Review of Ophthalmology Online

Volume 4, Number 52

Monday, December 27, 2004

In this issue: (click heading to view article)

		Predicting Corneal Haze After LASEK Using an Ablation Depth/Corneal Thickness Ratio

		Effect of Unilateral Blepharoptosis Repair on Contralateral Eyelid Position

		Massive Increase in Stiffness of Human Lens Nucleus with Age: The Basis for Presbyopia?

		Measurements of Ocular Aberrations and Light Scatter in Healthy Subjects

		Briefly

Review of Ophthalmology Online will not be published next week. Dr. Pascucci and the staff of ROO extend warmest wishes to you, your families and your staff members for a wonderful holiday and a healthy and productive new year!

Stephen E. Pascucci, MD, Medical Editor
Gretchyn Bailey, Editor	Therese DeAngelis, Associate Editor
Joe Morris, Art/Production Director	Janice Miller, Circulation Director

Predicting Corneal Haze After LASEK Using an Ablation Depth/Corneal Thickness Ratio

Investigators at the University of Texas-Houston Medical School conducted a retrospective, comparative, interventional case series study aimed at investigating the usefulness of ablation depth/corneal thickness (AD/CT) ratio to predict corneal haze after laser epithelial keratomileusis (LASEK).

Fifty patients (90 eyes; mean age of patients, 40.9 years) with myopia, hyperopia and/or astigmatism underwent bilateral or unilateral LASEK for correction of refractive error. After epithelial flaps were created using an 18 percent alcohol solution, bilateral or unilateral LASEK was performed using the Alcon Autonomous LADARVision 4000 excimer laser. Visual acuity (best spectacle-corrected and uncorrected) and refractive error were measured before and after LASEK. Corneas were assessed by two independent evaluators under a slit-lamp biomicroscope with broad tangential illumination. The relative haze scale was quantitated: 0 (clear), 0.5+ (trace), 1+ (mild), 2+ (moderate), 3+ (marked) and 4+ (severe). Mean preoperative spherical equivalent refraction was -5.46 +/- 3.74D (range, -12.375 to +5.00D), mean ablation depth was 93.04 +/- 45.03 microns (range, 21.2 to 207.2 microns) and mean AD/CT ratio was 0.18 +/- 0.09 (range, 0.04 to 0.41).

Of 90 eyes, 40 had a higher ablation depth (AD/CT ratio greater than 0.18) and 50 eyes had a lower ablation depth (AD/CT ratio less than 0.18); 92.5 percent of eyes in the higher ratio group developed clinically significant haze (1+ or greater). In the lower ratio group, 94 percent of eyes developed no more than 1+ corneal haze, if any. The authors concluded that the AD/CT ratio is useful for predicting corneal haze after LASEK. An AD/CT ratio of 0.18 or more suggests that patients have a high risk of developing clinically significant haze (1+ or more) after LASEK.

SOURCE: Lin N, Yee SB, Mitra S, et al. Prediction of corneal haze using an ablation depth/corneal thickness ratio after laser epithelial keratomileusis. J Refract Surg 2004;20(6):797-802.

Effect of Unilateral Blepharoptosis Repair on Contralateral Eyelid Position

A study by the ophthalmology department of the University of California at Irvine evaluated the effect of unilateral blepharoptosis repair on contralateral eyelid position and assessed the relation between preoperative eyelid height interdependence, consistent with Hering law, and surgical outcome.

Researchers reviewed the medical records of 54 patients (21 men, 33 women; mean age, 65 years) who underwent external levator advancement for unilateral aponeurotic blepharoptosis for preoperative and postoperative margin reflex distance (MRD) of the nonoperated eye. To assess the relation between preoperative Hering dependence (mechanical elevation of the ptotic eyelid causing a decrease in contralateral eyelid height) and postoperative eyelid position, they compared the change in MRD of the nonoperated eye between subjects who, on preoperative evaluation, did (n=18) and did not (n=36) demonstrate eyelid height interdependence, using the 2-sample t test.

After unilateral blepharoptosis repair, the mean (+/- SD) change in contralateral MRD was -0.2 +/- 0.8 mm. Investigators observed no significant difference in contralateral MRD change in subjects with and without preoperative Hering dependence (-0.3 +/- 0.8 mm versus -0.2 +/- 0.9 mm, respectively). Nine of 54 patients (17 percent) had a contralateral MRD decrease of more than 1 mm. Three patients (5.6 percent) required contralateral blepharoptosis repair within one year of initial surgery.

According to these results, investigators believe that the degree of change in contralateral eyelid height cannot be reliably predicted by preoperative assessment of Hering dependence.

SOURCE: Erb MH, Kersten RC, Yip CC, et al. Effect of unilateral blepharoptosis repair on contralateral eyelid position. Ophthal Plast Reconstr Surg 2004;20(6):418-22.

Massive Increase in Stiffness of Human Lens Nucleus with Age: The Basis for Presbyopia?

The lens is unique in that there appears to be no protein turnover in the center throughout the human lifespan. This lack of turnover in the nucleus leaves it prone to age-related changes. Mature lens fibers lack cellular organelles and contain a highly concentrated protein solution to enable light refraction. Investigators at the Australian Cataract Research Foundation and the Save Sight Institute (Sydney, Australia) aimed to determine the stiffness of different regions of human lenses as a function of age, and to correlate the biophysical measurements in the lens center with nuclear water content.

Researchers employed a custom-made probe fitted to a dynamic mechanical analyzer to measure stiffness values at 1-mm increments across equatorial sections of individual human lenses. They used thermogravimetric analysis to determine the percentage water content in the nuclei of human lenses. Results showed a pronounced increase in lens stiffness in ages ranging from 14 to 78. In the nucleus, stiffness values varied almost 1,000-fold over this age range, with the largest change observed in lenses aged 20 to 60. Nuclear stiffness values increased on average by a factor of 450. By contrast, in the cortex the average increase in stiffness was approximately twenty-fold over this same time period. In lenses younger than age 30, the nucleus was found to be softer than the cortex. This was true for all six lenses examined. In contrast, all lenses older than 30 years had nuclear values higher than those of the cortex. In lenses older than 50 years, the lens nucleus was typically an order of magnitude more rigid than that of the cortex. The crossover age, when the cortical and nuclear stiffness values were similar, was in the 30s. There was no significant change in the water content of the human lens nucleus from age 13 to age 82.

The authors concluded that a marked increase in the stiffness of the human lens occurs with age. This is most pronounced in the nucleus. Since in vivo data indicate that the nucleus must change shape significantly during accommodation, it is highly likely that these measured changes in physical properties will markedly diminish the ability of the lens to accommodate, and thus may be a major contributing factor to presbyopia. Since there was no measurable difference in the water contents of the nuclear regions of the lenses, this marked increase in stiffness is not due to compaction of the lens nucleus.

SOURCE: Heys KR, Cram SL, Truscott RJW. Massive increase in the stiffness of the human lens nucleus with age: the basis for presbyopia? Mol Vis 2004; 10:956-63.

Measurements of Ocular Aberrations and Light Scatter in Healthy Subjects

The University of Illinois Department of Ophthalmology has established a new optical imaging system that provides for combined measurements of age-related changes in ocular higher order aberrations and light scatter in human eyes.

Investigators expanded a laser beam and focused to a point on the retina by the optics of the eye. They performed wavefront sensing with a Shack-Hartmann aberrometer to determine the wavefront aberration function and calculate the point spread function, giving information on ocular aberrations. A cylindrical lens was placed in the path of the incident laser beam path, and the line spread function was derived from the laser slit, giving information on combined ocular aberrations and light scatter. A relative index for ocular light scatter was determined by subtracting the area under the two line spread functions. Measurements were performed in one eye of 20 normal healthy subjects, ranging in age from 21 to 78 years. The average for all the eyes was 43 +/- 17 years (mean +/- SD).

Higher-order ocular aberrations were correlated with subjects' ages; combined higher-order ocular aberrations and light scatter were correlated with age. Light scatter was also correlated with age. The authors believe that differentiating the contribution of ocular aberrations and light scatter to the retinal image quality has potential value for anticipating the outcome of procedures that attempt to compensate for ocular aberrations and for providing information on factors that degrade the optical performance of the eye in health and disease.

SOURCE: Shahidi M, Yang Y. Measurements of ocular aberrations and light scatter in healthy subjects. Optom Vis Sci 2004;81(11):853-7.

BRIEFLY

EYETECH AND PFIZER WILL CO-MARKET MACUGEN. Pfizer, Inc., and Eyetech Pharmaceuticals, Inc., will co-market Macugen, approved by the FDA for treating age-related macular degeneration on December 17 after clinical data showed that the drug slowed vision loss in patients using it for two years compared to those on a placebo. With the approval of Macugen, Pfizer will pay Eyetech a $90 million license fee payment and make an additional investment of $15 million in Eyetech's common stock within 35 business days. Macugen is administered through an injection in the eye; tests have shown that it is well-tolerated: two-thirds of patients treated with Macugen report no pain.

REFOCUS GROUP COMPLETES FIRST HALF OF PHASE II CLINICAL TRIAL SURGERIES FOR PRESBYOPIA. Refocus Group, Inc. recently reported preliminary data on surgical patients at the three- and six-month follow-up exam milestones and announced the completion of the first half of its FDA Phase II clinical trial surgeries for the treatment of presbyopia. To date, 50 of a planned total of 100 Phase II study participants have undergone the company's Scleral Spacing Procedure (SSP) for the surgical treatment of presbyopia. In addition, 26 of a planned 50 control participants have been enrolled for comparative monitoring. Of the 50 SSP surgical participants, 45 have now completed three- or six-month follow-up exams. Preliminary data on these surgical patients indicates that 80 percent experienced sufficient improvement to result in 20/40 or better reading vision. Surgical patients also experienced an improvement in Snellen near vision acuity, averaging almost three lines of improvement; 15 of the 45 patients experienced an improvement of four lines or better, and some experienced up to six or seven lines of improvement. About 90 percent of surgical patients described their reading vision as "better" or "significantly better"; and no changes were observed in any patient’s best-corrected distance vision as a result of SSP. The preliminary Phase II results were also favorable when compared to the non-surgical control group and when compared to the company's FDA Phase I results, which used an earlier surgical protocol without the new automated incisional handpiece. Refocus Group stresses that this data remains preliminary; the company expects to submit the clinical data to the FDA in a Phase II study report in 2005.

FDA APPROVES BAUSCH & LOMB'S ZYLET OPHTHALMIC COMBINATION DRUG; ANIKA RECEIVES B&L SUPPLY DEAL FOR EYE SURGERY PRODUCTS. Bausch & Lomb has received FDA approval of its New Drug Application (NDA) for the Company's novel combination product, Zylet (loteprednol etabonate 0.5% and tobramycin 0.3% ophthalmic suspension). Zylet is indicated for the treatment of steroid-responsive inflammatory ocular conditions for which a corticosteroid is indicated, and where superficial bacterial ocular infection or a risk of infection exists. The eye drop will be available in the United States early in the first quarter of 2005 in three sizes: 2.5 mL, 5 mL and 10 mL. The company will manufacture Zylet at its facility in Tampa, FL. In other B&L news, biotech company Anika Therapeutics, Inc., has signed a multi-year agreement to supply Bausch & Lomb with hyaluronic acid products used in eye surgery. Financial details of the agreement were not disclosed. Under the agreement, Anika will supply Bausch & Lomb with hyaluronic acid products used to protect eye tissue and maintain eye structure during cataract and other eye surgeries. According to terms of the agreement, Anika will spread out the payment to Bausch & Lomb as revenue over the 10 years of the agreement.


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