Off the Cuff: The Other Side of the Staining Debate

There has been so much controversy about corneal staining and its clinical significance that it has nearly ripped the contact lens community apart. What should have remained an open scientific and clinical discussion has, by unfortunate circumstance, devolved into strong feelings, closed minds and two distinct camps in the profession.

I have given this issue a good deal of thought over the past months. While I am still convinced that corneal staining is not a good thing and is a contributory risk factor, I have also come to realize that the issue is far more complicated than explanations based upon "That’s what we were taught," new "math" or real "truth" would support. The external epithelial barrier clearly serves an important protective function, but the ocular surface is far more complex than most of us realize. Our eyes come equipped with numerous defensive redundancies simply because vision is so critical to survival.

Some say that corneal staining in contact lens wearers is unavoidable. While not 100 percent true, staining among lens wearers is relatively common. If staining alone were an absolute risk factor for infection, a larger percentage of contact lens wearers would develop infections. Thankfully, this clearly has not been the case.

Ocular defenses are so complex that we may never fully understand how they function. One thing is certain: The only way we will learn more is by continuing to explore this issue with scientific vigor, discussing it respectfully and maintaining professional objectivity.

Congratulations to my colleagues and friends in the UK on gaining prescriptive authority.
See News and Notes. --AE

Arthur B. Epstein, OD, FAAO Chief Medical Editor artepstein@optometricphysician.com

 

The views expressed in this editorial are solely those of the author and do not necessarily represent the opinions of the editorial board, Jobson Publishing or any other entities or individuals.

Records of all anterior ischemic optic neuropathy (AION) patients seen between 1989 and 2006 were reviewed to characterize AION in patients younger than 50 years. Patients younger than 50 years when initial visual loss occurred were included.

Of 727 consecutive patients with AION, 169 (23 percent) were younger than 50 years (median, 43 years; range, 13 to 49 years; 58 percent men; 93 percent white). Involvement was unilateral in 59 percent of patients and bilateral in 41 percent. At least one cardiovascular risk factor was found in 74 percent of patients. Hypercoagulable states and vasculitis were found in 8 percent. An underlying small or anomalous optic disk was found in 92 percent of eyes (210 of 230 patients). Isolated disk anomalies (without systemic risk factors) were present in 26 percent of eyes. Final visual acuities were 20/40 or better in 64 percent of eyes and 20/200 or worse in 22 percent. Among patients with bilateral involvement, final visual acuity was similar in the two eyes in 70 percent of patients. Anemia and Type I diabetes were associated significantly with fellow eye involvement. Recurrent AION in the same eye occurred in 6 percent of patients.

AION in younger patients is common and represents 23 percent of AION patients in a tertiary neuro-ophthalmic service. Except for giant cell arteritis, ocular and systemic risk factors and associated disorders are similar to those described in older AION patients. Younger AION patients have better visual acuity outcomes but a higher risk of fellow eye involvement than older AION patients.

SOURCE: Preechawat P, Bruce BB, Newman NJ, Biousse V. Anterior ischemic optic neuropathy in patients younger than 50 years. Am J Ophthalmol 2007; Sep 12 [Epub ahead of print].

Ninety-seven children with a confirmed diagnosis of amblyopia associated with strabismus, anisometropia or both were prescribed two rates of occlusion (six hours a day and 12 hours a day) to compare visual outcome.

The mean age of children at study entry was 5.6 years. Ninety were eligible for occlusion, but 10 dropped out in this phase, leaving 80 children who were randomized to a prescribed dose rate of six hours a day (40 participants) or 12 hours a day (40 participants). The mean change in visual acuity of the amblyopic eye was not significantly different between the two groups (0.26 log units in six-hour group; 0.24 log units in 12-hour group). The mean dose rates (hours per day) actually received, however, were also not significantly different (4.2 in six-hour group vs. 6.2 in 12-hour group). The visual outcome was similar for those children who received three to six hours a day or more than six to 12 hours a day, but significantly better than that in children who received less than three hours a day. Children younger than age four required significantly less occlusion than older children. Visual outcome was not influenced by type of amblyopia.

Substantial (six hours a day) and maximal (12 hours a day) prescribed occlusion results in similar visual outcome. On average, the occlusion dose received in the maximal group was 50 percent more than in the substantial group and, in both groups, was much less than that prescribed. Younger children required the least occlusion.

SOURCE: Stewart CE, Stephens DA, Fielder AR, Moseley MJ. Objectively monitored patching regimens for treatment of amblyopia: randomised trial. Brit Med J 2007; Sep 13 [Epub ahead of print].

Visual Impairment in Children with Congenital Toxoplasmosis

Reliable information is needed to counsel parents of children with congenital toxoplasmosis regarding the long-term risk of visual impairment resulting from ocular toxoplasmosis. After three years of age, ophthalmologists reported the site of retinochoroidal lesions and visual acuity; parents reported visual impairment. An ophthalmologist predicted the child's vision based on the last retinal diagram. Selection biases were minimized by prospective enrollment and data collection, high rates of follow-up and exclusion of referred cases.

Two hundred and eighty-one of 284 infected children who underwent ophthalmic examinations were followed up to a median age of 4.8 years. One in six children (49 of 281; 17 percent) had at least one retinochoroidal lesion, two-thirds of whom (32 of 49; 65 percent) had a lesion at the posterior pole. In children with retinochoroiditis who had visual acuity measured after three years of age, 94 percent (31 of 33) had normal vision in the best eye (20/40 Snellen or better), as did 91 percent of those with a posterior pole lesion (21 of 23). Analyses based on affected eyes showed that 42 percent (29 of 69) had a posterior pole lesion, of which just more than half (15 of 29, 52 percent) had normal vision, as did 84 percent (16 of 19) of eyes with a peripheral lesion alone. Vision predicted by the ophthalmologist was moderately sensitive (59 percent) but overestimated impairment associated with posterior pole lesions. Of 44 children with information on acuity, four (9 percent) had bilateral visual impairment worse than 20/40 Snellen.

Severe bilateral impairment occurred in 9 percent of children with congenital toxoplasmic retinochoroiditis. Half the children with a posterior pole lesion and one in six of those with peripheral lesions alone were visually impaired in the affected eye.

SOURCE: Tan HK, Schmidt D, Stanford M, et al. Risk of visual impairment in children with congenital toxoplasmic retinochoroiditis. Am J Ophthalmol 2007; Sep 12 [Epub ahead of print].

Screening and Managing Diabetic Retinopathy

The anatomy of the eye and the pathogenesis, clinical features and prevalence of vision impairment from diabetic retinopathy (DR) are described. The macula and fovea play a critical role in vision. Several interrelated biochemical pathways involving aldose reductase, advanced glycation end products and protein kinase C link chronic hyperglycemia with retinal capillary endothelial cell damage and dysfunction in patients with DR.

Vision loss and blindness from DR usually are the result of vascular leakage or ischemia. Screening for DR should be performed within three to five years after the onset of Type I diabetes and shortly after the diagnosis of Type II disease with annual follow-up examinations in both types of diabetes. In patients with DR, severe vision impairment is less common and less readily corrected than mild vision impairment, and vision impairment is more common and less readily corrected in elderly patients with diabetes than in younger diabetics. Modifiable risk factors for DR include A1C level, hypertension, cigarette smoking and dyslipidemia. Tight control of blood glucose concentrations and blood pressure can reduce the risk for and progression of DR. Aspirin therapy and smoking cessation also are recommended. Dyslipidemia in patients with diabetes is associated with retinopathy progression and vision loss. Treatment of dyslipidemia provides cardiovascular benefits in patients with diabetes, but whether it provides vision benefits remains to be determined. Laser photocoagulation therapy reduces the risk of vision loss in patients with diabetic macular edema, severe non-proliferative DR or proliferative DR. Intraocular surgery may be used for patients with vitreous hemorrhage and retinal detachment of the macula.

Therapeutic approaches used for patients with or at risk for DR include drug therapy to reduce modifiable risk factors, laser photocoagulation and intraocular surgery. Screening plays an important role in early detection and intervention to prevent the progression of DR.

SOURCE: Bloomgarden ZT. Screening for and managing diabetic retinopathy: Current approaches. Am J Health Syst Pharm 2007;64 (17:S12):S8-14.

NEWS & NOTES

	NYAS PRESENTS SYMPOSIUM ON CORTICAL PLASTICITY AND THE VISUAL SYSTEM, SEPTEMBER 24. The New York Academy of Sciences (NYAS) will present a symposium on "Plasticity of Sensory Systems: Critical Periods Re-Examined" on Monday, September 24 at 6:00 pm, at the NYAS Building, 7 World Trade Center (250 Greenwich at Barclay St.), 40th floor, New York, NY. Included in the presentation are J. Anthony Movshon, PhD, New York University, speaking on "Sensitive Periods in Visual Development"; Brian A. Wandell, PhD, Stanford University, on "The Human Visual Pathways: Maps and Plasticity"; Charles D. Gilbert, PhD, Rockefeller University, on "Learning to See: Neural Mechanisms of Perceptual Learning"; and Takao K. Hensch, PhD, Harvard University, on "Unlocking Brakes on Plasticity." The symposium is open to the public. To RSVP, go to www.nyas.org/events and click on the September 24 date.
	UK OPTOMETRISTS GAIN NEW PRESCRIBING RIGHTS. Optometrists in the United Kingdom will be able to train to prescribe medicines independently, according to a recent announcement from the UK Department of Health. "This move has the potential to transform the public's perception of optometrists, as well as the ways in which the country's eye care services are delivered," said Roger Buckley, chairman of the standards committee of the General Optical Council (GOC). "Optometrists are highly qualified clinicians but they remain a largely untapped resource in health care, with the capacity to provide high quality, convenient services for patients with a wide range of common and long term eye conditions. GPs are likely to welcome the option of referring patients to a local prescribing optometrist, particularly where access to a hospital ophthalmology department is difficult or where there is a long waiting time for non-urgent appointments." Optometrists who wish to become independent prescribers will need to complete further GOC-approved training and enter their specialty in the GOC's register. Once trained, they will have to keep their skills updated. Optometrists are subject to regulatory controls in the same way as physicians; they do not prescribe outside their area of competence. UK optometrists may also train and register in two therapeutic prescribing specialties: Additional Supply specialists are qualified to write orders for, and supply in an emergency, a range of drugs in addition to those that can be ordered or supplied by a normal optometrist. Registrants with the Supplementary Prescribing specialty are qualified to manage a patient's clinical condition and prescribe medicines according to a clinical management plan set up in conjunction with an independent prescriber, such as a general practitioner or ophthalmologist. For more information, go to www.optical.org.
	RESEARCHERS IDENTIFY GENE RESPONSIBLE FOR BINOCULAR VISION. Massachusetts Institute of Technology researchers have identified the gene responsible for binocular vision. The discovery, announced in the Public Library of Science (PloS) Biology and in the journal Cerebral Cortex, shows that a novel gene is necessary for binocular vision, which allows us to perceive depth and carry out detailed visual processing. The images projected by each eye are aligned and matched up in the visual thalamus and cortex. The researchers discovered that the genes Ten_m3 and Bcl6 have a key role in the early development of brain pathways for vision and touch. The former appears to be critical for the brain to make sense of disparate images from each eye: In the study, projections were mismatched in the brains of mice whose eyes had the Ten_m3 gene knocked out. Because each eye's projection suppresses the other, the mice were essentially blind, even though their eyes worked normally. When the output of one eye was blocked at a molecular level, the knockout mice could see again, though only with monocular vision. Human disorders in which the Ten_m family of genes is affected are often accompanied by visual deficits. The authors of the study believe that these genes are at the heart of human visual conditions in which simply closing one eye allows a patient to see better.