General Ophthalmology

BACKGROUND AND OBJECTIVES:

To evaluate the benefit of measuring the intraocular pressure (IOP) on the first postoperative day after argon laser trabeculoplasty (ALT).

PATIENTS AND METHODS:

We retrospectively reviewed 407 ALT procedures with perioperative apraclonidine performed on 226 patients between January 1991 and December 1993. Data analyzed included type of glaucoma, extent of treatment, whether the procedure was initial or repeat, laser parameters, and IOP preoperatively and at 1 hour, 1 day, and 1 month postoperatively.

RESULTS:

The percentage of patients with an IOP rise of greater than 3 mm Hg at 1 hour, 1 day, and 1 month following ALT was 11.3%, 4.2%, and 5.2% respectively. The incidence of IOP elevations greater than 10 mm Hg was 2.2%, 1.0%, and 1.5% at 1 hour, 1 day and 1 month, respectively. Of 17 cases with an IOP elevation greater than 3 mm Hg at 1 day, four eventually required a trabeculectomy. However, there were no consistent factors that distinguished which cases with elevated IOP at 1 day ultimately needed further therapy, nor did the 1-day postoperative examination predict which patients would have IOP elevation at 1 month.

CONCLUSION:

IOP 1 day after ALT is rarely elevated and does not correlate with IOP elevation at 1 month. Therefore, an IOP check at 1 day is not felt to be necessary for most patients.

Authors' Abstract, Ophth Surg & Laser
Duke Univ

General Ophthalmology

Optic atrophy of uncertain etiology is a recurrent clinical dilemna. The authors investigate a theory based on the neurosurgical idea that a normal intracranial blood vessel can compress and adjacent nerve causing damage and potential atrophy. They seek to discover the anatyomical relationship between the intracranial portion of the internal carotid artery (ICA) and the optic nerve as it exits the optic canal on its way to the optic chiasm.

Methods:

Records were reviewed and 48 patients were identified as having gradual optic atrophy of uncertain etiology. All patients had optic disk pallor, visual field abnormalities, afferent defect (unless condition was bilateral - 3 patients), normal MRI scans and a negative work-up. They could not have any evidence of optic nerve swelling, progressive cupping, temporal arteritis, multiple scelerosis, loss of vision less than 46 years of age or a history of acute visual loss.

Each patient was age matched with an otherwise healthy indiviual to form a control group.

MRI scans including coronal images were performed within three months of the initial exam. Measurements for each were recorded in a masked fashion:

1. ICA Flow void to optic nerve
2. Optic nerve diameter
3. diameter of the ICA flow void

Results:

1. The affected nerves were anatomically closer to the ICA compared to the unaffected side and to controls.
2. The diameter of the optic nerves weres significantly smaller on the affected side.
3. The ICA flow voids were statistically similar, ie. the ICA were normal in all patients.

Raymond G. Magauran, M.D.
Buffalo, New York

General Ophthalmology

The investigators studied the adherence of Acanthamoeba cysts and trophozoites to unworn RGP (silicone acrylate and fluoropolymer) and low and high water content soft contact lenses. A corneal ulcer isolate of Acanthamoeba polyphaga was grown and harvested for this work. After exposure for zero to 7 hours, lenses were either "washed" (using a magnetic stirrer to simulate actual contact lens usage) or "not washed" and adherence was determined by light microscopy and a hemocytometer.

Both cysts and trophozoites adhered to all four types of lenses and adhesion increased with exposure time. The number of cysts and trophozoites was higher (P= 0.043-0.0003) in the unwashed group of lenses at all exposure times for all lenses. Among the washed groups, adherence was greatest with RGP silicone acrylate and high water soft contact lenses; trophozoites showed greater adherence to RGP's (P=0.033) and cysts showed greater adherence to the high water soft lenses.

This study highlights the fact that the risk of Acanthamoeba keratitis is as great for RGP lenses as with soft lenses if the contact lens wearer is non-compliant with a proper cleaning regimen. They have shown that "washing" plays an important role in dislodging the microorganisms; the "non-laboratory" definition of "washing" being surfactant cleaning and rinsing.

We have known that the sources of Acanthamoeba infection can be many, but they have taught us that when present, the cysts and trophozoites will adhere immediately to ANY contact lens.

In light of this study, the importance for RGP wearers to avoid "water rinsing" (ie. potential contamination before & after "disinfection") is underscored. Preserved saline solution should be recommended in lieu of tap water rinsing for RGP lenses and swimming with any type of contact lens must be taboo.

Todd Hostetter, COMT, NCLC
Lancaster, PA

General Ophthalmology

1. Does intensive therapy completely prevent the development of retinopathy?

2. Are some states of retinopathy too advanced to benefit from intensive therapy?

3. Are the retinopathy endpoints in the DCCT clinically important?

4. What other factors influence the effectiveness of therapy?

Methods:

The DCCT has shown that intensive treatment of IDDM using three or more daily injections of insulin along with frequent home monitoring with the purpose of keeping blood glucose within a narrow range reduces the progression of diabetes when compared with conventional therapy. The second phase of the trial attempted to answer the above questions. the methods used the two groups enrolled in the original DCCT. The primary prevention cohort included 726 patients with 1 to 5 years duration of IDDM who were free of retinopathy. The secondary intervention cohort included 715 patients with IDDM of 1 to 15 years duration and mild to moderate background diabetes. Of the 1441 patients in the trial, 11 died. Eight of the remaining 1430 failed to have follow-up. The patients in the primary and secondary cohorts were followed for an average of 6 and 7 years, respectively (range 4 to 9 years). Patients in both groups were assigned randomly to either intensive therapy or conventional therapy. Seven-field stereoscopic color fundus photographs were taken every six months and graded using the ETDRS protocol. The outcome for the primary prevention cohort was the presence of at leas 1 microaneurysm at two consecutive 6 month visits; the principal outcome for the secondary intervention cohort was a 3 or more step progression in retinopathy as determined by a table of worsening retinopathy. The presence of clinically significant macular edema (CSME) was also used as an outcome measure. Subjects and investigators were masked to outcome.

Results:

The cumulative incidence of sustained microaneurysm development (>1) for the primary cohort in the intensive group was 70% versus 90% for the conventional group. Intensive treatment slowed the development of retinopathy in the study, but did not ultimately prevent its onset for the majority of patients over the 9 year period. The development of a three step or more progression in retinopathy by the study criteria was, like-wise, shown to improve in the intensive treatment group. Similar results were found with the secondary intervention cohort. The 9 year cumulative incidence of a three or more step progression in disease was 56% for those with intensive treatment versus 78% for those treated conventionally. The cumulative incidence of CSME for the intensive and conventional treatment groups were 15% and 27%. Many other subgroup analysis were performed. Most showed a significant improvement with intensive treatment.

Summary:

The answer to the first question is yes. Although intensive treatment could not completely prevent retinopathy, it could reduce the first signs of retinopathy. Using less strict criteria, the intensive treatment had a greater effect in reducing more severe retinopathy from developing. The answer to the second question is that all levels of retinopathy appeared to benefit from intensive treatment. Those with severe retinopathy, however, appeared to benefit less. The third question is answered by looking at CSME, severe nonproliferative retinopathy and proliferative retinopathy patients in the study. The DCCT demonstrated a 23% to 64% reduction in these endpoints with intensive therapy. The answer to question 4 is that no distinct and separate factors were identified that influence the effectiveness of treatment. All of the analyses showed that 3 or more years of intensive treatment are necessary for beneficial effects on retinopathy and early worsening with intensive therapy may delay the benefit within the first 2 years of treatment.

Christopher Olivia, MD, MBA
HCP, Williamsville, NY

General Ophthalmology

The LI method uses low intensity laser projected onto the retina, and relatively unaffected by mild to moderate medial opacities. The low intensity coherent beam is optically manipulated produce a grating pattern of various sizes. The PAM projects a small Snellen chart onto the retina probably through clearer areas of the lens.

With the LOCS II, the density of the medial opacity was graded into levels, from mild to severe, for opacification at the level of the lens nucleus, capsule, and/ or cortex.

The authors used 67 eyes, 45 with cataract only, and 22 with cataract as well as retinal disease (ARMD, RP, and other retinal degeneration). The eyes with opacity only (and no retinal disease) were separated into subgroups based on this LOCS rating. One group with nucleus and psc scores of <4 and cortical ratings <5, had Snellen acuity ranging from 20/25-20/100. The rest, with denser opacities (nucleus and psc=4, cortex=5) had Snellen acuity of 20/25 to hand motions.

Another subgrouping was made, of these opacity only eyes, based solely on preop Snellen acuity: <1.> better than 20/200 <2.> 20/200 or worse. Postop VA in the 20/32 or better in 45 eyes with opacity only. In 39 of these eyes, vision was better than 20/20. Probably based on this result, the authors defined accuracy in the study as eyes predicted to support 20/40 vision or better. In every case the PAM and LI gave a correct prediction, or underestimated potential acuity.

In the normal group, when eyes were separated by the LOCS II system, the PAM gave significantly different results in mild vs dense opacities, while the LI did not. Accuracy ratings were:

Eyes with mild medial opacities: PAM 100% LI 92% Eyes with denser opacities: PAM 52% LI 79%

The results for the normal group, when separated by Snellen acuity only, were similar. Accuracy ratings for these were:

Eyes with better than 20/200 : PAM 74% LI 94% worse than 20/200 : PAM 43% LI 57%

The relative accuracy of LI and PAM was analyzed based on location of the opacity for these eyes: Where there was only PSC, the PAM and LI gave more false negatives than where there was only nuclear or cortical opacification. The remaining 22 eyes, with retinal disease in addition to cataract. There, PAM overestimated acuity by one line in two eyes, and the LI by one line in three eyes, two lines in two eyes, and three lines in one eye. A well documented false-positive (over-estimate of post-op acuity) is macular edema, where much of the acuity loss is due to retinal optical qualities, which have relatively little effect on imaging of the laser generated stimulus. This does not occur for the PAM, and may account for less false-positive results with PAM measurements. The combination of less false-positives by PAM (where pathology was present), and less false-negatives by LI (with denser cataract) leads the authors to suggest that the two methods could be most useful when used together. Since the pathological conditions are most often visualized, the instrument could be chosen based on the factors considered in this study.

Tom M, Maida
Gainesville, FL