease, primarily due to a reduction in defocus provided by the contact lens.

According to the study abstract, soft contact lenses caused a slight increase in tilt and coma as compared to the unaided eye. When comparing the total aberrations of a contact lens-corrected eye to the post-LASIK eye, the average difference increased by 0.57%, with the RMS ranging from 0.20 to 1.50 microns. Spherical aberration post-LASIK was slightly increased over soft contact lens correction.

Despite the increased aberrations with LASIK, no differences in Snellen acuity were seen.

The researchers concluded that, although higher-order aberrations increase somewhat, total wavefront aberrations with soft contact lenses are reduced compared to both the unaided eye and the post-LASIK eye. Increased aberrations found post-LASIK are the most likely reason for reports of blurry vision in spite of reading 20/20 or better.

AR coatings, polycarbonate lenses

A study by B. Ralph Chou, BSc, MSc, OD, FAAO; Alina Gupta; and Jeffery Hovis, OD, PhD, of the University of Waterloo, examined the effect of multiple anti-reflective coatings on impact resistance of polycarbonate spectacle lenses.

In this study, four groups of plano polycarbonate lenses were tested: 2-mm thickness with factory-applied scratch-resistant (SR) coating, 2-mm thickness with SR and MAR coatings (MC), 3-mm thickness with SR and 3-mm thickness with MC.

Missiles consisting of an industrial sewing machine needle mounted in an aluminum carrier were fired at lenses mounted in a specially designed lens support. Impact speed was varied using the ZEST protocol.

The results showed that when the needle penetrated the lens, the lens did not crack or shatter, with only a small area of deformity around the penetration point. The MAR coating showed severe crazing upon impact, regardless of whether the needle penetrated the lens.

The 2-mm lenses tended to deform on impact, but the 3-mm lenses did not, according to the study abstract. The mean penetration speeds for the 2- and 3-mm SR lenses were 32.0 meters per second and 46.2 meters per second, respectively, and the corresponding mean penetration speeds of the MC 2- and 3-mm lenses were 29.6 meters per second and 35.4 meters per second. All comparisons of the means were statistically significant.

The researchers concluded that polycarbonate lenses are more susceptible to penetration by small, sharp, high-speed missiles than blunt missiles. The study also found that the application of multiple AR coatings further reduces the penetration speed.

Pirenzepine and myopia progression

A presentation authored by Raymond H. Chu, OD, FAAO; Susan Cotter, OD, FAAO; and Soonsi Kwon, OD, FAAO, of the Southern California College of Optometry, showed that pirenzepine 2% retards myopia progression in 8- to 12-year-old children.

In a multicenter (n=13) controlled clinical trial, 174 children 8 to 12 years old were randomized to receive either pirenzepine 2% gel (n=117) or a placebo gel (n=57) twice daily for 1 year. Entry criteria included visual acuity of greater than 20/25, refractive error of –0.75 to –4.00 D spherical equivalent and less than 1.00 D of astigmatism in each eye. The primary outcome measure was cycloplegic autorefraction after 12 months.

The results showed that mean baseline refractive error was –2.10 D in the pirenzepine group and –1.93 D in the placebo group (p<0.0001), according to the study abstract. Only 11% of pirenzepine subjects had >0.75 D of myopic progression at 1 year vs. 31% of the placebo group (p<0.001). Treatment was generally well tolerated; however, 9.4% of pirenzepine subjects withdrew from the study due to adverse events vs. none of the placebo subjects. The most common adverse events were gel residue on the eyelids, blurred vision at near and asymptomatic conjunctival reactions.

The researchers concluded that pirenzepine 2% ophthalmic gel used twice daily reduced the rate of myopic progression at 1 year by 50% (0.26 D) compared to placebo.

Continuous wear vs. corneal reshaping

Pacific University researchers Mark Fast; Joseph Parks; Chad Premer; Jennifer L. Smythe, OD, MS, FAAO; Patrick Caroline, FAAO; and Peter Bergenske, OD, FAAO, assessed patient preferences of 30-day continuous wear with CIBA Vision’s (Duluth, Ga.) Focus Night & Day (FND) and overnight corneal reshaping with Paragon CRT (Mesa, Ariz.).

Nineteen subjects in this crossover study were initially fitted with each lens design, randomly placed into one of the contact lens modalities for 60 days and then — following a 2-week washout period — crossed over to the other modality for an additional 60 days. Afterwards, the subjects rated their subjective responses on a 50-point analog scale. Sixteen subjects (80%) participated in both phases of the study.

According to the study abstract, patients felt the overall visual acuity and handling was better with FND and daytime and evening dryness was better with CRT. Subjects indicated no major difference in overall comfort or visual function with either modality.

With regard to overall forced-choice preferences, 10 subjects preferred FND continuous wear lenses, five preferred corneal reshaping with Paragon CRT and one subject preferred their habitual contact lens correction of daily disposable soft lenses.

The study showed that 15 of the 16 subjects preferred either 30-day continuous wear or Corneal Refractive Therapy over their current correction modality, and no one lens modality was appropriate for all individuals. Therefore, the researchers concluded that all options should be presented to patients.

Outcomes with post-PK keratoconus

A study conducted by Charlotte Joslin, OD, FAAO, of the University of Illinois-Chicago, and Brad Wilson, MA; Joseph T. Barr, OD, MS, FAAO; Mae Gordon PhD; and Karla Zadnik, OD, PhD, of the Ohio State University, compared the pre- and post-penetrating keratoplasty status of scarring, staining, best-corrected visual acuity, mean steep and flat K and contact lens comfort among patients in the Collaborative Longitudinal Evaluation of Keratoconus study.

Of the 1,209 patients examined during 7 years of follow-up, PK was performed on 166 eyes of 139 of them. According to the study abstract, the presence of corneal scarring was statistically significantly lower post-PK (9.0%) compared to pre-PK (42.4%, n=144 eyes, p=<0.0001). High-contrast best-corrected acuity (n=69) was also significantly improved post-PK (33.4 ± 13.7) compared to pre-PK (18.1 ± 13.9, p=<0.0001). Both mean steep and flat K were significantly lower post-PK compared to pre-PK (steep K: 61.3 ± 5.9 vs. 47.7 ± 5.0, n=128, p<0.001 and flat K: 43.0 + 5.0 vs. 57.2 + 7.5, n=134, p<0.0001).

Among 26 patients who wore contact lenses both pre- and post-PK, contact lens comfort did not differ significantly between pre- and post-PK. A significantly lower percentage of eyes were classified as having scarring post-PK as compared to pre-K (86.1% vs. 11.8%, n=144, p=<0.0001).

The researchers concluded that significant improvements were noted in CLEK study patients after undergoing PK.

The CLEK study is sponsored in part by NEI/NIH grants. It is also supported by Conforma Contact Lenses, Paragon Vision Sciences, CIBA Vision Corp. and Ohio Lions Research Foundation.

Proview vs. Goldmann tonometry

David Castells, OD; Sara Fredrickson; Michelle Theesfeld; and Brandon Stalzer of Illinois College of Optometry, compared IOP readings found with Goldmann and Proview tonometry.

Measurements were taken on 101 subjects, which included patients from a large urban eye clinic and optometry students. Two masked examiners performed either Goldmann or Proview tonometry in random order. Results were recorded by a third individual.

According to the study abstract, with Goldmann tonometry, the mean IOP was 16.2 ± 2.6 mm Hg (range: 11 to 25 mm Hg) in the right eye and 16.2 ± 3.1 mm Hg (range: 11 to 33.5 mm Hg) for the left eye. With Proview tonometry, the mean was 13.9 ± 2.6 mm Hg (range: 8.5 to 30.0 mm Hg) in the right eye and 14.1 ± 2.6 mm Hg (range: 9 to 30 mm Hg) in the left eye. The t test for paired data shows a statistically significant mean difference of 2.3 ± 3.0 mm Hg (p<0.0001) in the right eye and 2.1 ± 3.6 mm Hg (p<0.001) in the left eye. Similar results are seen if the study group is broken down by age and by clinic patients vs. optometry students.

The researchers concluded that a significant difference in intraocular pressure measures was found between Goldmann and Proview tonometry, with the Proview mean being lower. This may indicate that Proview tonometry may not be as reliable a measure of IOP when compared to Goldmann, which is considered the gold standard. Further study is needed to evaluate the usefulness of this instrument, they said.

For Your Information:

• Colleen Riley, OD, is a professor at the Indiana University School of Optometry. She can be reached at 800 E. Atwater Avenue, Bloomington, IN 47405; (812) 855-2902; fax: (812) 855-5417; criley@indiana.edu.
• Mitchell W. Dul Jr., OD, MS, FAAO, is department chair of the SUNY State College of Optometry, Department of Clinical Sciences. He can be reached at 33 West 42nd St., New York, NY 10036; (212) 780-5007 ext. 2194; fax: (212) 780-4980; mdul@sunyopt.edu.
• Marc R. Bloomenstein, OD, FAAO, is a Primary Care Optometry News Editorial Board member who practices in Phoenix, Ariz. He can be reached at Barnet Dulaney Perkins Eye Center, 4800 N. 22nd St., Phoenix, AZ 85016; (602) 955-1000; fax: (602) 508-4744; Mbloomenstein@BDPEC.com.
• Sri Thota, OD, is a visiting assistant professor of optometry who has completed a fellowship in cornea and contact lens research at the University of Houston. Dr. Thota can be reached at 505 J.D. Armistead Building, Houston, TX 77204; (713) 743-1951; fax: (713) 743-2053.
• B. Ralph Chou, BSc, MSc, OD, FAAO, is an associate professor at the School of Optometry, University of Waterloo. He can be reached at University of Waterloo, Waterloo, ON N2L 3G1 Canada; (519) 888-4567 ext. 3741; fax: (519) 725-0784; bchou@sciborg.uwaterloo.ca.
• Raymond H. Chu, OD, FAAO, is a research optometrist at the Southern California College of Optometry. He can be reached at 2575 Yorba Linda Blvd., Fullerton, CA 92831; (714) 992-7876; fax: (714) 992-7846; rchu@scco.edu.
• Jennifer L. Smythe, OD, MS, FAAO, is a Primary Care Optometry News Editorial Board member, an associate professor of optometry and coordinator of the Cornea and Contact Lens residency at the Pacific University College of Optometry. She can be reached at 2043 College Way, Forest Grove, OR 97116; (503) 352-2770; fax: (503) 352-2929; smythej@pacificu.edu.
• Joseph T. Barr, OD, MS, FAAO, is assistant dean of clinical affairs at Ohio State University College of Optometry. He can be reached at 320 West 10th Ave., PO Box 182342, Columbus, OH 43218; (614) 292-0437; fax: (614) 292-7493; Barr.2@osu.edu.
• David Castells, OD, FAAO, is an assistant professor at Illinois College of Optometry. He can be reached at 1405 S. Plymouth Ct., Chicago, IL 60605; (312) 949-7247; dcastell@eyecare.ico.edu.