Effects of anti-inflammatory drugs following cataract extraction.

Cycloplegics, corticosteroids, and nonsteroidal anti-inflammatory drugs have been applied in the treatment of postoperative inflammation following cataract extraction. Of these, topical preparations of nonsteroidal anti-inflammatory drugs, such as ketorolac tromethamine 0.5% and diclofenac sodium 0.1%, offer comparable efficacy to corticosteroids in the reduction of postoperative inflammation, and offer lower risks of adverse events in most patients. Comparative studies of these drugs from the past 5 years are highlighted.

The effect of excimer laser photorefractive keratectomy on intraocular pressure measurements using the Goldmann applanation tonometer.

PURPOSE: The authors determined whether photorefractive keratectomy (PRK) affects Goldmann applanation readings in human eyes. METHODS: The intraocular pressure (IOP) of 111 patients was measured using Goldmann applanation tonometry at baseline and 12 months after PRK. Ultrasonic corneal thickness measurements and keratometry were also obtained. Contralateral eyes were used as controls. RESULTS: There was a statistically significant decrease in mean tonometer readings in the treated eyes when compared with the control eyes (0.5 +/- 2.1 mmHg, P = 0.01) accompanied by a significant reduction in mean central pachymetry in the treated eyes (23 +/- 23 microns, P < 0.001). In the treated eyes, the mean spherical equivalent and mean central keratometry readings were significantly reduced by 3.3 +/- 1.5 and 2.2 +/- 1.2 diopters, respectively (P < 0.001). CONCLUSION: Photorefractive keratectomy causes a mild lowering of the Goldmann tonometer readings. The reduction in IOP measurement is probably not enough to alter a therapeutic decision in an individual patient known to have glaucoma, but it may delay recognition and treatment of glaucoma.

Rapidly progressive outer retinal necrosis caused by varicella zoster virus in a patient infected with human immunodeficiency virus.

We describe a 21-year-old immunocompromised patient with a unique type of necrotizing herpetic retinitis. The retinitis progressed with loss of vision when acyclovir or ganciclovir alone was used for treatment. Examination of a chorioretinal biopsy specimen revealed that varicella zoster virus was the causative agent. Foscarnet monotherapy also failed to prevent progression of the retinal infection. Combination antiviral therapy with ganciclovir and foscarnet appeared to delay progression of disease and helped maintain a visual acuity of 20/200 for at least 6 months after the onset of infection.

Does decompression diminish the discomfort of severe dysthyroid orbitopathy?

We assessed whether patients perceived that surgical decompression had reduced the discomfort of dysthyroid orbitopathy. Standard pain instruments were administered to 13 consecutive patients of a university-based oculoplastic practice who had undergone two-wall orbital decompression for dysthyroid optic neuropathy. We used visual analog scale (VAS) ratings of pre- and postoperative orbital discomfort. On a 0 to 10 scale, relief of discomfort after decompression was rated as moderate or better (VAS > 9.0) in 13 of 13 patients (mean VAS = 9.22, SD = 0.91) and complete (VAS = 10.0) in 8 of 13. Patients perceived that surgical decompression was associated with a clinically and statistically significant (p < 0.001) reduction of discomfort.

Light distribution of ocular endophotocoagulator probes and its surgical implications.

Ophthalmic endophotocoagulator probe cone angle affects the spot size, working distance, laser output power requirement, tissue exposure time, and uniformity of tissue irradiance, which all affect ease and safety of clinical use. The cone angle and irradiance distribution of several ophthalmic endophotocoagulator delivery systems were studied by directing the laser energy emitted by them on a CCD video sensor at several angles of incidence. The irradiances followed a Gaussian distribution. The measured irradiances were compared to a mathematical model of tissue irradiance that adjusted for the cone angle, probe-tissue distance, and angle of incidence. Using this model, laser irradiances produced by endophotocoagulator probes can be estimated under a wide variety of conditions. At highly oblique angles of incidence, wide-angle probes produce unexpectedly higher and uneven tissue irradiance. When numerous characteristics are considered, probes with a cone angle in the range of 10 degrees have many advantages over narrower or wider angle probes.

Sources of error with use of Goldmann-type tonometers.

There are many sources of error in the use of Goldmann-type applanation tonometers. In clinically normal corneas hypofluorescence of the precorneal tear film, accommodation, the Valsalva maneuver and vertical gaze are preventable causes of large tonometric errors. Repeated tonometry may induce a decline in the intraocular pressure (IOP). Variations in the corneal resistance to indentation between eyes cause significant errors. The most significant cause of error in clinically abnormal eyes is corneal epithelial edema, which causes a marked underestimation of IOP. Measurements obtained with Goldmann-type tonometers can be used with confidence to monitor changes in the IOP of an individual, but should not be relied on to determine the absolute manometric pressure within an eye or to compare the IOPs in eyes of different individuals.

The effect of corneal thickness on applanation tonometry.

Simultaneous manometry and Perkins tonometry were performed at 10.0, 20.0, and 30.0 mm Hg on 15 eyes on which intraocular procedures were performed. There was a statistically significant relationship between corneal thickness and the error of Perkins tonometry. Thin corneas produced underestimations of the intraocular pressure by as much as 4.9 mm Hg, whereas thick corneas produced overestimations by as much as 6.8 mm Hg. Measuring the corneal thickness is necessary to interpret properly the results of Goldmann applanation tonometry, particularly in eyes with thin corneas.

Effect of buckling material on ocular rigidity.

Enucleated human eyes were banded with metal and silicone bands to produce reductions in their diameter of 2 mm and 4 mm. The ocular rigidity produced by each banding material at each diameter was measured in the pressure range of 10 mmHg to 40 mmHg. Metal bands produced mild reductions in ocular rigidity that were significantly (P less than 0.05 to 0.01) lower than the control ocular rigidities in some pressure ranges. Silicone bands produced large reductions in ocular rigidity that were significantly (P less than 0.01) lower than ocular rigidities observed in metal-banded or control conditions in all pressure ranges. The influence of the elastic silicone banding material on ocular rigidity was greater than the influence of altered shape and wall stress that occurred with metal banding.

Comparison of Oculab Tono-Pen readings obtained from various corneal and scleral locations.

When estimating intraocular pressure in patients who are uncooperative or who have central corneal disturbances, the physician may find it either impractical or undesirable to place the small tip of a portable electronic applanation tonometer (Tono-Pen) over the central cornea. To gauge better the usefulness of Tono-Pen readings obtained from various locations, we compared such readings measured through the central cornea, midperipheral cornea, limbal cornea, and sclera of 15 cannulated eye bank eyes. Mean Tono-Pen readings from the midperipheral and clear limbal cornea did not differ significantly from central corneal readings over a 10- to 35-mm Hg range of intraocular pressures and were within +/- 2.4 mm Hg of mean central corneal readings. Mean readings taken from the sclera, however, were 8.8 to 17.0 mm Hg higher than mean central corneal readings over the 10- to 40-mm Hg range. We concluded that multiple noncentral corneal readings with the Tono-Pen provided a useful approximation of intraocular pressure, whereas scleral readings did not.

B-scan ultrasonography of eyes containing intravitreal gas.

Contact B-scan ultrasonography was performed on postoperative eyes containing intravitreal gas. Correlation of the ultrasonograms with the ophthalmoscopic findings disclosed that intraocular gas had a characteristic appearance on B-scan ultrasonography. Gas-fluid and gas-tissue interfaces were so highly reflective that no structures within or behind a bubble could be visualized. Shadowing, reverberation, and reflection artifacts were prominent, and dominated ultrasonographic findings. If the ultrasonographic characteristics of gas are understood, it is possible to use B-scan ultrasonography to determine if intraocular gas is present, whether there are one or several bubbles, and what percentage of the vitreous cavity is filled by gas. Specular reflection from a gas-fluid interface may be used to examine portions of the eye that might not otherwise be easily seen with ultrasonography.

The effect of transcutaneous electrical nerve stimulation on ocular pain.

The effect of transcutaneous electrical nerve stimulation (TENS) on pain originating in the eye was studied in 10 patients. All three patients subjected to TENS during panretinal photocoagulation reported marked reduction in pain. Three of five patients who had persistent pain following scleral buckling and/or vitrectomy reported partial or complete relief of pain during the application of TENS. One patient had equivocal relief of pain when TENS was used during retinal cryopexy; 1 patient with acute pain following paracentesis and 1 patient with persistent pain following cyclocryotherapy had no relief. Among those patients whose pain was reduced by TENS, referred brow pain was relieved more than globe pain.

The effect of Perkins, Tono-Pen, and Schiötz tonometry on intraocular pressure.

We studied the intraocular pressure changes produced in five eye bank eyes by Perkins, Tono-Pen, and Schiötz tonometry performed by experienced and inexperienced personnel. When all users were considered together, Perkins tonometry produced a mean intraocular pressure increase of 0.7 mm Hg, significantly less than the mean increase of 12.1 mm Hg produced by Tono-Pen tonometry (P less than .05) or the mean increase of 16.5 mm Hg produced by Schiötz tonometry (P less than .01). There was no statistically significant difference between the intraocular pressure increase produced by Tono-Pen or Schiötz tonometry. Tonometry performed by inexperienced Tono-Pen users and experienced or inexperienced Schiötz users produced a significantly greater increase in intraocular pressure than that performed by experienced Tono-Pen users (P less than .05), and an extremely significant increase compared to tonometry performed by experienced or inexperienced Perkins users (P less than .01). The marked increase in intraocular pressure produced by Tono-Pen tonometry suggests that hand-held electronic applanation tonometers should be used with caution in eyes with a weakened cornea or sclera.

Tolerance of intravitreal povidone-iodine in rabbit eyes.

Povidone-iodine is frequently instilled on to the conjunctival surface prior to intraocular surgery in order to prevent septic endophthalmitis. A small amount of povidone-iodine is inevitably introduced into the eye when it is used in this manner. The toxicity of intravitreal povidone-iodine was assessed in rabbit eyes by injecting 0.1 ml of povidone-iodine in concentrations of 0.05%, 0.5% and 5% into the vitreous cavity. The injected eyes were evaluated by clinical examination, anterior segment and fundus photography, endothelial cell counts, electroretinography and histopathology. Compared to control eyes, no changes were observed in all 6 eyes injected with 0.1 ml of 0.05% povidone-iodine solution. 9 of 10 eyes tolerated a concentration of 0.5% with no detectable adverse changes. One eye developed a temporary mild iritis and mild suppression of the ERG. Intra-retinal hemorrhages, edema, arteriolar narrowing and retinal edema were seen one week following injection. Mild retinal necrosis of the same area was seen on histology. All 4 eyes injected with 5% povidone-iodine developed temporary hypotony and iridocyclitis. A dense cataract developed in all eyes. Full thickness retinal necrosis and a profound lasting reduction in the ERG was produced in all of these eyes. No corneal epithelial or endothelial changes were observed in any eye in this series. Low concentrations of intravitreal povidone-iodine likely to be produced by instillation prior to surgery are tolerated by rabbit eyes. The concentrations tolerated by the studied eyes are near reported bactericidal levels.

Hazards of laser beam reflections in eyes containing gas.

Three patients suffered photic or thermal laser injuries at unintended sites because of reflection from gas-fluid interfaces in eyes containing gas. Fresnel's equations predict the amount of light transmitted or reflected at optical interfaces. Application of Fresnel's equations demonstrate that significant laser reflection occurs at gas-fluid or fluid-gas interfaces, especially at high angles of incidence. Photocoagulation across gas-fluid or fluid-gas interfaces should be avoided to reduce the risk of unintended damage from reflected light. If photocoagulation must be performed across an interface, the surgeon should minimize the angle of incidence of the treatment laser beam, use a divergent beam, and consider the location and intensity of the reflected beam. Because of the higher phototoxicity of blue light, photocoagulation with blue-green lasers across gas-fluid or fluid-gas interfaces is undesirable. Proper polarization of the treatment laser beam may significantly reduce laser reflectance.

Argon indirect ophthalmoscopic photocoagulation: reduced potential phototoxicity with a fixed safety filter.

A new argon indirect ophthalmoscopic photocoagulator is presented which uses a red helium-neon laser aiming beam. An interference filter protects the operator from green or blue-green treatment beam reflections without impairing visualisation of the aiming beam or significant retinal anatomy. The protective filter is fixed in place, eliminating the weight, noise, and potential failure of mechanically switched filters. The red aiming beam has a negligible potential for producing photochemical retinal damage in the patient or operator.

The effect of intraocular gas and fluid volumes on intraocular pressure.

Large increases in the intraocular pressure (IOP) of postoperative gas-containing eyes may require the removal of gas or fluid to reduce the IOP to the normal range. Application of the ideal gas law to Friedenwald's equation provides a mathematical model of the relationship between IOP, intraocular gas and fluid volumes, and the coefficient of scleral rigidity. This mathematic model shows that removal of a given volume of gas or fluid produces an identical decrease in IOP and that the more gas an eye contains, the greater the volume reduction necessary to reduce the pressure. Application of the model shows that the effective coefficient of scleral rigidity is low (mean K, 0.0021) in eyes with elevated IOP that have undergone vitrectomy and retinal cryopexy and very low (mean K, 0.0013) in eyes with elevated IOP that have undergone placement of a scleral buckle and band. By using the appropriate mean coefficient of rigidity, the volume of material to be aspirated to produce a given decrease in IOP can be predicted with clinically useful accuracy.