December 2012 OVS Announces Preview - News from the Editor

Coming in the December 2012 Optometry & Vision Science

Although continuous wear is a convenient mode of lens wear, it is associated with an increased risk of complications. In a series of proof-of-principle studies, researchers set out to test if replacing lenses daily, either in the morning or evening, during a 30 day continuous wear schedule would impact on the rate of ocular adverse events. It did! Morning lens replacement during continuous wear reduced mechanical and overall ocular adverse events. Replacing lenses at night had no beneficial effects.

By self-assessment, 2154 CL wearers were separated into either “sensitive eyes” (12.5%) or "non-sensitive eyes" groups with similar gender, age and refraction characteristics. Perhaps not surprisingly the prevalence of dryness (43% vs. 19%, p<0.0001), irritation (25% vs. 11%, p<0.0001), redness (20% vs. 6%, p<0.0001) and stinging (6% vs. 1%, p<0.0001) was higher in "sensitive eyes" patients. Changing lens materials seemed to reduce these reported signs and symptoms.

While cycloplegia had no effect on the measured axial length or corneal curvature measures there was a small increase in anterior chamber length and measured iris width. There were no clinically significant differences in the measures by the Lenstar and IOLMaster biometers and only small clinically insignificant differences in the calculated IOL power by the 4 different methods used.

For a group of 320 eyes our authors made IOL power calculation for patients receiving sutureless cataract surgery. They report that the Zeiss IOLMaster yielded more accurate refractive outcomes than conventional automated keratometry and contact acoustic biometry. Apparently, the variables of age, diabetes, severity of cataract, axial length, and corneal curvature were unrelated to the predictability of postoperative refraction.

The authors evaluate the performance of two new designs of intraocular lens with extended depth of focus. They conclude, using the visual Strehl ratio computed in the spatial frequency domain, that the new extended depth of focus IOLs are a promising solution warranting further clinical study.

With the development of Fourier-domain technology, the optical coherence tomographer for corneal pachymetry is growing in popularity. The authors demonstrate that central corneal thickness measures, using the recently released Topcon 3D OCT-2000 tomographer, have high within-rater repeatability and agreement with standard ultrasound pachymetry. However they caution clinicians that Fourier domain optical coherence tomography significantly underestimates central corneal thickness compared to ultrasound pachymetry.

In type 2 diabetes patients with mild or moderate non-proliferative diabetic retinopathy and poor blood glucose control, higher diastolic blood pressure is associated with greater retinal thickness. But this relationship is absent in diabetes patients with no retinopathy or non-diabetic patients. Our authors believe that clinicians and clinical studies should be aware of the retinal thickness relationship for patients with diabetic retinopathy.

In comparisons of hundreds of corneal ulcers over two consecutive annual surveys, our authors found that while resistance to gatifloxacin, and tobramycin was significantly higher in samples tested in 2007 as compared to 2006, moxifloxacin resistance remained unchanged. The authors suggest that the static resistance pattern to moxifloxacin may indicate that such resistance in moxifloxacin is intrinsic in the antibiotic rather than new resistance stemming from mutations.

The authors describe the baseline results of the Beijing Myopia Progression Study (BMPS), a three-year cohort study of almost 400 school children between 7 and 17 years of age living in the inner city of Beijing. At this baseline session, the initial nearwork-induced transient myopia (NITM) and its decay were assessed objectively immediately after binocularly viewing and performing a sustained near task (5 minutes; 5D). Initial NITM and decay time were significantly larger / longer in the myopic versus the other hyperopic and emmetropic refractive groups. A goal of the 3-year study is to investigate the possible relationship between NITM and permanent myopia.

Our authors show that for children (6-13 year-olds) the most plus sphere measured using cycloplegia was significantly different to that measured using extended optical fogging as an accommodation control method for both retinoscopy and autorefraction. Their findings argue for the use of cycloplegic refraction rather than extended optical fogging as a means of controlling accommodation for refractive error studies in children.

Although convergence insufficiency (CI) is commonly reported in patients with traumatic brain injury (TBI), the prevalence of convergence insufficiency (CI) not associated with other vision or vestibular problems seen in TBI (saccade or pursuit dysfunction; 3rd, 4th, or 6th nerve palsy; visual field deficit; visual spatial inattention/neglect; nystagmus) is not known. A retrospective analysis of 557 medical records from civilian patients with TBI found 9% of this population had a diagnosis of CI without other visual or vestibular dysfunctions.

Almost 800 blind and vision-impaired students, studying in 67 integrated schools for the blind across Nepal, were examined using the WHO/ PBL Eye Examination Record for Children with Blindness and Low Vision. Optical aids provided useful distance and near vision to 20% and 40% of the low vision children, for distance and near vision respectively. Children with low vision actually represented 80% of the population enrolled in these schools for the blind. In fact about one third of the Braille learners could get good vision for print reading. Disappointingly, only a third of those given optical devices were using them a year later. The authors call for developing a national plan for students with low vision in Nepal.

The magnification produced by a low-vision telescope has been shown to compress perceived depth. Looking through a telescope also entails monocular viewing and visual field restriction which together compress perceived depth. While magnification compresses perceived depth, monocular viewing and severely restricted field of view (10 degrees) each also produce substantial compression. However, a moderately restricted (40°) field does not increase the compression found with unrestricted monocular viewing.

Normal observers viewed line stereo targets under conditions that elevated their stereothreshold 4-5X. Perceived stereoscopic depth judgments were reduced for some but not all of these same conditions. The data suggest that observers with impaired stereopsis may or may not exhibit an associated reduction of perceived stereoscopic depth.

Our authors' study suggests that expert optometrists, compared with optometrists newly admitted to the profession, are more patient-centered; construct a mental representation of their patient’s clinical situation more quickly; plan examinations more thoroughly; are able to reflect during cognitively demanding tasks, and draw up their care management plan throughout the encounter. Their results support the growing body of evidence in other health professions that learners can benefit from explicit guidance regarding both analytical and non-analytical clinical reasoning strategies.

OCT is affected by the positioning of the scanning circle used during image acquisition. Our authors provide a method and computer program that estimates how much misalignment occurs between scans, thus providing a useful measure of reliability for comparison to subsequent measures. The scan and is potentially useful when comparing RNFL thickness measures for patients from different scans and different visits. The software is available from the authors of the article.

There appears to be somewhat of a recurrent theme regarding the importance of accurate pupillary examination in recent clinical reports. In this case, there is a presentation of light-near dissociation with other neurologic signs of upgaze paralysis, eyelid retraction and convergence retraction nystagmus. In the current environment of delegation of so many studies to techs, the doctor may first see the patient dilated, which may mask neurological issues.

While rare, this case presentation points to the necessity of pursuing every potential association in neuro-ophthalmic disorders. A triad of neurological signs characterizes the Miller Fisher syndrome: bilateral external ophthalmoplegia, ataxia, and areflexia. The majority of these patients report an antecedent upper respiratory tract or gastrointestinal illness. Serological testing assists the diagnosis.

Another rare case regarding neuro-ophthalmic issues. The ocular neuromyotonia syndrome causing intermittent diplopia is due to an abnormal delay in extraocular muscle relaxation. In this particular case there is an associated bilateral miosis during the muscle spasm secondary to thyroid related orbitopathy. It is important to recognize ocular neuromyotonia syndrome as the condition is treatable.