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Question 1: What are the optical components of the eye?

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Question 1: What are the optical components of the eye?

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1. Cornea 🔦

Primary refractive surface

Contribute about 2/3 of eye's total refractive power

Highly transparent structure

2. Crystalline Lens 🔦

A transparent, biconvex structure

Fine-tunes the focus of light into retina

3. Aqueous Humour 🔦

A clear, watery fluid between cornea and lens

Maintains intraocular pressure and provide nutrients

4. Pupil 🔦

Opening in center of iris

Control amount of light that enters eye

5. Retina 🔦

Contain photoreceptors (rods and cones)

Act as a screen where image falls on

6. Vitreous Humour 🔦

A clear gel between lens and retina

Maintain eye shape and allow light pass through to retina

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Question 2: Explain why simplified model eyes are necessary? 

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Question 2: Explain why simplified model eyes are necessary? 

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1. Easy to understand the complex structures 👁️

Reduced to a single lens and surface in a simplified model, making it easier to study the basic principles of image formation and refraction

2. Easy to calculate 👁️

Allow for quicker, more intuitive calculations

3. Helps students easily understand fundamental concepts such as focal length, image formation, and refractive errors 👁️

4. Useful in Instrument Design and Prototyping 👁️

These models are fast and efficient for

simulation and testing

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What are the advantages and disadvantages of a reduced eye model?

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What are the advantages and disadvantages of a reduced eye model?

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ADVANTAGES

1. Easy to understand 🔎

Combines multiple refractive surfaces into one and makes calculations much easier

2. Useful for calculating image formation, focal length and refractive errors 🔎

3. Simplifies ray-tracing and vergence calculations without needing a full multi-surface model 🔎

DISADVANTAGES

1. Inaccuracy in depicting the eye's true anatomical structure 🔎

2. Not suitable for precise modeling of vision problems like astigmatism, presbyopia or complex refractive surgeries 🔎

3. Ignore Optical Abberations 🔎

Real eyes have spherical or chromatic aberrations and imperfections that the reduced eye model does not accounted for

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Question 3: How a pinhole disc reduces the blur disc diameter in an uncorrected myopic eye viewing a distant object.

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Question 3: How a pinhole disc reduces the blur disc diameter in an uncorrected myopic eye viewing a distant object.

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Pinhole disc will help increase the depth of field by reducing the 'blur circle' field on the back of retina.

The result is a perfectly focused image on the retina at the back of the eye.

This test is known as pinhole test.

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1. Clinical Diagnosis:

Pinhole discs are used to differentiate between refractive errors and pathological causes of reduced vision.

If vision improves with a pinhole, it suggests a refractive error.

2. Predicting Corrective Potential:

The pinhole test helps estimate how much visual acuity can improve with corrective lenses.

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Question 1: Determine and draw the cardinal points.

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Question 1: Determine and draw the cardinal points.

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Calculations: Steps 1-4

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Calculations: Steps 5-6

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Question 2: A system is made up of three surfaces. The distances between each surface are 3.5mm. Given the data below, calculate the back vertex power and back vertex focal length.

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Question 2: A system is made up of three surfaces. The distances between each surface are 3.5mm. Given the data below, calculate the back vertex power and back vertex focal length.

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Calculations involved.

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Question 3: How’s the keratometer give k reading just based on corneal reflex?

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Question 3: How’s the keratometer give k reading just based on corneal reflex?

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MAIN IDEA

📝Measure cornea’s curvature by treating it like a biological mirror to analyzing how light bounces off its surface (like a spoon’s reflection)

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1. Pattern Projection: A glowing ring or + symbol aimed at the eye. The cornea reflects this pattern like a mirror.

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Steep cornea → Small reflection

Flat cornea → Large reflection

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2. Image stabilization:

Use a doubling prism that splits the reflection into 2 overlapping images.

Aligns these images - Remove error from eye movement.

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3. Size Measurement

Calculate the curve’s radius (in mm) using the reflection’s size and a fixed target distance.

4. Conversion to Diopters (Using 337.5 shortcut)

📝 Why 337.5? A trick to account for how light bends through cornea’s front and back surfaces.

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Question 1: The length of an axially hyperopia is 20.50mm. Find the power of the thin lens correcting lens placed at 10mm from the principal point of the reduced eye.

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Question 1: The length of an axially hyperopia is 20.50mm. Find the power of the thin lens correcting lens placed at 10mm from the principal point of the reduced eye.

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Question 2: A lens is to made with front surface power +10D, back surface power -5D, axial thickness 9mm and refractive index 1.5. find the ocular refraction k if this is a correcting lens fitted 12mm from the eye.

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Question 2: A lens is to made with front surface power +10D, back surface power -5D, axial thickness 9mm and refractive index 1.5. find the ocular refraction k if this is a correcting lens fitted 12mm from the eye.

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Calculations involved.

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A refractive myopia eye is corrected with a 5.00D at 12mm. 

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A refractive myopia eye is corrected with a 5.00D at 12mm. 

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Calculations involved.

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An uncorrected myopia reduced eye of axial length 25mm views a distant object subtending 5'. if NE=1.3333, find the retinal image size. 

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An uncorrected myopia reduced eye of axial length 25mm views a distant object subtending 5'. if NE=1.3333, find the retinal image size. 

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Find the ocular refraction and thin spectacle lens power if the spectacle is worn at 14mm.

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Find the ocular refraction and thin spectacle lens power if the spectacle is worn at 14mm.

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Question 3: A thin +6D lens is used to correct an axially hyperopia at 12mm from the reduced surface. a distant object subtending 2' is viewed through the lens. 

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Question 3: A thin +6D lens is used to correct an axially hyperopia at 12mm from the reduced surface. a distant object subtending 2' is viewed through the lens. 

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Find the ocular refraction, the axial length of the eye and the retinal image size in the uncorrected and corrected eye.

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Find the ocular refraction, the axial length of the eye and the retinal image size in the uncorrected and corrected eye.

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Question 1: If the dioptric length of the eye is K'+ +60D and the object is an axial point at infinity, describe the nature of its representation on the retina, assuming the eye's power remains constant in each case. Also, if the pupil is 4mm in diameter and at the reduced surface, find the size of the light patch on the retina in cases (a) and (b).

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Question 1: If the dioptric length of the eye is K'+ +60D and the object is an axial point at infinity, describe the nature of its representation on the retina, assuming the eye's power remains constant in each case. Also, if the pupil is 4mm in diameter and at the reduced surface, find the size of the light patch on the retina in cases (a) and (b).

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Question 2: An eye with axial length 24.242mm and refractive index 1.3333 has reduced surface power of +58D and +64D horizontally and vertically, respectively.

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Question 2: An eye with axial length 24.242mm and refractive index 1.3333 has reduced surface power of +58D and +64D horizontally and vertically, respectively.

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a) Find the ocular refractions and the principle power of the thin lens at 12mm.

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a) Find the ocular refractions and the principle power of the thin lens at 12mm.

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b) Draw three types of diagram that show the same summation power of sphere and cylinder power in each meridian for that refractive error.

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b) Draw three types of diagram that show the same summation power of sphere and cylinder power in each meridian for that refractive error.

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Question 1: Your groups were assigned to do visual screening at
primary school which is located at rural area. Describe
how you want to categorize between ammetropic and
emmetropic group? Explain the optical concept behind it
and why you say that. Brief the general procedure to
run that program.

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Question 1: Your groups were assigned to do visual screening at
primary school which is located at rural area. Describe
how you want to categorize between ammetropic and
emmetropic group? Explain the optical concept behind it
and why you say that. Brief the general procedure to
run that program.

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Question 2: A line of letters 120mm tall can just be read at 6m. What is the minimum angle of resolution (MAR), decimal and clinical acuities in Snellen fraction?

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Question 2: A line of letters 120mm tall can just be read at 6m. What is the minimum angle of resolution (MAR), decimal and clinical acuities in Snellen fraction?

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Question 3: Describe the contruction of the original Snellen 5 x 5 letter E. How is the letter acuity determined and recorded in practice. A row of letter 20mm high can just be read at 6m. What are the decimal and Snellen acuities?

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Question 3: Describe the contruction of the original Snellen 5 x 5 letter E. How is the letter acuity determined and recorded in practice. A row of letter 20mm high can just be read at 6m. What are the decimal and Snellen acuities?

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Question 4: The 5 x 4 san serif letters B and L were found by Coates(1935) to have relative legibilities of 0.67 and 1.39, respectively. If the letter B was just legible at a distance  of 4500mm, at what distance would the letter L be read?

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Question 4: The 5 x 4 san serif letters B and L were found by Coates(1935) to have relative legibilities of 0.67 and 1.39, respectively. If the letter B was just legible at a distance  of 4500mm, at what distance would the letter L be read?

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Question 5: Write an account of the design characteristics involved in modern letter test type charts
for measuring acuity. Consider both the British Standards and logMAR charts.

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Question 5: Write an account of the design characteristics involved in modern letter test type charts
for measuring acuity. Consider both the British Standards and logMAR charts.

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👓 Find the spectacle magnification when an axially hypermetropia eye is corrected with 

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👓 Find the spectacle magnification when an axially hypermetropia eye is corrected with 

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a) A+5.00D thin lens

b) A thick lens where the BVP is F’v =+5.00D

The back surface power is F2= -6.00D, the axial thickness is t= 9mm, refractive index is ng = 1.5

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a) An eye with an ocular refraction of +7.50D is corrected by a thin lens at 13mm from the reduced surface. Calculate spectacle power and spectacle magnification.

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a) An eye with an ocular refraction of +7.50D is corrected by a thin lens at 13mm from the reduced surface. Calculate spectacle power and spectacle magnification.

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b) An uncorrected axial myopia, ocular refraction -5.00D views a distant object subtending 5Δ. Calculate the retinal image size.

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b) An uncorrected axial myopia, ocular refraction -5.00D views a distant object subtending 5Δ. Calculate the retinal image size.

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c) What is the spectacle correction in b) if the lens is 11mm from the reduced surface?

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c) What is the spectacle correction in b) if the lens is 11mm from the reduced surface?

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d) Calculate the retinal image size in the corrected eye for b).

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d) Calculate the retinal image size in the corrected eye for b).

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e) What would be the retinal image size in b) if a contact lens worn?

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e) What would be the retinal image size in b) if a contact lens worn?

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A refractively myopic eye whose ocular refraction is -12.50D is corrected by a thin lens at 15mm. Find:

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A refractively myopic eye whose ocular refraction is -12.50D is corrected by a thin lens at 15mm. Find:

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c)Retinal image sizes for a distant object subtending 4Δ, corrected and uncorrected

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c)Retinal image sizes for a distant object subtending 4Δ, corrected and uncorrected

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Here are the references used in completing these tutorials!

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Here are the references used in completing these tutorials!

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➤Bailey-Lovie chart set. (n.d.). Guide to Bailey-Lovie chart set. Schweizer Optik. https://www.schweizer-optik.de/userdata/filegallery/original/261_guide_bailey-lovie_chart_set.pdf

➤Bennett, A. G., & Rabbetts, R. B. (2007). Clinical visual optics (4th ed.). Butterworth-Heinemann. https://doi.org/10.1016/B978-0-7506-8874-1.X5000-3 (ISBN 9780750688741)

➤Chen, A.-H., Norazman, F. N., & Buari, N. (2012). Comparison of visual acuity estimates using three different letter charts under two ambient room illuminations. Indian Journal of Ophthalmology, 60(2), 101. https://doi.org/10.4103/0301-4738.90489

➤Hodges, I. (2023). Basic principles of ophthalmic lens and dispensing optics. Alexis Press. ISBN 978-1-64532-015-9

➤Holladay, J. T., & Prager, T. C. (1998). Clinical evaluation of keratometry and computerized videokeratography: Intraobserver and interobserver variability on normal and astigmatic corneas. British Journal of Ophthalmology, 82(6), 704–711. https://doi.org/10.1136/bjo.82.6.704

➤Kaiser, P. K. (2009). Prospective evaluation of visual acuity assessment: A comparison of Snellen versus ETDRS charts in clinical practice. American Journal of Ophthalmology, 147(1), 187–193. https://doi.org/10.1016/j.ajo.2008.07.027

➤Loshin, D. S. (2025). The geometrical optics workbook (1st ed.). Elsevier Health. ISBN 9780750690522

Tunnacliffe, A. H. (2024). Introduction to visual optics (4th ed.). ABDO College. ISBN 9780900099281