Cataract surgical problem

Experimental Model of Far Temporal Field Negative Dysphotopsia Generated in Phakic Eyes

Purpose

The axial separation between the iris and the intraocular lens (IOL) in pseudophakic eyes can cause rays originating from the far temporal field to miss the IOL, resulting in negative dysphotopsia (ND). We developed an experimental model to test the hypothesis that obstruction of rays from the far temporal field can generate ND and an accompanying loss of visual sensitivity in the far temporal field.

Methods

The right eyes of 10 phakic subjects were fitted with soft contact lenses containing a 5.50-mm central clear zone and a 12-mm outer diameter opaque annulus. In three of the subjects, eyes were dilated with 1% tropicamide solution, and effective aperture diameters were determined optically (pupil camera) and psychophysically (narrow beam detection). Visual field extent (Goldmann bowl) and temporal and inferotemporal meridian sensitivities (Octopus perimeter) were measured. A wide-angle model was constructed to quantify the impact of the annular opacity on retinal illuminance.

Results

All 10 subjects observed a dark crescent in the far temporal and inferotemporal fields. The opaque annulus reduced effective horizontal pupil diameters from 8 mm to 5.5 mm on-axis and from >2 mm to <1 mm at 90°. Perimetry revealed a 10° reduction in temporal and inferotemporal field extent and increasing loss of sensitivity beyond 70°. The wide-angle model confirmed significant vignetting (>50% beyond 70°), approaching zero retinal illuminance beyond 85°.

Conclusions

Vignetting of rays originating from the far temporal field by axially separated apertures can create symptoms mirroring perceptual reports of negative dysphotopsia in symptomatic pseudophakic patients.

Paradigm shifts, peregrinations and pixies in ophthalmology

Human ingenuity is challenged by defending vision, our highest bandwidth sense. Special challenges are presented by the replacement or repair of highly specialized but scarce tissue within the constraints of transparency, tissue shape and alignment, tissue borders and pressure maintenance. Many, mostly destructive, surgical procedures were developed prior to an understanding of underlying pathophysiology. For a number of conditions, both reconstructive and destructive procedures co-exist, yet there are few guidelines as to the better approach. Because the consequences of these procedures may take many years to surface (consistent with a stem cell role in long-term tissue maintenance), guidance may be provided by the elucidation of underlying principles from these approaches. Illustrative examples from clinical, basic research and biotechnology, particularly relating to pterygium, ocular surface squamous neoplasia, dry-eye syndrome, corneal rehabilitation and replacement, cataract surgery, strabismus surgery and bionic eye research, are described. An unexpected consequence of bionic device development has been an appreciation of the sophistication of tissues being replaced, given the limitations of available biomaterials. Examples of how this has provided insights into ocular disease will be illustrated. Stem cell and biomaterial technologies are starting to impact at a time when cost-effectiveness is under scrutiny. Both efficacy and cost will need to be considered as these interventions are introduced. It appears that the paradigm shift rate is accelerating and there is evidence of this in ophthalmology. Lessons learned from the areas of destructive versus reconstructive surgery and the limitations of development of bionic replacements will be used to illustrate how new procedures and technologies can be developed.

The Complexities of Negative Dysphotopsia

The appearance of a dark shadow in the temporal periphery, otherwise known as negative dysphotopsia, continues to be a problem for some patients after routine uncomplicated cataract surgery. Etiologies include type and design of intraocular lens (IOL), anatomical features and dimensions of the eye, pupil size, angle kappa, relationship of the optic to the anterior capsule, and the position of the optic/haptic junction of the IOL. Although the primary etiology remains controversial, it is clear that the cause is multifactorial. All of the factors should be considered when attempting to prevent or treat this phenomenon.

Ultraviolet radiation and the anterior eye

The eye is on the one hand dependent on visible light energy and on the other hand can be damaged by these and the contiguous ultraviolet (UV) and infrared wavelengths. Diseases of the eye in which sunlight has been implicated have been termed the ophthalmohelioses, and these conditions pose a significant problem to the eye health of many communities. The ophthalmohelioses have a tremendous impact on patients' quality of life and have significant implications on the cost of health care. Although cataract is not entirely caused by insolation, it now seems certain that sunlight plays a contributory role-cataract extraction is one of the, if not the most, commonly performed surgical procedures in many societies. Pterygium, typically afflicting a younger population, adds a tremendous burden, both human and financial, in many countries. We review evidence that peripheral light focusing by the anterior eye to the sites of usual locations of pterygium and cataract plays a role in the pathogenesis of these conditions. Recognition of the light pathways involved with foci at stem cell niches has directed our investigations into inflammatory and matrix metalloproteinase-related pathophysiologic mechanisms. An understanding of the intracellular mechanisms involved has provided some insight into how medical treatments have been developed for the effective management of ocular surface squamous neoplasia. The concept of peripheral light focusing has also provided direction in the prevention of these diseases. This has resulted in improved sunglass design and the further development of UV-blocking contact lenses. With the development of ocular UV fluorescence photographic techniques, we have been able to demonstrate preclinical ocular surface evidence of solar damage. Evidence that diet may play a role in the development of certain conditions is reviewed. The conundrum of the public health message about solar exposure is also reviewed, and in this context, the potential role of vitamin D deficiency is summarized. The eye may play a role in the development of individualized assessment techniques of solar damage, perhaps allowing us to provide better advice to both individuals and populations.

Negative dysphotopsia: long-term study and possible explanation for transient symptoms

PURPOSE

To study the incidence, course, and common factors of patients with negative dysphotopsia and consider the possible role of the corneal incision in cases in which symptoms are transient.

SETTING

Private practice and the University of Cincinnati, College of Medicine, Cincinnati, Ohio, USA.

METHODS

Phacoemulsification with implantation of a single-piece acrylic intraocular lens (IOL) was performed in 250 consecutive routine cataract procedures. Patients were asked whether they noticed a temporal shadow on the day after surgery and were followed by serial evaluations for 3 years. Evaluations included subjective questionnaires and objective testing.

RESULTS

The incidence of negative dysphotopsia was 15.2% on the first postoperative day, decreasing to 3.2% after 1 year, then 2.4% after 2 and 3 years. Common findings included a shallow orbit, prominent globe, space greater than 0.45 mm between the iris and IOL by ultrasound biomicroscopy, and perimetric comet-shaped light in the area corresponding to the shadow. Slitlamp revealed a transparent peripheral capsule and a shadow sign in which a linear shadow on the iris became curvilinear as the light from the slit beam was projected through the incision toward the pupil.

CONCLUSIONS

Two groups of patients experienced negative dysphotopsia that rapidly resolved or remained unchanged from the first postoperative day. It is hypothesized that the corneal edema associated with a beveled temporal incision contributes to transient negative dysphotopsia.

Comparison of pseudophakic dysphotopsia with Akreos Adapt and SN60-AT intraocular lenses

PURPOSE

To determine the relative incidence of unwanted light images with the AcrySof SN60-AT intraocular lens (IOL) (Alcon) and the Akreos Adapt (Bausch & Lomb) IOL.

SETTING

The Eye Clinic, Sir Charles Gairdner Hospital, Nedlands, Australia.

METHODS

In a prospective randomized study of 61 patients who had cataract surgery, the relative incidence of unwanted light images with 2 biconvex acrylic double square-edged IOLs, the SN60-AT and Akreos Adapt, was compared. Patients were followed at 1 week and for a minimum of 6 weeks. At both follow-ups, patients were asked to rate their experience of dysphotopic phenomenon according to a set of questionnaire criteria. The Mann-Whitney test was used to analyze the ordinal data.

RESULTS

All 61 patients were interviewed at both stages of follow-up. The mean follow-up was 8 weeks +/- 2 (SD). At 1 week, there was significantly more dysphotopsia (positive and negative) with the SN60-AT IOL (37.5%) than with the Akreos Adapt IOL (24.1%) (P = .042). Significantly more patients with the SN60-AT IOL reported negative dysphotopsia at 1 week only. At 8 weeks, the incidence of positive and negative dysphotopsia declined to 31.3% and 20.7% in the SN60-AT group and Akreos Adapt group, respectively, and there was no longer a statistically significant difference between the 2 groups.

CONCLUSIONS

More patients with the SN60-AT IOL than with the Akreos Adapt IOL reported dysphotopsia. One week postoperatively, the difference was significant. The difference was primarily a result of the higher incidence of negative dysphotopsia with the SN60-AT IOL. At 8 weeks, the incidence of all types of light phenomena was significantly lower in both groups.