Anesthesia and preoperative and postoperative medications

Retrobulbar blocks, although widely used, still have potentially serious complications. Topical anesthesia presents less risk of injury to the globe and less pain but requires careful usage and an experienced surgeon. New techniques, however, allow for an increase in the percentage of patients able to have topical anesthesia. Preoperatively, 2.5% phenylephrine is found to be just as effective as 10% phenylephrine, and, when compared with wound closure and surgeon's experience, the effect of prophylactic medications was found to be negated. Postoperatively, diclofenac is found to be as effective an anti-inflammatory agent as prednisolone. Also, the addition of 10% phenylephrine to 4% pilocarpine drops enhances the effectiveness of pharmacologic treatment of postoperative iridocorneal adhesions. In addition, ophthalmologists should be aware of emerging antibiotic resistance.     

Proximal and accommodative convergence and age

The authors have estimated the phoria for distant and near fixation in two groups of subjects (mean age 27.5 ± 4.4 and 59.2 ± 8.2 years). Different accommodative stimuli were induced by adding minus lenses for distant fixation and plus lenses for near fixation. Statistical analysis of the experimental data indicates that, for distant fixation, the value of phoria per unit of accommodative stimulus is significantly lower in presbyopic than in nonpresbyopic subjects. Also, during near fixation, the accommodative convergence (AC/A ratio) is more reliable in the presbyopic subjects when the accommodative stimulus is progressively reduced. This varying behavior indicates in presbyopic subjects that proximal convergence is of greater relative importance in the determination of the fusion-free position. In nonpresbyopic subjects, accommodative convergence is the more important component.     

Anesthesia and preoperative and postoperative medications

Although certain methods such as retrobulbar blocks are used extensively, improvements in procedure can always be implemented. The use of ultrasound, low concentrations of anesthesia, careful monitoring, and, in the case of risk patients, anesthesia standby are all important considerations to ensure uneventful treatments. Topical anesthesia eliminates needle risk as well as risk of ptosis and bruising. Because it has been demonstrated that bacteria routinely enter the anterior chamber during uncomplicated cataract surgery, certain irrigation solutions are helpful, but still debatable. Postoperatively, diclofenac, flurbiprofen, and timolol have all been proven to be effective in reducing ocular inflammation, reducing incidence of CME, and controlling pressure increase, respectively.     

Segmentation and accuracy in copying and drawing: Experts and beginners

As part of an ongoing investigation into real-world copying and drawing, I recorded the eye-hand drawing strategies of 16 subjects with drawing experiences ranging from expert to novice while they copied a line drawing of a standing nude. The experts produced accurate copies whereas all the beginners produced marked inaccuracies of overall scaling, proportion and shape. Analysis of eye and hand movements showed that the experts alone segmented the original drawing into simple line sections that were copied one at a time using a direct eye-hand strategy not requiring intermediary encoding to visual memory. The results suggest that segmentation into simple lines defines the task-specific process of accurate copying, and that this process is restricted to experts, i.e. acquired through training and practice. Additional preliminary tests also suggest that a similar process may apply to drawing a model from life.     

Paraneoplastic and non-paraneoplastic retinopathy and optic neuropathy: Evaluation and management

Paraneoplastic syndromes involving the visual system are a heterogeneous group of disorders occurring in the setting of systemic malignancy. Timely recognition of one of these entities can facilitate early detection and treatment of an unsuspected, underlying malignancy, sometimes months before it would have otherwise presented, and gives the patient an increased chance at survival. We outline the clinical features, pathogenesis, and treatment strategies for the retinal- and optic nerve–based paraneoplastic syndromes: cancer-associated retinopathy; melanoma-associated retinopathy; paraneoplastic vitelliform maculopathy; bilateral diffuse uveal melanocytic proliferation; paraneoplastic optic neuropathy; and polyneuropathy, organomegaly, endocrinopathy, monoclonal gammopathy, and skin changes syndrome. Distinguishing these disorders from their non-paraneoplastic counterparts (e.g., autoimmune-related retinopathy and optic neuropathy, and acute zonal occult outer retinopathy) and determining appropriate systemic evaluation for the responsible tumor can be challenging. In addition, we discuss the utility and interpretation of autoantibody testing.     

Sensitivity to first- and second-order motion and form in children and adults

We compared the sensitivity of adults and children aged 3-10 years to first- and second-order motion and form. For first-order stimuli, at all ages sensitivity was better for motion than form, and motion thresholds were better at 6 Hz than at 1.5 Hz. For second-order stimuli, at all ages sensitivity was better for form than motion, and motion thresholds were better at 0.25 cyc/deg than at 1 cyc/deg. Thresholds became adult-like later for motion than for form and later for first-order than second-order stimuli. For first-order stimuli, the changes with age were larger and more protracted.     

Nodes and nodal points and lines in eyes and other optical systems

The typical stigmatic optical system has two nodal points: an incident nodal point and an emergent nodal point. A ray through the incident nodal point emerges from the system through the emergent nodal point with its direction unchanged. In the presence of astigmatism nodal points are not possible in most cases. Instead there are structures, called nodes in this paper, of which nodal points are special cases. Because of astigmatism most eyes do not have nodal points a fact with obvious implications for concepts, such as the visual axis, which are based on nodal points. In order to gain insight into the issues this paper develops a general theory of nodes which holds for optical systems in general, including eyes, and makes particular allowance for astigmatism and relative decentration of refracting elements in the system. Key concepts are the incident and emergent nodal characteristics of the optical system. They are represented by 2 × 2 matrices whose eigenstructures define the nature and longitudinal position of the nodes. If a system's nodal characteristic is a scalar matrix then the node is a nodal point. Otherwise there are several possibilities: Firstly, a node may take the form of a single nodal line. Second, a node may consist of two separated nodal lines reminiscent of the familiar interval of Sturm although the nodal lines are not necessarily orthogonal. Third, a node may have no obvious nodal line or point. In the second and third of these classes one can define mid-nodal ellipses. Astigmatic systems exist with nodal points and stigmatic systems exist with no nodal points. The nodal centre may serve as an approximation for a nodal point if the node is not a point. Examples in the Appendix , including a model eye, illustrate the several possibilities.