A new device to noninvasively estimate the intraocular pressure produced during ocular compression.

PURPOSE: To describe a noninvasive instrument that estimates intraocular pressure during episodes of external globe compression and to demonstrate the accuracy and reliability of this device by comparing it to the intraocular pressures simultaneously and manometrically measured in cannulated eyes. METHODS: A thin fluid-filled bladder was constructed from flexible and inelastic plastic sheeting and was connected to a pressure transducer with high pressure tubing. The output of the pressure transducer was sent to an amplifier and recorded. This device was validated by measuring induced pressure in the fluid-filled bladder while digital pressure was applied to one surface, and the other surface was placed directly against a human cadaver eye or in vivo pig eye. The human cadaver and in vivo pig eyes were each cannulated to provide a manometric intraocular pressure control. RESULTS: The measurements obtained with the newly described device were within ~5% of simultaneously measured manometric intraocular pressures in both a human cadaver and in vivo pig eye model for a pressure range of ~15-100 mmHg. CONCLUSION: This novel noninvasive device is useful for estimating the intraocular pressure transients induced during any form of external globe compression; this is a clinical setting where no other devices can be used to estimate intraocular pressure.

Review of external ocular compression: clinical applications of the ocular pressure estimator.

PURPOSE: The authors have previously validated an Ocular Pressure Estimator (OPE) that can estimate the intraocular pressure (IOP) during external ocular compression (EOC). The authors now apply the OPE in clinical states where EOC is clinically important. The original work is described for two periods of risk: during sleep and during the digital ocular massage (DOM) maneuver used by surgeons after trabeculectomy to keep the operation functional. Other periods of risk for external ocular compression are then reviewed. METHODS: The first protocol estimated the IOP in the dependent eye during simulated sleep. Subjects had their IOPs initially measured in an upright-seated position, immediately upon assuming a right eye dependent side sleeping position (with nothing contacting the eye), and then 5 minutes later while still in this position. While maintaining this position, the fluid filled bladder of the OPE was then placed between the subject's closed eye and a pillow during simulated sleep. The IOP was continuously estimated in this position for 5 minutes. The subjects then had the IOP measured in both eyes in an upright-seated position. The second protocol determined if a larger vertical cup-to-disc ratio was more common on the side that patients reported they preferred to sleep on. The hypothesis was that chronic asymmetric, compression induced, elevations of IOP during sleep would be associated with otherwise unexplained asymmetry of the vertical cup-to-disc ratio. The third protocol assessed the IOP during DOM. The OPE was used to characterize the IOP produced during the DOM maneuver of five glaucoma surgeons. After this, 90 mmHg was chosen as a target pressure for DOM. The surgeons were then verbally coached during three additional compressions. After a 5-minute period, the surgeons were asked to reproduce this targeted IOP during subsequent compressions. RESULTS: The mean IOP during the "sleep session" was 22±5 mmHg (SEM). The mean peak pressure was 40±11 mmHg (SEM) and the mean trough pressure was 15±2 mmHg (SEM). There was a 78% agreement between the eye that was reported to be dependent during sleep and the eye with the larger vertical cup-to-disc ratio, for eyes with at least a 0.10 cup-to-disc ratio difference, P=0.001, n=137. The OPE estimated an average induced IOP during typical DOM of 104±8 mmHg (SEM), with each compression having an average range of 17±3 mmHg (SEM). After coaching, and a 5-minute waiting period, the average induced IOP reduced to 95±3 mmHg (SEM) with a reduced average range of IOP to 11±1 mmHg. CONCLUSION: The OPE was successfully used to estimate the IOP while subjects experienced EOC during normal sleep postures. These EOC-induced elevations of IOP were considerable, and likely contribute to significant ocular pathology, not only for glaucoma, but for retinal vascular occlusive diseases, retinal vascular leakage, and the induction of the ocular-cardiac reflex in infants, as well. The correlation of a larger vertical cup-to-disc ratio in patients with a sleep posture preference suggests a causal relationship, since patients with other conditions known to be associated with cup-to disc ratio asymmetry were excluded from this study. The OPE is a useful device to teach DOM to surgeons and patients for home use.

Neovascular glaucoma at king khaled eye specialist hospital - etiologic considerations.

BACKGROUND: Neovascular glaucoma (NVG) is a severe form of secondary glaucoma caused by the growth of new vessels over the trabecular meshwork. The principal causes are associated with retinal ischemia. Ablative treatment of the retina can prevent, halt, and even reverse the growth of new vessels on the iris and angle. It is an essential part of the management in most cases. AIMS: To determine the causes of NVG among Saudi patients, presented at the King Khaled Eye Specialist Hospital. METHODS: A retrospective review of 337 Saudi patients with NVG was obtained. All cases were reviewed for the evidence and causes of the disease, and their basic demographic information. A subset of 100 diabetic patients with PDR was further studied in greater detail for clinical findings and treatment history. RESULTS: The most common primary etiologic associations for NVG included diabetic retinopathy (DR) (56.06%), retinal venous obstruction (26.40%), and chronic retinal detachment (03.56%). A history of diabetes mellitus was reported in 65.04%, systemic arterial hypertension was noted in 61.00%, and evidence of renal impairment was documented in 22.00%. Vision was markedly reduced in most eyes with NVG (median: hand motion). The median best visual acuity in the fellow eye was 20/160. Among the 100 cases, with DR as a cause of NVG, 43 patients had bilateral neovascularization of the iris (NVI) and 72 had bilateral PDR. Sixty-one patients had no previous laser treatment before the diagnosis of NVG. Among these, who received treatment, the median number of total laser spots was 1,003. CONCLUSIONS: Diabetes is a major cause of NVG presented to this tertiary eye care center in the Kingdom of Saudi Arabia followed by retinal venous obstruction. Close monitoring and full pan-retinal photocoagulation (PRP) were absent in most of the diabetic cases. It is important to recognize that the "unaffected" fellow eye, particularly in diabetic patients, may require fairly urgent treatment as well.

Optic nerve head and retinal nerve fiber layer analysis: a report by the American Academy of Ophthalmology.

OBJECTIVE: To evaluate the current published literature on the use of optic nerve head (ONH) and retinal nerve fiber layer (RNFL) measurement devices in diagnosing open-angle glaucoma and detecting progression. METHODS: A search of peer-reviewed literature was conducted on February 15, 2006 in PubMed and the Cochrane Library for the period January 2003 to February 2006. The search was limited to studies of adults in English-language journals and yielded 442 citations. The panel reviewed the abstracts of these articles and selected 159 articles of possible clinical relevance for review. Of these 159 full-text articles, 82 were determined to be relevant for the first author and methodologist to review and rate according to the quality of evidence. RESULTS: There were no studies classified as having the highest level of evidence (level I). The ONH and RNFL imaging instruments reviewed in this assessment were determined to be highly effective in distinguishing eyes with glaucomatous visual field (VF) loss from normal eyes without VF loss, based on level II evidence. In addition, some studies demonstrated that parameters from ONH or RNFL imaging predicted the development of VF defects among glaucoma suspects. Studies on detecting glaucoma progression showed that although there was often agreement on progression between the structural and functional (VF) tests, a significant proportion of glaucoma patients progressed by either the structural or the functional test alone. CONCLUSIONS: The ONH and RNFL imaging devices provide quantitative information for the clinician. Based on studies that have compared the various available technologies directly, there is no single imaging device that outperforms the others in distinguishing patients with glaucoma from controls. Ongoing advances in imaging and related software, as well as the impracticalities associated with obtaining and assessing optic nerve stereophotographs, have made imaging increasingly important in many practice settings. The information obtained from imaging devices is useful in clinical practice when analyzed in conjunction with other relevant parameters that define glaucoma diagnosis and progression.

Corneal thickness measurement in the management of primary open-angle glaucoma: a report by the American Academy of Ophthalmology.

OBJECTIVE: To evaluate published literature to assess whether central corneal thickness (CCT) is a risk factor for the presence, development, or progression of glaucomatous optic nerve damage related to primary open-angle glaucoma (POAG). METHODS: A PubMed literature search limited to English language articles conducted on November 15, 2004 retrieved 195 articles. The authors reviewed these abstracts and selected 57 to review in full text to determine relevance to the assessment questions. A further 24 studies of interest were identified from periodic updates to the literature search, surveillance of the literature, and reference lists of reviewed articles. From the 81 published reports identified, the first author applied specified selection criteria that yielded 37 articles for methodological review because of relevance to the assessment questions. The articles were rated according to the strength of evidence by the panel methodologist. A level I rating was assigned to well-designed properly conducted randomized clinical trials or similar quality-validated cohort studies with appropriate reference standards. A level II rating was assigned to well-designed case-control studies, exploratory cohort studies, and other nonrandomized clinical studies lacking consistently applied reference standards. A level III rating was reserved for poorly designed case-control studies, case series, and papers consisting only of expert opinion without supporting evidence. In addition, each study was graded as positive if it supported a statistical association of CCT with the risk of having or developing glaucomatous optic nerve damage or as negative if no such association was found. RESULTS: There is strong and consistent level I and level II evidence that CCT is a risk factor for progression from ocular hypertension to POAG. Studies that were rated as providing the highest quality of evidence revealed mixed results with respect to glaucoma prevalence. One population-based study (level II) showed a positive association, another larger study (level I) revealed an association of marginal significance, and 3 studies (all level I) found no association of CCT with POAG prevalence. CONCLUSIONS: There is strong evidence that measuring CCT is an important component of a complete ocular examination, particularly for patients being evaluated for the risk of developing POAG. Therefore, CCT measurement should be included in the examination of all patients with ocular hypertension. Although the evidence supporting the necessity of measuring CCT as part of screening for POAG or as a risk factor for glaucoma progression is not as strong, intraocular pressure (IOP) is the only modifiable risk factor in the treatment of glaucoma, and CCT has the potential to significantly impact IOP measurement by applanation tonometry in all patients.

Comparison of optical coherence tomography and ultrasound biomicroscopy for detection of narrow anterior chamber angles.

OBJECTIVE: To assess the accuracy of classification of narrow anterior chamber (AC) angles using quantitative imaging by optical coherence tomography (OCT) and ultrasound biomicroscopy (UBM). DESIGN: Observational comparative study. METHODS: A high-speed (4000 axial scans/s) anterior segment OCT prototype was developed using a 1.3-microm light source. Seventeen normal subjects (17 eyes) and 7 subjects (14 eyes) with narrow angle glaucoma were enrolled. All subjects underwent gonioscopy, OCT, and UBM. Quantitative AC angle parameters (angle opening distance, angle recess area, and the trabecular-iris space area [a new parameter we have defined]) were measured from OCT and UBM images using proprietary processing software. MAIN OUTCOME MEASURES: Specificity and sensitivity in identifying narrow angles with image-derived AC angle parameters. RESULTS: Eight of 31 eyes were classified as having narrow angles (Shaffer grade < or =1 in all quadrants). The AC angle parameters measured by both OCT and UBM had similar mean values, reproducibility, and sensitivity-specificity profiles. Both OCT and UBM showed excellent performance in identifying eyes with narrow angles. Areas under the receiver operating characteristic curves for these parameters were all in the range of 0.96 to 0.98. CONCLUSIONS: Optical coherence tomography was similar to UBM in quantitative AC angle measurement and detection of narrow angles. In addition, it was easier to use and did not require contact with the eye. Optical coherence tomography is a promising method for screening individuals at risk for narrow angle glaucoma.

Automated perimetry: a report by the American Academy of Ophthalmology.

OBJECTIVE: The purpose of this document is to summarize and evaluate the effectiveness of new automated perimetry tests and algorithms in diagnosing glaucoma and detecting disease progression. METHODS: A literature search on automated perimetry retrieved over 300 citations from 1994 to 2001, of which 71 were selected as relevant to this assessment. The quality of the evidence obtained from these studies was assessed by the methodologist. RESULTS: The four automated perimetry techniques described in this assessment are short wavelength automated perimetry (SWAP), frequency doubling technology perimetry (FDT), high-pass resolution perimetry (HPRP), and motion automated perimetry (MAP). The algorithms described are Swedish interactive threshold algorithm (SITA) and SITA fast. With the exception of SWAP, these techniques and algorithms reduce testing time and inconsistent patient performance when compared with conventional full threshold testing. CONCLUSIONS: Short wavelength automated perimetry detected visual field loss earlier than standard threshold automated perimetry, with a sensitivity and specificity of about 88% and 92% respectively. However, it is a lengthy, demanding test, is sensitive to media opacities, and has a greater magnitude of long-term fluctuation compared with standard threshold automated perimetry, which make it difficult to assess disease progression accurately. When compared to standard threshold automated perimetry, FDT perimetry showed sensitivity and specificity greater than 97% for detecting moderate and advanced glaucoma, and sensitivity of 85% and specificity of 90% for early glaucoma. As FDT perimetry has a short testing time and is resistant to blur and pupil size, it may be a useful screening tool. In a longitudinal study, high-pass resolution perimetry was more effective than standard threshold automated perimetry in monitoring progressive glaucomatous loss, detecting progression at a median of 12 months earlier in 54% of patients studied. Motion automated perimetry demonstrated usefulness in detecting early glaucomatous visual loss in a longitudinal study. Studies on SITA demonstrated greater sensitivity and reproducibility and less intertest variability when compared to standard full threshold testing and a 50% reduction in testing times. A study comparing standard full threshold, SITA, and SITA fast found a sensitivity of 95% for the first two techniques and 93% for SITA fast. Long-term follow-up studies are needed to assess the ability of these techniques to detect progression of glaucoma over time.