Unit 4: Clinical Examination of the Visual System | 3rd Semester of Bachelor of Optometry

Photostress Recovery Test

Introduction:

The Photostress Recovery Test (PSRT) is a simple, non-invasive clinical procedure used to evaluate macular function and to distinguish between visual loss due to retinal (macular) disease and optic nerve disease. It is based on the principle that exposure of the retina to a bright light source temporarily bleaches photopigments in photoreceptors, resulting in decreased visual sensitivity. The time taken for visual acuity to return to baseline after bleaching reflects the ability of the macula to regenerate photopigments and recover function.

This test is valuable because many patients present with decreased central vision, and it can be difficult to clinically differentiate whether the cause lies in the macula (retinal) or the optic nerve. Photostress recovery testing provides an efficient and reliable method to make this distinction.

Principle of the Test

The retina, specifically the macula, contains photoreceptors (cones) that are responsible for high-acuity vision and color perception. When exposed to intense light, photopigments within these photoreceptors (particularly iodopsin in cones) undergo photobleaching.

Normal macula: Photopigments regenerate quickly due to healthy retinal pigment epithelium (RPE) function, and visual acuity returns to baseline within a short time.

Diseased macula: Delayed recovery occurs due to impaired photopigment regeneration or damage to photoreceptor–RPE interaction.

Optic nerve disease: Photostress recovery time is normal, since macular photopigment metabolism is unaffected. Thus, PSRT differentiates macular from optic nerve pathology.

Objectives

• To assess the functional integrity of the macula.
• To differentiate macular disease from optic nerve disease.
• To detect subtle macular dysfunction even before structural changes are visible.
• To provide a simple chair-side test in clinics lacking advanced imaging.

Procedure

1. Measure patient’s best corrected visual acuity (BCVA) for baseline.
2. Occlude one eye; test is performed monocularly.
3. Expose the tested eye to a bright light source (ophthalmoscope light or pen torch) held close to the eye for 10 seconds.
4. Immediately present the visual acuity chart and ask the patient to read the same line as baseline.
5. Record the time (in seconds) taken for the patient to regain pre-exposure visual acuity.
6. Repeat for the fellow eye.

Normal Values

• Recovery time: ≤ 50 seconds (average 20–40 seconds).
• Similar recovery times between the two eyes.

Abnormal Results

• Prolonged recovery (>60 seconds): Suggests macular pathology (e.g., age-related macular degeneration, central serous chorioretinopathy, diabetic maculopathy).
• Normal recovery with visual loss: Suggests optic nerve disease (e.g., optic neuritis, ischemic optic neuropathy, glaucoma).
• Asymmetry between eyes: Indicates unilateral or asymmetric macular disease.

Clinical Applications

• Early detection of macular dysfunction when fundus appears normal.
• Monitoring progression of macular diseases (AMD, CSR, diabetic macular edema).
• Differentiating macular disease from optic nerve disease in patients with central visual loss.
• Useful in resource-limited settings as a low-cost diagnostic tool.

Conditions Where Photostress Test is Prolonged

• Age-related macular degeneration (AMD).
• Central serous chorioretinopathy (CSR).
• Diabetic maculopathy.
• Macular hole or epiretinal membrane.
• Toxic maculopathy (e.g., chloroquine retinopathy).

Advantages

• Simple and quick (takes less than 2 minutes).
• Non-invasive and inexpensive.
• Does not require specialized equipment beyond a light source and visual acuity chart.
• Useful in differentiating macular vs optic nerve disease.

Limitations

• Not quantitative; only provides approximate recovery time.
• Less reliable in uncooperative patients or children.
• May be influenced by ambient lighting and patient fixation.
• Cannot localize specific macular pathology.
• Normal results do not rule out subtle or early macular disease detectable by OCT.

Comparison with Other Macular Function Tests

• Amsler grid: Detects metamorphopsia and central scotoma; subjective and home-based.
• Foveal threshold perimetry: Measures retinal sensitivity at fovea; requires perimeter.
• Multifocal ERG: Provides objective electrophysiological assessment of macula.
• OCT (Optical Coherence Tomography): Provides structural information, not functional.
• PSRT: Simple, functional test distinguishing macular from optic nerve pathology.

Slit Lamp Biomicroscopy

Introduction:

Slit lamp biomicroscopy is one of the most important clinical examination techniques in optometry and ophthalmology. It is a binocular, stereoscopic, high-magnification method of examining the anterior and posterior segments of the eye using a specialized microscope combined with an adjustable slit-shaped light beam.

The slit lamp allows detailed visualization of the eyelids, conjunctiva, cornea, anterior chamber, iris, lens, and, with additional lenses, even the vitreous and retina. It is indispensable in diagnosing anterior segment diseases, monitoring ocular conditions, and performing contact lens assessments.

Principle

The slit lamp works on the principle of illumination and magnification. A focused slit beam of light illuminates ocular structures, while a binocular microscope provides stereoscopic, magnified visualization.

By altering the width, height, angle, and intensity of the slit, different layers of the eye can be examined in cross-section, helping in precise localization of pathology.

Components of a Slit Lamp

• Illumination system: Provides variable slit beam with adjustable width, height, intensity, filters, and angle.
• Observation system: Binocular microscope with adjustable magnification (6x to 40x), providing stereoscopic view.
• Mechanical system: Joystick for precise movement, chin rest and headrest for patient stabilization.
• Accessories: Applanation tonometer (Goldmann), photographic attachments, and fundus lenses (90D, 78D, 60D) for posterior segment examination.

Techniques of Illumination

The versatility of slit lamp examination lies in its different illumination techniques, each highlighting specific ocular structures.

• Diffuse illumination: Wide, unfocused beam to survey general ocular surface.
• Direct focal illumination: Narrow, focused slit to examine cornea, lens, and anterior chamber layers.
• Specular reflection: Highlights corneal endothelium by reflection of light at equal angles.
• Sclerotic scatter: Beam directed at limbus; total internal reflection illuminates corneal opacities.
• Retro-illumination: Light reflected from iris or fundus used to view opacities in cornea, lens, or vitreous.
• Indirect illumination: Slit beam adjacent to lesion; allows study of subtle abnormalities.
• Conical beam: Narrow, short beam to assess anterior chamber depth and cells/flare.

Examination of Anterior Segment Structures

1. Eyelids and Conjunctiva

• Check lid margins for blepharitis, meibomian gland dysfunction, notching, tumors.
• Conjunctiva examined for injection, follicles, papillae, hemorrhages, and discharge.

2. Cornea

• Epithelium: Abrasions, ulcers, staining with fluorescein.
• Stroma: Edema, opacities, infiltrates.
• Endothelium: Specular reflection for guttata, pigmentation.

3. Anterior Chamber

• Depth assessment (Van Herrick technique).
• Cells and flare in uveitis using conical beam.
• Hyphema, hypopyon, or foreign bodies.

4. Iris

• Color, pattern, and neovascularization.
• Iridodialysis, synechiae, iris nodules (granulomatous uveitis).

5. Lens

• Clarity, opacities (cataract grading).
• Posterior capsular opacification (after cataract surgery).
• Use retro-illumination for cortical spokes and posterior subcapsular changes.

Examination of Posterior Segment Structures

With auxiliary lenses (78D, 90D, or 60D convex lenses) or fundus contact lenses, slit lamp can examine:

• Optic disc: Color, margins, cup-disc ratio (glaucoma).
• Macula: Foveal reflex, drusen, edema, hemorrhages.
• Retinal vessels: Hypertensive or diabetic changes.
• Peripheral retina (with contact lens): Lattice degeneration, tears, detachments.

Special Techniques with Slit Lamp

• Gonioscopy: With gonio lens to view anterior chamber angle.
• Applanation tonometry: Measurement of IOP with Goldmann prism.
• Pachymetry: Corneal thickness measurement with slit-lamp mounted devices.
• Contact lens fitting: Assessment of corneal shape, tear film, and lens–cornea relationship.
• Anterior segment photography: For documentation of clinical findings.

Clinical Applications

• Diagnosis of corneal diseases (ulcer, keratoconus, dystrophies).
• Assessment of anterior chamber inflammation (uveitis).
• Evaluation of cataract and pseudophakia.
• Glaucoma evaluation (optic disc, angle with gonioscopy, IOP measurement).
• Monitoring systemic diseases with ocular involvement (diabetes, hypertension).
• Contact lens practice: fitting, follow-up, and complication management.

Advantages

• Provides stereoscopic, magnified, detailed view of ocular structures.
• Versatile with multiple illumination techniques.
• Allows anterior and posterior segment examination.
• Essential for diagnostic accuracy and follow-up documentation.

Limitations

• Requires patient cooperation and stability.
• Peripheral retina difficult to visualize without auxiliary lenses.
• Dependent on examiner skill and experience.
• Not portable; requires clinic setting.

Comparison with Other Instruments

• Direct ophthalmoscope: Portable, small field, upright image; limited magnification.
• Indirect ophthalmoscope: Wide field, stereoscopic, inverted image; ideal for periphery.
• Slit lamp: Best for anterior segment and posterior pole with lenses; provides stereopsis and magnification.

Ophthalmoscopy

Introduction:

Ophthalmoscopy, also called fundoscopy, is the clinical technique of examining the interior structures of the eye, particularly the retina, optic disc, macula, and retinal vasculature. It is one of the most important diagnostic skills in ophthalmology and optometry, providing direct visualization of the only site in the body where blood vessels and neural tissue can be observed non-invasively.

Ophthalmoscopy not only helps diagnose ocular conditions such as diabetic retinopathy, glaucoma, and retinal detachment but also provides insight into systemic diseases like hypertension, diabetes, and intracranial hypertension.

History

The ophthalmoscope was first invented by Hermann von Helmholtz in 1851. Since then, it has undergone several modifications, leading to the development of direct ophthalmoscopes, indirect ophthalmoscopes, and slit lamp biomicroscopic ophthalmoscopy.

Principle

Ophthalmoscopy is based on the principle of illumination and magnification. Light is projected into the eye through the pupil, illuminating the retina. The examiner uses optical systems in the ophthalmoscope to observe the illuminated fundus directly or indirectly.

Types of Ophthalmoscopy

1. Direct Ophthalmoscopy

• Handheld instrument with built-in light source and lenses.
• Provides magnified (15x) upright image of a small fundus area (central retina, optic disc).
• Field of view: 6–10° (1–2 disc diameters).
• Best for optic disc, macula, and localized lesions.

2. Indirect Ophthalmoscopy

• Uses a head-mounted binocular ophthalmoscope with external light source and condensing lens (20D, 28D, or 30D).
• Provides stereoscopic, inverted, and reversed image of a wide fundus area (up to 30–40° with single view, 200° with scleral depression and scanning).
• Ideal for peripheral retina and vitreous evaluation.

3. Slit Lamp Biomicroscopic Ophthalmoscopy

• Uses slit lamp with high-powered convex lens (78D, 90D, or 60D) for indirect fundus view.
• Provides stereoscopic, magnified view of posterior pole.
• Best for optic disc, macula, and posterior pole assessment.

Procedure of Direct Ophthalmoscopy

1. Darken the room to dilate pupils naturally or use mydriatic drops if indicated.
2. Examiner holds ophthalmoscope close to their own eye and approaches patient at ~15° temporally.
3. Use right eye to examine patient’s right eye and left eye for left eye.
4. Focus on red reflex; move closer to visualize retina.
5. Examine optic disc, retinal vessels, macula, and periphery systematically.

Procedure of Indirect Ophthalmoscopy

1. Dilate patient’s pupils adequately.
2. Examiner wears binocular indirect ophthalmoscope.
3. Hold condensing lens (20D/28D) in front of patient’s eye at appropriate distance.
4. Obtain inverted aerial image of fundus between lens and examiner.
5. Systematically scan posterior pole and periphery, often with scleral depression for peripheral pathology.

Normal Fundus Appearance

• Optic disc: Round, pink, sharp margins, cup-disc ratio 0.3–0.4.
• Retinal vessels: Arteries narrower than veins (2:3 ratio), normal crossing.
• Macula: Central dark area, foveal reflex in young individuals.
• Peripheral retina: Gradual thinning, visible lattice or ora serrata in some cases.

Abnormal Fundus Findings

• Optic disc: Swelling (papilledema), pallor (optic atrophy), cupping (glaucoma).
• Retinal vessels: Hypertensive changes (AV nicking, hemorrhages), diabetic changes (microaneurysms, neovascularization).
• Macula: Drusen (AMD), edema, hemorrhage, macular hole.
• Peripheral retina: Tears, lattice degeneration, detachment.

Clinical Applications

• Diagnosis of ocular diseases: glaucoma, diabetic retinopathy, retinal detachment, AMD.
• Detection of systemic diseases: hypertension, diabetes, intracranial hypertension.
• Screening in emergencies: trauma, vascular occlusions.
• Follow-up in chronic retinal conditions.

Advantages

• Direct visualization of retina and optic nerve.
• Quick, inexpensive, and non-invasive.
• Portable instruments available (direct ophthalmoscope).
• Wide range of information about ocular and systemic health.

Limitations

• Direct ophthalmoscopy has small field of view and no stereopsis.
• Indirect ophthalmoscopy requires dilation, training, and equipment.
• Findings may be influenced by media opacities (corneal scar, cataract, vitreous hemorrhage).
• Dependent on examiner’s skill and interpretation.

Comparison of Ophthalmoscopy Types

Type	Image	Magnification	Field of View	Best Use
Direct	Upright	15x	6–10°	Optic disc, macula, central retina
Indirect	Inverted, reversed	2–5x	30–200°	Peripheral retina, vitreous, retinal detachment
Slit Lamp (90D/78D lens)	Inverted	7–10x	Posterior pole	Optic disc, macula, central pathologies

Tonometry

Introduction:

Tonometry is the clinical procedure used to measure intraocular pressure (IOP), an essential parameter in the diagnosis and management of glaucoma and other ocular conditions. Intraocular pressure reflects the balance between aqueous humor secretion and its drainage through trabecular and uveoscleral pathways. Abnormal IOP is a major risk factor for glaucomatous optic neuropathy.

Tonometry provides quantitative measurement of IOP and helps in early detection, monitoring, and treatment evaluation of glaucoma, one of the leading causes of irreversible blindness worldwide.

Normal Intraocular Pressure

• Normal IOP: 10–21 mmHg.
• Diurnal variation: ~3–6 mmHg, usually higher in the morning.
• Asymmetry between eyes: >2 mmHg difference may be significant.

Principle of Tonometry

Tonometry is based on the relationship between force and indentation or applanation of the cornea. By applying a known force and measuring the resulting corneal deformation, IOP can be estimated.

Two main principles are applied:

• Indentation tonometry: Measures depth of corneal indentation caused by a known weight (e.g., Schiøtz tonometer).
• Applanation tonometry: Measures force required to flatten a known corneal area (e.g., Goldmann applanation tonometer).

Types of Tonometers

1. Indentation tonometer: Schiøtz.
2. Applanation tonometers: Goldmann, Perkins, Tono-Pen, Pascal, Non-contact, Rebound.
3. Dynamic contour tonometer: Pascal, providing direct pressure measurement.
4. Rebound tonometer: Handheld, no anesthesia required (useful in children).

1. Schiøtz Indentation Tonometer

An early tonometer based on indentation principle.

Procedure

• Patient lies supine.
• Topical anesthesia instilled.
• Instrument placed vertically on cornea; plunger indents cornea by known weight.
• Scale reading converted to IOP using calibration chart.

Advantages

• Simple, inexpensive, portable.

Limitations

• Accuracy affected by corneal rigidity, scleral thickness.
• Not reliable for repeated follow-up in glaucoma.

2. Goldmann Applanation Tonometer (GAT)

Considered the gold standard for IOP measurement.

Principle

Based on Imbert-Fick law: Pressure inside a sphere = Force / Area, assuming perfectly elastic, thin, and dry surface.

Procedure

1. Patient seated at slit lamp; topical anesthesia and fluorescein instilled.
2. Tonometer prism gently placed on cornea.
3. Cobalt blue light used; examiner adjusts until two semicircles of fluorescein just touch.
4. Reading taken directly in mmHg.

Advantages

• Highly accurate, reproducible.
• Standard reference for glaucoma diagnosis.

Limitations

• Accuracy affected by corneal thickness (CCT), irregularities, edema.
• Requires slit lamp, trained examiner.

3. Perkins Tonometer

Portable, hand-held version of Goldmann, based on applanation principle.

• Useful in bedridden patients and children under anesthesia.
• Accuracy similar to Goldmann if used correctly.

4. Non-Contact Tonometer (NCT)

Also called air-puff tonometer.

Procedure

• Puff of air flattens cornea; device measures time/force needed to applanate cornea using light sensors.

Advantages

• No contact, no anesthesia required.
• Useful for mass screening.

Limitations

• Less accurate than GAT, especially at high/low IOP.
• Affected by corneal biomechanics.

5. Rebound Tonometer (iCare)

Uses a small probe that rebounds off the cornea; rebound speed correlates with IOP.

• Portable, quick, no anesthesia required.
• Useful in children, uncooperative patients, and home monitoring.
• Less influenced by corneal thickness than NCT.

6. Tono-Pen

Hand-held digital applanation tonometer.

• Useful for irregular corneas, post-keratoplasty, corneal edema.
• Portable and easy to use.

7. Pascal Dynamic Contour Tonometer

Measures IOP independent of corneal thickness/biomechanics by contour-matching sensor tip.

• Provides continuous IOP and ocular pulse amplitude.
• Expensive, not widely available.

Factors Affecting Tonometry Readings

• Central corneal thickness (CCT) — thick corneas overestimate IOP; thin corneas underestimate.
• Corneal rigidity and biomechanics.
• Patient cooperation and fixation.
• Examiner technique and calibration of instrument.

Clinical Applications

• Diagnosis of ocular hypertension and glaucoma.
• Monitoring IOP in glaucoma patients.
• Pre- and post-operative assessment in ocular surgery.
• Screening in community eye health programs.

Advantages

• Objective, quantitative measurement of IOP.
• Essential in glaucoma management.
• Multiple methods available for various clinical settings.

Limitations

• Most methods influenced by corneal thickness/biomechanics.
• Not all tonometers are equally accurate.
• Some require anesthesia, slit lamp, or expensive equipment.

Comparison of Tonometers

Type	Principle	Advantages	Limitations
Schiøtz	Indentation	Simple, inexpensive	Affected by rigidity, less accurate
Goldmann	Applanation	Gold standard, reproducible	Needs slit lamp, CCT affects accuracy
Perkins	Applanation	Portable Goldmann	Less stable readings
Non-Contact	Air applanation	No anesthesia, screening	Less accurate
Rebound	Probe rebound	Portable, kids, no anesthesia	Costly, probe replacement
Tono-Pen	Applanation	Hand-held, irregular cornea	Expensive, calibration needed
Pascal	Dynamic contour	Less CCT influence, continuous IOP	Very costly, less available

For more units of Clinical Examination of the Visual System click below 👇 

✅Unit 1

✅Unit 2

✅Unit 3

✅Unit 5